Controller for power converter and power converter

Abstract

A first controller for a power converter includes a driver, a power supply terminal, a branch switch, and a branch control device. The driver is configured to provide a drive signal to turn the power switch on and off. The power switch includes a first switch and a second switch coupled in a stacked configuration. The power supply terminal is coupled to a bypass capacitor that provides operating power to the first controller, wherein the bypass capacitor has a bypass voltage. The branch switch is coupled to a node between the first switch and the second switch. The branch control device is configured to receive an adjustment signal representing a comparison of the bypass voltage with a bypass reference, and is configured to: if the bypass voltage is below the bypass reference, turn on the branch switch to redirect at least a portion of the drain current of the power switch to the bypass capacitor.

Description

Technical Field

[0001] This disclosure relates generally to power converters, and more specifically to controllers for power converters. Prior Technology

[0002] Electronic devices operate using electricity. Switch-mode power converters (SMPCs) are commonly used to power many modern electronic devices due to their high efficiency, small size, and light weight. Conventional wall outlets provide high-voltage alternating current (AC). In a SMPC, the high-voltage AC input is converted by energy transfer elements to provide a well-regulated direct current (DC) output. SMPC controllers typically provide output regulation by sensing one or more signals representing one or more output quantities and controlling the output in a closed loop. During operation, the desired output is provided by using switches to change the duty cycle (typically the ratio of the switch's on-time to the total switching cycle), changing the switching frequency, or changing the number of pulses per unit time of the switches in the SMPC.

[0003] Power converters typically include one or more controllers that sense and regulate the converter's output. These controllers typically require a regulated or unregulated voltage source to power their circuitry. Bypass capacitors coupled to the controllers can provide operating power to the controller's circuitry. Summary of the Invention

[0004] A first controller for a power converter is provided, the first controller including a driver, a power terminal, a branch switch, and a branch control device. The driver is configured to provide a drive signal to turn a power switch on and off to control energy delivery between an input and an output of the power converter, wherein the power switch includes a first switch and a second switch coupled in a cascode configuration, wherein the first switch is a normally open device and the second switch is a normally closed device. The power terminal is coupled to a bypass capacitor that provides operating power to the first controller, wherein the bypass capacitor has a bypass voltage. The branch switch is coupled to a node between the first switch and the second switch. The branch control device is configured to receive a regulation signal representing a comparison of the bypass voltage with a bypass reference, wherein the branch control device is configured to: if the bypass voltage is below the bypass reference, turn on the branch switch to redirect at least a portion of a drain current of the power switch from the node to the bypass capacitor.

[0005] A first controller for a power converter is provided, the first controller including a power switch, a branch switch, a driver, a main control unit, a comparator, and a branch control unit. The power switch includes a first switch and a second switch coupled in a stacked configuration, wherein the first switch is a normally open device and the second switch is a normally closed device. The branch switch is coupled to a node between the first switch and the second switch, and the branch switch is also coupled to a bypass capacitor. The driver is configured to provide a drive signal to control the on and off of the power switch to control energy delivery between an input side and an output side of the power converter, wherein the driver is configured to turn the second switch on and off to control the on and off of the power switch. The main control unit is configured to receive a request signal representing turning on the power switch, wherein the main control unit determines whether the power switch should be turned on or off. The comparator is coupled to receive a bypass reference and a bypass voltage of the bypass capacitor. The branch control device is coupled to the comparator and the main control device, wherein the branch control device is configured to: if the bypass voltage is below the bypass reference and the main control device determines to turn on the power switch, turn on the branch switch, wherein a branch current conducted by the branch switch is at least a portion of a drain current conducted by the first switch. Simple Explanation of the Diagram

[0006] The following figures illustrate non-limiting and non-exhaustive embodiments of the invention, wherein, unless otherwise stated, similar symbols refer to similar parts in all the various views.

[0007] Figure 1 is a schematic diagram of an example isolated power converter according to an embodiment of the present disclosure, the power converter including a controller having a branch switch and a branch control.

[0008] Figure 2 illustrates a timing diagram of example waveforms of the power converter and controller with branch switches and branch control devices of Figure 1 according to an embodiment of the present disclosure.

[0009] Figure 3 is a functional block diagram of another example controller having a branch switch, a branch control device, and a shunt regulator according to an embodiment of the present disclosure.

[0010] Figure 4A illustrates a timing diagram of an example waveform of the controller of Figure 3, which has a branch switch, a branch control device, and a shunt regulator, when the power converter is operating in discontinuous conduction mode (DCM) according to an embodiment of the present disclosure.

[0011] Figure 4B illustrates a timing diagram of an example waveform of the controller of Figure 3, which has a branch switch, a branch control device, and a shunt regulator, when the power converter is operating in continuous conduction mode (CCM) according to an embodiment of the present disclosure.

[0012] Figure 5A is a schematic diagram of yet another example controller having a branch switch, a branch control device and a branch regulator according to an embodiment of the present disclosure.

[0013] Figure 5B illustrates a timing diagram of an example waveform of a controller having a branch switch, a branch control device, and a branch regulator according to an embodiment of the present disclosure, as shown in Figure 5A.

[0014] Figure 6 illustrates a timing diagram of one embodiment of the bypass voltage and branch control signal of the bypass capacitor according to an embodiment of the present disclosure.

[0015] Figure 7 is a schematic diagram of another example isolated power converter including a controller with branch switches and branch control devices according to an embodiment of the present disclosure.

[0016] In all views of the drawings, corresponding reference numerals indicate the corresponding components. Those skilled in the art will understand that the elements in the drawings are illustrated for simplicity and clarity and are not necessarily drawn to scale. For example, the dimensions of some elements in the drawings may be exaggerated relative to other elements to aid in understanding the various embodiments of the invention. Furthermore, common but easily understood elements that are useful or necessary in commercially viable embodiments are generally not depicted to facilitate viewing of these embodiments of the invention with less hindrance. Implementation

[0017] In the following description, numerous specific details are set forth to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art to which this invention pertains that these specific details are not required to practice the invention. In other instances, well-known materials or methods have not been described in detail to avoid obscuring the invention.

[0018] Throughout this specification, the references to "one embodiment," "an embodiment," "one example," or "an example" mean that a specific feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the invention. Therefore, the terms "one embodiment," "an embodiment," "one example," or "an example" appearing throughout this specification do not necessarily all refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics may be combined in any suitable combination and / or sub-combinations in one or more embodiments or examples. Specific features, structures, or characteristics may be included in integrated circuits, electronic circuits, combinational logic circuits, or other suitable components that provide the described functionality. Additionally, it should be understood that the accompanying drawings are for the purpose of explanation to those skilled in the art to which this invention pertains, and the drawings are not necessarily drawn to scale.

[0019] Power converters typically include one or more controllers that sense and regulate the output of the power converter. These controllers typically require a regulated or unregulated voltage source to power their circuitry. A bypass capacitor is one embodiment of a voltage source that can be coupled to the controller, providing operating power to the controller's circuitry. This bypass capacitor is typically regulated to provide sufficient operating power to the controller.

[0020] An isolated power converter may include a primary controller, also referred to as a first controller or input controller; and a secondary controller, also referred to as a second controller or output controller, which are current-isolated from each other through energy transfer elements (e.g., coupling inductors, transformers, etc.). In other words, a DC voltage applied between the input and output sides of the power converter will produce approximately zero current.

[0021] The primary controller is configured to control the power switch on the primary side of the isolated power converter to control the energy transfer from the primary winding of the energy transfer element to the secondary winding of the energy transfer element. The secondary controller is coupled to the circuitry on the secondary side of the isolated power converter. It should be understood that the primary side may also be referred to as the input side, and the secondary side may be referred to as the output side. The secondary controller may also be configured to control a secondary switch coupled to the secondary winding of the energy transfer element, such as a transistor used as a synchronous rectifier for the power converter. Although the primary and secondary controllers are currently isolated from each other, the secondary controller can transmit signals to the primary controller that control how the primary controller switches the power switch to transfer energy to the secondary side.

[0022] Typically, power converters include bypass capacitors on both the primary and secondary sides to provide operating power to the circuitry of the primary or secondary controller, respectively. The bypass capacitor for the primary controller is usually coupled to an auxiliary (or bias) winding of an energy transfer element (such as a transformer or coupled inductor) and charged from that auxiliary winding. The bypass voltage across the bypass capacitor is typically regulated to a level sufficient to operate the primary controller circuitry. For example, this bypass voltage may be regulated to approximately 5 volts (V).

[0023] As mentioned above, the primary controller is configured to control the power switch on the primary side of the isolated power converter to control the energy transfer between the input and output of the power converter. In one embodiment, the power switch may be a cascode switch (or a hybrid switch). The cascode switch (or hybrid switch) may include a first switch and a second switch. The first switch is typically a normally on device, while the second cascode switch is typically a normally off device. The cascode switch has three terminals: a source, a gate, and a drain. In one embodiment, the normally on device (e.g., the first switch) may be a high-voltage GaN transistor, while the normally off device (e.g., the second switch) may be a low-voltage MOSFET. The source and gate of the normally off device (e.g., the MOSFET) are used as the source and gate of the cascode switch, while the drain of the normally on device (e.g., the GaN transistor) is used as the drain of the cascode switch. The source of the normally on device (e.g., the GaN transistor) is coupled to the drain of the normally off device (e.g., the MOSFET). Normally closed devices (e.g., MOSFETs) are typically used to turn normally open devices (e.g., GaN transistors) on and off. An off (or open) switch cannot conduct current, while an on (or closed) switch can. The node between a normally closed and a normally open device can be referred to as an intermediate node.

[0024] Embodiments of the present invention include a power switch in a stacked configuration and a bypass capacitor coupled to an intermediate node between a first switch and a second switch of the stacked power switch. The power switch is controlled such that at least a portion of the current conducted by the first switch is redirected to the bypass capacitor and used to charge the bypass capacitor. In other words, the power switch is controlled such that at least a portion of the current conducted by the first switch is used to regulate the bypass voltage across the bypass capacitor. In yet another embodiment, the second switch may also be used to control the amount of current redirected to charge the bypass capacitor. In other words, the second switch may also be used to control the amount of that portion of the current redirected from the first switch to the bypass capacitor. As mentioned above, the bypass capacitor provides operating power.

[0025] In an embodiment of the invention, a controller includes a branch switch and a branch control device. In one embodiment, the branch switch is coupled between an intermediate node of a stacked power switch and a bypass capacitor for the controller. The branch control device is configured to control the switching on and off of the branch switch. In an embodiment, the branch control device switches on the branch switch when the bypass capacitor voltage drops below a bypass reference. Current conducted by the first switch is redirected to and conducted by the branch switch to charge the bypass capacitor. In other words, the branch switch is controlled such that the current conducted by the first switch is used to regulate the bypass voltage of the bypass capacitor.

[0026] In another embodiment, the controller further includes a shunt regulator to control the amount of current conducted by the branch switch. Thus, a portion of the current conducted by the first switch is redirected and conducted by the branch switch to charge the bypass capacitor. The second switch of the power cascade switch is controlled to shunt the remaining current conducted by the first switch, thereby controlling the amount of current conducted by the branch switch. The bypass capacitor provides operating power to the controller.

[0027] Figure 1 illustrates a power converter 100 according to an embodiment of the present disclosure, which includes a first controller 132 (e.g., a primary controller) including a branch switch 152 and a branch control device 150. The illustrated power converter 100 also includes a clamping circuit 104, an energy transfer element T1 106, an input winding 108 of the energy transfer element T1 106, an output winding 110 of the energy transfer element T1 106, an auxiliary winding 112 of the energy transfer element T1 106, a power switch S1 114, an input return line 111, an output rectifier S2 122, an output capacitor C0 124, an output return line 127, an output sensing circuit 129, a second controller 134 (e.g., a secondary controller), a first controller 132 (e.g., a primary controller), a bypass capacitor 144 (e.g., a power supply capacitor for the first controller 132), and a diode D1 146. A communication link 136 between the second controller 134 and the first controller 132 is also illustrated. The power switch S1 114 is shown as a stacked switch (or hybrid switch) including a first switch 116, a second switch 118, and an intermediate node A 117 between the first switch 116 and the second switch 118. The first controller 132 is shown as including a main control unit 148, a branch control unit 150, a branch switch 152, a diode D2 154, a comparator 156, and a driver 158.

[0028] Figure 1 also shows the input voltage VIN 102, drain current ID 119, second switching current I1 120, output voltage VO 123, output current IO 125, output quantity UO 126, feedback signal FB 130, request signal REQ 133, second drive signal SR 135, primary drive signal DR 138, current sensing signal ISNS 140, bypass voltage VBP 142, turn-on signal ON 160, turn-off signal OFF 162, bypass adjustment signal BP_REG 163, main turn-on signal MAIN_ON 164, branch drive signal BR 165, reference REF 167 (e.g., bypass reference), and branch current IBR 168.

