Switching power supply and control circuit thereof

Abstract

A switching power supply and a control circuit thereof are provided. The control circuit used in the switching power supply according to an embodiment of the present application, wherein the switching power supply comprises a power tube, the control circuit is configured to, when the power tube is in a conducting state: based on a drain voltage or a source voltage of the power tube, detect whether the power tube enters a saturation state; and when it is detected that the power tube enters the saturation state, control the power tube to change from the conducting state to an off state.

Description

Technical Field

[0001] This invention relates to the field of circuits, and more specifically to a switching power supply and its control circuit. Background Technology

[0002] A switching power supply, also known as a switching converter or switching power supply, is a type of power supply. The function of a switching power supply is to convert a voltage level from one voltage level to the voltage or current required by the user through different architectures (e.g., flyback, buck, or boost architectures). Summary of the Invention

[0003] According to an embodiment of the present invention, a control circuit for use in a switching power supply includes a power transistor. The control circuit is configured to, when the power transistor is in the on state: detect whether the power transistor has entered a saturation state based on the drain voltage or source voltage of the power transistor; and when the power transistor is detected to have entered a saturation state, control the power transistor to change from the on state to the off state.

[0004] The switching power supply according to an embodiment of the present invention includes the control circuit described above. Attached Figure Description

[0005] The invention can be better understood from the following description of specific embodiments of the invention in conjunction with the accompanying drawings, wherein:

[0006] Figure 1 A schematic diagram of a conventional LED driver circuit is shown.

[0007] Figure 2 It shows Figure 1 The diagram shows the relevant signal waveforms when the power transistor is in normal operating condition.

[0008] Figure 3 It shows Figure 1 The diagram shows the relevant signal waveforms when the power transistor is in saturation.

[0009] Figure 4 A system schematic diagram of an LED driving circuit according to an embodiment of the present invention is shown.

[0010] Figure 5 It shows Figure 4 The diagram shows an example circuit implementation of the saturation detection module.

[0011] Figure 6 It shows Figure 5 The diagram shows the relevant signal waveforms of the saturation detection module.

[0012] Figure 7A system schematic diagram of another LED driving circuit according to an embodiment of the present invention is shown.

[0013] Figure 8 It shows Figure 7 The diagram shows an example circuit implementation of the saturation detection module.

[0014] Figure 9 It shows Figure 8 The diagram shows the relevant signal waveforms of the saturation detection module. Detailed Implementation

[0015] The features and exemplary embodiments of various aspects of the present invention will now be described in detail. Numerous specific details are set forth in the following detailed description to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention. The invention is by no means limited to any specific configurations and algorithms presented below, but covers any modifications, substitutions, and improvements to elements, components, and algorithms without departing from the spirit of the invention. Well-known structures and techniques are not shown in the drawings and the following description in order to avoid unnecessarily obscuring the invention.

[0016] Power transistors are critical components in switching power supplies. Currently, the control circuits used in switching power supplies detect whether the power transistor has entered saturation through a temperature detection mechanism. When saturation is detected, the power transistor is shut down or its output power is reduced to protect it. However, because the temperature of a power transistor changes relatively slowly, this protection mechanism can only protect the power transistor after it has been in an abnormal state for a period of time, making the power transistor highly susceptible to damage.

[0017] Figure 1 A system schematic diagram of a conventional LED driver circuit is shown. Figure 1 In the LED driver circuit 100 shown, the control circuit 102 controls the power transistor M1 to turn on and off by controlling the gate voltage of the power transistor M1, thereby controlling the current output to the LED load (i.e., making the current flowing through the LED load constant). The power transistor M1 can be a gallium nitride (GaN) power transistor, a metal-oxide-semiconductor field-effect transistor (MOSFET), or a bipolar junction transistor (BJT), etc.

