Switching power supply and control circuit thereof

Abstract

A switching power supply and a control circuit thereof are provided, wherein the switching power supply includes a transformer and a power switch, a drain of the power switch is connected to a primary winding of the transformer, a source of the power switch is connected to a reference ground of the control circuit via a current sampling element or directly connected to the reference ground of the control circuit, the control circuit is configured to, when the power switch is in a conducting state: detect one or more of a drain voltage of the power switch, a voltage on an auxiliary winding of the transformer, and a current flowing through the power switch; and control the power switch to change from the conducting state to an off state when one or more of the following conditions are met: the drain voltage of the power switch is greater than a first threshold voltage, a variation amount of the voltage on the auxiliary winding of the transformer is greater than a second threshold voltage, and a variation slope of the current flowing through the power switch is less than a current variation slope threshold.

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 transformer and a power switch. The drain of the power switch is connected to the primary winding of the transformer, and the source is connected to the reference ground of the control circuit via a current sampling element or directly connected to the reference ground of the control circuit. The control circuit is configured to, when the power switch is in the on state, detect one or more of the following: the drain voltage of the power switch, the voltage on the auxiliary winding of the transformer, and the current flowing through the power switch; and control the power switch to change from the on state to the off state when one or more of the following conditions are met: the drain voltage of the power switch is greater than a first threshold voltage, the change in voltage on the auxiliary winding of the transformer is greater than a second threshold voltage, and the slope of the change in current flowing through the power switch is less than a current change slope threshold.

[0004] According to an embodiment of the present invention, a switching power supply includes the control circuit described above used in a switching power supply. 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 The diagram shows the waveforms of the relevant signals of the power switch used in a switching power supply.

[0007] Figure 2 A circuit schematic diagram of a switching power supply according to an embodiment of the present invention is shown.

[0008] Figure 3 The diagram shows the waveforms of the relevant signals used to control the power switch from the on state to the off state based on the drain voltage of the power switch.

[0009] Figure 4 It shows Figure 2 The diagram shows a schematic block diagram of the relevant example circuits in the drain voltage detection module and the main controller module.

[0010] Figure 5The diagram shows the waveforms of the relevant signals used to control the power switch from the on state to the off state based on the voltage on the auxiliary winding of the transformer.

[0011] Figure 6 It shows Figure 2 The diagram shows a schematic block diagram of the relevant example circuits in the excitation inductor voltage detection module and the main controller module.

[0012] Figure 7 The diagram shows the waveforms of the relevant signals used to control the power switch from the on state to the off state based on the slope of the change in current flowing through the power switch.

[0013] Figure 8 It shows Figure 2 The diagram shows a schematic block diagram of the relevant example circuits in the current detection module and the main controller module. Detailed Implementation

[0014] 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 comprehensive 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 configuration and algorithm 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. Furthermore, it should be noted that the term "A connected to B" as used herein can mean "A and B are directly connected" or "A and B are indirectly connected via one or more other elements." Also, the number and connection methods of comparators, logic gates, subtractors, and flip-flops mentioned herein are not limited to the number and connection methods shown in the embodiments.

[0015] With the continuous development of electronic information technology, various electronic products (such as Internet of Things (IoT) devices) are becoming increasingly common, leading to a surge in the number of switching power supplies used for power supply. While the failure rate of switching power supplies remains constant, the number of failures increases with the total number of switching power supplies, making it crucial to improve their reliability and safety. Simultaneously, third-generation semiconductor power devices, such as GaN metal-oxide-semiconductor field-effect transistors (MOSFETs), are increasingly used in switching power supplies. Compared to traditional silicon-based MOSFETs, GaN MOSFETs improve efficiency and reduce size. However, with the same on-resistance (Rdson), the saturation current of GaN MOSFETs is lower than that of traditional silicon-based MOSFETs. This makes GaN MOSFETs more susceptible to damage under high-current surges, resulting in a higher risk of power supply failure when using GaN MOSFETs.

