Power supply backflow prevention circuit and dc-dc converter

Abstract

The utility model discloses a power supply anti -inversion protection circuit and DC DC converter belongs to electronic circuit technical field, including main switch tube, auxiliary power supply and triode mirror image circuit. Among them, main switch tube connects between power output side and load side, and auxiliary power supply is used for driving main switch tube, and triode mirror image circuit is according to the comparison result of load side and power output side voltage automatic control main switch tube on -off, thereby realizes when load side voltage normal, power output side normal power supply to load side, and when load side voltage is too high, cut off the power supply loop between power output side and load side, prevent current from load side to power output side inverts. The utility model discloses a power supply anti -inversion protection circuit does not need to configure additional control signal or reference threshold, only needs to depend on hardware circuit self structure can accurately, in time to the power supply loop between power output side and load side realizes on -off control, thereby effectively solved the problem of the protection reliability of insufficient of prior art.

Description

Technical Field

[0001] This utility model belongs to the field of electronic circuit technology, and relates to a DC-DC converter. Specifically, it relates to a reverse current protection circuit applied on the power output side of a DC-DC converter. Background Technology

[0002] A DC-DC converter is an electronic device that converts direct current (DC) voltage to another DC voltage. It uses switching power supply technology to boost, buck, or reverse the voltage, and is widely used in electronic devices to meet the power supply needs of different modules.

[0003] As electronic devices continue to develop towards higher-end and more precise directions, the reliability requirements for DC-DC converters are becoming increasingly stringent. In particular, it is necessary to consider the problem of reverse power flow from the load side to the DC-DC converter caused by misoperation of the output voltage of the DC-DC converter (such as shorting to other power supplies with higher voltage values), in order to protect the DC-DC converter from overvoltage damage.

[0004] To address the aforementioned issues, Chinese invention patent applications with publication numbers CN102291022A and CN104092388A employ a method of adding a detection resistor to the circuit. The direction of current flow across the detection resistor is used to determine whether a backflow problem has occurred. If backflow occurs, the switch on the output side of the circuit is turned off to prevent reverse current surge. However, this circuit design cannot guarantee that the switch will remain permanently off during periods of excessively high load voltage, leading to frequent switch startups and thus failing to provide reliable protection for the circuit.

[0005] Chinese invention patent application CN105305797A adds a MOSFET between the output side and the load side of a DC-DC power supply and sets up a comparator to detect whether the output voltage of the DC-DC power supply is too high. If an overvoltage problem occurs, the MOSFET is turned off to prevent reverse current flow. However, this circuit design requires a reference threshold to be set in advance for the comparator. If the reference threshold is not set properly, current can still flow from the load side to the DC-DC power supply. Therefore, there are still some shortcomings in terms of the safety and reliability of the protection measures. Summary of the Invention

[0006] This utility model addresses at least one of the aforementioned technical problems in the prior art by proposing a power supply backflow protection circuit that can automatically cut off the power supply circuit between the power supply output side and the load when the load side voltage is higher than the power supply output side voltage, thereby achieving the purpose of protecting the power supply.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] In one aspect, this utility model proposes a power supply reverse current protection circuit, connected between the power supply output side and the load side, comprising:

[0009] The main switching transistor is connected between the power output side and the load side;

[0010] An auxiliary power supply, which outputs a DC voltage, is used to drive the main switching transistor;

[0011] A transistor mirror circuit includes a first transistor and a second transistor connected in a mirror relationship. The first transistor is connected between the auxiliary power supply and the power output side, and the second transistor is connected between the auxiliary power supply and the load side. The second transistor adjusts its on / off state according to the voltage difference between the load side and the power output side, and controls the first transistor to conduct in a complementary manner. By changing the on / off state of the first transistor, the main switch is controlled to connect the power supply circuit between the power output side and the load side when the load side voltage is less than or equal to the power output side voltage, and disconnect the power supply circuit between the power output side and the load side when the load side voltage is greater than the power output side voltage.

[0012] In some embodiments of this application, the main switch can be a MOSFET, with its source and gate connected between the power output side and the load side, and its gate connected to the first transistor, so that the MOSFET and the first transistor are in a complementary conduction state.

