DCDC switching power supply

Abstract

The DCDC switching power supply comprises a BUCK circuit, a push-pull circuit, a BUCK driving circuit, a push-pull driving circuit, an isolation driving transmission circuit, a synchronous rectification driving circuit, a main control circuit, a current detection circuit, a bus voltage detection circuit and an output voltage detection circuit. According to the invention, by optimizing the control circuit for outputting current backward flowing, the control circuit for inputting forward impact current and the like, the backward flowing current of output-to-input and the forward impact current of input-to-output are effectively reduced, so that the problem that devices such as a power tube are damaged is effectively avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic circuits, and particularly to a DCDC switching power supply. Background Art

[0002] For high-power (200W and above) DCDC switching power supplies with wide-voltage input isolation, in order to reduce the voltage / current stress of power devices, facilitate the selection of power devices, optimize the design of power transformers / inductors, optimize the thermal design of power devices, and improve the efficiency of DCDC switching power supplies, etc., a two-stage circuit topology is usually selected for the design of DCDC switching power supplies.

[0003] Such as Figure 1 The shown DC / DC converter circuit block diagram includes a BUCK circuit, a push-pull circuit, a BUCK drive circuit, a push-pull drive circuit, an isolation drive transmission circuit, a synchronous rectification drive circuit, a main control circuit, a current detection circuit, a bus voltage detection circuit, and an output voltage detection circuit.

[0004] For high-power DCDC switching power supplies with high-voltage wide-voltage input, such as a DCDC switching power supply with an input of 40 - 160V and an output of 12V and 400W, the front-stage power circuit usually selects a BUCK circuit topology, and the rear-stage power circuit usually selects a push-pull circuit topology, and the push-pull circuit adopts a synchronous rectification scheme. When the synchronous rectification tube has a drive signal, the BUCK + push-pull circuit can work bidirectionally.

[0005] The DCDC switching power supplies composed of the above BUCK + push-pull circuits can all work bidirectionally, but they have the following three problem points:

[0006] Problem point 1: For a bidirectional DCDC switching power supply that uses a two-stage circuit topology, when the output is no-load or lightly loaded and there is a large capacitor, after the input is powered off and shut down, the voltage of the output large capacitor will not discharge quickly. At this time, when the input is powered off and shut down and then powered on again to start the machine and a synchronous rectification drive signal is generated, it will cause the output large capacitor to backfeed to the input. Seriously, a large backfeed current will cause damage to devices such as the power tubes of the DCDC switching power supply.

[0007] Problem point 2: For a bidirectional DCDC switching power supply that uses a two-stage circuit topology, when the input is powered off and shut down or interrupted for a short time, if the synchronous rectification drive signal continues to be generated, it will cause the output to backfeed to the input. Seriously, a large backfeed current will cause damage to devices such as the power tubes of the DCDC switching power supply.

[0008] Problem 3: The bidirectional DCDC switching power supply adopts a two-stage circuit topology. During the shutdown process, if the voltage on the input filter capacitor of the push-pull circuit cannot be effectively discharged, when the input is shut down and then restarted, the input capacitor of the push-pull circuit will discharge the output capacitor through the transformer. Since the AC impedance of the input and output filter capacitors is small, a large forward impact current will be generated. In severe cases, the large forward impact current will cause damage to components such as the power tube of the push-pull circuit.

[0009] Therefore, in order to solve the problem of damage to components such as power tubes caused by the above three reasons, it is necessary to propose a technical solution that effectively reduces output reverse current and forward impact current. Summary of the invention

[0010] The object of the present invention is to provide a DCDC switching power supply which can overcome the problem in the prior art that output back injection current and forward surge current may damage components such as power tubes.

[0011] In order to achieve the above object, the present invention adopts the following technical solution:

[0012] Figure 1 A circuit block diagram of a DCDC switching power supply of the present invention, wherein the DCDC switching power supply includes a BUCK circuit, a push-pull circuit, a BUCK driving circuit, a push-pull driving circuit, an isolation driving transmission circuit, a synchronous rectification driving circuit, a main control circuit, a current detection circuit, a bus voltage detection circuit, and an output voltage detection circuit;

[0013] The input end of the BUCK circuit is the input end of the DCDC switching power supply, the output end of the BUCK circuit is connected to the input end of the push-pull circuit, the output end of the push-pull circuit is the output end of the DCDC switching power supply, the BUCK driving circuit is connected between the BUCK circuit and the main control circuit, the push-pull driving circuit is connected between the push-pull circuit and the main control circuit, the synchronous rectification circuit is connected between the push-pull circuit and the isolation drive transmission circuit, the isolation drive transmission circuit is connected between the synchronous rectification circuit and the main control circuit, the current detection circuit is connected between the BUCK circuit and the main control circuit, the bus voltage detection circuit is connected between the output end of the BUCK circuit and the main control circuit, and the output voltage detection circuit is connected between the output end of the DCDC switching power supply and the main control circuit.