[0029] In the illustrated embodiment, power converter 100 is shown with a flyback topology, but it should be understood that other known topologies and configurations of power converters may also benefit from the teachings of this disclosure. Furthermore, the input side of power converter 100 is currently isolated from the output side, such that input loop 111 is currently isolated from output loop 127. Because the input and output sides of power converter 100 are currently isolated, there is no DC path across the isolation barrier of energy transfer element TI 106, or between input winding 108 and output winding 110, or between auxiliary winding 112 and output winding 110, or between input loop 111 and output loop 127.

[0030] Power converter 100 provides output power to load 128 from an unregulated input voltage VIN 102. In one embodiment, the input voltage VIN 102 is a rectified and filtered AC line voltage. In another embodiment, the input voltage VIN 102 is a DC input voltage. The input voltage VIN 102 is coupled to energy transfer element 106. In some embodiments, energy transfer element 106 may be a coupling inductor, transformer, or inductor. Energy transfer element 106 is shown as comprising three windings: input winding 108 (also referred to as the primary winding), output winding 110 (also referred to as the secondary winding), and auxiliary winding 112 (also referred to as the bias winding or third winding). However, energy transfer element 106 may have more than three windings. The input winding 108 of the energy transfer element is also coupled to power switch S1 114, which is further coupled to input return line 111. Coupled in parallel to the input winding 108 is clamping circuit 104. Clamping circuit 104 limits the maximum voltage on power switch S1 114.

[0031] As shown in Figure 1, the power switch S1 114 is a stacked switch comprising a first switch 116 and a second switch 118. The first switch 116 is typically a normally open device, while the second switch 118 is typically a normally closed device. The stacked power switch S1 114 has three terminals: a source, a gate, and a drain. In one embodiment, the normally open device (e.g., the first switch 116) may be a high-voltage transistor, while the normally closed device (e.g., the second switch 118) may be a low-voltage transistor. In one embodiment, the high-voltage transistor used for the first switch 116 may be rated to approximately 750 volts (V), while the low-voltage transistor used for the second switch 118 may be rated between 25 and 30 V. The source and gate of the second switch 118 (e.g., a normally closed device) are used as the source and gate of the stacked power switch 114, while the drain of the first switch 116 (e.g., a normally open device) is used as the drain of the stacked power switch 114. In one embodiment, the source of a first transistor 116 (e.g., a normally open device) is coupled to the drain of a second transistor 118 (e.g., a normally closed device). The gate of the first transistor 116 is shown coupled to the source of the second transistor 118, and the source of the second transistor 118 is coupled to the input loop 111. It should be understood that the gate of the first transistor 116 may also be directly coupled to the input loop 111. An intermediate node A 117 is shown coupled between the source of the first transistor 116 and the drain of the second transistor 118. The second transistor 118 is typically used to turn the first transistor 116 (normally open device) on and off. In one embodiment, the first switch 116 may be a transistor, such as a gallium nitride (GaN)-based transistor or a silicon carbide (SiC)-based transistor. The second switch 118 may be a transistor, such as a metal-oxide-semiconductor field-effect transistor (MOSFET), a bipolar junction transistor (BJT), or an insulated gate bipolar transistor (IGBT). In one embodiment, the current conducted by the first switch 116 is represented by the drain current ID 119, while the current conducted by the second switch 118 is represented by the second switch current I1 120.

[0032] Output winding 110 is coupled to output rectifier S2 122, which is exemplified as a transistor used as a synchronous rectifier. However, the output rectifier may be exemplified as a diode. Output capacitor CO 124 is shown coupled to output rectifier S2 122 and output return line 127. Power converter 100 also includes circuitry for regulating output quantity UO 126, which in one embodiment may be output voltage VO 123, output current IO 125, or a combination of both. Output sensing circuitry 129 is configured to sense output quantity UO 126 to provide a feedback signal FB 130 representing the output of power converter 100 to a second controller 134.

[0033] The second controller 134 is configured to output a request signal REQ 133 in response to the feedback signal FB 130. In another embodiment, the second controller 134 is configured to pass the feedback signal FB 130 to the first controller 132. For the embodiment of the request signal REQ 133, the request signal REQ 133 represents a request to turn on the power switch S1 114. The request signal REQ 133 may include a request event generated in response to the feedback signal FB 130. In an example operation, the second controller 134 is configured to compare the feedback signal FB 130 with an adjustment reference. In response to this comparison, the second controller 134 may output a request event in the request signal REQ 133 to request the first controller 132 to turn on the power switch S1 114. The request signal REQ 133 may be a rectangular pulse waveform that bounces to a logic high value and quickly returns to a logic low value. The logic high pulse may be referred to as the request event. In other embodiments, it should be understood that the request signal REQ 133 may be an analog, continuously varying signal rather than a pulse waveform, while still benefiting from the teachings of this disclosure.

[0034] The second controller 134 and the first controller 132 can communicate via a communication link 136. In the illustrated embodiment, the second controller 134 is coupled to the secondary side of the power converter 100 and references the output return line 127, while the first controller 132 is coupled to the primary side of the power converter 100 and references the input return line 111. In embodiments, the first controller 132 and the second controller 134 are current-isolated from each other, and the communication link 136 uses inductive coupling (such as a transformer or coupling inductor, optocoupler), capacitive coupling, or other devices that maintain isolation to provide current isolation. However, it should be understood that in some embodiments, the second controller 134 is not current-isolated from the first controller 132. In one embodiment, the communication link 136 may be an inductive coupling formed by a lead frame supporting the first controller 132 and / or the second controller 134.

[0035] In one embodiment, the first controller 132 and the second controller 134 may be formed as part of an integrated circuit, which is manufactured as a hybrid integrated circuit or a monolithic integrated circuit. In one embodiment, the power switch S1 114 may also be integrated with the first controller 132 and the second controller 134 in a single integrated circuit package. Alternatively, in one embodiment, the first controller 132 and the second controller 134 may be formed as separate integrated circuits. The power switch S1 114 may also be integrated with the first controller 132 in the same integrated circuit or may be formed on its own integrated circuit. Specifically, the second switch 118 of the power switch S1 114 may be integrated with the first controller 132 in the same integrated circuit, while the first switch 116 of the power switch S1 114 is integrated in its own integrated circuit. Furthermore, it should be understood that the first controller 132, the second controller 134, and the power switch S1 114 do not necessarily need to be included in a single package, but may be implemented in separate controller packages or combinations of separate packages.

[0036] The first controller 132 is coupled to: receive a current sensing signal ISNS 140 representing the drain current ID 119 of the power switch S1 114 and a request signal REQ 133 or a feedback signal FB 130 via the communication link 136, and output a primary drive signal DR 138. The first controller 132 provides the primary drive signal DR 138 to the power switch S1 114 to control various switching parameters of the power switch S1 114 to control energy transfer from the input to the output of the power converter 100 via the energy transfer element 106. Examples of such parameters include the switching frequency fSW (or switching period TSW), duty cycle, on-time and off-time, or a change in the number of pulses per unit time of the power switch S1 114. Additionally, the power switch S1 114 can be controlled to have a fixed switching frequency or a variable switching frequency.

[0037] In one embodiment, the first controller 132 outputs a primary drive signal DR 138 to control the conduction of the power switch S1 114. Specifically, the first controller 132 outputs the primary drive signal DR 138 to control the conduction of the second switch 118. In one embodiment, the first controller 132 outputs the primary drive signal DR 138 to turn on the power switch S1 114 in response to a request event in the request signal REQ 133 or in response to information provided by the feedback signal FB 130. In another embodiment, the first controller 132 outputs the primary drive signal DR 138 to turn off the power switch S1 114 when the drain current ID 119 provided by the current sensing signal ISNS 140 reaches the current limit. It should be understood that other control methods may be used.

[0038] The power transfer element Tl 106 includes an auxiliary winding 112 of the reference input return line 111. The auxiliary winding 112 is shown coupled to diode Dl 146 and bypass capacitor 144. For the power converter 100 shown in Figure 1, the bypass voltage VBP 142 of the bypass capacitor 144 can be obtained from the voltage across the auxiliary winding 112. The bypass capacitor 144 is coupled to a first controller 132 to provide operating power to the circuitry of the first controller 132.

[0039] The bypass voltage VBP 142 can also be obtained from the drain current ID 119 of the bypass capacitor 144, which is redirected from the first switch 116 of the self-power switch S1 114. In one embodiment, all or a portion of the drain current ID 119 is redirected to the bypass capacitor 144. As will be discussed with respect to this figure, the branch switch 152 is controlled to redirect the drain current ID 119 (e.g., the current conducted by the first switch 116) to charge the bypass capacitor 144. In another embodiment discussed with respect to Figure 3, the branch switch redirects a portion of the drain current ID 119 to charge the bypass capacitor 144, and the second switch 118 is used to control that portion of the drain current ID 119 redirected to charge the bypass capacitor 144.

[0040] Comparator 156 is coupled to bypass capacitor 144 and receives bypass voltage VBP 142 at its inverting input. Comparator 156 also receives reference REF 167, also referred to as the bypass reference, at its non-inverting input. The output of comparator 156 is represented as bypass adjustment signal BP_REG 163. In one embodiment, reference REF 167 represents the desired adjusted value of bypass voltage VBP 142. Comparator 156 compares bypass voltage VBP 142 with reference REF 167. As shown, if bypass voltage VBP 142 is less than reference REF 167, bypass adjustment signal BP_REG 163 is a logic high value, and if bypass voltage VBP 142 is greater than reference REF 167, bypass adjustment signal BP_REG 163 is a logic low value. In other words, the asserted bypass adjustment signal BP_REG 163 indicates that the bypass voltage VBP 142 has dropped below the reference REF 167 (e.g., a logic high value). It should be understood that comparator 156 may also utilize hysteresis.

[0041] In the illustrated embodiment, when the bypass voltage VBP 142 is less than the reference REF 167, the branch switch 152 is controlled to redirect the drain current ID 119 to the bypass capacitor 144. In another embodiment, when the bypass voltage VBP 142 is less than the reference REF 167, the branch switch 152 is controlled to redirect a portion of the drain current ID 119. In other words, when the bypass voltage VBP 142 is less than the reference REF 167, the branch switch 152 is turned on. Furthermore, the first controller 132 is configured to control the power switch S1 114 such that at least a portion of the drain current ID 119 is used to charge the bypass capacitor 144.

[0042] The first controller 132 is shown as including a main control unit 148, a branch control unit 150, a branch switch 152, a diode D2 154, a comparator 156, and a driver 158. The main control unit 148 is configured to receive a request signal REQ 133 or a feedback signal FB 130 and a current sensing signal ISNS 140, and output an ON signal ON 160 and an OFF signal OFF 162. In one embodiment, both the ON signal ON 160 and the OFF signal OFF 162 are rectangular pulse waveforms with varying durations of logic high and low segments. The ON signal ON 160 represents that the control power switch S1 114 is turned on, while the OFF signal OFF 162 represents that the control power switch S1 114 is turned off. A logic high value (e.g., active) of the ON signal ON 160 corresponds to turning on the power switch S1 114, and specifically, to turning on the second switch 118. Similarly, a high logic value (e.g., active) of the OFF signal 162 corresponds to turning off power switch S1 114, and specifically, to turning off the second switch 118. It should be understood that the OFF signal 162 is the inverted form of the ON signal 160.

[0043] The main control unit 148 determines to turn on the power switch S1 114 in response to either the request signal REQ 133 or the feedback signal FB 130. During operation, the main control unit 148 determines to turn on the power switch S1 114 in response to a request event in the request signal REQ 133, specifically turning on the second switch 118. In another embodiment, the main control unit 148 determines to turn on the power switch S1 114 in response to the feedback signal FB 130 indicating that the output of the power converter 100 has dropped to a point of loss of regulation, specifically turning on the second switch 118. During operation, the ON signal 160 is active and the OFF signal 162 is deasserted.

[0044] The main control unit 148 also determines to turn off the power switch S1 114 in response to the current sensing signal ISNS 140 indicating that the drain current ID 119 has reached the current limit ILIM. It should be understood that other control schemes can be implemented by the main control unit 148 to control the energy transfer from the input side to the output side of the power converter 100. To turn off the power switch S1 114, the off signal OFF 162 is activated while the on signal ON 160 is deactivated.