[0013] In some embodiments of this application, both the first and second transistors can be NPN transistors, with their bases interconnected. The collector of the first transistor is connected to the auxiliary power supply through a first current-limiting resistor, and its emitter is connected to the power supply output side. The collector of the second transistor is connected to the auxiliary power supply through a second current-limiting resistor, and its emitter is connected to the load side, thus forming a transistor mirror circuit. The collector of the second transistor is connected to its base so that the second transistor conducts when the load-side voltage is normal and cuts off when the load-side voltage is too high, while simultaneously controlling the first transistor to conduct in a complementary manner. The collector of the first transistor is connected to the gate of the MOSFET to control the MOSFET to conduct in a complementary manner, that is, when the load-side voltage is normal, the MOSFET conducts, transmitting the voltage from the power supply output side to the load side to supply power to the load; while when the load-side voltage is too high, the MOSFET cuts off, cutting off the power supply loop between the power supply output side and the load side, preventing current from flowing back from the load side to the power supply output side, thus protecting the power supply.

[0014] In some embodiments of this application, in order to limit the base current of the two transistors, a first damping resistor can be connected to the base of the first transistor, and a second damping resistor can be connected to the base of the second transistor. The first damping resistor and the second damping resistor are connected together, and the connection node is connected to the collector of the second transistor.

[0015] In some embodiments of this application, the MOSFET generally has a parasitic diode. The anode of the parasitic diode in the MOSFET can be connected to the power output side, and the cathode of the parasitic diode can be connected to the load side to ensure the correct flow of the power supply current.

[0016] In some embodiments of this application, the MOSFET may be an N-channel MOSFET, with the source of the N-channel MOSFET connected to the power output side and the drain connected to the load side, so that the on / off state of the MOSFET is complementary to the on / off state of the first transistor.

[0017] In some embodiments of this application, the DC voltage output by the auxiliary power supply can be configured to be higher than the voltage on the power supply output side. The auxiliary power supply can be generated by a bootstrap circuit connected to the power supply output side. Specifically, the bootstrap circuit can be connected to the power supply output side, and the auxiliary power supply can be generated by adding a bootstrap voltage to the voltage on the power supply output side. The bootstrap voltage should be greater than 0.7V to control the conduction of the MOSFET.

[0018] In another aspect, this utility model also proposes a DC-DC converter for converting an input DC voltage into a required DC voltage and outputting it through a power supply output side. A backflow prevention protection circuit is connected between the power supply output side and the load side; the backflow prevention protection circuit includes:

[0019] The main switching transistor is connected between the power output side and the load side;

[0020] An auxiliary power supply, which outputs a DC voltage, is used to drive the main switching transistor;

[0021] A transistor mirror circuit includes a first transistor and a second transistor connected in a mirror relationship. The first transistor is connected between the auxiliary power supply and the power output side, and the second transistor is connected between the auxiliary power supply and the load side. The second transistor adjusts its on / off state according to the voltage difference between the load side and the power output side, and controls the first transistor to conduct in a complementary manner. By changing the on / off state of the first transistor, the main switch is controlled to connect the power supply circuit between the power output side and the load side when the load side voltage is less than or equal to the power output side voltage, and disconnect the power supply circuit between the power output side and the load side when the load side voltage is greater than the power output side voltage.

[0022] In some embodiments of this application, the DC-DC converter is configured with:

[0023] The DC-DC converter chip includes a power input pin, a high-side switch pin, a low-side switch pin, and high-low-side switch node pins; the power input pin receives the input DC voltage.

[0024] A high-side MOSFET is connected between the power input pin and the high-side and low-side switch node pins, and receives the switching control signal output from the high-side switch pin.

[0025] A low-side MOSFET is connected between the high-side and low-side switch node pins and ground, and receives the switching control signal output from the low-side switch pins.

[0026] An output capacitor is connected to the high-low side switching node pins via an inductor and a current-limiting resistor. The charging and discharging process of the inductor and the output capacitor is controlled by the PWM signal output from the high-low side switching node pins to generate the required DC voltage on the output capacitor. The output capacitor is used as the power output side and connected to the reverse current protection circuit to provide a stable DC voltage to the load side.

[0027] In some embodiments of this application, a bootstrap circuit can be included in the DC-DC converter to generate the required auxiliary power supply. Preferably, the bootstrap circuit can be connected to the output capacitor, specifically including:

[0028] A boost capacitor, which generates the auxiliary power supply;

[0029] The first diode has its anode connected to the output capacitor and its cathode connected to the boost capacitor, and the output capacitor is used to charge the boost capacitor.

[0030] The second diode has its anode connected to the high-low side switch node pins via a DC blocking capacitor, and its cathode connected to the boost capacitor. The alternating power output from the high-low side switch node pins is used to charge the boost capacitor, thereby adding a bootstrap voltage to the voltage of the output capacitor. This generates an auxiliary power supply with a voltage higher than the power supply output voltage, in order to meet the operating requirements of the reverse current protection circuit.