[0018] Figure 2 It shows Figure 1The diagram shows the relevant signal waveforms when power transistor M1 is in normal operating condition. Here, Gate represents the gate voltage of power transistor M1, Drain represents the drain voltage of power transistor M1, and CS represents the source voltage of power transistor M1 (i.e., the voltage generated across the current sensing resistor Rcs by the current flowing through power transistor M1). Figure 1 and Figure 2 As shown, when the Gate voltage is low, the power transistor M1 is in the off state, and the Drain voltage is high (i.e., the input line voltage VIN of the LED driver circuit 100 is equal to the conduction voltage V of the freewheeling diode D1). D1 The sum of (VIN+V) D1 The inductor current decreases linearly through the freewheeling diode D1, while the CS voltage is zero. When the Gate voltage is high, the power transistor M1 is in the conducting state, the Drain voltage is low, and the CS voltage increases linearly with the linear increase of the inductor current (at this time, the power transistor M1 is in the linear operating region, exhibiting resistive characteristics, therefore the Drain voltage increases linearly but is much smaller than (VIN + V). D1 )).

[0019] Figure 3 It shows Figure 1 The diagram shows the relevant signal waveforms when power transistor M1 is in saturation. Here, Gate represents the gate voltage of power transistor M1, Drain represents the drain voltage of power transistor M1, and CS represents the source voltage of power transistor M1 (i.e., the voltage generated across the current sensing resistor Rcs by the current flowing through power transistor M1). Figure 1 and Figure 3 As shown, when the power transistor M1 enters saturation at time t1, the inductor current reaches the maximum current supported by the power transistor M1 and remains constant. The drain voltage increases rapidly, the voltage across the inductor drops to zero, and the CS voltage remains basically unchanged. Under this state, the power consumption on the power transistor M1 increases, and the temperature of the power transistor M1 rises rapidly.

[0020] exist Figure 1 In the LED driver circuit 100 shown, the control circuit 102 detects whether the power transistor M1 has entered a saturation state through a temperature detection module. When the power transistor M1 is detected to be in a saturation state, the gate drive module performs a protection action on the power transistor M1, such as turning off the power transistor M1 or reducing the output current. Since temperature propagation takes a certain amount of time, this power transistor protection mechanism cannot detect the abnormality of the power transistor M1 and perform the protection action in time. During this process, the power transistor M1 is easily damaged.

[0021] In view of the problems existing in the power transistor protection mechanisms used in current switching power supplies, a control circuit for switching power supplies according to embodiments of the present invention is proposed, applicable to switching power supplies employing various architectures (e.g., flyback architecture, boost architecture, or buck architecture). The control circuit for switching power supplies according to embodiments of the present invention will be described in detail below with reference to the accompanying drawings, taking an LED driver circuit employing a buck architecture as an example.

[0022] Figure 4 A system schematic diagram of an LED driving circuit according to an embodiment of the present invention is shown. Figure 4 In the LED driving circuit 400 shown, the control circuit 402 includes a saturation detection module 4022 and a gate driving module 4024. The saturation detection module 4022 is configured to detect whether the power transistor M1 has entered a saturation state based on the drain voltage Drain of the power transistor M1 when the power transistor M1 is in the on state. The gate driving module 4024 is configured to control the power transistor M1 to change from the on state to the off state when the saturation detection module 4022 detects that the power transistor M1 has entered a saturation state.

[0023] Specifically, in Figure 4 In the LED driver circuit 400 shown, when the power transistor M1 enters the saturation state from the normal operating state, the drain voltage Drain of the power transistor M1 increases rapidly. Therefore, the saturation detection module 4022 can determine whether the power transistor M1 has entered the saturation state by detecting the change in the drain voltage Drain of the power transistor M1. For example, when the power transistor M1 is in the conducting state, the saturation detection module 402 can detect whether the drain voltage Drain of the power transistor M1 is greater than the drain voltage threshold, and determine that the power transistor M1 has entered the saturation state when the drain voltage Drain of the power transistor M1 is detected to be greater than the drain voltage threshold.