[0016] Figure 1 The diagram shows the operating waveforms of relevant signals from a power switch used in a switching power supply, where VD represents the drain voltage of the power switch, GATE represents the gate voltage of the power switch, CS represents the current flowing through the power switch, Vaux represents the voltage on the auxiliary winding of the transformer in the switching power supply, and V... Bulk This represents the voltage across the bus capacitor in a switching power supply. Figure 1 It can be seen that when the power switch is in the ON state (i.e., GATE is high), if the current flowing through the power switch exceeds its saturation current, the current cannot continue to increase linearly. This leads to a larger voltage change on the transformer's auxiliary winding, increasing the difference between the drain and source voltages of the power switch, and causing the power switch to exhibit higher resistive characteristics. At this point, due to the large current flowing through the power switch and the significant difference between its drain and source voltages, the power switch consumes a large amount of power, generates excessive heat, and is prone to damage.

[0017] In view of the above problems, a switching power supply and its control circuit are provided to prevent damage to the power switches (e.g., GaN MOSFETs) in the switching power supply. The switching power supply and its control circuit according to embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0018] Figure 2 A circuit schematic diagram of a switching power supply according to an embodiment of the present invention is shown. Figure 2As shown, the switching power supply 200 according to an embodiment of the present invention includes a transformer T, a power switch Q1, and a control chip 202. The drain and source of the power switch Q1 are respectively connected to the primary winding of the transformer T and the reference ground of the control chip 202 (the source of the power switch Q1 can be directly connected to the reference ground of the control chip 202 or connected to the reference ground of the control chip 202 via a current sampling element Rcs). The control chip 202 is configured to detect the drain voltage VD of the power switch Q1 and the voltage of the transformer T when the power switch Q1 is in the on state. The power switch Q1 is switched off when one or more of the following conditions are met: the drain voltage VD of the power switch Q1 is greater than the first threshold voltage Vdrain_full; the change in the voltage Vaux on the auxiliary winding of the transformer T is greater than the second threshold voltage Vaux_drain_full; and the slope of the change in the current CS flowing through the power switch Q1 is less than the current change slope threshold Kdrain_full. It should be noted that since the voltage on the auxiliary winding of the transformer is proportional to the voltage on its primary winding, the voltage on the primary winding of the transformer T (i.e., the magnetizing inductance voltage of the transformer T) can be indirectly detected by detecting the voltage Vaux on the auxiliary winding of the transformer T.

[0019] exist Figure 2 In the switching power supply 200 shown, the control chip 200 can determine that the current CS flowing through the power switch Q1 has reached the saturation current of the power switch Q1 when it detects that the drain voltage VD of the power switch Q1 is greater than the first threshold voltage Vdrain_full, the change in voltage Vaux on the auxiliary winding of the transformer T is greater than the second threshold voltage Vaux_drain_full, or the slope of the change in current CS flowing through the power switch Q1 is less than the current change slope threshold Kdrain_full. In this way, the control chip 200 controls the power switch Q1 to change from the on state to the off state, thereby avoiding damage caused by continuous heating of the power switch Q1.

[0020] like Figure 2 As shown, in some embodiments, the control chip 202 includes one or more of the following pins:

[0021] The chip's power supply pin (i.e., the VDD pin) is connected to the auxiliary winding of transformer T, as shown by the dashed line ①. The DC voltage Vaux on the auxiliary winding of transformer T, after being rectified and filtered by diodes and rectifier capacitors, is used to power the control chip 202.

[0022] The gate drive pin (i.e., the GATE pin) is connected to the gate of the power switch Q1, as shown by the dashed line ②, and is used to drive the power switch Q1 to turn on and off.

[0023] The current sampling pin (i.e., the CS pin), connected to the current sampling element Rcs, as shown by dashed line ③, is used to detect the current CS flowing through the power switch Q1. For example, the current CS flowing through the power switch Q1 is detected by detecting the voltage across the current sampling element Rcs, which is connected between the source of the power switch Q1 and the reference ground of the control chip 202.