[0045] Branch control device 150 is configured to receive an on signal ON 160 and a bypass adjustment signal BP_REG 163, and output a branch drive signal BR 165 and a dominant on signal MAIN_ON 164. The branch drive signal BR 165 is a control signal for turning branch switch 152 on and off, and in one embodiment is a rectangular pulse waveform with a logic high segment and a logic low segment of varying duration. The logic high segment represents a valid signal for turning branch switch 152 on, while the logic low segment represents an invalid signal for turning branch switch 152 off. The dominant on signal MAIN_ON 164 is a control signal for turning power switch S1 114 on and off—specifically, turning second switch 118 on and off—and is also a rectangular pulse waveform with a logic high segment and a logic low segment of varying duration. The logic high segment represents a valid signal for turning second switch 118 on, while the logic low segment represents an invalid signal for turning second switch 118 off. If the branch control device does not control the branch switch 152 to be on (e.g., the branch drive signal BR 165 is not valid), the main on signal MAIN_ON 164 essentially follows the on signal ON 160.

[0046] Branch switch 152 and diode D2 154 are shown coupled between the intermediate node A 117 of bypass capacitor 144 and power switch S1 114. Branch current IBR 168 is the current conducted by branch switch 152. In the illustrated embodiment, one end of branch switch 152 is coupled to the intermediate node A 117 of power switch S1 114, while the other end is coupled to the anode of diode D2 154. The cathode of diode D2 154 is coupled to bypass capacitor 144. Diode D2 is used to prevent current from flowing from bypass capacitor 144 to power switch S1 114. However, it should be understood that other configurations of branch switch 152 and diode D2 154 can be utilized. As shown, the sum of branch current IBR 168 and the second switch current I1 120 is essentially the drain current ID 119, or mathematically: .

[0047] During operation, when the bypass adjustment signal BP_REG 163 indicates that the bypass voltage VBP 142 has dropped below the reference REF 167, the branch control device 150 outputs the branch drive signal BR 165 to turn on the branch switch 152. If the bypass adjustment signal BP_REG 163 indicates that the bypass voltage VBP 142 has not yet dropped below the reference REF 167, the branch switch 152 is not turned on, and the main turn signal MAIN_ON 164 is essentially the turn signal ON 160.

[0048] If the bypass adjustment signal BP_REG 163 indicates that the bypass voltage VBP 142 has dropped below the reference REF 167, the branch control device 150 turns on the branch switch 152 in sync with the turn-on signal. As will be further shown with respect to Figure 2, if the bypass voltage VBP 142 drops below the reference REF 167 during one switching cycle of the power switch S1 114, the branch switch 152 is turned on at the beginning of the next (or subsequent) switching cycle. In one embodiment, the branch switch 152 is turned on for the same duration as the turn-on signal ON 160 is active, or until the bypass voltage VBP 142 reaches the reference REF 167. When the drain current ID 119 reaches the current limit, the turn-on signal ON 160 may be deactivated, and thus, the branch switch 152 remains on until the drain current ID 119 reaches the current limit or until the bypass voltage VBP 142 reaches the reference REF 167. In another embodiment, branch switch 152 can be turned on for a fixed amount of time. Furthermore, if branch switch 152 is turned off before the ON signal 160 is deactivated, the dominant ON signal MAIN_ON 164 is activated and subsequently followed by the ON signal 160 to turn on power switch S1 114. When the ON signal 160 is deactivated, the dominant ON signal MAIN_ON 164 is deactivated. For the embodiment shown in Figure 1, when branch switch 152 is conducting, the branch current IBR 168 is substantially equal to the drain current ID 119.

[0049] Driver 158 is configured to receive a branch drive signal BR 165, a dominant on signal MAIN_ON 164, and an off signal OFF 162, and output a primary drive signal DR 138 to control the conduction of power switch S1 114. Specifically, the primary drive signal DR 138 controls the conduction of the second switch 118 of the superimposed power switch S1 114. For example, driver 158 can control the conduction of the second switch 118 and the amount of current conducted by the second switch 118. In operation, in response to a valid branch drive signal BR 165, driver 158 outputs the primary drive signal DR 138, causing the second switch 118 to be off or not conducted. If the dominant on signal MAIN_ON 164 is valid, driver 158 outputs the primary drive signal DR 138, causing the second switch 118 to be on or positively conducted. If the off signal OFF 162 is valid, driver 158 outputs the primary drive signal DR 138, causing the second switch 118 to be off or not conducted. In the illustrated embodiment, when the second switch 118 is conducting, the second switch current I1 120 is essentially the drain current ID 119.

[0050] Thus, the first controller 132 uses at least a portion of the current conducted by the first switch 116 (e.g., at least a portion of the drain current ID 119) to charge the bypass capacitor 144, which provides operating power to the first controller 132. In the embodiment shown in Figure 1, the branch switch 152 is turned on and directs all of the drain current ID 119 to charge the bypass capacitor 144. In other words, when the branch switch 152 is turned on, the branch current IBR 168 is substantially equal to the drain current ID 119. Furthermore, since the power switch S1 114 is a stacked device with a normally open transistor (first switch 116) and a normally closed transistor (second switch 118), there are energy savings. Previous solutions may have used normally closed transistors as power switches, such as bipolar junction transistors (BJTs). Normally closed transistors (e.g., BJTs) will require a higher voltage power source to maintain transistor conduction, or the base-emitter capacitor (or gate-source capacitor) will be pre-charged to allow any energy to flow through the branch switch to the bypass capacitor. Furthermore, for BJTs, both turn-on and turn-off transistors will be utilized. However, since the power switch S1 114 is a stacked device with both normally open and normally closed devices, a higher voltage power source or charging of the gate-source or base-emitter capacitor is necessary.

[0051] Figure 2 illustrates a diagram 200 with example waveforms for the power converter 100 of Figure 1, including bypass voltage VBP 142, drain current ID 119, request signal REQ 133, on signal ON 160, off signal OFF 162, main on signal MAIN_ON 164, branch drive signal BR 165, and primary drive signal DR 138. It should be understood that similarly named and numbered components are coupled and function as described above. For the waveforms in Figure 2, when a request event is received in the request signal REQ 133, the first controller 132 turns on either power switch S1 114 or branch switch 152, and turns off power switch S1 114 when drain current ID 119 reaches current limit ILIM 221. The first controller 132 turns on branch switch 152 in response to the sensed bypass voltage VBP 142.

[0052] At time t1, a request event (e.g., a pulse) is received in the request signal REQ 133, and the turn-on signal ON 160 is activated to turn on the power switch S1 114. Since the bypass voltage VBP 142 is substantially equal to the reference REF 167 at time t1, the main turn-on signal MAIN_ON 164 substantially follows the turn-on signal ON 160, and the primary drive signal DR 138 is provided to turn on the power switch S1 114. As shown, the primary drive signal DR 138 transitions to the turn-on voltage VON 268, which is the voltage used to turn on the device used for the second switch 118, such that the second switching current I1 120 conducted by the second switch 118 is determined by the components coupled to the second switch 118. Furthermore, the branch drive signal BR 165 is not activated, and the branch switch 152 is not conducted.

[0053] Between time t1 and time t3, the drain current ID 119 increases at a rate proportional to the input voltage VIN 102 divided by the inductance of the input winding 108. Furthermore, the power converter 100 is operating in discontinuous conduction mode (DCM), as indicated by the drain current ID 119. Since branch switch 152 is not conducting, the second switching current I1 120 is substantially equal to the drain current ID 119, and the branch current IBR 168 is substantially zero. At time t3, the drain current ID 119 reaches the current limit ILIM 221, and the first controller 132 turns off the power switch S1 114. Thus, the on signal ON 160 and the main on signal MAIN_ON 164 are invalidated (transitioned to logic low), and the off signal OFF 162 is valid (transitioned to logic high). The main drive signal DR 138 transitions to the off voltage VOFF 269, which is the voltage used for the device applied to the second switch 118, preventing the second switch 118 and the power switch S1 114 from conducting current (e.g., turning off). Once the second switch 118 is open, the drain current ID 119 drops to zero.

[0054] However, at time t2, the bypass voltage VBP 142 drops below the reference REF 167. During the next switching cycle of power switch S1 114, at time t4, branch switch 152 is turned on to charge bypass capacitor 144 and bypass voltage VBP 142 increases. After time t2, bypass voltage VBP 142 continues to decrease until branch switch 152 is turned on at time t4.

[0055] At time t4, another request event is received in request signal REQ 133, and bypass voltage VBP 142 is less than reference REF 167. Main control unit 148 activates on signal ON 160 and deactivates off signal OFF 162, while branch control unit 150 activates branch drive signal BR 165. Because branch drive signal BR 165 is activated, primary on signal MAIN_ON 164 does not follow on signal ON 160, and primary on signal MAIN_ON 164 remains deactivated, while primary drive signal DR 138 remains at off voltage VOFF 269. Branch switch 152 is turned on (e.g., conducts current), and second switch 118 is prevented from conducting current (e.g., turned off). Drain current ID 119 increases, and branch switch 152 conducts all of drain current ID 119 to charge bypass capacitor 144, and bypass voltage VBP 142 increases. In other words, the branch current IBR 168 is essentially equal to the drain current ID 119, while the second switching current I1 120 is essentially zero.

[0056] At time t5, the drain current ID 119 reaches the current limit ILIM 221, and the main control unit 148 disables the ON signal 160 and enables the OFF signal 162. The branch control unit 150 disables the branch drive signal BR 165 to turn off the branch switch 152. Furthermore, the OFF signal 162 is received by the driver 158, and the primary drive signal DR 138 is held at the OFF voltage VOFF 269 to prevent the second switch 118 from conducting, and the drain current ID 119 decreases to zero. However, as shown, the bypass voltage VBP 142 remains below the reference REF 167, and between time t5 and time t6, the bypass voltage VBP 142 decreases.

[0057] At time t6, another request event is received in request signal REQ 133, and main control device 148 activates on signal ON 160 and deactivates off signal OFF 162. Bypass voltage VBP 142 remains below reference REF 167, and thus, branch control device 150 activates branch drive signal BR 165 to turn on branch switch 152, while main on signal MAIN_ON 164 remains deactivated to prevent second switch 118 from turning on. Branch switch 152 conducts drain current ID 119 to charge bypass capacitor 144, and bypass voltage VBP 142 increases. Between time t6 and time t7, branch current IBR 168 is substantially equal to drain current ID 119, while second switch current I1 120 is substantially zero.

[0058] As shown in Figure 2, the bypass voltage VBP 142 reaches the reference REF 167 at time t7 before the drain current ID 119 reaches the current limit ILIM 221 at time t8. At time t7, the branch control device 150 deactivates the branch drive signal BR 165 to prevent the branch switch 152 from turning on and activates the master on signal MAIN_ON 164 to turn on the second switch 118. In other words, the branch control device 150 allows the master on signal MAIN_ON 164 to follow the on signal ON 160. The driver 158 receives the active master on signal MAIN_ON 164 and transitions the primary drive signal DR 138 to the on voltage VON 268 to turn on the second switch 118, causing the second switch 118 to conduct the drain current ID 119. Between time t7 and time t8, the second switch current I1 120 is substantially equal to the drain current ID 119 and the branch current IBR 168 is substantially zero.

[0059] At time t8, the drain current ID 119 reaches the current limit ILIM 221, and the main control unit 148 disables the ON signal 160 and enables the OFF signal 162. Furthermore, the OFF signal 162 is received by the driver 158, and the primary drive signal DR 138 transitions to the off voltage VOFF 269 to prevent the second switch 118 from conducting, and the drain current ID 119 decreases to zero.

[0060] At time t9, a request event is received in the request signal REQ 133, and the main control unit 148 activates the ON signal 160 and deactivates the OFF signal 162. Since the bypass voltage VBP 142 is substantially equal to the reference REF 167 at time t9, and the main ON signal MAIN_ON 164 substantially follows the ON signal ON 160, the branch drive signal BR 165 remains deactivated. The driver 158 switches the primary drive signal DR 138 to the on-state voltage VON 268, allowing the second switch 118 to conduct the drain current ID 119. At time t10, the drain current ID 119 reaches the current limit ILIM 221, and the main control unit 148 deactivates the ON signal ON 160 and activates the OFF signal OFF 162 to turn off the second switch 118. The primary drive signal DR 138 transitions to the off voltage VOFF 269 to prevent the second switch 118 from conducting, and the drain current ID 119 decreases to zero.

[0061] Figure 3 illustrates another embodiment of the first controller 332, which includes a main control unit 148, a branch control unit 150, a branch switch 152, a diode D2 154, a comparator 156, a driver 358, and a shunt regulator 349. Further shown in Figure 3 is a power switch S1 114—which includes a first switch 116 and a second switch 118, a bypass capacitor 144, a diode D1 146, and an auxiliary winding 112. The power switch S1 114, the bypass capacitor 144, the diode D1 146, and the auxiliary winding 112 are included to provide background information on the first controller 332 in Figure 1. The drain current ID 119, the second switching current I1 120, the feedback / request signal FB / REQ 130 / 133, the primary drive signal DR 138, the current sensing signal ISNS 140, the bypass voltage VBP 142, the on signal ON 160, the off signal OFF 162, the bypass regulation signal BP_REG 163, the primary on signal MAIN_ON 164, the branch drive signal BR 165, the reference REF 167, the branch current IBR 168, and the shunt regulator output 372 are also illustrated in Figure 3. It should be understood that the first controller 332 can be used in conjunction with the power converter 100 shown in Figure 1.