[0014] Optionally, the BUCK circuit includes a capacitor C1, a capacitor C2, a MOS transistor Q1, a MOS transistor Q2, an inductor L1 and a resistor R1;

[0015] The capacitor C1 is connected between the positive input terminal Vin and the input ground terminal GND1 of the BUCK circuit. The capacitor C2 is connected between the positive output terminal V1 and the output ground terminal GND of the BUCK circuit. The drain of the MOS transistor Q1 is connected to the positive input terminal Vin of the BUCK circuit. The source of the MOS transistor Q1 is connected to the drain of the MOS transistor Q2. The gate of the MOS transistor Q1 is connected to the output terminal GS1 of the BUCK driving circuit. The source of the MOS transistor Q2 is connected to the input ground terminal GND1 of the BUCK circuit. The gate of the MOS transistor Q2 is connected to the output terminal GS2 of the BUCK driving circuit. The inductor L1 is connected between the source of the MOS transistor Q1 and the positive output terminal V1 of the BUCK circuit. The resistor R1 is connected between the input ground terminal GND1 and the output ground terminal GND of the BUCK circuit.

[0016] Optionally, the push-pull circuit includes a capacitor C3, a capacitor C4, MOS transistors Q3, Q4, Q5, Q6, and a transformer T1.

[0017] The capacitor C3 is connected between the positive input terminal V1 and the input ground terminal GND of the push-pull circuit. The capacitor C4 is connected between the positive output terminal Vo and the output ground terminal GND2 of the push-pull circuit. The common input terminal of the transformer T1 is connected to the positive input terminal V1 of the push-pull circuit. The common output terminal of the transformer T1 is connected to the positive output terminal Vo of the push-pull circuit. The drain of the MOS transistor Q3 is connected to the positive-phase input terminal of the transformer T1. The source of the MOS transistor Q3 is connected to the input ground terminal GND of the push-pull circuit. The gate of the MOS transistor Q3 is connected to the output terminal GS3 of the push-pull driving circuit. The drain of the MOS transistor Q4 is connected to the negative-phase input terminal of the transformer T1. The source of the MOS transistor Q4 is connected to the input ground terminal GND of the push-pull circuit. The gate of the MOS transistor Q4 is connected to the output terminal GS4 of the push-pull driving circuit. The drain of the MOS transistor Q5 is connected to the positive-phase output terminal of the transformer T1. The source of the MOS transistor Q5 is connected to the output ground terminal GND2 of the push-pull circuit. The gate of the MOS transistor Q5 is connected to the output terminal GS5 of the push-pull driving circuit. The drain of the MOS transistor Q6 is connected to the negative-phase output terminal of the transformer T1. The source of the MOS transistor Q6 is connected to the output ground terminal GND2 of the push-pull circuit. The gate of the MOS transistor Q6 is connected to the output terminal GS6 of the push-pull driving circuit.

[0018] Optionally, the current detection circuit includes resistors R2, R3, R4, R5, R6, R7, a capacitor C7, and a chip U1.

[0019] The power supply terminal of the chip U1 is connected to the voltage terminal VCC1, the ground terminal of the chip U1 is connected to the input ground terminal GND1 of the BUCK circuit, the positive input terminal of the chip U1 is connected to one ends of the resistor R2, the resistor R3 and the resistor R4, the other end of the resistor R2 is connected to the voltage terminal VCC1, the other end of the resistor R3 is connected to the output ground terminal GND of the BUCK circuit, the other end of the resistor R4 is connected to the input ground terminal GND1 of the BUCK circuit, the negative input terminal of the chip U1 is connected to one ends of the resistor R5 and the resistor R6, the other end of the resistor R5 is connected to the input ground terminal GND1 of the BUCK circuit, the other end of the resistor R6 is connected to the output terminal of the chip U1, one end of the resistor R7 is connected to the output terminal of the chip U1, the other end of the resistor R7 is connected to the output terminal of the current detection circuit, one end of the capacitor C7 is connected to the input ground terminal GND1 of the BUCK circuit, the other end of the capacitor C7 is connected to the output terminal of the current detection circuit, and the output terminal of the current detection circuit is connected to the input terminal of the main control circuit.

[0020] Optionally, the current detection circuit further includes a capacitor C5 and a capacitor C6. The capacitor C5 is connected between the positive input terminal of the chip U1 and the input ground terminal GND1 of the BUCK circuit, and the capacitor C6 is connected between the negative input terminal of the chip U1 and the output terminal of the chip U1.

[0021] Optionally, the bus voltage detection circuit includes a resistor R7 and a resistor R9;

[0022] One end of the resistor R7 is connected to the output positive terminal V1 of the BUCK circuit, the other end of the resistor R7 is connected to the output terminal of the bus voltage detection circuit, one end of the resistor R9 is connected to the input ground terminal GND1 of the BUCK circuit, the other end of the resistor R9 is connected to the output terminal of the bus voltage detection circuit, and the output terminal of the bus voltage detection circuit is connected to the input terminal of the main control circuit.

[0023] Optionally, the bus voltage detection circuit further includes a capacitor C8, and the capacitor C8 is connected between the output terminal of the bus voltage detection circuit and the input ground terminal GND1 of the BUCK circuit.

