DCDC power supply quick starting circuit with threshold value judgment function

Abstract

The invention relates to a DCDC power supply quick starting circuit with a threshold value judgment function, belongs to the technical field of DCDC power supplies, and solves the problems that the starting time is too long and a starting voltage threshold value cannot be controlled in the prior art. Comprising a charging circuit, a threshold starting circuit, a turn-off circuit and an auxiliary winding circuit. A switch is arranged on the charging circuit, and the threshold starting circuit is used for enabling the switch to be in an on state when an input voltage is greater than or equal to a threshold voltage, so that the charging circuit is used for charging a starting power supply; and the turn-off circuit is used for turning off the switch when the charging circuit charges to the voltage of the starting power supply, and the auxiliary winding circuit supplies power to the starting power supply. The DCDC power supply quick starting function with threshold value judgment is realized.

Description

Technical Field

[0001] This invention relates to the field of DC-DC power supply technology, and in particular to a DC-DC power supply fast start-up circuit with threshold judgment. Background Technology

[0002] Flyback DC-DC power supplies are widely used in various electrical equipment because of their small size, simple structure, low cost, and electrical isolation characteristics, making them very suitable for low-power applications.

[0003] Flyback DC-DC power supplies typically use an RC charging circuit to provide the startup voltage, powering the PWM controller and driver. After the PWM controller and driver are powered, the main power circuit of the flyback power supply starts working. Once the auxiliary winding of the main power circuit establishes a voltage, this voltage replaces the charging voltage of the RC charging circuit, completing the startup process of the flyback power supply. Thereafter, the auxiliary winding continuously powers the driver and PWM controller. Although the circuit structure and working principle of the RC charging circuit plus auxiliary winding are simple, they have drawbacks such as long startup time and uncontrollable startup voltage threshold. Summary of the Invention

[0004] Based on the above analysis, the present invention aims to provide a DC-DC power supply fast start-up circuit with threshold judgment to solve the problems of excessively long start-up time and uncontrollable start-up voltage threshold of existing DC-DC power supplies.

[0005] This invention provides a DC-DC power supply fast start-up circuit with threshold judgment, including: a charging circuit, a threshold start-up circuit, a turn-off circuit, and an auxiliary winding circuit;

[0006] A switch is provided on the charging circuit.

[0007] The threshold start-up circuit is used to turn the switch on when the input voltage is greater than or equal to the threshold voltage, so as to charge the start-up power supply using the charging circuit.

[0008] The shutdown circuit is used to turn off the switch when the charging circuit is charged to the starting power supply voltage, so that the starting power supply is powered by the auxiliary winding circuit.

[0009] Based on a further improvement of the above scheme, the switch set on the charging circuit is a field-effect transistor Q3; the drain and source of the field-effect transistor Q3 are connected to the charging circuit.

[0010] Based on a further improvement of the above scheme, the threshold start-up circuit includes Zener diodes VZ1 and VZ2, and resistors R1, R3, and R4.

[0011] The cathode of the Zener diode VZ1 is connected to the positive terminal of the input voltage through a resistor R1, and the anode is connected to one end of a resistor R3 and the cathode of the Zener diode VZ2. The other end of the resistor R3 is connected to the gate of the field-effect transistor Q3. The anode of the Zener diode VZ2 is connected to the gate of the field-effect transistor Q3. The resistor R4 is connected between the gate and the source of the field-effect transistor Q3.

[0012] Based on a further improvement to the above scheme, the breakdown voltage of the Zener diode VZ1 is equal to the input startup voltage V of the power supply product to be started. th The breakdown voltage of the Zener diode VZ2 is equal to the gate drive voltage of the field-effect transistor Q3.

[0013] Based on a further improvement of the above scheme, the shutdown circuit includes: transistor VT1, resistor R5, Zener diode VZ5, resistor R8, and capacitor C5.

[0014] The base of transistor VT1 is connected to one end of resistor R5, one end of resistor R8, and one end of capacitor C5. The collector is connected to the gate of field-effect transistor Q3 through resistor R3, and the emitter is connected to the negative terminal of the input voltage. The other end of resistor R5 is connected to the anode of Zener diode VZ5, and the cathode of Zener diode VZ5 is connected to the power supply. The other ends of resistor R8 and capacitor C5 are respectively connected to the negative terminal of the input voltage.

