A DCDC switching power supply

Abstract

The application discloses a DCDC switching power supply, comprising 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. The application effectively reduces the back-feeding current of the output to the input and the forward impact current of the input to the output through optimization of the control circuit of the output current back-feeding and the control circuit of the input forward impact current, thereby effectively avoiding the problem of damage of power tubes and other devices.

Description

TECHNICAL FIELD

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

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

[0003] As shown in the DC / DC converter circuit block diagram shown in Figure 1 , including BUCK circuit, push-pull circuit, BUCK drive circuit, push-pull drive circuit, isolation drive transmission circuit, synchronous rectification drive circuit, main control circuit, current detection circuit, bus voltage detection circuit and output voltage detection circuit.

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

[0005] The DCDC switching power supply composed of the above BUCK+push-pull circuit can work bidirectionally, but it has the following three problem points:

[0006] Problem point 1: The DCDC switching power supply that can work bidirectionally adopts a two-stage circuit topology, when the output is empty or light load and has a large capacitor, after the input power is turned off and the machine is shut down, the output large capacitor voltage will not be discharged quickly. At this time, when the input power is turned on and the machine is started again and the synchronous rectification drive signal is generated, the output large capacitor will cause the input to be back-primed, and in severe cases, the large back-primed current will cause the DCDC switching power supply power tube and other devices to be damaged.

[0007] Problem point 2: The DCDC switching power supply that can work bidirectionally adopts a two-stage circuit topology, when the input power is turned off or interrupted for a short time, if the synchronous rectification drive signal is continued to be generated, it will cause the output to be back-primed to the input, and in severe cases, the large back-primed current will cause the DCDC switching power supply power tube and other devices to be damaged.

[0008] Problem 3: The bidirectional DCDC switching power supply adopts two-stage circuit topology, and if the voltage on the input filter capacitor of the push-pull circuit cannot be effectively discharged during the input power-off shutdown process, the input capacitor of the push-pull circuit will discharge the output capacitor through the transformer when the input is started again after shutdown. Due to the small AC impedance of the input and output filter capacitors, a large forward shock current will be generated, and in severe cases, the large forward shock current will cause damage to the power tube and other devices of the push-pull circuit.

[0009] Therefore, in order to solve the problem of damage to power tubes and other devices caused by the above three reasons, a technical solution for effectively reducing output backflow current and forward shock current is needed. SUMMARY

[0010] The purpose of the present application is to provide a DCDC switching power supply that can overcome the problem of damage to power tubes and other devices caused by output backflow current and forward shock current in the prior art.

[0011] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0012] Figure 1 The circuit block diagram of the DCDC switching power supply of the present application, the DCDC switching power supply comprises 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.

[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 drive circuit is connected between the BUCK circuit and the main control circuit, the push-pull drive 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 comprises a capacitor C1, a capacitor C2, a MOS tube Q1, a MOS tube Q2, an inductor L1 and a resistor R1.

[0015] 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.

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

[0017] 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, 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.

[0018] Optionally, the current detection circuit comprises 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.

[0019] 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.

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

[0021] Optionally, the bus voltage detection circuit comprises a resistor R7 and a resistor R9.

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

[0023] Optionally, the bus voltage detection circuit further comprises 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.

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

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

[0026] Optionally, the output voltage detection circuit further comprises a capacitor C9 and a capacitor C10, 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.

[0027] The present application has the following beneficial effects:

[0028] 1. When the DCDC switching power supply is restarted after shutdown, the output can effectively reduce the back-feeding current of the input, thereby effectively avoiding the damage of power tubes and other devices.

[0029] 2. When the DCDC switching power supply is restarted after shutdown, the output can effectively reduce the back-feeding current of the input, thereby effectively avoiding the damage of power tubes and other devices.

[0030] 3. When the DCDC switching power supply is restarted after shutdown, the output can effectively reduce the back-feeding current of the input, thereby effectively avoiding the damage of power tubes and other devices. BRIEF DESCRIPTION OF DRAWINGS

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

[0032] Figure 2 It is a circuit principle diagram of the BUCK circuit in the DCDC switching power supply of the present application;

[0033] Figure 3 It is a circuit principle diagram of the push-pull circuit in the DCDC switching power supply of the present application;

[0034] Figure 4 It is a circuit principle diagram of the current detection circuit in the DCDC switching power supply of the present application;

[0035] Figure 5A circuit schematic of a bus voltage detection circuit in a DCDC switching power supply according to the present application;

[0036] Figure 6 A circuit schematic of an output voltage detection circuit in a DCDC switching power supply according to the present application;

[0037] Figure 7 A circuit schematic of a main control circuit in a DCDC switching power supply according to the present application;

[0038] Figure 8 A circuit schematic of a BUCK drive circuit in a DCDC switching power supply according to the present application;

[0039] Figure 9 A circuit schematic of a push-pull drive circuit in a DCDC switching power supply according to the present application;

[0040] Figure 10 A circuit schematic of an isolation drive transmission circuit in a DCDC switching power supply according to the present application;

[0041] Figure 11 A circuit schematic of a synchronous rectification drive circuit in a DCDC switching power supply according to the present application. DETAILED DESCRIPTION

[0042] The present application and its advantages will be understood more fully in conjunction with the specific embodiments and the accompanying drawings, which are described below.