[0024] Optionally, the output voltage detection circuit includes a resistor R10, a resistor R11 and a chip U2;

[0025] The input power supply terminal of the chip U2 is connected to the voltage terminal VCC2, the output power supply terminal of the chip U2 is connected to the voltage terminal VCC2, the input ground terminal of the chip U2 is connected to the output ground terminal GND2 of the push - pull circuit, the output ground terminal of the chip U2 is connected to the input ground terminal GND1 of the BUCK circuit, the input terminal of the chip U2 is connected to one ends of the resistor R10 and the resistor R11, the other end of the resistor R10 is connected to the output positive terminal Vo of the push - pull circuit, the other end of the resistor R11 is connected to the output ground terminal GND2 of the push - pull circuit, the output terminal of the chip U2 is connected to the output terminal of the output voltage detection circuit, and the output terminal of the output voltage detection circuit is connected to the output terminal of the output voltage detection circuit.

[0026] Optionally, the output voltage detection circuit further includes a capacitor C9 and a capacitor C10. The capacitor C9 is connected between the output terminal of the output voltage detection circuit and the input ground terminal GND1 of the BUCK circuit. The capacitor C10 is connected between the input terminal of the chip U2 and the output ground terminal GND2 of the push - pull circuit.

[0027] The beneficial effects of the present invention are as follows:

[0028] 1. When the DCDC switching power supply is restarted after the input is shut down, the reverse - injection current from the output to the input can be effectively reduced, thereby effectively avoiding damage to devices such as power transistors.

[0029] 2. When the input of the DCDC switching power supply is powered off and shut down or interrupted for a short time, the reverse - injection current from the output to the input can be effectively reduced, thereby effectively avoiding damage to devices such as power transistors.

[0030] 3. When the DCDC switching power supply is restarted after the input is powered off and shut down, the forward impact current from the input of the push - pull circuit to the output can be effectively reduced, thereby effectively avoiding damage to devices such as power transistors. Description of the Drawings

[0031] Figure 1 It is a circuit block diagram of a DCDC switching power supply according to the present invention;

[0032] Figure 2 It is a circuit schematic diagram of the BUCK circuit in a DCDC switching power supply according to the present invention;

[0033] Figure 3 It is a circuit schematic diagram of the push - pull circuit in a DCDC switching power supply according to the present invention;

[0034] Figure 4 It is a circuit schematic diagram of the current detection circuit in a DCDC switching power supply according to the present invention;

[0035] Figure 5This is the circuit schematic diagram of the bus voltage detection circuit in a DCDC switching power supply of the present invention;

[0036] Figure 6 This is the circuit schematic diagram of the output voltage detection circuit in a DCDC switching power supply of the present invention;

[0037] Figure 7 This is the circuit schematic diagram of the main control circuit in a DCDC switching power supply of the present invention;

[0038] Figure 8 This is the circuit schematic diagram of the BUCK drive circuit in a DCDC switching power supply of the present invention;

[0039] Figure 9 This is the circuit schematic diagram of the push - pull drive circuit in a DCDC switching power supply of the present invention;

[0040] Figure 10 This is the circuit schematic diagram of the isolation drive transmission circuit in a DCDC switching power supply of the present invention;

[0041] Figure 11 This is the circuit schematic diagram of the synchronous rectification drive circuit in a DCDC switching power supply of the present invention. Specific embodiments

[0042] The present invention and its beneficial effects will be further described in detail below in conjunction with the specific embodiments and the accompanying drawings of the specification. However, the specific embodiments of the present invention are not limited thereto.

[0043] The first embodiment

[0044] Figures 1 to 11 The following shows the circuit diagram of the first embodiment of a DCDC switching power supply of the present invention, including a BUCK circuit, a push - pull circuit, a current detection circuit, a bus voltage detection circuit, an output voltage detection circuit, a BUCK drive circuit, a push - pull drive circuit, an isolation drive transmission circuit, a synchronous rectification drive circuit, and a main control circuit.

[0045] The positive input terminal Vin of the BUCK circuit is connected to the positive input terminal of the DCDC switching power supply, the input ground terminal GND1 of the BUCK circuit is connected to the input ground terminal of the DCDC switching power supply, the positive output terminal V1 of the BUCK circuit is connected to the positive input terminal of the push - pull circuit, and the output ground terminal GND of the BUCK circuit is connected to the input ground terminal of the push - pull circuit.

[0046] The BUCK circuit includes a capacitor C1, a capacitor C2, a MOS transistor Q1, a MOS transistor Q2, an inductor L1, and a resistor R1.

[0047] The capacitor C1 is connected between the positive input terminal Vin and the input ground terminal GND1 of the BUCK circuit. The capacitor C2 is connected between the positive output terminal V1 and the output ground terminal GND of the BUCK circuit. The drain of the MOS transistor Q1 is connected to the positive input terminal Vin of the BUCK circuit. The source of the MOS transistor Q1 is connected to the drain of the MOS transistor Q2. The gate of the MOS transistor Q1 is connected to the output terminal GS1 of the BUCK drive circuit. The drain of the MOS transistor Q2 is connected to the source of the MOS transistor Q1. The source of the MOS transistor Q2 is connected to the input ground terminal GND1 of the BUCK circuit. The gate of the MOS transistor Q2 is connected to the output terminal GS2 of the BUCK drive circuit. The inductor L1 is connected between the source of the MOS transistor Q1 and the positive output terminal V1 of the BUCK circuit. The resistor R1 is connected between the input ground terminal GND1 and the output ground terminal GND of the BUCK circuit.