[0024] Figure 5 It shows Figure 4 The diagram shows an example circuit implementation of the saturation detection module. Figure 5 As shown, in some embodiments, the saturation detection module 4022 can generate a drain sampling voltage Dr_di of the power transistor M1 by dividing the drain voltage Drain of the power transistor M1, and generate a saturation state indication signal Dr_sat indicating whether the power transistor M1 has entered a saturation state by comparing the drain sampling voltage Dr_di of the power transistor M1 with the drain reference voltage Vref, wherein the drain reference voltage Vref is related to the drain voltage threshold and the voltage divider resistors (e.g., R1 and R2) used to divide the drain voltage Drain of the power transistor M1.

[0025] like Figure 5As shown, in some embodiments, the saturation detection module 4022 can also generate a conduction state confirmation signal leb for determining whether the power transistor M1 is indeed in the conduction state based on the gate drive signal Gate used to drive the power transistor M1 to turn on and off, and generate a shutdown control signal Gate_off for controlling the power transistor M1 to change from the conduction state to the shutdown state based on the saturation state indication signal Dr_sat, the conduction state confirmation signal leb, and the gate drive signal Gate.

[0026] Figure 6 It shows Figure 5 The diagram shows the relevant signal waveforms of the saturation detection module. Here, Gate represents the gate drive signal used to turn power transistor M1 on and off, leb represents the on-state confirmation signal used to determine whether power transistor M1 is indeed in the on state, Drain represents the drain voltage of power transistor M1, Dr_di represents the drain sampling voltage of power transistor M1, and Gate_off represents the turn-off control signal used to control power transistor M1 to change from the on state to the off state. Figure 4 , Figure 5 ,as well as Figure 6 As shown, when the gate drive signal Gate is high, the power transistor M1 is in the on state. When the power transistor M1 is in normal operation, the inductor current increases linearly, the drain voltage Drain of the power transistor M1 is relatively small, so the drain sampling voltage Dr_di is less than the drain reference voltage Vref, and the turn-off control signal Gate_off is low (at this time, the saturation state indicator signal Dr_sat is also low). Once the power transistor M1 enters the saturation state, the drain voltage Drain of the power transistor M1 increases rapidly, so the drain sampling voltage Dr_di also increases rapidly and is greater than the drain reference voltage Vref, and the turn-off control signal Gate_off is high (at this time, the saturation state indicator signal Dr_sat is also high).

[0027] Furthermore, such as Figure 4 , Figure 5 ,as well as Figure 6As shown, in each switching cycle of the power transistor M1, the turn-on confirmation signal leb changes from high to low when the power transistor M1 changes from the off state to the on state, and changes from low to high before the power transistor M1 changes from the on state to the off state (for example, it changes from high to low when the gate drive signal Gate changes from low to high, and changes from low to high before the gate drive signal Gate changes from high to low). When the drain sampling voltage Dr_di of the power transistor M1 is greater than the drain reference voltage Vref and both the gate drive signal Gate and the turn-on confirmation signal leb are high, the turn-off control signal Gate_off is high. This allows the gate drive module 4024 to drive the power transistor M1 from the on state to the off state based on the turn-off control signal Gate_off, thereby protecting the power transistor.

[0028] Figure 7 A circuit diagram of another LED driving circuit according to an embodiment of the present invention is shown. Figure 7 In the LED driving circuit 700 shown, the control circuit 702 includes a saturation detection module 7022 and a gate driving module 7024. The saturation detection module 7022 is configured to detect whether the power transistor M1 has entered a saturation state based on the source voltage of the power transistor M1 when the power transistor M1 is in the on state. The gate driving module 7024 is configured to control the power transistor M1 to change from the on state to the off state when the saturation detection module 7022 detects that the power transistor M1 has entered a saturation state.