[0024] The drain detection pin (i.e., the drain pin) is connected to the drain of the power switch Q1, as shown by the dashed line ④, and is used to detect the drain voltage VD of the power switch Q1.

[0025] The ground pin (i.e., the GND pin) is connected to the system ground of the switching power supply 200, as shown by the dashed line ⑤, and serves as the reference ground for the control chip 202.

[0026] The output feedback pin (i.e., the FB pin) is connected to the optocoupler, as shown by dashed line ⑥, and is used to receive the output feedback signal from the secondary side of transformer T.

[0027] The over-temperature protection pin (i.e., the OTP pin) is connected to a thermistor (i.e., the NTC resistor), as shown by the dashed line ⑦, and is used to detect the voltage across the NTC resistor and provide over-temperature protection for the control chip 202.

[0028] The demagnetization detection pin (i.e., the DEM pin) is connected to the auxiliary winding of transformer T, as shown by the dashed line ⑧, and is used to detect the voltage Vaux on the auxiliary winding of transformer T.

[0029] In some embodiments, when the power switch Q1 is in the on state, the control chip 202 can detect the drain voltage VD of the power switch Q1 through the Drain pin, and when the drain voltage VD of the power switch Q1 is greater than the first threshold voltage Vdrain_full, control the power switch Q1 to immediately change from the on state to the off state, so as to avoid high voltage and large current appearing simultaneously between the drain and source of the power switch Q1, thereby avoiding continuous heating of the power switch Q1 and preventing damage to the power switch Q1.

[0030] Figure 3 The diagram shows the waveforms of the relevant signals controlling the power switch Q1 from the on state to the off state based on the drain voltage of the power switch Q1. Here, VD represents the drain voltage of the power switch Q1, GATE represents the gate voltage of the power switch Q1, CS represents the current flowing through the power switch Q1, Vaux represents the voltage on the auxiliary winding of the transformer T, and V... Bulk This represents the voltage across the bus capacitor Cbulk in the switching power supply 200. (Combined with...) Figure 2 and Figure 3As can be seen, when GATE is at a high level (i.e., power switch Q1 is in the on state), when the drain voltage VD of power switch Q1 is greater than the first threshold voltage Vdrain_full, GATE immediately changes from a high level to a low level (i.e., power switch Q1 immediately changes from the on state to the off state). The current flowing through power switch Q1 immediately decreases to zero. Therefore, it can avoid the simultaneous occurrence of high voltage and large current between the drain and source of power switch Q1, thereby preventing power switch Q1 from continuously heating up and preventing damage to power switch Q1.

[0031] Figure 4 It shows Figure 2 The diagram shows a schematic block diagram of the relevant example circuits in the drain voltage detection module and the main controller module. (See attached diagram.) Figure 4 As shown, in some embodiments, the control chip 202 can be configured to: generate a first comparison result signal using a comparator based on the drain voltage of the power switch Q1 and a first threshold voltage Vdrain_full; generate a first logic signal using an AND gate based on a first trigger signal and the first comparison result signal; generate a first trigger signal using an RS trigger based on the first logic signal and an oscillation signal; and generate a gate drive signal (e.g., the gate voltage GATE of the power switch Q1) for driving the power switch Q1 to turn on and off using logic control circuitry and a driver based on the first trigger signal. Here, the oscillation signal may be generated by an oscillator based on an operating mode indication signal from a multi-mode control circuitry, the operating mode indication signal being used to indicate the operating mode of the switching power supply (e.g., continuous current mode (CCM), discontinuous current mode (DCM), or burst mode (Burst mode)).

[0032] In some embodiments, when the power switch Q1 is in the on state, the control chip 202 can detect the voltage Vaux on the auxiliary winding of the transformer T through the DEM pin, and when the change in the voltage Vaux on the auxiliary winding of the transformer T is greater than the second threshold voltage Vaux_drain_full, control the power switch Q1 to immediately change from the on state to the off state, so as to avoid the simultaneous occurrence of high voltage and large current between the drain and source of the power switch Q1, thereby avoiding the continuous heating of the power switch Q1 and preventing damage to the power switch Q1.