[0048] The positive input terminal V1 of the push-pull circuit is connected to the positive output terminal V1 of the BUCK circuit. The input ground terminal GND of the push-pull circuit is connected to the output ground terminal GND of the BUCK circuit. The positive output terminal Vo of the push-pull circuit is connected to the positive output terminal of the DCDC switching power supply. The output ground terminal GND2 of the push-pull circuit is connected to the output ground terminal of the DCDC switching power supply.

[0049] The push-pull circuit includes a capacitor C3, a capacitor C4, MOS transistors Q3, Q4, Q5, Q6, and a transformer T1.

[0050] The capacitor C3 is connected between the positive input terminal V1 and the input ground terminal GND of the push-pull circuit, and the capacitor C4 is connected between the positive output terminal Vo and the output ground terminal GND2 of the push-pull circuit. The transformer T1 has six ports, namely the positive-phase input terminal, the negative-phase input terminal, the common input terminal, the positive-phase output terminal, the negative-phase output terminal, and the common output terminal. The positive-phase input terminal and the positive-phase output terminal are the same-name terminals, the negative-phase input terminal and the negative-phase output terminal are the same-name terminals, the positive-phase input terminal and the negative-phase input terminal are the different-name terminals, and the negative-phase input terminal and the positive-phase input terminal are the different-name terminals. The common input terminal of the transformer T1 is connected to the positive input terminal V1 of the push-pull circuit, and the common output terminal of the transformer T1 is connected to the positive output terminal Vo of the push-pull circuit. The D pole of the MOS transistor Q3 is connected to the positive-phase input terminal of the transformer T1, the S pole of the MOS transistor Q3 is connected to the input ground terminal GND of the push-pull circuit, and the G pole of the MOS transistor Q3 is connected to the output terminal GS3 of the push-pull drive circuit. The D pole of the MOS transistor Q4 is connected to the negative-phase input terminal of the transformer T1, the S pole of the MOS transistor Q4 is connected to the input ground terminal GND of the push-pull circuit, and the G pole of the MOS transistor Q4 is connected to the output terminal GS4 of the push-pull drive circuit. The D pole of the MOS transistor Q5 is connected to the positive-phase output terminal of the transformer T1, the S pole of the MOS transistor Q5 is connected to the output ground terminal GND2 of the push-pull circuit, and the G pole of the MOS transistor Q5 is connected to the output terminal GS5 of the push-pull drive circuit. The D pole of the MOS transistor Q6 is connected to the negative-phase output terminal of the transformer T1, the S pole of the MOS transistor Q6 is connected to the output ground terminal GND2 of the push-pull circuit, and the G pole of the MOS transistor Q6 is connected to the output terminal GS6 of the push-pull drive circuit.

[0051] The current detection circuit includes a resistor R2, a resistor R3, a resistor R4, a resistor R5, a resistor R6, a resistor R7, a capacitor C7, and a chip U1.

[0052] The chip U1 has 5 ports, namely the power supply terminal, the ground terminal, the positive input terminal, the negative input terminal and the output terminal. The power supply terminal of the chip U1 is connected to the voltage terminal VCC1, the ground terminal of the chip U1 is connected to the input ground terminal GND1 of the BUCK circuit, the positive input terminal of the chip U1 is connected to one ends of the resistor R2, the resistor R3 and the resistor R4. The other end of the resistor R2 is connected to the voltage terminal VCC1, the other end of the resistor R3 is connected to the output ground terminal GND of the BUCK circuit, the other end of the resistor R4 is connected to the input ground terminal GND1 of the BUCK circuit. The negative input terminal of the chip U1 is connected to one ends of the resistor R5 and the resistor R6. The other end of the resistor R5 is connected to the input ground terminal GND1 of the BUCK circuit, the other end of the resistor R6 is connected to the output terminal of the chip U1. One end of the resistor R7 is connected to the output terminal of the chip U1, the other end of the resistor R7 is connected to the output terminal Vcs of the current detection circuit. One end of the capacitor C7 is connected to the input ground terminal GND1 of the BUCK circuit, the other end of the capacitor C7 is connected to the output terminal Vcs of the current detection circuit. The output terminal Vcs of the current detection circuit is connected to the input terminal Vcs of the main control circuit.

[0053] Preferably, the current detection circuit further includes a capacitor C5 and a capacitor C6. The capacitor C5 is connected between the positive input terminal of the chip U1 and the input ground terminal GND1 of the BUCK circuit, and the capacitor C6 is connected between the negative input terminal of the chip U1 and the output terminal Vcs of the chip U1.

[0054] The bus voltage detection circuit includes a resistor R7 and a resistor R9.