[0031] Compared with the prior art, the advantages and positive effects of this utility model are mainly reflected in:

[0032] 1. This utility model sets a main switch between the power supply output side and the load side, and designs a transistor mirror circuit to automatically control the on and off of the main switch according to the comparison result of the voltage between the load side and the power supply output side. This enables the power supply output side to supply power to the load side normally when the load side voltage is normal, and to cut off the power supply circuit between the power supply output side and the load side when the load side voltage is too high, so as to prevent the current from flowing back from the load side to the power supply output side.

[0033] 2. The backflow prevention protection circuit of this utility model has a simple structure and low cost. It does not require additional control signals or reference thresholds. It can accurately and timely control the power supply circuit between the power output side and the load side by relying on the hardware circuit itself, thereby effectively solving the problem of insufficient protection reliability in the prior art.

[0034] 3. Applying the backflow prevention protection circuit of this utility model to a DC-DC converter can protect the DC-DC converter from overvoltage damage.

[0035] Other features and advantages of this utility model will become clearer after reading the detailed embodiments of this utility model in conjunction with the accompanying drawings. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the embodiments will be briefly described below. Obviously, the drawings described below are some embodiments of this utility model. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0037] Figure 1 This is a circuit block diagram of one embodiment of the power supply reverse flow protection circuit proposed in this utility model;

[0038] Figure 2 yes Figure 1 A detailed circuit diagram of one embodiment of the power supply reverse flow protection circuit is shown.

[0039] Figure 3This is a circuit diagram of the part of a DC-DC converter associated with the power supply reverse current protection circuit. Detailed Implementation

[0040] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present utility model, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present utility model without creative effort are within the protection scope of the present utility model.

[0041] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" or "linked" should be interpreted broadly, for example, it can refer to a direct connection, an indirect connection, or a connection within components. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances. In the description of the embodiments, specific features, structures, or characteristics can be combined in any suitable manner in one or more embodiments or examples.

[0042] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature.

[0043] In order to reliably protect the power supply (such as a DC-DC converter or other circuit or product that provides power to the load), this embodiment adopts a pure hardware structure design for the power supply reverse current protection circuit, such as... Figure 1 As shown, it mainly includes key components such as the main switching transistor, transistor mirror circuit, and auxiliary power supply.

[0044] The main switch is connected between the power supply output side and the load side, used to connect or disconnect the power supply circuit between them. Specifically, when the load side voltage is normal, the voltage from the power supply output side is transmitted to the load side to supply power; when the load side voltage is abnormal, the return path is cut off to prevent high voltage from the load side from flowing back to the power supply output side, thus achieving reliable protection for the power supply.

[0045] This embodiment uses two identical transistors connected in a mirror relationship, and the on / off states of the two transistors are configured to be complementary. One transistor is connected between the auxiliary power supply and the load side, allowing it to automatically adjust its on / off state based on the comparison between the voltage on the load side and the voltage on the power supply output side. This, in turn, controls the other transistor, which is in a complementary conduction state, to adjust its on / off state accordingly. The other transistor is connected between the auxiliary power supply and the power supply output side, and configured with the main switch transistor to form a complementary conduction relationship with it. This allows for automatic on / off control of the main switch transistor, achieving backflow protection.

[0046] The auxiliary power supply is a DC voltage source that drives the main switch to provide a DC voltage. The DC voltage is higher than the voltage output by the power supply output side, and is more than 0.7V higher.

[0047] In some embodiments, such as Figure 2 As shown, the main switch can be an N-channel MOSFET M13 with a built-in parasitic diode D11 connected between the power output side POWER and the load side LOAD to realize the on / off control of the power supply circuit.

[0048] Specifically, the source of the N-channel MOSFET M13 can be connected to the power output side (POWER), the drain to the load side (LOAD), and the gate to the auxiliary power supply (BST) via a current-limiting resistor. A parasitic diode D11 is connected in parallel between the source and drain of the N-channel MOSFET M13, with the anode of D11 connected to the power output side (POWER) and the cathode connected to the load side (LOAD).

[0049] In a transistor mirror circuit, two NPN transistors Q11 and Q12 are used, such as Figure 2 As shown. To make a clear distinction, NPN transistor Q11 can be called the first transistor Q11, and NPN transistor Q12 can be called the second transistor Q12.