[0015] Based on further improvements to the above scheme, the breakdown voltage of the Zener diode VZ5 and the base conduction voltage of the transistor VT1 satisfy the following relationship:

[0016] V Z5 =V CC -V t1be

[0017] Among them, V Z5 This represents the breakdown voltage of the Zener diode, V. CC This indicates the voltage value of the starting power supply, V. t1be This represents the base conduction voltage of transistor VT1.

[0018] Based on further improvements to the above scheme, the charging circuit also includes a resistor R2, a diode VD2, and a capacitor C2;

[0019] One end of the resistor R2 is connected to the positive terminal of the input voltage, and the other end is connected to the drain of the field-effect transistor Q3; the anode of the diode VD2 is connected to the source of the field-effect transistor Q3, and the cathode is connected to the power supply and one end of the capacitor C2; the other end of the capacitor C2 is connected to the negative terminal of the input voltage.

[0020] Based on a further improvement of the above scheme, the auxiliary winding circuit includes an auxiliary winding T1C and a diode VD3; one end of the auxiliary winding T1C is connected to the anode of the diode VD3; the cathode of the diode VD3 is connected to the starting power supply, and the other end of the auxiliary winding T1C is connected to the negative terminal of the input voltage.

[0021] Further improvements to the above scheme also include a Zener diode VZ3, wherein the cathode of the Zener diode VZ3 is connected to the power supply and the anode is connected to the negative terminal of the input voltage.

[0022] On the other hand, embodiments of the present invention provide a power supply including the aforementioned startup circuit, and further including a main circuit and a drive control circuit; wherein,

[0023] The main circuit includes a transformer, which is used to sequentially perform power conversion, isolation transmission, rectification and filtering on the input voltage to obtain the output voltage;

[0024] The drive control circuit includes a driver and a PWM controller, both of which are powered by a startup power supply. The driver is used to control the startup of the main circuit and generate an output voltage. The PWM controller is used to generate control signals to the main circuit through the driver and adjust the output voltage of the main circuit.

[0025] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0026] 1. Based on the traditional flyback power supply startup circuit, a threshold startup circuit is added to determine the threshold of the input voltage, and a field-effect transistor is added to control the on / off state of the RC charging circuit. This prevents the main circuit from operating when the input voltage is lower than the input startup voltage of the power supply product to be started, thus ensuring the normal startup of the power supply product.

[0027] 2. A shutdown circuit has been added to disconnect the RC charging circuit when the charging voltage reaches the startup power supply voltage, shortening the working time of the resistors and capacitors in the RC charging circuit. This allows the resistors in the RC charging circuit to operate under overpower for a short period of time, thereby improving the charging speed of the startup power supply and shortening the charging time, thus meeting the fast response requirements of power supply products.

[0028] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0029] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0030] Figure 1 This is a circuit diagram of a DC-DC power supply fast start-up circuit with threshold judgment, as shown in an embodiment of the present invention.

[0031] Figure 2 The circuit diagram of a power supply including a DC-DC power supply fast start-up circuit with threshold judgment is shown in another embodiment of the present invention.

[0032] Among them, 1-charging circuit; 2-threshold start circuit; 3-turn-off circuit; 4-auxiliary winding circuit; 5-main circuit; 6-drive control circuit. Detailed Implementation

[0033] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0034] A specific embodiment of the present invention discloses a DC-DC power supply fast startup circuit with threshold judgment, such as... Figure 1 As shown, it includes a charging circuit 1, a threshold start circuit 2, a turn-off circuit 3, and an auxiliary winding circuit 4.

[0035] A switch is provided on the charging circuit.

[0036] The threshold start-up circuit is used to turn the switch on when the input voltage is greater than or equal to the threshold voltage, so as to charge the start-up power supply using the charging circuit.

[0037] The shutdown circuit is used to turn off the switch when the charging circuit is charged to the starting power supply voltage, so that the starting power supply is powered by the auxiliary winding circuit.

