Switching converter on-resistor

Abstract

The invention relates to a switching converter on-resistance. A circuit includes a first transistor (202), a second transistor (204), and a controller (206). The first transistor (202) has a first terminal coupled to a switch terminal, a second terminal coupled to a reference terminal, and a control terminal. The first transistor (202) is a gallium nitride transistor. The second transistor (204) has a first terminal coupled to the switch terminal, a second terminal coupled to the reference terminal, and a control terminal. The controller (206) has a first output coupled to the control terminal of the first transistor (202) and a second output coupled to the control terminal of the second transistor (204).

Description

Technical Field

[0001] This application relates to the on-resistance of a switching converter. Background Technology

[0002] A DC-DC converter is an electronic circuit that converts an input direct current (DC) voltage into one or more DC output voltages that are higher or lower than the input DC voltage. A DC-DC converter that produces an output voltage lower than the input voltage is called a buck converter. A DC-DC converter that produces an output voltage higher than the input voltage is called a boost converter. A DC-DC converter that produces an output voltage higher or lower than the input voltage is called a buck-boost converter.

[0003] A flyback converter is a type of switching converter based on a buck-boost converter, but incorporating a transformer instead of an inductor. The transformer includes a primary winding and a secondary winding, across which the voltage ratio is scaled. The transformer also provides current isolation between the input and the corresponding output. The flyback converter controls transistors and / or switches to charge and / or discharge inductors and / or capacitors to maintain the desired output voltage. Summary of the Invention

[0004] In one example, a circuit includes a first transistor, a second transistor, and a controller. The first transistor has a first terminal coupled to a switching terminal, a second terminal coupled to a reference terminal, and a control terminal. The first transistor is a gallium nitride transistor. The second transistor has a first terminal coupled to the switching terminal, a second terminal coupled to the reference terminal, and a control terminal. The controller has a first output coupled to the control terminal of the first transistor and a second output coupled to the control terminal of the second transistor.

[0005] In another example, a circuit includes a first transistor, a second transistor, and a controller. The first and second transistors are coupled in parallel between a switch terminal and a reference terminal. The first transistor is a gallium nitride transistor and has a gate. The second transistor has a gate. The controller has a first output coupled to the gate of the first transistor and a second output coupled to the gate of the second transistor. The controller is configured to provide a first control signal having a first state to turn off the first transistor in response to a valley of voltage at the switch terminal, and to provide a second control signal having a second state to turn on the second transistor.

[0006] In another example, a system includes a transformer, a voltage source, and a flyback converter control circuit. The transformer includes a primary winding and a secondary winding. The primary winding has a first primary terminal and a second primary terminal. The voltage source is coupled to the first primary terminal. The flyback converter control circuit has an output coupled to the second primary terminal and a reference terminal. The flyback converter control circuit includes a first transistor, a second transistor, and a controller. The second transistor is smaller than the first transistor. The first transistor and the second transistor are coupled in parallel between the output and the reference terminal. The first transistor is a gallium nitride transistor and has a gate. The second transistor has a gate. The controller has a first output coupled to the gate of the first transistor and a second output coupled to the gate of the second transistor. The controller is configured to provide a first control signal having a first state to turn off the first transistor in response to a valley of the voltage at the output of the flyback converter control circuit, and to provide a second control signal having a second state to turn on the second transistor. Attached Figure Description

[0007] Figure 1 This is a block diagram of an instance system containing a flyback converter.

[0008] Figure 2 This is a schematic diagram of an example flyback converter control circuit that includes a main drive transistor and an auxiliary drive transistor.

[0009] Figure 3 and 4 These are examples of main driving transistor layouts and auxiliary driving transistor layouts in integrated circuits.

[0010] Figure 5 It includes Figure 2 A graph of an example signal in a flyback converter control circuit.

[0011] Figure 6 It is a display containing Figure 2 A graph comparing the resistor in an example flyback converter control circuit with the resistor in a flyback converter using a signal-driven transistor. Detailed Implementation

[0012] Figure 1This is a block diagram of example system 100. System 100 includes a flyback converter 101 and a voltage source 110. The voltage source 110 can be a circuit that provides a DC voltage for input to the flyback converter. For example, the voltage source 110 can be an AC-DC converter circuit with a rectifier and filter to convert the AC voltage into a DC voltage suitable for use by the flyback converter 101. The flyback converter 101 includes a flyback converter control circuit 102, a transformer 104, a secondary control circuit 106, and an isolator circuit 108. The transformer 104 includes a primary winding and a secondary winding. A first terminal of the primary winding is coupled to the output of the voltage source 110. A second terminal of the primary winding is coupled to the flyback converter control circuit 102.