[0050] The bases of two NPN transistors Q11 and Q12 are interconnected. The collector of the first transistor Q11 is connected to the auxiliary power supply BST through a first current-limiting resistor R11, and the emitter of the first transistor Q11 is connected to the power output side POWER. The collector of the second transistor Q12 is connected to the auxiliary power supply BST through a second current-limiting resistor R12, and the emitter of the second transistor Q12 is connected to the load side LOAD, thus forming a mirror circuit.

[0051] In some embodiments, in order to limit the base current of the two transistors Q11 and Q12 and thus protect them, a first damping resistor R13 can be connected in series with the base of the first transistor Q11, and a second damping resistor R14 can be connected in series with the base of the second transistor Q12. By connecting the first damping resistor R13 and the second damping resistor R14, the two transistors Q11 and Q12 can be mirrored.

[0052] In order for the second transistor Q12 to be able to respond to the load-side load voltage V Load The transistor automatically adjusts its on / off state according to the change, allowing the collector of the second transistor Q12 to be connected to its base. If a damping resistor is connected to the base, the collector of the second transistor Q12 can be connected to node B, the midpoint between the first damping resistor R13 and the second damping resistor R14; the voltage at this point is denoted as the base voltage Vb.

[0053] In order to make the first transistor Q11 and the MOSFET M13 conduct in a complementary manner, the collector of the first transistor Q11 can be connected to the gate of the MOSFET M13.

[0054] The working principle of the power supply backflow protection circuit in this embodiment is as follows:

[0055] When the voltage V of the load side LOAD Load Normally, that is, V Load ≤V Power At that time, the voltage V on the power output side of the power supply is... Power First, the voltage is transferred to the load side LOAD through the parasitic diode D11 in MOSFET M13, forming the load side LOAD voltage V. Load At this time, V Load With V Power There is a diode voltage drop between them, namely, V Load =V Power -0.7V. Since the emitter of the second transistor Q12 is connected to the load side LOAD, the emitter voltage Ve2 of the second transistor Q12 is V. Load =V Power -0.7V. Since the base of the second transistor Q12 is connected to node B through the second damping resistor R14, and node B is connected to the collector of the second transistor Q12, and since the collector of the second transistor Q12 is connected to the auxiliary power supply BST through the second current-limiting resistor R12, Vb = Vc2 = BST at this time; where Vc2 is the collector voltage of the second transistor Q12. Since BST > V Power Therefore, Vb - Ve2 = BST - V Power +0.7V>0.7V, therefore, the second transistor Q12 is turned on at this time.

[0056] After transistor Q12 is turned on, its collector voltage Vc2 is approximately equal to its emitter voltage Ve2. Therefore, Vb = Vc2 ≈ Ve2 = V Load =V Power -0.7V.

[0057] Since the emitter of the first transistor Q11 is connected to the power output side, the emitter voltage Ve1 of the first transistor Q11 is V. Power Since the base of the first transistor Q11 is connected to node B through the first damping resistor R13, Vb-Ve1=-0.7V<0, therefore, the first transistor Q11 is cut off.

[0058] At this time, the auxiliary power supply BST is applied to the gate of MOSFET M13 through the first current-limiting resistor R11, making the gate voltage of MOSFET M13 equal to BST. Since the source voltage of MOSFET M13 is equal to V... Power , while BST> V Power That is, the gate voltage of MOSFET M13 is greater than its source voltage, therefore MOSFET M13 is turned on. After MOSFET M13 is turned on, V eventually... Load =V Power Vb = Vc² ≈ Ve² ≈ V Power .

[0059] When the load-side LOAD is raised by an external force, for example, when the load-side LOAD is mistakenly connected to a power supply with a higher voltage than the power supply output voltage, i.e., Ve2 = V Load > V Power At this time, since Vb≈V Power Therefore, Vb-Ve2<0, and the second transistor Q12 is cut off.

[0060] After the second transistor Q12 is cut off, Vb = BST, Vb - Ve1 = BST - V Power Since the voltage is greater than 0.7V, the first transistor Q11 becomes conductive. After the first transistor Q11 is turned on, its collector voltage Vc1 is approximately equal to its emitter voltage Ve1, i.e., Vc1≈Ve1≈V Power Since the gate of MOSFET M13 is connected to the collector of the first transistor Q11, the gate voltage of MOSFET M13 is approximately equal to its source voltage, which cannot meet the conduction condition. Therefore, MOSFET M13 is turned off, cutting off the power supply loop between the power output side POWER and the load side LOAD, preventing current from flowing back from the load side LOAD to the power output side POWER, and eliminating the risk of backflow.