[0033] Figure 5The diagram shows the waveforms of the signals controlling the power switch Q1 from the on state to the off state based on the voltage on the auxiliary winding of transformer T. Here, VD represents the drain voltage of power switch Q1, GATE represents the gate voltage of power switch Q1, CS represents the current flowing through power switch Q1, Vaux represents the voltage on the auxiliary winding of transformer T, and VBulk represents the voltage on the bus capacitor Cbulk in the switching power supply 200. (Combined with...) Figure 2 and Figure 5 It can be seen that when GATE is at a high level (i.e., power switch Q1 is in the on state), when the change in voltage Vaux on the auxiliary winding of transformer T is greater than the second threshold voltage Vaux_drain_full, GATE immediately changes from a high level to a low level (i.e., power switch Q1 immediately changes from the on state to the off state). The current flowing through power switch Q1 immediately decreases to zero. Therefore, it can avoid the simultaneous occurrence of high voltage and large current between the drain and source of power switch Q1, thereby avoiding continuous heating of power switch Q1 and preventing damage to power switch Q1.

[0034] Figure 6 It shows Figure 2 The diagram shows a schematic block diagram of the relevant example circuits in the excitation inductor voltage detection module and the main controller module. (See attached diagram.) Figure 6 As shown, in some embodiments, the control chip 202 can be configured to: obtain the change in voltage Vaux on the auxiliary winding of transformer T using a sample-and-hold circuit and a subtractor based on the voltage Vaux on the auxiliary winding of transformer T and a second trigger signal; generate a second comparison result signal using a comparator based on the change in voltage Vaux on the auxiliary winding of transformer T and a second threshold voltage Vaux_drain_full; generate a second trigger signal using an RS trigger based on the second comparison result signal and an oscillation signal; and generate a gate drive signal (e.g., the gate voltage GATE of power switch Q1) for driving the power switch to turn on and off using a logic control circuit and a driver based on the second trigger signal. Here, the oscillation signal may be generated by an oscillator based on an operating mode indication signal from a multi-mode control circuit, which indicates the operating mode of the switching power supply (e.g., CCM, DCM, or Burst mode).

[0035] In some embodiments, when the power switch Q1 is in the ON state, the control chip 202 can detect the voltage on the current sampling element Rcs through the CS pin, and when the slope of the voltage change on the current sampling element Rcs (i.e., the slope of the current change flowing through the power switch Q1) is less than the current change slope threshold Kdrain_full, the control chip 202 controls the power switch Q1 to immediately change from the ON state to the OFF state, so as to avoid high voltage and large current appearing simultaneously between the drain and source of the power switch Q1, thereby avoiding continuous heating of the power switch Q1 and preventing damage to the power switch Q1.

[0036] Figure 7 The diagram shows the waveforms of the relevant signals controlling the power switch Q1 from the on state to the off state based on the slope of the change in current flowing through the power switch Q1. Here, VD represents the drain voltage of power switch Q1, GATE represents the gate voltage of power switch Q1, CS represents the current flowing through power switch Q1, Vaux represents the voltage on the auxiliary winding of transformer T, and CS slope ratio represents the slope of the change in current flowing through power switch Q1. Bulk This represents the voltage across the bus capacitor Cbulk in the switching power supply 200. (Combined with...) Figure 2 and Figure 7 It can be seen that when GATE is at a high level (i.e., power switch Q1 is in the on state), when the slope of the current change flowing through power switch Q1 is less than the current change slope threshold Kdrain_full, GATE immediately changes from a high level to a low level (i.e., power switch Q1 immediately changes from the on state to the off state), and the current flowing through power switch Q1 immediately decreases to zero. Therefore, it can avoid the simultaneous occurrence of high voltage and large current between the drain and source of power switch Q1, thereby avoiding continuous heating of power switch Q1 and preventing damage to power switch Q1.