[0062] Figure 3 shares many similarities with the first controller 132 discussed with respect to Figure 1, and it should be understood that similarly named and numbered elements are coupled and function as described above with respect to Figures 1 and 2. However, at least one difference is the addition of the shunt regulator 349 and the shunt regulator output 372, and how the driver 358 responds to the shunt regulator output 372. Furthermore, the branch control device 150 is also configured to receive the disconnect signal OFF 162 from the main control device 148 and determine whether the bypass voltage VBP 142 has dropped below the reference REF 167 during the disconnection time of the power switch S1 114 to determine whether the branch switch 152 should be turned on. However, it should be understood that the branch control device 150 may utilize the inverted phase of the on signal ON 160 instead of the disconnect signal OFF 162.

[0063] In the illustrated embodiment, the first controller 332 controls the amount of the branch current IBR 168 conducted by the branch switch 152. Furthermore, the first controller 332 controls the amount of the branch current IBR 168 conducted by the branch switch 152 by controlling the magnitude of the second switching current I1 120 conducted by the second switch 118. In other words, the first controller 332 uses the second switch 118 to regulate the branch current IBR 168. Therefore, the first controller 332 determines how much of the drain current ID 119 is redirected by the branch switch 152 to charge the bypass capacitor 144. The remaining drain current ID 119 not used to charge the bypass capacitor 144 is conducted by the second switch 118.

[0064] The physical size of the branch switch is determined in part by the maximum amount of the branch current IBR 168 conducted by branch switch 152 and the duration for which branch switch 152 conducts the maximum current. For example, to enable branch switch 152 to conduct the entire drain current ID 119, the physical size of branch switch 152 will be similar to the physical size of the second switch 118. Depending on the package used to house the first controller 332 and the second switch 118, if the size of branch switch 152 is similar to that of the second switch 118, there may not be enough space to accommodate both the second switch 118 and branch switch 152. Thus, the physical size of branch switch 152 can be controlled by regulating the branch current IBR 168 to be below a branch current threshold. If the second switch 118 is controlled to shunt a portion of the drain current ID 119 to regulate the branch current IBR 168 below the branch current threshold, a smaller branch switch 152 can be used.

[0065] For the embodiment shown in Figure 3, if the bypass voltage VBP 142 is below the reference REF 167 before the start of a switching cycle, the branch control device 150 outputs a branch drive signal BR 165 to turn on the branch switch 152 during that switching cycle. In one embodiment, the branch switch 152 remains on until the bypass voltage VBP 142 rises above the reference REF 167 or the off signal OFF 162 is activated. In another embodiment discussed with respect to Figures 5A and 5B, the branch switch 152 is on for a fixed amount of time or until the off signal OFF 162 is activated. The branch control device 150 receives the off signal OFF 162, and when the off signal OFF 162 is activated, if the bypass voltage VBP 142 is below the reference REF 167, the branch control device 150 can determine that the branch switch 152 will be turned on for the upcoming switching cycle. Alternatively, branch control device 150 can utilize the ON signal 160, and when the ON signal 160 is not active, if the bypass voltage VBP 142 is below the reference REF 167, branch control device 150 can determine that branch switch 152 is activated for an upcoming switching cycle. In one embodiment, when the drain current ID 119 reaches the current limit, the OFF signal 162 is active (or the ON signal 160 is deactivated), and the OFF signal 162 remains active until the next request event is received in the request signal REQ 133. When the OFF signal 162 is active, power switch S1 114 and branch switch 152 are deactivated and conduction is prevented.

[0066] The shunt regulator 349 is configured to receive a branch drive signal BR 165 from the branch control device 150 and sense the branch current IBR 168. The shunt regulator 349 outputs a shunt regulator output 372 to the driver 358. In operation, the shunt regulator 349 senses the branch current IBR 168 when the branch drive signal BR 165 indicates that the branch switch 152 is turned on (e.g., conducted). Furthermore, the shunt regulator 349 senses when the branch current IBR 168 has reached a branch current threshold value and outputs the shunt regulator output 372. Together with the driver 358, this prevents the branch current IBR 168 from exceeding the branch current threshold value. In one embodiment, the shunt regulator output 372 may be a voltage regulated by the shunt regulator 349 to determine the level of the primary drive signal DR 138. In one embodiment, the shunt regulator 349 functions as a linear amplifier.

[0067] Driver 358 is configured to receive a dominant on signal MAIN_ON 164, a branch drive signal BR 165, and a shunt regulator output 372. The dominant on signal MAIN_ON 164 represents the second switch 118 being fully on. In response to a valid dominant on signal MAIN_ON 164, driver 358 outputs a drive signal DR 138 to a level that ensures the second switch 118 is fully on (e.g., on-state voltage VON). In other words, the current conducted by the second switch 118 is determined by external components coupled to the second switch 118.

[0068] Branch drive signal BR 165 represents the conduction of branch switch 152. In response to a valid branch drive signal BR 165, driver 358 determines the level of primary drive signal DR 138 in response to shunt regulator output 372 representing branch current IBR 168, to control the value of second switching current I1 120 conducted by second switch 118.

[0069] When branch switch 152 is turned on (e.g., conducted), driver 358 responds to shunt regulator output 372 by changing the level of primary drive signal DR 138 to control the conduction of second switch 118. The sum of branch current IBR 168 and second switch current I1 120 is essentially the drain current ID 119, or mathematically: In the illustrated embodiment, the second switch 118 is a voltage-controlled device, exemplified as a MOSFET, and the primary drive signal DR 138 is a voltage signal. Driver 358 changes the voltage level of the primary drive signal DR 138 to control the value of the second switching current I1 120 conducted by the second switch 118. The voltage level of the primary drive signal DR 138 can be selected such that the value of the second switching current I1 120 is determined by the gate-source voltage of the second switch 118. In one embodiment, the voltage level of the primary drive signal DR 138 can be selected such that the second switch 118 operates in a linear mode.

[0070] In another embodiment, driver 358 is configured to receive a dominant on signal MAIN_ON 164 and a shunt regulator output 372, but not a branch drive signal BR 165. The dominant on signal MAIN_ON 164 represents turning on the second switch 118 to fully turn on the second switch 118 or to turn on the second switch 118 in response to the shunt regulator output 372. Thus, when branch switch 152 is not turned on, the dominant on signal MAIN_ON 164 can be activated to fully turn on the second switch 118. When branch switch 152 is turned on, the dominant on signal MAIN_ON 164 can also be activated, causing driver 358 to determine the level of the primary drive signal DR 138 in response to the shunt regulator output 372 to control the value of the second switch current I1 120 and regulate the branch current IBR 168 below the branch current threshold value.

[0071] Thus, the shunt regulator 349 and driver 358 regulate the value of the branch current IBR 168 below the branch current threshold by controlling the amount of the drain current ID 119 (e.g., the second switch current I1 120) conducted by the second switch 118. In other words, the shunt regulator 349 and driver 358 regulate the amount of the drain current ID 119 (e.g., the branch current IBR 168) used to charge the bypass capacitor 144. The remaining portion of the drain current ID 119 is conducted by the second switch 118 as the second current I1 120.

[0072] Furthermore, when the power converter 100 operates in discontinuous conduction mode (DCM) or continuous conduction mode (CCM), the first controller 332 can change the operation of the branch switch 152 and the second switch 118. During DCM, when power switch S1 114 or branch switch 152 is turned on, the switching current ID 119 is zero. In CCM, when power switch S1 114 or branch switch 152 is turned on, the switching current ID 119 is substantially non-zero.

[0073] During DCM operation, if the bypass voltage VBP 142 is below reference REF 167 when a switching cycle is requested (e.g., the ON signal 160 is active), the branch drive signal BR 165 controls the branch switch 152 to be turned on (e.g., conducted). The shunt regulator 349 and driver 358 regulate the branch current IBR 168 by controlling how much of the second switching current I1 120 is conducted by the second switch 118.

[0074] However, in CCM, when power switch S1 114 is turned on, the drain current ID 119 is non-zero. Thus, a large current spike can occur when power switch S1 114 or branch switch 152 is turned on. This large current spike may damage branch switch 152. To enable branch switch 152 to conduct the full drain current ID 119, the physical dimensions of branch switch 152 can be similar to those of the second switch 118. However, as mentioned above, a physically smaller branch switch 152 can be utilized by adjusting the branch current IBR 168. During CCM operation, the second switch 118 is turned on at the beginning of a switching cycle to conduct the large current spike before branch switch 152 is turned on. After a given period of time, branch switch 152 is then turned on, causing branch current IBR 168 to charge bypass capacitor 144. Branch regulator 349 and driver 358 regulate branch current IBR 168 by controlling how much second switch current I1 120 is conducted through second switch 118. Thus, second switch 118 is used to protect branch switch 152.

[0075] Figure 4A is a timing diagram 400 illustrating example waveforms of the first controller 332 in Figure 3 when the power converter 100 is operating in discontinuous conduction mode (DCM). The bypass voltage VBP 142, request signal REQ 133, drain current ID 119, branch current IBR 168, second current I1 120, on signal ON 160, off signal OFF 162, voltage at node A 117, main on signal MAIN_ON 164, branch drive signal BR 165, and primary drive signal DR 138 are illustrated. Similar to Figure 2, the primary drive signal DR 138 is shown as a voltage signal, and the voltage level of the primary drive signal DR 138 controls the value of the second switching current I1 120. It should be understood that similarly named and numbered components are coupled and function as described above.

[0076] In the illustrated embodiment, comparator 156 utilizes hysteresis, and the upper reference REF+ 167a and lower reference REF- 167b illustrated in Figures 4A and 4B represent hysteresis threshold values ​​for referencing REF 167. When the bypass voltage VBP 142 drops below the lower reference REF- 167b, the bypass adjustment signal BP_REG 163 transitions to a logic high value, and when the bypass voltage VBP 142 exceeds the upper reference REF+ 167a, the bypass adjustment signal BP_REG 163 transitions to a logic low value. In other words, when the bypass voltage VBP 142 drops below the lower reference REF- 167b, the first controller 332 can determine to turn on the branch switch 152 to charge the bypass capacitor 144. When the bypass voltage VBP 142 exceeds the upper reference REF+ 167a, the controller 332 can also determine to turn off the branch switch 152.

[0077] The period between time t11 and time t13 and before time t20 represents the normal switching cycle of power switch S1 114, during which second switch 118 is fully turned on and energy is transferred from the input of power converter 100 to the output of power converter 100. However, the switching cycles between time t13 and time t16 and between time t16 and time t20 represent the charging cycle during which branch switch 152 is turned on to charge bypass capacitor 144. During these cycles, second switch 118 is used to regulate branch current IBR 168 below the branch current threshold value IBRTH 490. However, it should be understood that the switching cycle between time t16 and time t20 transitions from the charging cycle to the normal switching cycle.

[0078] At time t11, a request event (e.g., a pulse) is received in the request signal REQ 133, and the ON signal 160 is activated, while the OFF signal 162 is deactivated via the main control device 148. When the request event is received, the bypass voltage VBP 142 is greater than the lower reference REF-167b, and thus, the branch switch 152 is not turned on to charge the bypass capacitor 144. The branch control device 150 activates the main ON signal MAIN_ON 164, such that the main ON signal MAIN_ON 164 substantially follows the ON signal ON 160. The branch drive signal BR 165 is also deactivated via the branch control device 150, and the branch switch 152 is not conducted—indicated by the substantially zero branch current IBR 168 between time t11 and time t12.

[0079] With the primary on signal MAIN_ON 164 active, the primary drive signal DR 138 provided by driver 358 is essentially an on-state voltage VON 268, which is used to turn on the second switch 118 such that the drain current ID 119 and the second current I1 120 are determined by the components coupled to the power switch S1 104. Thus, between time t11 and time t12, the second switch 118 is fully on and the voltage at node A 117 is a small value close to zero. In one embodiment, when the second switch 118 is fully on, the voltage at node A 117 can be essentially 100 mV. The second switch 118 is conducting and the second current I1 120 is essentially equal to the drain current ID 119.

[0080] At time t12, the drain current ID 119 reaches the current limit ILIM 221 and the power switch S1 114 is turned off. The on signal ON 160 and the main on signal MAIN_ON 164 are both invalidated, while the off signal OFF 162 is valid. Driver 358 switches the drive signal DR 138 to the off voltage VOFF 269, which is the voltage value that prevents the second switch 118 from conducting current and causes the drain current ID 119 and the second current I1 120 to drop to zero. Between time t12 and time t13, when the power switch S1 114 is off, the voltage at node A 117 is at a high value above the threshold value VTH116 491 of the first switch 116, causing the first switch 116 to be cut off and not conducting current.