[0029] Specifically, in Figure 7 In the LED driver circuit 100 shown, when the power transistor M1 is in normal operating condition, the source voltage CS of the power transistor M1 rises linearly at a certain rate. When the power transistor M1 enters saturation, the source voltage CS of the power transistor M1 stops rising and remains constant, with its rising slope slowing down to zero. Therefore, the saturation detection module 7022 can determine whether the power transistor M1 has entered saturation by detecting the change in the rising slope of the source voltage CS of the power transistor M1. For example, when the power transistor M1 is in the on state, the saturation detection module 7022 can detect whether the rising slope of the source voltage CS of the power transistor M1 is less than a source voltage slope threshold, and determine that the power transistor M1 has entered saturation when the rising slope of the source voltage CS of the power transistor M1 is less than the source voltage slope threshold.

[0030] Figure 8 It shows Figure 7 The diagram shows an example circuit implementation of the saturation detection module. Figure 8As shown, in some embodiments, the saturation detection module 7022 can generate a source voltage characterization voltage Vramp that varies with the source voltage CS of the power transistor M1 using an emitter follower and an operational amplifier buffer; based on the source voltage characterization voltage Vramp, it can generate a source voltage characterization current I3 that varies with the slope of the source voltage CS of the power transistor M1 using a capacitor and a current mirror; and based on the source voltage characterization current I3 and the current source threshold current Ix, it can generate a saturation state indication signal Dr_sat indicating whether the power transistor M1 has entered a saturation state. Here, the current source threshold current Ix is related to the source voltage slope threshold.

[0031] For example, in Figure 8 In the saturation detection module 7022 shown, a PNP or PMOS transistor Q1 and a current source I1 form an emitter follower, causing voltage V1 to follow the source voltage CS of power transistor M1. Voltage V1 is increased by voltage Vbe on top of the source voltage CS of power transistor M1, i.e., V1 = Vcs + Vbe1 (Vbe is the voltage between the base and emitter of Q1). Operational amplifier buffer A2 causes voltage Vramp to follow voltage V1, i.e., Vramp = V1. When power transistor M1 is in the on state, voltage Vramp increases linearly with the source voltage CS of power transistor M1, and the voltage across capacitor C, Vc = Vramp - Vbe = Vcs (Vbe is the voltage between the base and emitter of Q2), also increases linearly (i.e., the voltage change across capacitor C is proportional to the change in the source voltage CS of power transistor M1). NPN transistor Q2 detects the charging current I2 of capacitor C, and the NPN transistor Q3 mirrors the charging current I2 of capacitor C to obtain current I3. Current I3 is compared with current Ix. When I3 is greater than Ix, Dr_sat is low. When I3 is less than Ix, Dr_sat is high. When power transistor M1 is off, the voltage across capacitor C is discharged to zero, so that when power transistor M1 is turned on again, the voltage across capacitor C starts from zero. Therefore, the increase in voltage across capacitor C is equal to the change in the source voltage CS of power transistor M1. Here, circuit design can ensure that I3 is greater than Ix under the gentlest rising slope of the source voltage CS of power transistor M1.

[0032] like Figure 8 As shown, in some embodiments, the saturation detection module 7022 can also generate a conduction state confirmation signal leb for determining whether the power transistor M1 is indeed in the conduction state based on the gate drive signal Gate used to drive the power transistor M1 to conduct and turn off, and generate a turn-off control signal Gate_off for controlling the power transistor M1 to change from the conduction state to the turn-off state based on the saturation state indication signal Dr_sat, the conduction state confirmation signal leb, and the gate drive signal Gate.