[0043] First embodiment

[0044] Figures 1-11 A circuit schematic of a first embodiment of a DCDC switching power supply according to the present application is shown, which includes 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 input positive terminal Vin of the BUCK circuit is connected to the input positive 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 output positive terminal V1 of the BUCK circuit is connected to the input positive 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 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 D pole of the MOS tube Q2 is connected to the S pole of the MOS tube Q1, 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.

[0048] The input positive terminal V1 of the push-pull circuit is connected to the output positive 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 output positive terminal Vo of the push-pull circuit is connected to the output positive terminal of the DCDC switching power supply, and 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 comprises a capacitor C3, a capacitor C4, a MOS tube Q3, a MOS tube Q4, a MOS tube Q5, a MOS tube Q6, and a transformer T1.

[0050] The capacitor C3 is connected between the input positive terminal V1 of the push-pull circuit and the input ground terminal GND, and the capacitor C4 is connected between the output positive terminal Vo of the push-pull circuit and the output ground terminal GND2. The transformer T1 has six ports, which are 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 opposite name terminals, and the negative-phase input terminal and the positive-phase input terminal are the opposite name terminals. The common input terminal of the transformer T1 is connected to the input positive terminal V1 of the push-pull circuit, and 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, 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.

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

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

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

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

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

[0056] Preferably, the bus voltage detection circuit further comprises a capacitor C8. The capacitor C8 is connected with the output end V1_S of the bus voltage detection circuit and the input ground end GND1 of the BUCK circuit.

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

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

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

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

[0061] The BUCK driving circuit includes chip U4.

[0062] The chip U4 includes 6 ports, respectively, power supply end, ground end, 2 input ends, 2 output ends. The power supply end of the chip U4 is connected to the power supply VCC3, the ground end of the chip U4 is connected to the input ground end GND1 of the BUCK circuit, one input end of the chip U4 is connected to the input end GS_1 of the BUCK driving circuit, the other input end of the chip U4 is connected to the input end GS_2 of the BUCK driving circuit, one output end of the chip U4 is connected to the output end GS1 of the BUCK driving circuit, and the other output end of the chip U4 is connected to the output end GS2 of the BUCK driving circuit.

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

[0064] The chip U5 includes 6 ports, respectively, power supply end, ground end, 2 input ends, 2 output ends. The power supply end of the chip U5 is connected to the power supply VCC3, the ground end of the chip U5 is connected to the input ground end GND1 of the BUCK circuit, one input end of the chip U5 is connected to the input end GS_3 of the BUCK driving circuit, the other input end of the chip U5 is connected to the input end GS_4 of the BUCK driving circuit, one output end of the chip U5 is connected to the output end GS3 of the BUCK driving circuit, and the other output end of the chip U5 is connected to the output end GS4 of the BUCK driving circuit.

[0065] The isolation driving circuit includes chip U6.

[0066] The chip U6 has 8 ports, respectively, input power supply end, output power supply end, input ground end, output ground end, 2 input ends, 2 output ends.

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

[0068] The output end GS_5S of the isolation driving circuit is connected with the input end GS_5S of the synchronous driving circuit, and the output end GS_5S of the isolation driving circuit is connected with the input end GS_5S of the synchronous driving circuit.

[0069] The synchronous rectification driving circuit comprises a chip U7.

[0070] The chip U7 comprises six ports, namely a power supply end, a ground end, two input ends and two output ends. The power supply end of the chip U7 is connected with a power supply VCC3, the ground end of the chip U7 is connected with an input ground end GND1 of the BUCK circuit, one input end of the chip U7 is connected with an input end GS_5S of the synchronous rectification driving circuit, another input end of the chip U7 is connected with an input end GS_6S of the synchronous rectification driving circuit, one output end of the chip U7 is connected with an output end GS5 of the synchronous rectification driving circuit, and another output end of the chip U7 is connected with an output end GS6 of the BUCK driving circuit.

[0071] The working principle of the application is 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. It is known 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 empty or lightly loaded and has a large capacitor, the output large capacitor voltage will not be discharged quickly after the input power of the DCDC switching power supply is turned off and shut down. At this time, when the input power is turned on and started again and the synchronous rectification driving signal is generated, the output large capacitor will cause the input backflow. The current value of I1 can be indirectly calculated to obtain the current value of Io without directly detecting the output current Io. If the output current Io is directly detected, it also needs to be isolated and transmitted to the primary side control circuit. The indirect detection of the output current value optimizes the circuit scheme, reduces the PCB layout area and reduces the cost of the DCDC switching power supply.

[0074] The current flowing through the resistor R1 is I1 when the DCDC switching power supply is working normally, and the forward voltage drop formed on the resistor R1 is VR1=I1*R1, which is the voltage between the output end GND of the BUCK circuit and the input end GND1 of the BUCK circuit. The resistor R2 plays a compensating 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 resistor R7 and C7 play a filtering role and can filter the alternating voltage signal into a direct voltage signal.