[0055] One end of the resistor R7 is connected to the output positive terminal V1 of the BUCK circuit, the other end of the resistor R7 is connected to the output terminal V1_S of the bus voltage detection circuit. One end of the resistor R9 is connected to the input ground terminal GND1 of the BUCK circuit, the other end of the resistor R9 is connected to the output terminal V1_S of the bus voltage detection circuit. The output terminal V1_S of the bus voltage detection circuit is connected to the input terminal V1_S of the main control circuit.

[0056] Preferably, the bus voltage detection circuit further includes a capacitor C8, and the capacitor C8 is connected between the output terminal V1_S of the bus voltage detection circuit and the input ground terminal GND1 of the BUCK circuit

[0057] The output voltage detection circuit includes a resistor R10, a resistor R11 and a chip U2.

[0058] The chip U2 has 6 ports, namely an input power supply terminal VDD2, an output power supply terminal VDD1, an input ground terminal GND2, an output ground terminal GND1, an input terminal IN, and an output terminal OUT. The input power supply terminal of the chip U2 is connected to the voltage terminal VCC2, the output power supply terminal of the chip U2 is connected to the voltage terminal VCC2, the input ground terminal of the chip U2 is connected to the output ground terminal GND2 of the push-pull circuit, the output ground terminal of the chip U2 is connected to the input ground terminal GND1 of the BUCK circuit, the input terminal of the chip U2 is connected to one ends of the resistor R10 and the resistor R11, the other end of the resistor R10 is connected to the output positive terminal Vo of the push-pull circuit, the other end of the resistor R11 is connected to the output ground terminal GND2 of the push-pull circuit, the output terminal of the chip U2 is connected to the output terminal Vo_S of the output voltage detection circuit, and the output terminal Vo_S of the output voltage detection circuit is connected to the output terminal Vo_S of the output voltage detection circuit.

[0059] Preferably, the output voltage detection circuit further includes a capacitor C9 and a capacitor C10. The capacitor C9 is connected between the output terminal Vo_S of the output voltage detection circuit and the input ground terminal GND1 of the BUCK circuit. The capacitor C10 is connected between the input terminal of the chip U2 and the output ground terminal GND2 of the push-pull circuit.

[0060] The main control circuit includes 1 power supply terminal, 1 ground terminal, 4 input terminals, and 6 output terminals. The power supply terminal of the main control circuit is connected to the voltage terminal VCC1, and the ground terminal of the main control circuit is connected to the input ground terminal GND1 of the BUCK circuit. The 4 input terminals of the main control circuit include an input terminal Vin, an input terminal V1_S, an input terminal Vo_S, and an input terminal Vcs. The input terminal Vin of the main control circuit is connected to the input positive terminal Vin of the BUCK circuit, the input terminal V1_S of the main control circuit is connected to the output terminal V1_S of the bus voltage detection circuit, the input terminal Vo_S of the main control circuit is connected to the output terminal Vo_S of the output voltage detection circuit, and the input terminal Vcs of the main control circuit is connected to the output terminal Vcs of the current detection circuit. The 6 output terminals of the main control circuit include an output terminal GS_1, an output terminal GS_2, an output terminal GS_3, an output terminal GS_4, an output terminal GS_5, and an output terminal GS_6. The output terminal GS_1 of the main control circuit is connected to the input terminal GS_1 of the BUCK drive circuit, the output terminal GS_2 of the main control circuit is connected to the input terminal GS_2 of the BUCK drive circuit, the output terminal GS_3 of the main control circuit is connected to the input terminal GS_3 of the push-pull drive circuit, the output terminal GS_4 of the main control circuit is connected to the input terminal GS_4 of the push-pull drive circuit, the output terminal GS_5 of the main control circuit is connected to the input terminal GS_5 of the isolation drive circuit, and the output terminal GS_6 of the main control circuit is connected to the input terminal GS_6 of the isolation drive circuit.

[0061] The BUCK drive circuit includes chip U4.

[0062] The chip U4 includes 6 ports, namely a power supply terminal, a ground terminal, 2 input terminals, and 2 output terminals. The power supply terminal of the chip U4 is connected to the power supply VCC3, the ground terminal of the chip U4 is connected to the input ground terminal GND1 of the BUCK circuit, one input terminal of the chip U4 is connected to the input terminal GS_1 of the BUCK drive circuit, the other input terminal of the chip U4 is connected to the input terminal GS_2 of the BUCK drive circuit, one output terminal of the chip U4 is connected to the output terminal GS1 of the BUCK drive circuit, and the other output terminal of the chip U4 is connected to the output terminal GS2 of the BUCK drive circuit.

[0063] The push-pull drive circuit includes chip U5.

[0064] The chip U5 includes 6 ports, namely a power supply terminal, a ground terminal, 2 input terminals, and 2 output terminals. The power supply terminal of the chip U5 is connected to the power supply VCC3, the ground terminal of the chip U5 is connected to the input ground terminal GND1 of the BUCK circuit, one input terminal of the chip U5 is connected to the input terminal GS_3 of the BUCK drive circuit, the other input terminal of the chip U5 is connected to the input terminal GS_4 of the BUCK drive circuit, one output terminal of the chip U5 is connected to the output terminal GS3 of the BUCK drive circuit, and the other output terminal of the chip U5 is connected to the output terminal GS4 of the BUCK drive circuit.

[0065] The isolation drive circuit includes chip U6.