[0081] At time t13, a request event is received in the request signal REQ 133, and the ON signal 160 is activated while the OFF signal 162 is deactivated. Additionally, the bypass voltage VBP 142 is below the lower reference REF-167b, and thus, at least a portion of the drain current ID 119 is used to charge the bypass capacitor 144. Since the bypass voltage VBP 142 has dropped below the lower reference REF-167b, the branch control device 150 does not activate the main ON signal MAIN_ON 164, but instead activates the branch drive signal BR 165 to turn on the branch switch 152 and conduct the branch current IBR 168. The primary drive signal DR 138 is held at the OFF voltage VOFF 269 to prevent the second switch S1 118 from conducting. At time t13, the voltage at node 117 drops to a value above the input loop 111 (shown as 0 V in Figures 4A and 4B) but below the threshold value VTH116 491 of the first switch 116.

[0082] Between time t13 and time t14, the branch current IBR 168 is less than the branch current threshold value IBRTH 490. Thus, the primary drive signal DR 138 remains at the off-voltage VOFF 269 and the second switch 118 does not conduct. The branch current IBR 168 is essentially the drain current ID 119 and the second current I1 120 is essentially zero.

[0083] However, at time t14, the branch current IBR 168 reaches the branch current threshold value IBRTH 490, and the shunt regulator 349 provides a shunt regulator output 372, causing the driver 358 to control the second switch 118 to be turned on and control the amount of current (e.g., the second current I1 120) conducted by the second switch 118. As shown, at time t14, the primary drive signal DR 138 transitions to a value above the threshold value VTH118 492 of the second switch 118, such that the current conducted by the second switch 118 (e.g., the second current I1 120) depends on the value of the gate voltage of the second switch 118 (e.g., the primary drive signal DR 138). Thus, the shunt regulator 349 is able to regulate the branch current IBR 168 to at or below the branch current threshold value IBRTH 490.

[0084] Between time t14 and time t15, shunt regulator 349 and driver 358 are controlling the conduction of second switch 118, such that branch current IBR 168 is maintained at branch current threshold value IBRTH 490. The remaining drain current ID 119, which is not redirected by branch switch 152 to bypass capacitor 144, is conducted by second switch 118 as second current I1 120. It should be understood that the sum of second current I1 120 and branch current IBR 168 is essentially the drain current ID 119. Between time t14 and time t15, bypass voltage VBP 142 has increased above lower reference REF- 167b, but has not yet reached upper reference REF+ 167a. Thus, the output of comparator 156 (e.g., bypass adjustment signal BP_REG 163) remains unchanged until the bypass voltage VBP 142 has reached the upper reference REF+ 167a and the branch switch 152 remains on to charge the bypass capacitor 144.

[0085] At time t15, the drain current ID 119 reaches the current limit ILIM 221 and the power switch S1 114 is turned off. The on signal ON 160 is invalidated, while the off signal OFF 162 is valid. The driver switches the drive signal DR 138 to the off voltage VOFF 269, and the voltage at node A 117 is at a high value above the threshold value VTH 116 of the first switch 116. Thus, neither the first switch 116 nor the second switch 118 conducts, and the drain current ID 119, the second current I1 120, and the branch current IBR 168 drop to zero. Before time t15, the bypass voltage VBP 142 has not reached the upper reference REF+ 167a.

[0086] At time t16, a request event is received and the bypass voltage VBP 142 is below the upper reference REF+ 167a. Thus, a portion of the drain current ID 119 is used to charge the bypass capacitor 144. The ON signal ON 160 is activated, while the OFF signal OFF 162 is deactivated. The branch control device 150 deactivates the main ON signal MAIN_ON 164 and activates the branch drive signal BR 165 to turn on the branch switch 152 to conduct the branch current IBR 168. The primary drive signal DR 138 is held at the OFF voltage VOFF 269 to prevent the second switch S1 118 from conducting. The voltage at node 117 drops to a value above the input loop 111 (shown as 0 V in Figures 4A and 4B) but below the threshold value VTH116 491 of the first switch 116.

[0087] Similar to the duration between time t13 and time t14, between time t16 and time t17, the branch current IBR 168 is less than the branch current threshold value IBRTH 490. Thus, the second switch 118 is not turned on for conduction current and the branch current IBR 168 is essentially the drain current ID 119 and the second current I1 120 is essentially zero.

[0088] At time t17, the branch current IBR 168 reaches the branch current threshold value IBRTH 490, and the shunt regulator 349 and driver 358 control the second switch 118 to be turned on. Furthermore, the amount of current conducted by the second switch 118 (e.g., the second current I1 120) is a function of the sensed branch current IBR 168. As shown, at time t17, the primary drive signal DR 138 transitions to a value above the threshold value VTH118 492 of the second switch 118, such that the current conducted by the second switch 118 (e.g., the second current I1 120) depends on the value of the gate voltage of the second switch 118 (e.g., the primary drive signal DR 138).

[0089] Between time t17 and time t18, shunt regulator 349 and driver 358 control the conduction of second switch 118 such that branch current IBR 168 is maintained at branch current threshold value IBRTH 490. The remaining drain current ID 119, not utilized by branch switch 152 to charge bypass capacitor 144, is conducted by second switch 118 as second current I1 120. It should be understood that the sum of second current I1 120 and branch current IBR 168 is essentially the drain current ID 119.

[0090] At time t18, the bypass voltage VBP 142 reaches the upper reference REF+ 167a before the drain current ID 119 has reached the current limit ILIM 221. The on signal ON 160 remains active, and the branch control device 150 deactivates the branch drive signal BR 165 to turn off the branch switch 152 and activates the main on signal MAIN_ON 164 to fully turn on the second switch 118. The cycle returns to the normal switching cycle, and the second switch 118 conducts the full drain current ID 119. Or in other words, the second current I1 120 is essentially the drain current ID 119. The voltage at node A 117 drops to a value far below the threshold value VTH116 491 of the first switch 116, and the primary drive signal DR 138 increases to the on-state voltage VON 268.

[0091] At time t19, the drain current ID 119 reaches the current limit ILIM 221 and the power switch S1 114 is turned off. The main control unit 148 invalidates the on signal ON 160 and enables the off signal OFF 162. The main on signal MAIN_ON 164 is also invalidated, while the off signal OFF 162 is enabled. The driver 358 causes the drive signal DR 138 to switch off at the off voltage VOFF 269, and the voltage at node A 117 is at a high value above the threshold value VTH116 491 of the first switch 116. Thus, neither the first switch 116 nor the second switch 118 conducts, and the drain current ID 119, the second current I1 120, and the branch current IBR 168 drop to zero. The power switch S1 114 remains off until another request event is received in the request signal REQ 133 at time t20.

[0092] Figure 4B illustrates a timing diagram 401 of an example waveform of the first controller 332 in Figure 3 when the power converter 100 is operating in continuous conduction mode (CCM). The bypass voltage VBP 142, request signal REQ 133, drain current ID 119, branch current IBR 168, second current I1 120, on signal ON 160, off signal OFF 162, voltage at node A 117, main on signal MAIN_ON 164, branch drive signal BR 165, and primary drive signal DR 138 are illustrated in Figures 4A and 4B. Furthermore, the upper reference REF+ 167a and lower reference REF- 167b illustrated in Figures 4A and 4B represent the hysteresis threshold values ​​used by comparator 156 for reference REF 167. It should be understood that similarly named and numbered components are coupled and function as described above.

[0093] The period between time t22 and time t23 and before time t31 represents the normal switching cycle of power switch S1 114, during which second switch 118 is fully turned on and energy is transferred from the input of power converter 100 to the output of power converter 100. However, the switching cycles between time t24 and time t27 and time t27 and time t31 represent the charging cycle in which branch switch 152 is turned on to charge bypass capacitor 144. During these cycles, second switch 118 is also used to regulate branch current IBR 168 below the branch current threshold value IBRTH 490. The charging cycle begins when bypass voltage VBP 142 drops below lower reference REF- 167b and ends when bypass voltage VBP 142 reaches upper reference REF+ 167a.

[0094] Similar to the normal switching cycle discussed above regarding Figure 4A between times t11 and t13 and at time t22, at times t22 and t31, when a request event (e.g., a pulse) is received in the request signal REQ 133, the bypass voltage VBP 142 is greater than the lower reference REF- 167b or has reached the upper reference REF+ 167a, and the branch switch 152 is not turned on to charge the bypass capacitor 144. The ON signal 160 is active, while the OFF signal 162 is deactivated by the main control unit 148. The branch control unit 150 activates the main ON signal MAIN_ON 164, and the main ON signal MAIN_ON 164 substantially follows the ON signal 160. The branch drive signal BR 165 is also not valid by the branch control device 150 and the branch switch 152 is not conducted—indicated by the essentially zero branch current IBR 168 between time t22 and time t23 and before time t31.

[0095] The primary drive signal DR 138 is essentially equal to the turn-on voltage VON 268, which is the voltage used to turn on the second switch 118 so that the drain current ID 119 and the second current I1 120 are determined by the components coupled to the power switch S1 104. Thus, between times t22 and t23 and forward to time t31, the second switch 118 is fully on and the voltage at node A 117 is small, close to zero. For example, when the second switch 118 is fully on, the voltage at node A 117 can be essentially 100 mV. When the second switch 118 is fully on and conducting, the second current I1 120 is essentially equal to the drain current ID 119. As shown, the drain current ID 119 is essentially non-zero at the beginning of the switching cycle, thus indicating CCM operation. Current spikes are visible when the power switch S1 114 is turned on at times t22 and t31.

[0096] At times t23 and t32, the drain current ID 119 reaches the current limit ILIM 221 and the power switch S1 114 is turned off. The on signal ON 160 and the main on signal MAIN_ON 164 are both invalidated, while the off signal OFF 162 is valid. The driver causes the drive signal DR 138 to switch off to the off voltage VOFF 269, which is the voltage value at which the second switch 118 cannot conduct current and the drain current ID 119 and the second current I1 120 drop to zero. Between times t23 and t24, when the power switch S1 114 is off, the voltage at node A 117 is at a high value above the threshold value VTH116 491 of the first switch 116, causing the first switch 116 to be cut off and not conducting current.

[0097] At time t24, a request event is received in the request signal REQ 133, and the main control unit 148 activates the ON signal 160 and deactivates the OFF signal 162. However, at time t24, the bypass voltage VBP 142 is below the lower reference REF-167b, and a portion of the drain current ID 119 is used to charge the bypass capacitor 144 by turning on the branch switch 152. However, during CCM operation, the second switch 118 is briefly fully turned on between time t24 and time t25 to conduct the CCM current spike seen at the beginning of the switching cycle. The branch control unit 150 activates the main ON signal MAIN_ON 164, but the branch drive signal BR 165 is not activated until time t25. The primary drive signal DR 138 transitions to the on-state voltage VON 268, and the voltage at node A 117 is a small value close to zero, and the second switch 118 is fully on and conducts the drain current ID 119 (e.g., the second current I1 120 is essentially the drain current ID 119).

[0098] At time t25, branch control device 150 activates branch drive signal BR 165 to turn on branch switch 152 and deactivates main on signal MAIN_ON 164. Driver 358 causes primary drive signal DR 138 to shift to a value above the threshold value VTH118 492 of second switch 118, such that the current conducted by second switch 118 (e.g., second current I1 120) depends on the value of the gate voltage of second switch 118 (e.g., the value of primary drive signal DR 138). As shown, the voltage at node A 117 shifts to a value below the threshold value VTH116 491 of first switch 116. It should be understood that the duration between time t24 and time t25 can be fixed or variable.

[0099] Between time t25 and time t26, the branch current IBR 168 is less than or has reached the branch current threshold value IBRTH 490. The shunt regulator 349 provides the shunt regulator output 372 to the driver 358 to control the amount of current (e.g., the second current I1 120) conducted by the second switch 118, such that the branch current IBR 168 is maintained at or below the branch current threshold value IBRTH 490. The remaining drain current ID 119, not conducted by the branch switch 152 to charge the bypass capacitor 144, is conducted by the second switch 118 as the second current I1 120. It should be understood that the sum of the second current I1 120 and the branch current IBR 168 is essentially the drain current ID 119. During this switching cycle, the bypass voltage VBP 142 has increased above the lower reference REF- 167b but not to the upper reference REF+ 167a, and the output of comparator 156 (e.g., the bypass adjustment signal BP_REG 163) does not change state.