[0038] Specifically, the charging circuit includes a switch, which is a field-effect transistor Q3; the drain and source of the field-effect transistor Q3 are connected to the charging circuit; the charging circuit also includes a resistor R2, a diode VD2, and a capacitor C2.

[0039] One end of the resistor R2 is connected to the positive terminal of the input voltage, and the other end is connected to the drain of the field-effect transistor Q3; the anode of the diode VD2 is connected to the source of the field-effect transistor Q3, and the cathode is connected to the power supply and one end of the capacitor C2; the other end of the capacitor C2 is connected to the negative terminal of the input voltage.

[0040] It should be noted that resistor R2 is a charging current-limiting resistor; capacitor C2 is a charging and filtering capacitor with a capacitance of 10-100uF; the function of diode VD2 is to prevent VCC from being pulled down to zero through the Zener diode VZ2 and the transistor VT1 when the transistor VT1 is turned on, thereby ensuring the normal operation of the circuit.

[0041] Specifically, the threshold start-up circuit is used to turn the switch on when the input voltage is greater than or equal to the threshold voltage, so as to charge the start-up power supply using the charging circuit; it includes Zener diodes VZ1 and VZ2, and resistors R1, R3, and R4.

[0042] The cathode of the Zener diode VZ1 is connected to the positive terminal of the input voltage through a resistor R1, and the anode is connected to one end of a resistor R3 and the cathode of the Zener diode VZ2. The other end of the resistor R3 is connected to the gate of the field-effect transistor Q3. The anode of the Zener diode VZ2 is connected to the gate of the field-effect transistor Q3. The resistor R4 is connected between the gate and the source of the field-effect transistor Q3.

[0043] It should be noted that the breakdown voltage of the Zener diode VZ1 is equal to the input startup voltage V of the power supply product to be started. th The breakdown voltage of the Zener diode VZ2 is equal to the gate drive voltage of the field-effect transistor Q3; resistor R1 is a current-limiting resistor used to limit the current when supplying power to the gate of the field-effect transistor Q3. For example, the value of resistor R1 is... Among them, I R1 This represents the current limiting value, typically ranging from 10-100uA, V. in Indicates the input voltage value, V cc This represents the stable sustaining voltage of the RC charging circuit, i.e., the startup power supply value, in V. Z1 and V Z2 These represent the breakdown voltages of Zener diodes VZ1 and VZ2, respectively. Zener diode VZ2 is mainly used to limit the drive voltage of MOSFET Q3. For example, the gate drive voltage of MOSFET Q3 is typically 2.5-12V, and the reverse breakdown voltage of VZ2 needs to be within this range. Resistor R3 is the drive resistor for MOSFET Q3, used to limit the drive current and reduce the switching speed of MOSFET Q3, improving anti-interference capability. Resistor R3 typically has a value of 1-10Ω. Resistor R4 is the turn-off discharge resistor for MOSFET Q3, used to provide a fast discharge path for the drive voltage when MOSFET Q3 is turned off, and to prevent electrostatic discharge after MOSFET Q3 is turned off. Its typical value is 10kΩ. Specifically, the turn-off circuit is used to turn off the switch when the charging circuit charges to the startup power supply voltage, and the auxiliary winding circuit supplies power to the startup power supply.

[0044] The shutdown circuit includes: transistor VT1, resistor R5, Zener diode VZ5, resistor R8, and capacitor C5.

[0045] The base of transistor VT1 is connected to one end of resistor R5, one end of resistor R8, and one end of capacitor C5. The collector is connected to the gate of field-effect transistor Q3 through resistor R3, and the emitter is connected to the negative terminal of the input voltage. The other end of resistor R5 is connected to the anode of Zener diode VZ5, and the cathode of Zener diode VZ5 is connected to the power supply. The other ends of resistor R8 and capacitor C5 are respectively connected to the negative terminal of the input voltage.