[0075] The current detection circuit transmits the detected DCDC switching power supply output current Io to the main control circuit in real time, and the main control circuit compares the output current Io with a certain set current value. When the current Io is less than a certain set current value, the main control circuit does not generate a synchronous rectification driving signal, and transmits the synchronous rectification driving circuit through the isolation driving transmission circuit, so that the synchronous rectification tube in the push-pull circuit has no driving signal and is in a unidirectional conduction state. Therefore, when the DCDC switching power supply is turned off and then turned on again, the output can effectively reduce the reverse current of the input, thereby effectively avoiding the damage of power tubes and other devices.

[0076] 2、The DCDC switching power supply detects the output voltage V1 of the BUCK circuit through the bus voltage detection circuit, detects the output voltage Vo of the DCDC switching power supply through the output voltage detection circuit, and converts the output voltage Vo of the DCDC switching power supply to the input voltage Vo' of the push-pull circuit through the transformer. When V1 is less than Vo', current reverse flow 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, and the main control circuit compares V1 and Vo'. When the voltage V1-Vo' is lower than a certain voltage value, the main control circuit does not generate a synchronous rectification driving signal, and transmits the synchronous rectification driving circuit through the isolation driving transmission circuit, so that the synchronous rectification tube in the push-pull circuit has no driving signal and is in a unidirectional conduction state.

[0078] The DCDC switching power supply detects the output current I1 of the BUCK circuit through the current detection circuit, and when the output current I1 is negative current, it indicates that the output current reverse flow 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, and the main control circuit compares the output current I1 with a certain set current value, and when the current I1 is lower than the certain set current value, the main control circuit does not generate a synchronous rectification driving signal, and through the isolation driving transmission circuit and the synchronous rectification driving circuit, the synchronous rectification tube in the push-pull circuit has no driving signal, and the synchronous rectification tube is in a unidirectional conduction state.

[0080] Therefore, when the DCDC switching power supply is restarted after shutdown, the reverse current of the output to the input can be effectively reduced, and the damage of the power tube and other devices can be effectively avoided.

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

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

[0083] Therefore, when the DCDC switching power supply is restarted after shutdown, the positive impact current of the input of the push-pull circuit to the output can be effectively reduced, and the damage of the power tube and other devices can be avoided.

[0084] The above-described embodiments of the present application are merely examples for describing the present application and are not intended to limit the embodiments of the present application. Based on the above description, those skilled in the art can make other different forms of changes and modifications. Here, all the embodiments cannot be exhausted. Any obvious changes or modifications derived from the technical solutions of the present application are still within the protection scope of the present application.

Claims

1. A DCDC switching power supply, characterized by, The DCDC switching power supply comprises 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; 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 drive circuit is connected between the BUCK circuit and the main control circuit, the push-pull drive 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 drive 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. During the power-off shutdown process, the main control circuit continues to generate a driving signal for a certain period of time, and the driving signal is transmitted to the primary side power tube of the push-pull circuit through the push-pull drive circuit, so that the primary side power tube continues to work.

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

3. The DCDC switching power supply of claim 1, wherein: The push-pull circuit comprises a capacitor C3, a capacitor C4, a MOS tube Q3, a MOS tube Q4, a MOS tube Q5, a MOS tube 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 drive circuit, 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 drive 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 drive 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 drive circuit.

4. The DCDC switching power supply of claim 1, wherein: The current detection circuit includes resistors R2, R3, R4, R5, R6, R7, a capacitor C7, and a chip U1. The 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 end 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 end 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.

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

6. The DCDC switching power supply of claim 1, wherein: The bus voltage detection circuit comprises a resistor R7 and a resistor R9. One end of the resistor R7 is connected to the output positive end V1 of the BUCK circuit, the other end of the resistor R7 is connected to the output end of the bus voltage detection circuit, one end of the resistor R9 is connected to the input ground end GND1 of the BUCK circuit, and the other end of the resistor R9 is connected to the output end of the bus voltage detection circuit, and the output end of the bus voltage detection circuit is connected to the input end of the main control circuit.

7. A DC-DC switching power supply according to claim 6, characterized in that: The bus voltage detection circuit further comprises 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. The DCDC switching power supply of claim 1, wherein: The output voltage detection circuit comprises a resistor R10, a resistor R11 and a chip U2. The input power supply end of the chip U2 is connected to the voltage end VCC2, the output power supply end of the chip U2 is connected to the voltage end VCC2, the input ground end of the chip U2 is connected to the output ground end GND2 of the push-pull circuit, the output ground end of the chip U2 is connected to the input ground end GND1 of the BUCK circuit, the input end of the chip U2 is connected to one end of the resistor R10 and the resistor R11, the other end of the resistor R10 is connected to the output positive end Vo of the push-pull circuit, the other end of the resistor R11 is connected to the output ground end GND2 of the push-pull circuit, the output end of the chip U2 is connected to the output end of the output voltage detection circuit, and the output end of the output voltage detection circuit is connected to the output end 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 comprises a capacitor C9 and a capacitor C10, 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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