[0100] At time t26, the drain current ID 119 reaches the current limit ILIM 221 and the power switch S1 114 is turned off. The on signal ON 160 and the main on signal MAIN_ON 164 are both invalidated, while the off signal OFF 162 is valid. The driver causes the drive signal DR 138 to switch off at VOFF 269, and the voltage at node A 117 is at a high value above the threshold value VTH116 491 of the first switch 116. Thus, neither the first switch 116 nor the second switch 118 conducts, and the drain current ID 119, the second current I1 120, and the branch current IBR 168 drop to zero. With branch switch 152 open, the bypass voltage VBP 142 decreases.

[0101] At time t27, a request event is received in the request signal REQ 133, and the main control unit 148 activates the ON signal 160 and deactivates the OFF signal 162. The bypass voltage VBP 142 is below the upper reference REF+ 167a at time t27, and a portion of the drain current ID 119 is used to charge the bypass capacitor 144. As previously discussed, the second switch 118 is briefly fully turned on between time t27 and time t28 to conduct the CCM current spike seen at the beginning of the switching cycle. The branch control unit 150 activates the main on signal MAIN_ON 164 but not the branch drive signal BR 165 until time t28. The primary drive signal DR 138 transitions to the on-state voltage VON 268, and the voltage at node A 117 is a small value close to zero, and the second switch 118 is fully turned on and conducts the drain current ID 119, and thus the second current I1 120 is essentially the drain current ID 119.

[0102] At time t28, branch control device 150 activates branch drive signal BR 165 to turn on branch switch 152 to conduct branch current IBR 168, and deactivates main on signal MAIN_ON 164. Driver 358 causes primary drive signal DR 138 to transition to a value above the threshold value VTH118 492 of second switch 118, such that the current conducted by second switch 118 (e.g., second current I1 120) depends on the value of the gate voltage of second switch 118 (e.g., the value of primary drive signal DR 138). As shown, the voltage at node A 117 transitions to a value just below the threshold value VTH116 491 of first switch 116. It should be understood that the duration between time t27 and time t28 can be fixed or variable.

[0103] Between time t28 and time t29, the branch current IBR 168 is controlled to be less than the branch current threshold value IBRTH 490. During this time period, the shunt regulator 349 provides the shunt regulator output 372 to the driver 358 to control the amount of current (e.g., the second current I1 120) conducted by the second switch 118, such that the branch current IBR 168 is maintained at or below the branch current threshold value IBRTH 490. The remaining drain current ID 119, which is not conducted by the branch switch 152 to charge the bypass capacitor 144, is conducted by the second switch 118 as the second current I1 120.

[0104] At time t29, the bypass voltage VBP 142 reaches the upper reference REF+ 167a before the drain current ID 119 has reached the current limit ILIM 221, and the branch control device 150 invalidates the branch drive signal BR 165 to turn off the branch switch 152. The on signal ON 160 remains active, and the branch control device 150 then activates the primary on signal MAIN_ON 164 to fully turn on the second switch 118. The voltage at node A 117 drops to a value far below the threshold value VTH116 491 of the first switch 116, and the primary drive signal DR 138 increases to the on-state voltage VON 268. The cycle returns to the normal switching cycle, and the second switch 118 conducts the full drain current ID 119, and the second current I1 120 is essentially the drain current ID 119.

[0105] At time t30, the drain current ID 119 reaches the current limit ILIM 221 and the power switch S1 114 is turned off. The on signal ON 160 and the main on signal MAIN_ON 164 are both invalidated, while the off signal OFF 162 is valid. The primary drive signal DR 138 transitions to the off voltage VOFF 269, and the voltage at node A 117 is at a high value above the threshold value VTH116 491 of the first switch 116. Thus, neither the first switch 116 nor the second switch 118 conducts, and the drain current ID 119, the second current I1 120, and the branch current IBR 168 drop to zero. The power switch S1 114 remains off until another request event is received in the request signal REQ 133 at time t31.

[0106] Figure 5A illustrates another embodiment of the first controller 532, which includes a branch control device 550, a branch switch 152, a diode D2 154, a comparator 156, a driver 558, and a shunt regulator 349. A power switch S1 114—which includes a first switch 116 and a second switch 118—and a bypass capacitor 144 are shown to provide background information on the first controller 532 in Figure 1. A drain current ID 119, a second switch current I1 120, a primary drive signal DR 138, a bypass voltage VBP 142, an on signal ON 160, an off signal OFF 162, a bypass regulator signal BP_REG 163, a primary on signal MAIN_ON 164, a branch drive signal BR 165, a reference REF 167, a branch current IBR 168, and a shunt regulator output 372 are also illustrated in Figure 5A. It should be understood that the first controller 532 can be used in conjunction with the power converter 100 shown in Figure 1. The main control unit is not illustrated in Figure 5A; however, it should be understood that the first controller 532 also includes a main control unit to provide an ON signal 160 and an OFF signal 162.

[0107] Figure 5A illustrates an example embodiment of the branch control device 550 and the driver 558. The branch control device 550 is shown as including a gate 574, a latch 575, a gate 576, a capacitor C1 581, a resistor R1 582, an inverter 577, an inverter 578, a gate 579, and a gate 580. The driver 558 is illustrated as including switches 585, 586, and 587 and a resistor R3 588. In the illustrated embodiment, a diode 589 is illustrated as coupled between the shunt regulator 349 and the driver 558 to illustrate the direction of the shunt regulator output 372. It should be understood that the diode 589 may be optional.

[0108] Figure 5A shares many similarities with the first controller 132 discussed with respect to Figure 1, and it should be understood that similarly named and numbered elements are coupled and function as described above with respect to Figures 1 and 2. However, at least one difference is the addition of the shunt regulator 349 and the shunt regulator output 372, and how the driver 558 responds to the shunt regulator output 372. Similar to the first controller 332 discussed with respect to Figure 3, the first controller 532 regulates the branch current IBR 168 to at or below the branch current threshold value IBRTH.

[0109] Figure 5A shares many similarities with the first controller 332 in Figure 3, and it should be understood that similarly named and numbered elements are coupled and function as described above with respect to Figures 3, 4A, and 4B. However, at least one difference is that branch switch 152 is turned on to charge bypass capacitor 144 during a portion of the on-time of power switch S1 114. As will be discussed, if the bypass voltage VBP 142 is less than reference REF 167, branch control device 550 determines to turn on branch switch 152 for a period T1 at the beginning of the on-time of power switch S1 114. During period T1, branch regulator 349 and driver 558 regulate branch current IBR 168 below the branch current threshold value IBRTH by controlling the second current I1 120 conducted by second switch 118. Once time period T1 has passed, the switching cycle returns to the normal switching cycle, and the branch control device 550 controls the branch switch 152 to be open, and the driver 558 controls the second switch 118 to be fully open to conduct all the drain current ID 119.

[0110] Branch control device 550 determines whether the bypass voltage VBP 142 has dropped below reference REF 167 during the off-time of power switch S1 114, as indicated by the off-state signal OFF 162 (or alternatively, an inverted on-state signal ON 160) and bypass adjustment signal BP_REG 163. Branch control device 550 then determines whether branch switch 152 should be turned on such that a portion of the drain current ID 119 is used to charge bypass capacitor 144. Gate 574 is illustrated as being coupled to comparator 156 and receiving bypass adjustment signal BP_REG 163 and off-state signal OFF 162. Alternatively, gate 574 may receive an inverted on-state signal ON 160 instead of off-state signal OFF 162.

[0111] Locker 575 is coupled to gate 574. As shown, the output of gate 574 is received at the S-input of locker 575. The reset input of locker 575 is coupled to capacitor C2 583 and resistor R2 584. Gate 576 is coupled to receive the Q output and ON signal ON 160 of locker 575. The output of gate 576 is coupled to capacitor C1 581, which is then coupled to resistor R1 582 and inverter 577. Capacitor C1 581 and resistor R1 582 are coupled together as a monostable multivibrator to provide pulses for duration T1.

[0112] Inverter 577 is coupled to inverter 578 and gate 580. Gates 579 and 580 are both coupled to receive the ON signal 160. Furthermore, gate 579 is coupled to receive the output of inverter 578, while gate 580 is coupled to receive the output of inverter 577. The output of gate 579 is the branch drive signal BR 165, while the output of gate 580 is the main ON signal MAIN_ON 164.

[0113] During operation, if the bypass voltage VBP 142 is less than the reference REF 167, the bypass adjustment signal BP_REG 163 is logic high. The OFF signal 162 is logic high (e.g., active) during the off-time of power switch S1 114. If the bypass adjustment signal BP_REG 163 indicates that the bypass voltage VBP 142 is less than the reference REF 167 during the off-time of power switch S1 114, the output of gate 574 is logic high, latch 575 is set, and the Q output is logic high. The ON signal 160 is logic high (e.g., active) at the start of the next switching cycle of power switch S1 114. Because the Q output is high due to the bypass voltage VBP 142 being below the reference REF 167 in the previous switching cycle, the output of gate 576 is logic high. In other words, the output of gate 576 transitions to a logic high value on the rising edge of the ON signal ON 160. Capacitor C1 581 and resistor R1 582 are coupled together as a monostable multivibrator. When the output of gate 576 transitions to a logic high value (e.g., a rising edge), capacitor C1 581 and resistor R1 582 provide a pulse with a duration substantially equal to time period T1.

[0114] Inverter 577 provides the inverted pulse of time period T1 to gate 580, while inverter 578 provides the pulse of time period T1 to gate 579. When the ON signal 160 is initially valid, gate 579 provides a logic high (e.g., valid) value for the branch drive signal BR 165, and the branch switch 152 is turned on during time period T1. In other words, the branch drive signal BR 165 is logic high for a duration substantially equal to the duration of time period T1.

[0115] Since inverter 577 provides the inverted pulse of time period T1 to gate 580, when the on signal ON 160 is initially valid, the dominant on signal MAIN_ON 164 is logic low (e.g., invalid) during time period T1. At the end of time period T1, the pulse provided by capacitor C1 581 and resistor R1 582 transitions to a logic low value and the branch drive signal BR 165 is invalid (e.g., logic low), and branch switch 152 is turned off. The output of inverter 577 is logic high after time period T1, so the dominant on signal MAIN_ON 164 transitions to a logic high value (e.g., valid) after time period T1 has passed and remains valid to turn on the second switch S1 118 until the on signal ON 160 is invalidated. Capacitor C2 583 and resistor R2 584 provide edge triggering to reset latch 575.

[0116] If the bypass adjustment signal BP_REG 163 remains low—indicating that the bypass voltage VBP 142 is greater than the reference REF 167—the latch 575 is not set and its Q output is low, the gate 576 is low, while the inverter 577 is high and the inverter 578 is low. Thus, when the ON signal 160 is high (e.g., active), the branch drive signal BR 165 remains low (e.g., inactive) and the main ON signal MAIN_ON 164 is high (e.g., active).

[0117] Driver 558 is illustrated as including switches 585, 586, and 587 and resistor R3 588. Diode 589 is illustrated as coupled between shunt regulator 349 and driver 558 to illustrate the direction of shunt regulator output 372. However, it should be understood that diode 589 is optional. As shown, switch 585 is coupled between the gate of second switch 118 and the on-state voltage VON 268 and is controlled by the dominant on-state signal MAIN_ON 164. In operation, switch 585 is coupled as a pull-up switch to the gate of second switch 118 to drive second switch 118 fully on. If the dominant on-state signal MAIN_ON 164 is active, switch 585 is closed and the primary drive signal DR 138 (e.g., the gate voltage of second switch 118) is essentially the on-state voltage VON 268. As mentioned above, the value of the turn-on voltage VON 268 can be selected so that the second switch 118 is fully turned on and conducts the drain current ID 119.

[0118] Switch 586 is coupled between the gate of second switch 118 and the off-state voltage VOFF 269. Switch 586 is controlled by the off-state signal OFF 162. In operation, switch 586 acts as a pull-down switch coupled to the gate of second switch 118 to drive second switch 118 to turn off completely. If the off-state signal OFF 162 is active, switch 585 is closed and the primary drive signal DR 138 (e.g., the gate voltage of second switch 118) is essentially the off-state voltage VOFF 269. The value of the off-state voltage VOFF 269 can be selected such that second switch 118 is completely open and cannot conduct current.

[0119] Resistor 588 and switch 587 are shown coupled between the gate of second switch 118 and input return line 111. As shown, switch 587 is controlled by branch drive signal BR 165. The shunt regulator output 372 is coupled to resistor R3 588 and the gate of second switch 118 via diode 589. In operation, if branch drive signal BR 165 is active, both branch switch 152 and switch 587 are on. The level of primary drive signal DR 138 (e.g., the gate voltage of second switch 118) is determined by shunt regulator 349. When branch drive signal BR 165 indicates that branch switch 152 is on (e.g., conducting), shunt regulator 349 senses branch current IBR 168 and provides shunt regulator output 372. Furthermore, the shunt regulator 349 senses when the branch current IBR 168 has reached the branch current threshold value IBRTH and changes the shunt regulator output 372 to prevent the branch current IBR 168 from exceeding the branch current threshold value IBRTH. As shown, the shunt regulator output 372 can be a voltage value determined by the shunt regulator 349. The shunt regulator output 372 is used as the value of the primary drive signal DR 138 (e.g., the gate voltage of the second switch 118) and regulates the branch current IBR 168 below the branch current threshold value IBRTH by controlling the conduction of the second current I1 120 by the second switch 118.