[0066] The chip U6 has 8 ports, namely an input power supply terminal, an output power supply terminal, an input ground terminal, an output ground terminal, 2 input terminals, and 2 output terminals.

[0067] The input power supply terminal of the chip U6 is connected to the voltage terminal VCC1, the output power supply terminal of the chip U6 is connected to the voltage terminal VCC2, the input ground terminal of the chip U6 is connected to the input ground terminal GND1 of the power supply BUCK circuit, the output ground terminal of the chip U6 is connected to the output ground terminal GND2 of the power supply push-pull circuit, one input terminal GS_5 of the chip U6 is connected to the input terminal GS_5 of the isolation drive circuit, the other input terminal GS_6 of the chip U6 is connected to the input terminal GS_6 of the isolation drive circuit, one output terminal GS_5S of the chip U6 is connected to the output terminal GS_5S of the isolation drive circuit, and the other output terminal GS_6S of the chip U6 is connected to the output terminal GS_6S of the isolation drive circuit.

[0068] The output terminal GS_5S of the isolation drive circuit is connected to the input terminal GS_5S of the synchronous drive circuit, and the output terminal GS_5S of the isolation drive circuit is connected to the input terminal GS_5S of the synchronous drive circuit.

[0069] The synchronous rectification drive circuit includes a chip U7.

[0070] The chip U7 includes 6 ports, namely a power supply terminal, a ground terminal, 2 input terminals, and 2 output terminals. The power supply terminal of the chip U7 is connected to the power supply VCC3, the ground terminal of the chip U7 is connected to the input ground terminal GND1 of the BUCK circuit, one input terminal of the chip U7 is connected to the input terminal GS_5S of the synchronous rectification drive circuit, the other input terminal of the chip U7 is connected to the input terminal GS_6S of the synchronous rectification drive circuit, one output terminal of the chip U7 is connected to the output terminal GS5 of the synchronous rectification drive circuit, and the other output terminal of the chip U7 is connected to the output terminal GS6 of the BUCK drive circuit.

[0071] The working principle of the present invention is specifically analyzed as follows:

[0072] 1. The DCDC switching power supply detects the output current I1 of the BUCK circuit through a current detection circuit, detects the output voltage V1 of the BUCK circuit through a bus voltage detection circuit, and detects the output voltage Vo of the DCDC switching power supply through an output voltage detection circuit. Given that the efficiency of the push-pull circuit is η and the output current of the DCDC switching power supply is Io, according to the law of conservation of energy: V1 * I1 * η = Vo * Io, that is, Io = V1 * I1 * η / Vo.

[0073] When the output is no-load or light load and there is a large capacitor, after the DCDC switching power supply is powered off and shut down, the voltage of the large capacitor at the output will not discharge quickly. At this time, when the power is turned on again after the input is powered off and shut down and a synchronous rectification drive signal is generated, it will cause the large capacitor at the output to back-feed to the input. By detecting the current value of I1, the current value of Io can be indirectly calculated without directly detecting the value of the output current Io. If the value of the output current Io is directly detected, it still needs to be isolated and transmitted to the primary control circuit. The scheme of indirectly detecting the output current value optimizes the circuit scheme, reduces the PCB layout area, and reduces the cost of the DCDC switching power supply.

[0074] When the DCDC switching power supply works normally, the current flowing through the resistor R1 is I1. The forward voltage drop formed on the resistor R1 is VR1=I1*R1 from the output end GND of the BUCK circuit to the input end GND1 of the BUCK circuit. The resistor R2 plays a compensation role and can transmit the negative current to the main control circuit through the current detection circuit. The current detection circuit amplifies the lower detection voltage VR1 and outputs it through the output end of the chip. The resistors R7 and C7 play a filtering role and can filter the AC voltage signal into a DC voltage signal.

[0075] The current detection circuit transmits the detected output current Io of the DCDC switching power supply to the main control circuit in real time. The main control circuit compares the output current Io with a certain set current value. When the current of Io is less than a certain set current value, the main control circuit does not generate a synchronous rectification drive signal, and through the isolation drive transmission circuit and the synchronous rectification drive circuit, the synchronous rectifier tube in the push-pull circuit has no drive signal, and the synchronous rectifier tube is in a unidirectional conduction state. Therefore, when the DCDC switching power supply input is shut down and then restarted, the reverse current of the output to the input can be effectively reduced, thereby effectively avoiding damage to components such as power tubes.

[0076] 2. The above-mentioned DCDC switching power supply detects the output voltage V1 of the BUCK circuit through the bus voltage detection circuit, and detects the output voltage Vo of the DCDC switching power supply through the output voltage detection circuit. The output voltage Vo is converted to the input voltage of the push-pull circuit through the transformer as Vo'. When V1 is less than Vo', current backflow may occur.

[0077] The bus voltage detection circuit transmits the detected output voltage V1 of the BUCK circuit and the detected output voltage Vo of the DCDC switching power supply to the main control circuit in real time. The main control circuit compares V1 and Vo'. When the voltage of V1-Vo' is lower than a certain voltage value, the main control circuit does not generate a synchronous rectification drive signal, and through the isolation drive transmission circuit and the synchronous rectification drive circuit, the synchronous rectifier tube in the push-pull circuit has no drive signal, and the synchronous rectifier tube is in a unidirectional conduction state.