[0061] To avoid requiring additional power, this embodiment uses a bootstrap circuit configured on top of the original DC / DC circuit, that is, outputting voltage V on the power supply output side. Power Based on this, a bootstrap voltage is added, for example, a bootstrap voltage of 0.7V or higher, to generate the auxiliary power supply BST.

[0062] In some embodiments, the bootstrap circuit can be configured to generate a 5V bootstrap voltage so that the DC voltage output by the auxiliary power supply BST is much greater than the voltage V on the power supply output side. Power This satisfies the condition for the main switch MOSFET M13 to conduct properly, namely, the difference between the gate voltage and the source voltage must be greater than the conduction threshold.

[0063] Industrial applicability

[0064] The power supply backflow protection circuit of this embodiment is applied to a DC-DC converter to prevent current from flowing back into the DC-DC converter from the load side, thereby protecting the DC-DC converter.

[0065] like Figure 3 As shown, the DC-DC converter in this embodiment can be designed using a DC-DC conversion chip U1 in conjunction with peripheral circuitry. The DC-DC conversion chip U1 can be an integrated chip such as LTC7063 or MPQ2908, and its peripheral circuitry can be configured according to the chip's datasheet to convert the input DC voltage into the required DC voltage, which is then transmitted to the load side via a power supply reverse current protection circuit to power the load.

[0066] Since the peripheral circuit design of the DC-DC converter chip U1 is existing technology, this embodiment will not elaborate on it, but will only describe in detail the circuit part related to the power supply reverse flow protection circuit in the DC-DC converter circuit.

[0067] like Figure 3 As shown, the DC-DC converter chip U1 in this embodiment mainly includes a power input pin Vin, a high-side switch pin TG, a low-side switch pin BG, and a high-low side switch node pin SW. Of course, the DC-DC converter chip U1 also includes other pins, but since they are not directly or indirectly connected to the backflow prevention circuit, they will not be described in detail here.

[0068] The DC-DC converter chip U1 receives the input DC voltage through its power input pin Vin. The high-side switch pin TG drives the high-side MOSFET M1 to turn on and off, and the low-side switch pin BG drives the low-side MOSFET M2 to turn on and off. The high-low side switch node pin SW is connected to the output capacitor C1 through the inductor L1 and the current-limiting resistor R1 connected in series with it.

[0069] In some embodiments, both the high-side MOSFET M1 and the low-side MOSFET M2 can be N-channel MOSFETs. The gate of the high-side MOSFET M1 is connected to the high-side switch pin TG of the DC-DC converter chip U1, its drain is connected to the power input pin Vin of the DC-DC converter chip U1, and its source is connected to the high-side / low-side switch node pin SW of the DC-DC converter chip U1. The gate of the low-side MOSFET M2 is connected to the low-side switch pin BG of the DC-DC converter chip U1, its drain is connected to the high-side / low-side switch node pin SW of the DC-DC converter chip U1, and its source is grounded. The DC-DC converter chip U1 provides complementary drive for the high-side MOSFET M1 and the low-side MOSFET M2. Simultaneously, the PWM signal output from the high-side / low-side switch node pin SW controls the charging and discharging process of the inductor L1 and the output capacitor C1 to generate a stable DC voltage across the output capacitor C1, i.e., the required DC voltage V. Power Power is supplied to the load through a backflow prevention protection circuit.

[0070] To generate the auxiliary power supply BST required for the power supply reverse current protection circuit, a bootstrap circuit U2 can be connected to the output capacitor C1, such as... Figure 3 As shown, the main components include a first diode D4, a second diode D3, a DC blocking capacitor C2, and a boost capacitor C3.

[0071] In this configuration, the anode of the first diode D4 is connected to the output capacitor C1, and the cathode is connected to the boost capacitor C3. The output capacitor C1 is used to charge the boost capacitor C3 until the voltage on the boost capacitor C3 is equal to the voltage on the output capacitor C1.

[0072] The anode of the second diode D3 is connected to the high / low side switching node pin SW of the DC-DC converter chip U1 via a DC blocking capacitor C2 connected in series with it. The cathode of the second diode D3 is connected to the boost capacitor C3. The DC blocking capacitor C2 allows the alternating power output from the high / low side switching node pin SW to pass through the second diode D3 to the boost capacitor C3, thereby adding a bootstrap voltage to the boost capacitor C3. This makes the voltage on the boost capacitor C3 greater than the voltage on the output capacitor C1, thus forming the required auxiliary power supply BST, which is used by the reverse current protection circuit.