[0013] The flyback converter control circuit 102 controls the current flow in the primary winding of the transformer 104. For example, the flyback converter control circuit 102 may include a switch coupled between the switch output of the flyback converter control circuit 102 and a reference voltage (e.g., ground). The flyback converter control circuit 102 modulates the closing of the switch to control the current flow in the primary winding and to control the voltage generated on the secondary side of the transformer 104.

[0014] Secondary control circuit 106 has an input coupled to the secondary winding of transformer 104. Secondary control circuit 106 may include a rectifier and a filter for generating a DC voltage from the AC voltage supplied by the secondary winding. The output of secondary control circuit 106 provides an output voltage VOUT to power load circuit 112. Load circuit 112 can be any circuit powered by flyback converter 101. Secondary control circuit 106 also includes a feedback circuit system that generates a feedback signal for flyback converter control circuit 102 to control current modulation in the primary winding of transformer 104.

[0015] Secondary control circuit 106 provides a feedback signal to flyback converter control circuit 102 via isolator circuit 108. Isolator circuit 108 may include an optical isolator, capacitive isolator, inductive isolator, or other type of isolation circuit. Isolator circuit 108 has an input coupled to the feedback output of secondary control circuit 106 and an output coupled to the feedback input of flyback converter control circuit 102. Flyback converter control circuit 102 applies the feedback signal (FB) received from isolator circuit 108 to generate a switching signal (SW), which is provided at the output of flyback converter control circuit 102 to modulate the current in transformer 104.

[0016] In some instances of the flyback converter control circuit 102, the switches used to modulate the current flow in the transformer 104 may be implemented using gallium nitride (GaN) transistors. GaN transistors have lower gate capacitance than silicon transistors, which enables higher switching frequencies and allows for a smaller transformer 104. However, the on-resistance and saturation current of the GaN transistor may degrade when switching high voltages and / or currents. For example, the on-resistance of the GaN transistor may increase over time when switching high voltages and / or currents, which may reduce the efficiency of the flyback converter 101. The flyback converter control circuit 102 includes circuitry to reduce the degradation of the on-resistance of the switching transistors to improve the efficiency of the flyback converter 101.

[0017] Figure 2 This is a schematic diagram of an example flyback converter control circuit 102. The flyback converter control circuit 102 includes a main transistor 202, an auxiliary transistor 204, and a controller 206. The main transistor 202 may be an n-channel GaN transistor. The auxiliary transistor 204 may be an n-channel GaN transistor or an n-channel field-effect transistor (N-FET). In one example of the flyback converter control circuit 102, the main transistor 202 and the auxiliary transistor 204 are disposed on a first integrated circuit, and the controller 206 is disposed on a second integrated circuit. In another example of the flyback converter control circuit 102, the main transistor 202 is disposed on the first integrated circuit, and the controller 206 and the auxiliary transistor 204 are disposed on the second integrated circuit. The main transistor 202 and the auxiliary transistor 204 are coupled in parallel between the output (or switching terminal) SW of the flyback converter control circuit 102 and a reference terminal (e.g., ground terminal) of the flyback converter control circuit 102. The main transistor 202 has a first terminal (e.g., drain) coupled to the output (or switching terminal) SW of the flyback converter control circuit 102, a second terminal (e.g., source) coupled to a reference terminal of the flyback converter control circuit 102, and a control terminal (e.g., gate) coupled to the controller 206. The auxiliary transistor 204 has a first terminal (e.g., drain) coupled to the first terminal of the main transistor 202, a second terminal (e.g., source) coupled to the second terminal of the main transistor 202, and a control terminal (e.g., gate) coupled to the controller 206. The auxiliary transistor 204 may be smaller than the main transistor 202 (e.g., having a smaller channel width). For example, the auxiliary transistor 204 may be one-quarter the size of the main transistor 202. Therefore, the main transistor 202 may be larger than the auxiliary transistor 204.

[0018] Controller 206 controls the switching on and off of main transistor 202 and auxiliary transistor 204. Controller 206 has a first input coupled to a feedback input of flyback converter control circuit 102 for receiving the FB signal, and a second input coupled to the primary winding of transformer 104 via the output of flyback converter control circuit 102. Controller 206 has a first output coupled to a control terminal of auxiliary transistor 204, and a second output coupled to a control terminal of main transistor 202. Controller 206 provides a control signal AON at the first output for switching auxiliary transistor 204 on or off, and a control signal MON at the second output for switching main transistor 202 on or off.