[0078] The above-mentioned DCDC switching power supply simultaneously detects the output current I1 of the BUCK circuit through the current detection circuit. When the output current I1 is a negative current, it indicates that current backflow from the output to the input occurs.

[0079] The current detection circuit transmits the detected output current I1 of the BUCK circuit to the main control circuit in real time. The main control circuit compares the output current I1 with a certain set current value. When the current of I1 is lower than a certain set current value, the main control circuit does not generate a synchronous rectification drive signal, and through the isolation drive transmission circuit and the synchronous rectification drive circuit, the synchronous rectifier tube in the push-pull circuit has no drive signal, and the synchronous rectifier tube is in a unidirectional conduction state.

[0080] Therefore, when the DCDC switching power supply input is turned off and then turned on again, the reverse current from the output to the input can be effectively reduced, thereby effectively avoiding damage to components such as power tubes.

[0081] 3. During the shutdown process of the above DCDC switching power supply input, if the voltage on the input filter capacitor of the push-pull circuit cannot be effectively discharged, when the input is restarted after shutdown, the input capacitor of the push-pull circuit will discharge to the output capacitor through the transformer. Due to the small AC impedance of the input and output filter capacitors, a large forward impact current will be generated.

[0082] Therefore, during the shutdown process of the DCDC switching power supply input, the main control circuit continues to generate a driving signal for a certain period of time, and transmits the driving signal to the primary power tube of the push-pull circuit through the push-pull driving circuit, so that it continues to work for a period of time. The output capacitor of the BUCK circuit can be effectively discharged through the primary power tube loss of the secondary power circuit, the transformer loss and the output load of the DCDC switching power supply. Even when the output end of the DCDC switching power supply is unloaded, it can still be effectively discharged through the primary power tube loss and transformer loss. And this solution does not affect the efficiency and other performance of the DCDC switching power supply when the product is working normally.

[0083] Therefore, when the DCDC switching power supply input is turned off and then turned on again, the forward impact current of the push-pull circuit input to the output can be effectively reduced, thereby avoiding damage to components such as power tubes.

[0084] The above-mentioned embodiments of the present invention are merely examples for explaining the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes and modifications can be made based on the above description. It is impossible to list all the embodiments here. Any obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A DCDC switching power supply, characterized in that: The DCDC switching power supply includes a BUCK circuit, a push-pull circuit, a BUCK driving circuit, a push-pull driving circuit, an isolation driving transmission circuit, a synchronous rectification driving circuit, a main control circuit, a current detection circuit, a bus voltage detection circuit and an output voltage detection circuit; The input end of the BUCK circuit is the input end of the DCDC switching power supply, the output end of the BUCK circuit is connected to the input end of the push-pull circuit, the output end of the push-pull circuit is the output end of the DCDC switching power supply, the BUCK driving circuit is connected between the BUCK circuit and the main control circuit, the push-pull driving circuit is connected between the push-pull circuit and the main control circuit, the synchronous rectification circuit is connected between the push-pull circuit and the isolation drive transmission circuit, the isolation drive transmission circuit is connected between the synchronous rectification circuit and the main control circuit, the current detection circuit is connected between the BUCK circuit and the main control circuit, the bus voltage detection circuit is connected between the output end of the BUCK circuit and the main control circuit, and the output voltage detection circuit is connected between the output end of the DCDC switching power supply and the main control circuit.

2. A DCDC switching power supply according to claim 1, characterized in that: The BUCK circuit includes a capacitor C1, a capacitor C2, a MOS tube Q1, a MOS tube Q2, an inductor L1 and a resistor R1; The capacitor C1 is connected between the input positive terminal Vin and the input ground terminal GND1 of the BUCK circuit, the capacitor C2 is connected between the output positive terminal V1 and the output ground terminal GND of the BUCK circuit, the D pole of the MOS tube Q1 is connected to the input positive terminal Vin of the BUCK circuit, the S pole of the MOS tube Q1 is connected to the D pole of the MOS tube Q2, the G pole of the MOS tube Q1 is connected to the output terminal GS1 of the BUCK driving circuit, the S pole of the MOS tube Q2 is connected to the input ground terminal GND1 of the BUCK circuit, the G pole of the MOS tube Q2 is connected to the output terminal GS2 of the BUCK driving circuit, the inductor L1 is connected between the S pole of the MOS tube Q1 and the output positive terminal V1 of the BUCK circuit, and the resistor R1 is connected between the input ground terminal GND1 of the BUCK circuit and the output ground terminal GND of the BUCK circuit.