[0120] Figure 5B illustrates a timing diagram 500 of an example waveform of the first controller 532 in Figure 5A. The example waveforms illustrate a power converter 100 operating in discontinuous conduction mode (DCM). Examples include bypass voltage VBP 142, request signal REQ 133, drain current ID 119, branch current IBR 168, second current I1 120, on signal ON 160, off signal OFF 162, voltage at node A 117, main on signal MAIN_ON 164, branch drive signal BR 165, and primary drive signal DR 138. In the illustrated embodiment, comparator 156 has hysteresis, and the upper reference REF+ 167a and lower reference REF- 167b illustrated in Figure 5B represent hysteresis threshold values ​​used for referencing REF 167. When the bypass voltage VBP 142 drops below the lower reference REF-167b, the bypass adjustment signal BP_REG 163 is logic high, and when the bypass voltage VBP 142 reaches the upper reference REF+167a, the bypass adjustment signal BP_REG 163 is logic low. Similar to other diagrams, the primary drive signal DR 138 is a voltage signal, and the voltage value of the primary drive signal DR 138 controls the value of the second switching current I1 120 conducted by the second switch 118. It should be understood that similarly named and numbered components are coupled and function as described above.

[0121] The switching cycle between time t32 and time t34 represents a normal switching cycle of power switch S1 114, during which second switch 118 is fully turned on and energy is transferred from the input of power converter 100 to the output of power converter 100. However, the switching cycles between time t34 and time t38, between time t38 and time t42, and before time t42 represent charging cycles in which branch switch 152 is turned on to charge bypass capacitor 144. During these cycles, second switch 118 is used to regulate branch current IBR 168 below the branch current threshold value IBRTH 590. At least one difference shown in timing diagram 500 compared to other timing diagrams is that during a charging cycle, branch switch 152 is turned on to charge bypass capacitor 144 within time period T1 570 of each charging cycle. The remainder of the charging cycle resumes the normal switching cycle after time period T1 570.

[0122] At time t32, a request event (pulse) is received in the request signal REQ 133, and the ON signal 160 is activated, while the OFF signal 162 is deactivated by the main control device 148. Furthermore, the bypass voltage VBP 142 is greater than the lower reference REF-167b, and the branch switch 152 is not turned on to redirect a portion of the drain current ID 119 to charge the bypass capacitor 144. The branch control device 150 activates the main ON signal MAIN_ON 164, such that the main ON signal MAIN_ON 164 substantially follows the ON signal ON 160. The branch drive signal BR 165 is also not activated by the branch control device 150, and the branch switch 152 is not conducted, as indicated by the substantially zero branch current IBR 168 between time t32 and time t33.

[0123] Between time t32 and time t33, the primary drive signal DR 138 is essentially the turn-on voltage VON 268, which is the voltage used to turn on the second switch 118 such that the drain current ID 119 and the second current I1 120 are determined by the components coupled to the power switch S1 104. Thus, the second switch 118 is fully turned on and the voltage at node A 117 is a small value close to zero. For example, when the second switch 118 is fully turned on, the voltage at node A 117 can be essentially 100 mV. When the second switch 118 is conducting, the second current I1 120 is essentially equal to the drain current ID 119.

[0124] At time t33, the drain current ID 119 reaches the current limit ILIM 221 and the power switch S1 114 is turned off. The off signal OFF 162 is activated, while the on signal ON 160 and the main on signal MAIN_ON 164 are deactivated. The drive signal DR 138 transitions to the off voltage VOFF 269, which is the voltage value that prevents the second switch 118 from conducting current and causes the drain current ID 119 and the second current I1 120 to drop to zero. Between time t33 and time t34, when the power switch S1 114 is off, the voltage at node A 117 is at a high value above the threshold value VTH116 591 of the first switch 116, causing the first switch 116 to be cut off and not conducting current.

[0125] At time t34, a request event is received in the request signal REQ 133, and the ON signal 160 is activated while the OFF signal 162 is deactivated. When a portion of the drain current ID 119 is used to charge the bypass capacitor 144, the bypass voltage VBP 142 is below the lower reference REF-167b. The branch control device 550 activates the branch drive signal BR 165 to turn on the branch switch 152 during period T1 570, which is shown as the duration between time t34 and time t36. As shown, the bypass voltage VBP 142 begins to increase. The primary drive signal DR 138 is held at the OFF voltage VOFF 269 to prevent the second switch S1 118 from conducting; however, the voltage at node 117 drops to a value above the input loop 111 (shown as 0 V in Figure 5A) but below the threshold value VTH116 591 of the first switch 116.

[0126] Between time t34 and time t35, the branch current IBR 168 is less than the branch current threshold value IBRTH 590. Thus, the shunt regulator 349 does not change the primary drive signal DR 138 and the second switch 118 does not conduct. The branch current IBR 168 is essentially the drain current ID 119 and the second current I1 120 is essentially zero.

[0127] At time t35, the branch current IBR 168 reaches the branch current threshold value IBRTH 590, and the shunt regulator 349 provides a shunt regulator output 372, causing the driver 358 to control the second switch 118 to be turned on and to control the amount of current (e.g., the second current I1 120) conducted by the second switch 118. As shown, the primary drive signal DR 138 transitions to a value above the threshold value VTH118 592 of the second switch 118, such that the current conducted by the second switch 118 (e.g., the second current I1 120) depends on the gate voltage of the second switch 118 (e.g., the primary drive signal DR 138). Therefore, the shunt regulator 349 regulates the branch current IBR 168.

[0128] Between time t35 and time t36, shunt regulator 349 and driver 358 are controlling the conduction of second switch 118, such that branch current IBR 168 is maintained at branch current threshold value IBRTH 490. The remaining drain current ID 119, which is not conducted as branch current IBR 168 by branch switch 152, is conducted as second current I1 120 by second switch 118. Between time t35 and time t36, bypass voltage VBP 142 has increased above lower reference REF- 167b, but has not yet reached upper reference REF+ 167a.

[0129] At time t36, period T1 570 ends. It should be understood that the duration of period T1 570 can be determined by capacitor C1 581 and resistor R1 582 as shown in Figure 5A. Branch control device 550 deactivates branch drive signal BR 165 and activates primary on signal MAIN_ON 164 to substantially follow on signal ON 160. The voltage at node A 117 drops to near zero, while primary drive signal DR 138 transitions to on voltage VON 268. Second switch 118 is fully on, while branch switch 152 is off. Between time t36 and time t37, branch current IBR 168 is substantially zero, while second current I1 120 is substantially drain current ID 119. Once branch switch 152 is off, bypass voltage VBP 142 begins to decrease.

[0130] At time t37, the drain current ID 119 reaches the current limit ILIM 221 and the power switch S1 114 is turned off. The on signal ON 160 is invalidated, while the off signal OFF 162 is valid. The drive signal DR 138 transitions to the off voltage VOFF 269, and the voltage at node A 117 is at a high value above the threshold value VTH116 591 of the first switch 116. Thus, neither the first switch 116 nor the second switch 118 conducts, and the drain current ID 119 and the second current I1 120 drop to zero. At time t38, another request event is received in the request signal REQ 133, and the bypass voltage VBP 142 is below the upper reference REF+ 167a and the lower reference REF- 167b. It should be understood that the period shown between time t38 and time t42 is similar to the period discussed above between time t34 and time t38. Branch drive signal BR 165 is activated to turn on branch switch 152 during period T1 570 to charge bypass capacitor 144. During period T1 570, branch current IBR 168 is regulated below branch current threshold value IBRTH 590 by controlling second current I1 120. After period T1 570, branch switch 152 is turned off and second switch 118 is fully turned on, and second switch 118 conducts drain current ID 119 until drain current ID 119 reaches current limit ILIM 221 and power switch S1 114 is turned off. During this switching cycle, bypass voltage VBP 142 does not reach upper reference REF+ 167a.

[0131] At time t42, another request event is received in the request signal REQ 133 and the bypass voltage VBP 142 is above the upper reference REF+ 167a. For the switching period that begins at time t42, the bypass voltage VBP 142 reaches the upper reference REF+ 167a at time t44. Thus, at time t44, the cycle returns to the normal switching cycle, the dominant on signal MAIN_ON 164 is activated and the second switch 118 is fully turned on to conduct the drain current ID 119.

[0132] Figure 6 illustrates a timing diagram 600 of an example bypass voltage VBP 142 and branch drive signal BR 165. It should be understood that similarly named and numbered components are coupled and function as described above. In one embodiment, branch switch 152 can be turned on for a fixed number of consecutive switching cycles. In yet another embodiment, branch switch 152 cannot be turned on for more than a fixed number of consecutive switching cycles. For the embodiment shown in Figure 6, branch switch 152 is turned on for three consecutive switching cycles. As shown, when bypass voltage VBP 142 reaches lower reference REF-167b, a charging cycle can begin and branch drive signal BR 165 turns on branch switch 152. The charging cycle stops when bypass voltage VBP 142 reaches upper reference REF+167a. When bypass voltage VBP 142 reaches lower reference REF-167b, branch drive signal BR 165 jumps to a logic high value to turn on branch switch 152.

[0133] In one embodiment, branch switch 152 is turned on during time period T1 as discussed with respect to Figures 5A and 5B; however, branch switch 152 may be turned on as discussed with Figures 1, 2, 3, 4A, and 4B. When branch switch 152 is on, bypass voltage VBP 142 increases. When branch switch 152 is off, bypass voltage VBP 142 decreases. As shown in timing diagram 600, branch drive signal BR 165 turns on branch switch 152 for three consecutive switching cycles, and bypass voltage VBP 142 has reached the upper reference REF+ 167a. Time period T1 can be selected such that it takes three consecutive switching cycles for bypass voltage VBP 142 to reach upper reference REF+ 167a from lower reference REF- 167b. However, it should be understood that another number of consecutive switching cycles may also be used.

[0134] Figure 7 illustrates an example isolated power converter 700, which includes a first controller 132 having a branch switch 152 and a branch control device 150. It should be understood that the power converter 700 shares many similarities with the power converter 100 of Figure 1, and the elements, similarly named and numbered, are coupled and function as described above. However, at least one difference is that the power converter 700 does not include the auxiliary winding 112 and the diode D1 146. Thus, the bypass voltage VBP 142 of the bypass capacitor 144 is generated by the first controller 132. Although the first controller 132 of Figure 1 is shown, it should be understood that embodiments of the first controller discussed with respect to Figures 3, 4A, 4B, 5A, and 5B can also be used with the power converter 700.

[0135] The above description of the illustrative embodiments of the invention, including those described in the abstract, is not intended to be exhaustive or to limit the precise forms disclosed. While specific embodiments and examples of the invention have been described herein for illustrative purposes, various equivalent modifications are possible without departing from the broader spirit and scope of the invention. Indeed, it should be understood that specific examples of voltage, current, frequency, power range values, time, etc., are provided for illustrative purposes, and other values ​​may be used in other embodiments and examples according to the teachings of the invention.

[0136] Although the invention is defined in the claims, it should be understood that the invention may be alternatively defined according to the following embodiments:

[0137] Example 1. A first controller for a power converter, the first controller comprising: a driver configured to provide a drive signal to turn a power switch on and off to control energy delivery between an input and an output of the power converter, wherein the power switch includes a first switch and a second switch coupled in a stacked configuration, wherein the first switch is a normally open device and the second switch is a normally closed device; a supply terminal coupled to a bypass capacitor that provides operating power to the first controller, wherein the bypass capacitor has a bypass voltage; a branch switch coupled to a node between the first switch and the second switch; and a branch control device configured to receive an adjustment signal representing a comparison of the bypass voltage with a bypass reference, wherein the branch control device is configured to: if the bypass voltage is below the bypass reference, turn on the branch switch to redirect at least a portion of the drain current of the power switch from the node to the bypass capacitor.

[0138] Example 2. According to the first controller of Example 1, wherein the driver is configured to turn the second switch on and off to control the power switch on and off.

[0139] Example 3. The first controller according to Example 1 or 2, wherein the branch control device is configured to turn on the branch switch simultaneously with one switching cycle of the power switch.

[0140] Example 4. A first controller according to any one of Examples 1 to 3, wherein the branch control device is configured to turn on the branch switch for a fixed time period.