[0019] Controller 206 provides quasi-resonant control of the main transistor 202 and the auxiliary transistor 204. Controller 206 can turn on the main transistor 202 and the auxiliary transistor 204 in response to detecting a valley in the voltage at the output of the flyback converter control circuit 102 (e.g., the drain-to-source voltage of the main transistor 202 and the auxiliary transistor 204). The valley is the minimum value (negative half-cycle) of the voltage oscillation at the output of the flyback converter control circuit 102 that occurs when the main transistor 202 and the auxiliary transistor 204 have been turned off and after the secondary winding of the transformer 104 has discharged. Controller 206 may include circuitry for detecting the valley in the voltage at the output of the flyback converter control circuit 102.

[0020] Controller 206 turns on main transistor 202 and auxiliary transistor 204 in response to detecting a valley value, in such a manner that auxiliary transistor 204 is turned on first, followed by main transistor 202. By turning on auxiliary transistor 204 first, auxiliary transistor 204 is subjected to the stress of a high switching voltage (e.g., 60 volts, 250 volts, etc.), while main transistor 202 is spared the stress of a high switching voltage. Because main transistor 202 is not subjected to the stress of a high voltage supplied by the switch across main transistor 202 and auxiliary transistor 204 when auxiliary transistor 204 is turned on, the increase in on-resistance of main transistor 202 caused by switching is reduced or eliminated. Therefore, flyback converter control circuit 102 provides improved efficiency compared to using a single GaN transistor.

[0021] Figure 3 A main transistor 202 and an auxiliary transistor 204 are shown on an integrated circuit. Each transistor includes a gate ring for isolation, a first gate ring 302 surrounding the main transistor 202, and a second gate ring 304 surrounding the auxiliary transistor 204. The gate rings surrounding the auxiliary transistor 204 significantly increase the size of the flyback converter control circuit 102, which increases the cost of the flyback converter control circuit 102.

[0022] Figure 4This illustrates a main transistor 202 and an auxiliary transistor 204 on an integrated circuit, where the gate ring of the main transistor 202 serves as isolation for the auxiliary transistor 204. Figure 4 In this example, the auxiliary transistor 204 is placed within the gate ring of the main transistor 202, and the gate ring of the main transistor 202 isolates the auxiliary transistor 204. Therefore, in Figure 4 In this case, the lack of a separate gate ring surrounding the auxiliary transistor 204 is relative to Figure 3 The proposed implementation significantly reduces the size of the flyback converter control circuit 102, which is relative to... Figure 3 The use of this implementation scheme reduces the circuit area and cost of the flyback converter control circuit 102.

[0023] Figure 5 This is a graph of an example signal in the flyback converter 101. Figure 5 The transistor control signals AON and MON are shown, as well as the voltage SW at the output of the flyback converter 101 and the current I flowing in the primary winding of the transformer 104. 电力 During time interval 502, main transistor 202 and auxiliary transistor 204 are turned off, and transformer 104 discharges. At the end of time interval 502, transformer 104 discharges, and the voltage at the output of flyback converter 101 begins to oscillate. At time 504, the voltage at the output of flyback converter 101 is at a valley value. Controller 206 detects the valley value and changes the state of AON to turn on auxiliary transistor 204, while main transistor 202 remains off. With auxiliary transistor 204 on, the current flowing in the primary winding of transformer 104 increases, and the voltage at the output of flyback converter 101 decreases. At time 506, controller 206 monitors the voltage transition at the output of flyback converter 101 and detects no voltage change. In response to the unchanged voltage, controller 206 changes the state of MON to turn on main transistor 202, while auxiliary transistor 204 remains on. With the main transistor 202 turned on, the current flowing in the primary winding of the transformer 104 continues to increase, and the voltage at the output of the flyback converter 101 continues to decrease. Because the voltage across the main transistor 202 is relatively low at time 506, the switching stress experienced by the main transistor 202 is relatively low, and the degradation of the on-resistance of the main transistor 202 due to switching is reduced.