[0073] When the voltage across the boost capacitor C3 is greater than the voltage across the output capacitor C1, the first diode D4 is reverse-biased and cut off to ensure that the voltage across the output capacitor C1 can be stabilized at the required DC voltage V. Power .

[0074] Add between the output capacitor C1 and the load Figure 2The power supply backflow protection circuit shown can prevent current from flowing back from the load side to the output capacitor C1 and the DC-DC converter chip U1, thereby protecting the DC-DC converter.

[0075] Of course, the above embodiments are only used to illustrate the technical solutions of this utility model, and are not intended to limit it; although the utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions claimed by this utility model.

Claims

1. A power supply reverse current protection circuit, connected between the power supply output side and the load side, characterized in that, include: The main switching transistor is connected between the power output side and the load side; An auxiliary power supply, which outputs a DC voltage, is used to drive the main switching transistor; A transistor mirror circuit includes a first transistor and a second transistor connected in a mirror relationship. The first transistor is connected between the auxiliary power supply and the power output side, and the second transistor is connected between the auxiliary power supply and the load side. The second transistor adjusts its on / off state according to the voltage difference between the load side and the power output side, and controls the first transistor to conduct in a complementary manner. By changing the on / off state of the first transistor, the main switch is controlled to connect the power supply circuit between the power output side and the load side when the load side voltage is less than or equal to the power output side voltage, and disconnect the power supply circuit between the power output side and the load side when the load side voltage is greater than the power output side voltage.

2. The power supply reverse flow protection circuit according to claim 1, characterized in that, The main switch is a MOSFET, which is in a complementary conduction state with the first transistor.

3. The power supply reverse flow protection circuit according to claim 2, characterized in that, The first transistor and the second transistor are NPN transistors, and their bases are interconnected; The collector of the first transistor is connected to the gate of the MOS transistor and is connected to the auxiliary power supply through the first current-limiting resistor. The emitter of the first transistor is connected to the power supply output side. The collector of the second transistor is connected to its base and is connected to the auxiliary power supply through a second current-limiting resistor. The emitter of the second transistor is connected to the load side.

4. The power supply reverse flow protection circuit according to claim 3, characterized in that, The base of the first transistor is connected to a first damping resistor, and the base of the second transistor is connected to a second damping resistor. The first damping resistor and the second damping resistor are connected together, and the connection node is connected to the collector of the second transistor.

5. The power supply reverse flow protection circuit according to any one of claims 2 to 4, characterized in that, The MOS transistor has a parasitic diode, the anode of which is connected to the power output side and the cathode of which is connected to the load side.

6. The power supply reverse flow protection circuit according to claim 5, characterized in that, The MOSFET is an N-channel MOSFET, with its source connected to the power output side and its drain connected to the load side.

7. The power supply reverse flow protection circuit according to any one of claims 1 to 4, characterized in that, The auxiliary power supply outputs a DC voltage higher than the voltage on the power supply output side, and the auxiliary power supply is generated by a bootstrap circuit connected to the power supply output side.

8. A DC-DC converter for converting an input DC voltage into a desired DC voltage and outputting it through a power supply output side, characterized in that, A power supply backflow protection circuit as described in any one of claims 1 to 7 is connected to the power output side.

9. The DC-DC converter according to claim 8, characterized in that, include: The DC-DC converter chip includes a power input pin, a high-side switch pin, a low-side switch pin, and high-low-side switch node pins; the power input pin receives the input DC voltage. A high-side MOSFET is connected between the power input pin and the high-side and low-side switch node pins, and receives the switching control signal output from the high-side switch pin. A low-side MOSFET is connected between the high-side and low-side switch node pins and ground, and receives the switching control signal output from the low-side switch pins. An output capacitor is connected to the high- and low-side switch node pins via an inductor and a current-limiting resistor. The charging and discharging process of the inductor and the output capacitor is controlled by the PWM signal output from the high- and low-side switch node pins to generate the required DC voltage on the output capacitor. The output capacitor is connected to the backflow prevention protection circuit.

10. The DC-DC converter according to claim 9, characterized in that, A bootstrap circuit is also connected to the output capacitor, and the bootstrap circuit includes: A boost capacitor, which generates the auxiliary power supply; The first diode has its anode connected to the output capacitor and its cathode connected to the boost capacitor; The second diode has its anode connected to the high / low side switch node pins via a DC blocking capacitor, and its cathode connected to the boost capacitor.

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