[0033] Figure 9 It shows Figure 8 The diagram shows the relevant signal waveforms of the saturation detection module. Here, Gate represents the gate drive signal used to turn power transistor M1 on and off, leb represents the on-state confirmation signal used to determine whether power transistor M1 is indeed in the on state, CS represents the source voltage of power transistor M1, I2 represents the charging current of capacitor C, Dr_sat represents the saturation state indication signal used to indicate whether power transistor M1 is in the saturation state, and Gate_off represents the shutdown control signal used to control power transistor M1 to change from the on state to the off state. Figure 7 , Figure 8 ,as well as Figure 9 As shown, when the gate drive signal Gate is high, power transistor M1 is in the on state. When power transistor M1 is in normal operation, the inductor current increases linearly, the source voltage CS of power transistor M1 also increases linearly, the charging current I2 of capacitor C remains unchanged, and its mirror current I3 is greater than the current source threshold current Ix. The saturation state indicator signal Dr_sat is low, and the turn-off control signal Gate_off is low. When power transistor M1 enters the saturation state, the source voltage CS of power transistor M1 stops increasing and remains unchanged. The charging current I2 of capacitor C decreases to zero, so its mirror current I3 is less than the current source threshold current Ix. The saturation state indicator signal Dr_sat is high, and the turn-off control signal Gate_off is low.

[0034] Furthermore, such as Figure 7 , Figure 8 ,as well as Figure 9 As shown, in each switching cycle of the power transistor M1, the turn-on confirmation signal leb changes from high to low when the power transistor M1 changes from the off state to the on state, and changes from low to high before the power transistor M1 changes from the on state to the off state (for example, it changes from high to low when the gate drive signal Gate changes from low to high, and changes from low to high before the gate drive signal Gate changes from high to low). When the mirror current I3 of the charging current I2 of capacitor C is less than the current source threshold current Ix and both the gate drive signal Gate and the turn-on confirmation signal leb are high, the turn-off control signal Gate_off is high. This allows the gate drive module 7024 to drive the power transistor M1 from the on state to the off state based on the turn-off control signal Gate_off, thereby protecting the power transistor.

[0035] This invention can be implemented in other specific forms without departing from its spirit and essential characteristics. For example, the algorithm described in a particular embodiment can be modified without departing from the basic spirit of the invention. Therefore, the present embodiments are to be regarded as exemplary rather than limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and all changes falling within the meaning and scope of the claims and their equivalents are thus included within the scope of the invention.

Claims

1. A control circuit used in a switching power supply, wherein, The switching power supply includes a power transistor, and the control circuit is configured to, when the power transistor is in the ON state: Detect whether the rise slope of the source voltage of the power transistor is less than the source voltage slope threshold. When the rising slope of the source voltage of the power transistor is less than the source voltage slope threshold, it is determined that the power transistor has entered the saturation state. as well as When the power transistor is detected to have entered saturation, the power transistor is controlled to change from the on state to the off state, wherein... The control circuit is further configured to: Based on the source voltage of the power transistor, a source voltage characterization voltage that varies with the source voltage of the power transistor is generated using an emitter follower and an operational amplifier buffer. Based on the source voltage characterization voltage, a source voltage characterization current that varies with the slope of the source voltage of the power transistor is generated using a capacitor and a current mirror. as well as Based on the source voltage characterizing current and the current source threshold current, a saturation state indication signal is generated to indicate whether the power transistor has entered a saturation state, wherein the current source threshold current is related to the source voltage slope threshold.

2. The control circuit according to claim 1, wherein, When the source voltage representing the current is less than the current source threshold current, the saturation state indication signal is at a high level.

3. The control circuit according to claim 1, further configured as follows: Based on the gate drive signal used to drive the power transistor to turn on and off, a conduction state confirmation signal is generated to determine whether the power transistor is indeed in the conduction state; and Based on the saturation state indication signal, the conduction state confirmation signal, and the gate drive signal, a turn-off control signal is generated to control the power transistor to change from the conduction state to the turn-off state.

4. The control circuit according to claim 3, wherein, In each switching cycle of the power transistor, the conduction state confirmation signal changes from high to low at the moment when the power transistor changes from the off state to the on state, and changes from low to high before the moment when the power transistor changes from the on state to the off state.

5. The control circuit according to claim 4, wherein, When the source voltage characterizing the current is less than the current source threshold current and both the gate drive signal and the turn-on state confirmation signal are at a high level, the turn-off control signal is at a high level.

6. A switching power supply, comprising the control circuit according to any one of claims 1 to 5.

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