[0024] Figure 6This is a graph comparing the resistance of an example switch in flyback converter 101. Curve 602 shows the resistance when the switch contains a single GaN transistor. Curve 604 shows the resistance of the switch in flyback converter 101, which contains a main transistor 202 and an auxiliary transistor 204. In both cases (single transistor and flyback converter 101), the initial switch resistance (resistance at time t = 0) is approximately 170 milliohms. After approximately 10 days of switching, the resistance of the switch containing the single GaN transistor has increased to approximately 221 milliohms (resistance increase of 30%), while the resistance of the switch in flyback converter 101 has increased to only approximately 177 milliohms (resistance increase of 4%). Therefore, in this example, the change in on-resistance of flyback converter 101 is approximately one-seventh of the change in resistance of the switch with a single GaN transistor. The lower on-resistance of flyback converter 101 improves the efficiency of flyback converter 101.

[0025] In this specification, the term "coupled" may encompass a connection, communication, or signaling path that enables the functional relationship to be consistent with this specification. For example, if device A generates a signal to control device B to perform an action, then: (a) in a first instance, device A is coupled to device B via a direct connection; or (b) in a second instance, device A is coupled to device B via an intermediate component C, provided that the intermediate component C does not alter the functional relationship between device A and device B, such that device B is controlled by device A via a control signal generated by device A.

[0026] As used herein, the terms “terminal,” “node,” “interconnect,” “pin,” and “lead” are used interchangeably. Unless otherwise specified, these terms are generally used to refer to interconnects or the ends thereof between device elements, circuit elements, integrated circuits, devices, or other electronic devices or semiconductor components.

[0027] The circuits or devices described herein as containing certain components may alternatively be adapted to be coupled to those components to form the described circuit system or device. For example, a structure described as containing one or more semiconductor elements (e.g., transistors), one or more passive elements (e.g., resistors, capacitors, and / or inductors), and / or one or more sources (e.g., voltage sources and / or current sources) may alternatively contain only semiconductor elements within a single physical device (e.g., a semiconductor die and / or integrated circuit (IC) package) and may be adapted to be coupled to at least some of the said passive elements and / or sources to form the described structure during or after manufacturing, for example, by an end user and / or a third party.

[0028] While the use of specific transistors is described herein, other transistors (or equivalent devices) may be used alternatively with little or no change to the rest of the circuit system. For example, field-effect transistors (“FETs”) (e.g., n-channel FETs (NFETs) or p-channel FETs (PFETs)), bipolar junction transistors (BJTs – e.g., NPN or PNP transistors), insulated-gate bipolar transistors (IGBTs), and / or junction field-effect transistors (JFETs) may be used in place of or in combination with the devices described herein. The transistors may be depletion-mode devices, drain-extended devices, enhancement-mode devices, natural transistors, or other types of device structure transistors. Furthermore, the devices may be implemented on / above a silicon (Si) substrate, a silicon carbide (SiC) substrate, a gallium nitride (GaN) substrate, or a gallium arsenide (GaAs) substrate.

[0029] Reference may be made to the control input and current terminals of the transistor in the claims. In the case of a FET, the control input (or transistor control terminal) is the gate, and the current terminals are the drain and source. In the case of a BJT, the control input is the base, and the current terminals are the collector and emitter.

[0030] In this article, "FET on" means that there is a conductive channel in the FET and drain current can flow through it. "FET off" means that there is no conductive channel, and therefore no drain current flows through it. However, a "off" FET can still have current flowing through the body diode of a transistor.

[0031] The circuits described herein can be reconfigured to include additional or different components to provide functionality at least partially similar to that available before the component replacement. Unless otherwise stated, components shown as resistors generally represent any one or more elements coupled in series and / or parallel to provide the amount of impedance represented by the shown resistor. For example, a resistor or capacitor shown and described herein as a single component may alternatively be multiple resistors or capacitors coupled in parallel between the same nodes. For example, a resistor or capacitor shown and described herein as a single component may alternatively be multiple resistors or capacitors coupled in series between the same two nodes as the single resistor or capacitor.

[0032] While some elements of the described examples are contained within the integrated circuit and others are external to the integrated circuit, in other example embodiments, additional or fewer features may be incorporated into the integrated circuit. Additionally, some or all features described as external to the integrated circuit may be contained within the integrated circuit, and / or some features described as internal to the integrated circuit may be incorporated externally. As used herein, the term "integrated circuit" means one or more circuits that are: (i) incorporated in / above a semiconductor substrate; (ii) incorporated in a single semiconductor package; (iii) incorporated in the same module; and / or (iv) incorporated in / on the same printed circuit board.