[0141] Example 5. A first controller according to any one of Examples 1 to 4, wherein the branch control device is configured to: turn off the branch switch if the bypass voltage reaches the bypass reference or the drain current of the power switch reaches the current limit.

[0142] Example 6. A first controller according to any one of Examples 1 to 5, wherein the driver is configured to: turn on the second switch if the branch switch is open and the drain current is less than the current limit.

[0143] Example 7. A first controller according to any one of Examples 1 to 6, wherein the driver is configured to: turn off the second switch when the branch switch is turned on and the branch switch conducts the drain current of the power switch from the node to the bypass capacitor.

[0144] Example 8. The first controller according to any one of Examples 1 to 7 further includes: a shunt regulator configured to sense a branch current conducted by the branch switch and regulate the branch current to be less than a branch current threshold value, wherein the shunt regulator and the driver regulate the branch current by controlling a second current conducted by the second switch, and wherein the branch current is substantially the portion of the drain current that is redirected from the node to the bypass capacitor, and the second current is the remainder of the drain current.

[0145] Example 9. A first controller according to any one of Examples 1 to 8, wherein the shunt regulator is configured to provide a shunt output voltage to the driver, wherein the driver determines the gate voltage of the second switch in response to the shunt output voltage, and wherein the second current conducted by the second switch responds to the gate voltage of the second switch.

[0146] Example 10. A first controller according to any one of Examples 1 to 9, wherein if the power converter is operating in continuous conduction mode, the driver turns on the second switch before the branch control device turns on the branch switch.

[0147] Example 11. A first controller according to any one of Examples 1 to 10, wherein the branch switch is turned on for a fixed number of consecutive switching cycles.

[0148] Example 12. A first controller for a power converter, the first controller comprising: a power switch, wherein the power switch includes a first switch and a second switch coupled in a stacked configuration, wherein the first switch is a normally open device and the second switch is a normally closed device; a branch switch coupled to a node between the first switch and the second switch, the branch switch also being coupled to a bypass capacitor; a driver configured to provide a drive signal to control the switching on and off of the power switch to control energy delivery between the input and output sides of the power converter, wherein the driver is configured to switch the second switch on and off to control the power switch. The system includes: a power switch for turning on and off; a main control unit configured to receive a request signal representing turning on the power switch, wherein the main control unit determines whether the power switch should be turned on or off; a comparator coupled to receive a bypass reference and a bypass voltage of the bypass capacitor; and a branch control unit coupled to the comparator and the main control unit, wherein the branch control unit is configured to: turn on the branch switch if the bypass voltage is below the bypass reference and the main control unit determines that the power switch should be turned on, wherein the branch current conducted by the branch switch is at least a portion of the drain current conducted by the first switch.

[0149] Example 13. The first controller according to Example 12, wherein the branch control device is configured to turn on the branch switch for a fixed time period.

[0150] Example 14. The first controller according to Example 12 or 13, wherein the branch control device is configured to: turn off the branch switch if the bypass voltage reaches the bypass reference or the main control device determines to turn off the power switch.

[0151] Example 15. A first controller according to any one of Examples 12 to 14, wherein the driver is configured to: turn on the second switch if the branch switch is off and the main control device determines to turn on the power switch.

[0152] 16. A first controller according to any one of embodiments 12 to 15, wherein the driver is configured to turn off the second switch when the branch switch is turned on and the branch current is substantially the drain current conducted by the first switch.

[0153] 17. The first controller according to any one of embodiments 12 to 16 further includes: a shunt regulator coupled to the branch control device and the driver, wherein the shunt regulator is configured to sense the branch current and regulate the branch current to be less than a branch current threshold value, and wherein the driver controls the second current conducted by the second switch in response to the shunt regulator.

[0154] Example 18. A first controller according to any one of Examples 12 to 17, wherein the shunt regulator is configured to provide a shunt output voltage to the driver, wherein the driver responds to the shunt output voltage to determine the gate voltage of the second switch and the second current responds to the gate voltage of the second switch.

[0155] Example 19. A first controller according to any one of Examples 12 to 18, wherein if the power converter is operating in continuous conduction mode, the driver turns on the second switch before the branch control device turns on the branch switch.

[0156] Example 20. A first controller according to any one of Examples 12 to 19, wherein the first controller is coupled to the input of the power converter, and the request signal is received from a second controller coupled to the output of the power converter, and wherein the request signal is received via a magnetic communication link between the first controller and the second controller.

[0157] Example 21. A first controller according to any one of Examples 12 to 20, wherein the bypass capacitor is coupled to provide operating power to the first controller.

[0158] 100: Power Converter 102. VIN: Input voltage 104: Clamping Circuit 106. T1: Energy transfer element 108: Input winding 110: Output winding 111: Input return line 112: Auxiliary winding 114, S1: Power switch 116: First Switch 117. A: Node 118: Second Switch 119. ID: Drain Current 120, I1: Second switching current 122, S2: Output rectifier 123, VO: Output voltage 124. CO: Output capacitor 125. IO: Output current 126. UO: Output quantity 127: Output loop 128: Load 129: Output sensing circuit 130. FB: Feedback Signal 132: First Controller 133. REQ: Request signal 134: Second Controller 135, SR: Second drive signal 136: Communication Link 138. DR: Primary drive signal 140. ISNS: Current sensing signal 142. VBP: Bypass Voltage 144: Bypass capacitor 146. D1: Diode 148: Main control device 150: Branch control device 152: Branch Switch 154. D2: Diode 156: Comparator 158: Driver 160: On signal 162: Disconnect signal 163. BP_REG: Bypass adjustment signal 164. MAIN_ON: Dominant signal 165. BR: Branch drive signal 167. REF: Reference 167a, REF+: Reference 167b, REF-: See below for reference 168. IBR: Branch current 200: Chart 221. ILIM: Current Limit 268. VON: On-state voltage 269. VOFF: Disconnect voltage 332: First Controller 349: Branch Regulator 358: Driver 372: Branch Regulator Output 400, 401, 500, 600: Timing Diagram 490, 590, IBRTH: Branch current threshold values 491, 591, VTH116: Threshold values 492, 592, VTH118: Threshold values 532: First Controller 550: Branch control device 558: Driver 570, T1: Time period 574, 576, 579, 580: and gates 575: Bolt / Locking device 577, 578: Inverters 581, C1: Capacitor 582, R1: Resistor 583, C2: Capacitor 584, R2: Resistor 585, 586, 587: Switches 588, R3: Resistors 589: Diode 700: Power Converter t1, t2, t3, t4, t5, t6, t7, t8, t9, t10: Time t11, t12, t13, t14, t15, t16, t17, t18, t19, t20, t21: Time t22, t23, t24, t25, t26, t27, t28, t29, t30, t31, t32: Time t33, t34, t35, t36, t37, t38, t39, t40, t41, t42, t43, t44, t45: Time

[0159] none

Claims

1. A first controller for a power converter, the power converter including a power switch for delivering energy between an input and an output of the power converter, wherein the power switch includes a first switch and a second switch coupled in a stacked configuration, the first switch being a normally open device and the second switch being a normally closed device, the first controller comprising: A driver configured to provide a drive signal to turn the power switch on and off to control the energy delivery between the input and the output of the power converter, wherein the driver is configured to turn the second switch on and off to control the on and off of the power switch; a power terminal configured to be coupled to a bypass capacitor that provides operating power to the first controller, wherein the bypass capacitor has a bypass voltage; and a branch switch configured to be coupled to a node between the first switch and the second switch. A branch control device configured to receive an adjustment signal representing a comparison between the bypass voltage and a bypass reference, wherein the branch control device is configured to: if the bypass voltage is below the bypass reference, simultaneously with a switching cycle of the power switch, turn on the branch switch to redirect at least a portion of a drain current of the power switch from the node to the bypass capacitor. And a shunt regulator configured to sense a branch current conducted by the branch switch and regulate the branch current to be less than a branch current threshold value, wherein the shunt regulator and the driver regulate the branch current by controlling a second current conducted by the second switch, and wherein the branch current is substantially the portion of the drain current redirected from the node to the bypass capacitor, and the second current is the remainder of the drain current.

2. The first controller as claimed in claim 1, wherein the branch control device is configured to turn on the branch switch simultaneously with the switching cycle of the power switch.

3. The first controller as claimed in claim 2, wherein the branch control device is configured to: shut off the branch switch if the bypass voltage reaches the bypass reference or the drain current of the power switch reaches a current limit.

4. The first controller as claimed in claim 3, wherein the driver is configured to: turn on the second switch if the branch switch is open and the drain current is less than the current limit.

5. The first controller as claimed in claim 2, wherein the driver is configured to turn off the second switch when the branch switch is turned on and the branch switch conducts the drain current of the power switch from the node to the bypass capacitor.

6. The first controller as claimed in claim 1, wherein the shunt regulator is configured to provide a shunt output voltage to the driver, wherein the driver is configured to determine a gate voltage of the second switch in response to the shunt output voltage, and wherein the second current conducted by the second switch responds to the gate voltage of the second switch.

7. The first controller as claimed in claim 1, wherein if the power converter is operating in continuous conduction mode, the driver is configured to turn on the second switch before the branch control device turns on the branch switch.

8. The first controller as claimed in claim 1, wherein the branch switch is turned on for a fixed number of consecutive switching cycles.

9. A power converter, comprising: The first controller as described in any one of claims 1 to 8; The power switch controls the energy delivery between the input and the output of the power converter, wherein the power switch includes a first switch that is normally open and a second switch that is normally closed, coupled in a stacked configuration. The bypass capacitor is coupled to provide operating power to the first controller.

10. The power converter as claimed in claim 9, wherein the branch switch is physically smaller than the second switch.

11. The power converter of claim 9, wherein the first switch is a gallium nitride-based transistor or a silicon carbide-based transistor.

12. The power converter of claim 9, wherein the first controller is coupled and configured to generate the bypass voltage of the bypass capacitor.

13. A first controller for a power converter having an input side and an output side, the first controller comprising: A power switch, wherein the power switch includes a first switch and a second switch coupled in a stacked configuration, wherein the first switch is a normally open device and the second switch is a normally closed device; a branch switch coupled to a node between the first switch and the second switch, the branch switch being further configured to be coupled to a bypass capacitor. A driver configured to provide a drive signal to control the on and off of the power switch to control energy delivery between the input and output sides of the power converter, wherein the driver is configured to turn the second switch on and off to control the on and off of the power switch; a main control unit configured to receive a request signal representing the on / off of the power switch, wherein the main control unit determines whether the power switch should be on or off; a comparator configured to be coupled to receive a bypass reference and a bypass voltage of the bypass capacitor; A branch control device coupled to the comparator and the main control device, wherein the branch control device is configured to: simultaneously turn on the branch switch with a switching cycle of the power switch if the bypass voltage is below the bypass reference and the main control device determines to turn on the power switch, wherein a branch current conducted by the branch switch is at least a portion of a drain current conducted by the first switch; and a shunt regulator coupled to the branch control device and the driver, wherein the shunt regulator is configured to sense the branch current and regulate the branch current to be less than a branch current threshold value, and wherein the driver controls a second current conducted by the second switch in response to the shunt regulator.

14. The first controller as claimed in claim 13, wherein the branch control device is configured to turn on the branch switch for a fixed period of time.

15. The first controller as claimed in claim 13, wherein the branch control device is configured to: turn off the branch switch if the bypass voltage reaches the bypass reference or the main control device determines to turn off the power switch.

16. The first controller as claimed in claim 13, wherein the driver is configured to turn on the second switch if the branch switch is off and the main control device determines to turn on the power switch.

17. The first controller as claimed in claim 13, wherein the driver is configured to turn off the second switch when the branch switch is turned on and the branch current is substantially the drain current conducted by the first switch.

18. The first controller as claimed in claim 13, wherein the shunt regulator is configured to provide a shunt output voltage to the driver, wherein the driver responds to the shunt output voltage to determine a gate voltage of the second switch and the second current responds to the gate voltage of the second switch.

19. The first controller as claimed in claim 13, wherein if the power converter is operating in continuous conduction mode, the driver turns on the second switch before the branch control device turns on the branch switch.

20. The first controller as claimed in claim 13, wherein the first controller is coupled to the input of the power converter, and the request signal is received from a second controller coupled to the output of the power converter, and wherein the request signal is received through a magnetic communication link between the first controller and the second controller.

21. The first controller as claimed in claim 13, wherein the branch switch is physically smaller than the second switch.

22. The first controller as claimed in claim 13, wherein the first switch is a gallium nitride-based transistor or a silicon carbide-based transistor.

23. A power converter, comprising: The first controller as described in any one of claims 13 to 22; and the bypass capacitor, wherein the bypass capacitor is coupled to provide operating power to the first controller.

24. The power converter as claimed in claim 23, wherein the first controller is coupled and configured to generate the bypass voltage of the bypass capacitor.

Images