3. A DCDC switching power supply according to claim 1, characterized in that: The push-pull circuit includes a capacitor C3, a capacitor C4, a MOS transistor Q3, a MOS transistor Q4, a MOS transistor Q5, a MOS transistor Q6 and a transformer T1; The capacitor C3 is connected between the input positive terminal V1 and the input ground terminal GND of the push-pull circuit, the capacitor C4 is connected between the output positive terminal Vo and the output ground terminal GND2 of the push-pull circuit, the common input terminal of the transformer T1 is connected to the input positive terminal V1 of the push-pull circuit, the common output terminal of the transformer T1 is connected to the output positive terminal Vo of the push-pull circuit, the D pole of the MOS tube Q3 is connected to the positive phase input terminal of the transformer T1, the S pole of the MOS tube Q3 is connected to the input ground terminal GND of the push-pull circuit, the G pole of the MOS tube Q3 is connected to the output terminal GS3 of the push-pull driving circuit, and the D pole of the MOS tube Q4 is connected to the negative phase input terminal of the transformer T1. The S pole of the MOS tube Q4 is connected to the input ground terminal GND of the push-pull circuit, the G pole of the MOS tube Q4 is connected to the output terminal GS4 of the push-pull driving circuit, the D pole of the MOS tube Q5 is connected to the positive phase output terminal of the transformer T1, the S pole of the MOS tube Q5 is connected to the output ground terminal GND2 of the push-pull circuit, the G pole of the MOS tube Q5 is connected to the output terminal GS5 of the push-pull driving circuit, the D pole of the MOS tube Q6 is connected to the negative phase output terminal of the transformer T1, the S pole of the MOS tube Q6 is connected to the output ground terminal GND2 of the push-pull circuit, and the G pole of the MOS tube Q6 is connected to the output terminal GS6 of the push-pull driving circuit.

4. A DCDC switching power supply according to claim 1, characterized in that: The current detection circuit includes a resistor R2, a resistor R3, a resistor R4, a resistor R5, a resistor R6, a resistor R7, a capacitor C7, and a chip U1; The power supply end of the chip U1 is connected to the voltage end VCC1, the ground end of the chip U1 is connected to the input ground end GND1 of the BUCK circuit, the positive input end of the chip U1 is connected to one end of the resistor R2, the resistor R3 and the resistor R4, the other end of the resistor R2 is connected to the voltage end VCC1, the other end of the resistor R3 is connected to the output ground end GND of the BUCK circuit, the other end of the resistor R4 is connected to the input ground end GND1 of the BUCK circuit, the negative input end of the chip U1 is connected to one end of the resistor R5 and the resistor R6, the other end of the resistor R5 is connected to the input ground end GND1 of the BUCK circuit, the other end of the resistor R6 is connected to the output end of the chip U1, one end of the resistor R7 is connected to the output end of the chip U1, the other end of the resistor R7 is connected to the output end of the current detection circuit, one end of the capacitor C7 is connected to the input ground end GND1 of the BUCK circuit, the other end of the capacitor C7 is connected to the output end of the current detection circuit, and the output end of the current detection circuit is connected to the input end of the main control circuit.

5. A DCDC switching power supply according to claim 4, characterized in that: The current detection circuit further includes a capacitor C5 and a capacitor C6. The capacitor C5 is connected to the positive input terminal of the chip U1 and the input ground terminal GND1 of the BUCK circuit. The capacitor C6 is connected between the negative input terminal of the chip U1 and the output terminal of the chip U1.

6. A DCDC switching power supply according to claim 1, characterized in that: The bus voltage detection circuit includes a resistor R7 and a resistor R9; One end of the resistor R7 is connected to the positive output terminal V1 of the BUCK circuit, the other end of the resistor R7 is connected to the output terminal of the bus voltage detection circuit, one end of the resistor R9 is connected to the input ground terminal GND1 of the BUCK circuit, the other end of the resistor R9 is connected to the output terminal of the bus voltage detection circuit, and the output terminal of the bus voltage detection circuit is connected to the input terminal of the main control circuit.

7. A DCDC switching power supply according to claim 6, characterized in that: The bus voltage detection circuit further includes a capacitor C8, and the capacitor C8 is connected between the output end of the bus voltage detection circuit and the input ground end GND1 of the BUCK circuit.

8. A DCDC switching power supply according to claim 1, characterized in that: The output voltage detection circuit includes a resistor R10, a resistor R11 and a chip U2; The input power supply terminal of the chip U2 is connected to the voltage terminal VCC2, the output power supply terminal of the chip U2 is connected to the voltage terminal VCC2, the input ground terminal of the chip U2 is connected to the output ground terminal GND2 of the push-pull circuit, the output ground terminal of the chip U2 is connected to the input ground terminal GND1 of the BUCK circuit, the input terminal of the chip U2 is connected to the resistor R10 and one end of the resistor R11, the other end of the resistor R10 is connected to the output positive terminal Vo of the push-pull circuit, the other end of the resistor R11 is connected to the output ground terminal GND2 of the push-pull circuit, the output terminal of the chip U2 is connected to the output terminal of the output voltage detection circuit, and the output terminal of the output voltage detection circuit is connected to the output terminal of the output voltage detection circuit.

9. A DCDC switching power supply according to claim 8, characterized in that: The output voltage detection circuit further includes capacitors C9 and C10, wherein the capacitor C9 is connected between the output end of the output voltage detection circuit and the input ground end GND1 of the BUCK circuit, and the capacitor C10 is connected between the input end of the chip U2 and the output ground end GND2 of the push-pull circuit.

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