[0033] The use of the phrase "grounding" in the foregoing description includes base grounding, wire grounding, floating grounding, virtual grounding, digital grounding, general grounding, and / or any other form of grounding connection applicable to or suited to the teachings of this specification. In this specification, unless otherwise stated, "about," "approximately," or "substantially" preceding a parameter means within + / - 10% of that parameter, or, if the parameter is zero, within a reasonable range near zero.

[0034] Within the scope of the claims, modifications may be made to the described embodiments, and other embodiments are possible.

Claims

1. A circuit comprising: A first transistor has a first terminal coupled to a switching terminal, a second terminal coupled to a reference terminal, and a control terminal, wherein the first transistor is a gallium nitride (GaN) transistor. The second transistor has a first terminal coupled to the switch terminal, a second terminal coupled to the reference terminal, and a control terminal; as well as A controller having a first output coupled to the control terminal of the first transistor and a second output coupled to the control terminal of the second transistor.

2. The circuit according to claim 1, wherein the second transistor is a GaN transistor.

3. The circuit according to claim 1, wherein the second transistor is a silicon transistor.

4. The circuit of claim 1, wherein the first transistor and the second transistor are on the first die, and the controller is on the second die.

5. The circuit of claim 4, wherein the first transistor includes a gate ring surrounding the first transistor, and the second transistor is located within the gate ring.

6. The circuit of claim 4, wherein the first transistor includes a first gate ring, and the second transistor includes a second gate ring.

7. The circuit according to claim 1, wherein the first transistor is larger than the second transistor.

8. The circuit of claim 1, wherein the controller is configured to: A first control signal is provided at the first output, and a second control signal is provided at the second output; and In response to a valley in the voltage at the switch terminal, the state of the second control signal is changed to turn on the second transistor, and the first control signal is provided with a state that turns off the first transistor.

9. The circuit of claim 8, wherein the controller is configured to change the state of the first control signal in response to the voltage at the switch terminal not changing, and to provide the second control signal having a state in which the second transistor is turned on.

10. A circuit comprising: A first transistor and a second transistor are coupled in parallel on the same die between a switching terminal and a reference terminal. The first transistor is a gallium nitride transistor with a gate, and the second transistor has a gate. as well as A controller having a first output coupled to the gate of the first transistor, and an output coupled to the gate of the first transistor. The controller is configured to provide a first control signal having a first state to turn off the first transistor and a second control signal having a second state to turn on the second transistor in response to a valley of voltage at the switching terminal.

11. The circuit of claim 10, wherein the controller is configured to provide the first control signal having the second state to turn on the first transistor in response to the voltage at the switch terminal being less than a threshold and the second control signal having the second state.

12. The circuit of claim 10, wherein the second transistor is a GaN transistor.

13. The circuit of claim 10, wherein the first transistor and the second transistor are on a first die, and the controller is on a second die.

14. The circuit of claim 13, wherein the first transistor includes a gate ring surrounding the first transistor, and the second transistor is located within the gate ring.

15. The circuit of claim 13, wherein the first transistor includes a first gate ring, and the second transistor includes a second gate ring.

16. The circuit of claim 10, wherein the first transistor is larger than the second transistor.

17. A system comprising: A transformer comprising a primary winding and a secondary winding, the primary winding having a first primary terminal and a second primary terminal; A voltage source coupled to the first primary terminal; A flyback converter control circuit having an output coupled to a second primary terminal and a reference terminal, the flyback converter control circuit comprising: A first transistor and a second transistor smaller than the first transistor are coupled in parallel between the output and the reference terminal. The first transistor is a gallium nitride transistor with a gate, and the second transistor has a gate. as well as A controller having a first output coupled to the gate of the first transistor and a second output coupled to the gate of the second transistor, the controller being configured to provide a first control signal having a first state to turn off the first transistor and to provide a second control signal having a second state to turn on the second transistor in response to a valley of voltage at the output of the flyback converter control circuit.

18. The system of claim 17, wherein the controller is configured to provide the first control signal having the second state to turn on the first transistor in response to the voltage at the output being less than a threshold and the second control signal having the second state.

19. The system of claim 17, wherein the flyback converter control circuit is part of an integrated circuit, and the first transistor includes a gate ring surrounding the first transistor, and the second transistor is located within the gate ring.

20. The system of claim 17, wherein the flyback converter control circuit is part of an integrated circuit, and the first transistor includes a first gate ring surrounding the first transistor, and the second transistor includes a second gate ring.

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