[0037] Figure 8 It shows Figure 2 The diagram shows a schematic block diagram of the relevant example circuits in the current detection module and the main controller module. Figure 8As shown, in some embodiments, the control chip 202 can be configured to: generate a third comparison result signal using a comparator based on the slope of the voltage change on the current sampling element Rcs and the current change slope threshold Kdrain_full; generate a third logic signal using an AND gate based on the third flip-flop signal and the third comparison result signal; generate a third flip-flop signal using an RS flip-flop based on the third logic signal and the oscillation signal; and generate a gate drive signal (e.g., the gate voltage GATE of the power switch Q1) for driving the power switch Q1 to turn on and off using logic control circuitry and a driver based on the third flip-flop signal. Here, the oscillation signal may be generated by an oscillator based on an operating mode indication signal from a multi-mode control circuit, which indicates the operating mode of the switching power supply (e.g., CCM, DCM, or Burst mode).

[0038] 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 transformer and a power switch. The drain of the power switch is connected to the primary winding of the transformer, and the source is connected to the reference ground of the control circuit via a current sampling element or directly to the reference ground of the control circuit. The control circuit is configured to, when the power switch is in the ON state: Detect one or more of the following: the drain voltage of the power switch, the voltage on the auxiliary winding of the transformer, and the current flowing through the power switch; and The power switch is controlled to change from the on state to the off state when one or more of the following conditions are met: the drain voltage of the power switch is greater than the first threshold voltage, the change in voltage on the auxiliary winding of the transformer is greater than the second threshold voltage, and the slope of the change in current flowing through the power switch is less than the current change slope threshold.

2. The control circuit according to claim 1 is further configured as follows: The current flowing through the power switch is detected by detecting the voltage on the current sampling element connected between the source of the power switch and the reference ground of the control circuit.

3. The control circuit according to claim 2, wherein, The control circuit is implemented in a control chip, and the control chip includes: A gate drive pin is connected to the gate of the power switch and is used to drive the power switch to turn on and off. A drain detection pin is connected to the drain of the power switch and is used to detect the drain voltage of the power switch. A demagnetization detection pin, connected to the auxiliary winding of the transformer, is used to detect the voltage on the auxiliary winding of the transformer; and A current sampling pin, connected to the current sampling element, is used to detect the current flowing through the power switch.

4. The control circuit according to claim 2 is further configured as follows: Based on the drain voltage of the power switch and the first threshold voltage, a comparator is used to generate a first comparison result signal; Based on the first flip-flop signal and the first comparison result signal, a first logic signal is generated using a logic AND gate; Based on the first logic signal and the oscillation signal, the first flip-flop signal is generated using an RS flip-flop, wherein... The oscillation signal is related to the operating mode of the switching power supply; as well as Based on the first trigger signal, a gate drive signal for driving the power switch to turn on and off is generated using a logic control circuit and a driver.

5. The control circuit according to claim 2 is further configured as follows: Based on the voltage change on the auxiliary winding of the transformer and the second threshold voltage, a second comparison result signal is generated using a comparator; Based on the second comparison result signal and the oscillation signal, a second trigger signal is generated using an RS trigger, wherein... The oscillation signal is related to the operating mode of the switching power supply; as well as Based on the second trigger signal, a gate drive signal for driving the power switch to turn on and off is generated using a logic control circuit and a driver.

6. The control circuit according to claim 2 is further configured as follows: Based on the slope of the voltage change on the current sampling element and the current change slope threshold, a third comparison result signal is generated using a comparator; Based on the third flip-flop signal and the third comparison result signal, a third logic signal is generated using a logic AND gate; Based on the third logic signal and the oscillation signal, the third flip-flop signal is generated using an RS flip-flop, wherein the oscillation signal is related to the operating mode of the switching power supply; as well as Based on the third trigger signal, a gate drive signal for driving the power switch to turn on and off is generated using a logic control circuit and a driver.

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

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