[0046] It should be noted that the breakdown voltage of the Zener diode VZ5 and the base turn-on voltage of the transistor VT1 satisfy the following relationship:

[0047] V Z5 =V CC -V t1be

[0048] Among them, V Z5 This represents the breakdown voltage of the Zener diode, V. CC This indicates the voltage value of the starting power supply, V. t1be This indicates the base conduction voltage of transistor VT1. For example, the base conduction voltage is 0.3-0.7V.

[0049] The function of Zener diode VZ5 and transistor VT1 is to charge VCC to V using the charging circuit consisting of resistor R2, MOSFET Q3, diode VD2, and capacitor C2. CC Then, the charging circuit is quickly disconnected; resistor R5 is a current-limiting resistor used to limit the base current of VT1. For example, the value of resistor R5 is 1-10kΩ; the function of resistor R8 is to prevent electrostatic discharge of the device after VT1 is turned off. For example, the value of resistor R8 is more than 10 times that of R5; the function of capacitor C5 is to filter the base voltage of transistor VT1. For example, the value of capacitor C5 is 10-100pF.

[0050] Specifically, the auxiliary winding circuit includes an auxiliary winding T1C and a diode VD3; one end of the auxiliary winding T1C is connected to the anode of the diode VD3; the cathode of the diode VD3 is connected to the starting power supply, and the other end of the auxiliary winding T1C is connected to the negative terminal of the input voltage.

[0051] It should be noted that the power supply fast start-up circuit in this invention also includes a Zener diode VZ3, the cathode of which is connected to the start-up power supply, and the anode of which is connected to the negative terminal of the input voltage; the reverse breakdown voltage V of the Zener diode VZ3 is... Z3 The voltage value is equal to the starting power supply voltage. Its function is to prevent the charging voltage of capacitor C2 from rising indefinitely, which could lead to overvoltage damage to the circuit.

[0052] Specifically, the reverse breakdown voltage V of the Zener diode VZ1 z1 The input startup voltage V of the power supply product to be started th Equal; the voltage between the positive terminal HV+ and the negative terminal HV- of the input voltage is established from 0, and when the input voltage HV+ is lower than V... th At this time, Zener diode VZ1 experiences reverse voltage, and the entire input voltage HV+ is applied across Zener diode VZ1. Since MOSFET Q3 has no driving voltage and cannot conduct, the circuit consisting of resistor R2, MOSFET Q3, diode VD2, and capacitor C2 is not conducting, thus preventing capacitor C2 from charging. Therefore, the value of the starting power supply VCC is V... cc When the input voltage is 0, the drive control circuit receives no power, and the main circuit does not start. This achieves threshold judgment of the input voltage, preventing power loss when the input voltage is below V. th The power supply abnormality is caused by the operation of the main circuit.

[0053] Furthermore, when the input voltage is greater than the startup voltage V th When the voltage regulation diode VZ1 reverse-biased breakdown occurs and conducts, the input voltage is applied to the gate of the field-effect transistor Q3. Zener diode VZ2 stabilizes the voltage at the gate of Q3 within the driving voltage range of Q3, and Q3 conducts. For example, the driving voltage range of Q3 is 2.5-12V, and Zener diode VZ2... Z2 The breakdown voltage is 5.6V, meaning the gate voltage of MOSFET Q3 is 5.6V. At this time, the fast charging circuit consisting of resistor R2, MOSFET Q3, diode VD2, and capacitor C2 is turned on. The input voltage HV+ charges capacitor C2 through this circuit, and the voltage across capacitor C2 gradually increases. The reverse breakdown voltage V of Zener diode VZ3 is... Z3 With the starting power supply voltage value V cc When the charging voltage of capacitor C2 is greater than the reverse breakdown voltage of VZ3, the voltage across capacitor C2 no longer increases and stabilizes at VZ3. cc The charging time t of capacitor C2 can be obtained using the following formula:

[0054]

[0055] Among them, V in Indicates the input voltage, V cc P represents the stable sustaining voltage of the RC charging circuit, i.e., the startup power supply value. R Let represent the power of resistor R2, and n represent the overpower factor of resistor R2.

[0056] After charging time t2, the voltage of capacitor C2 is charged to V. cc V ccPower is supplied to the driver U1 and PWM controller U2 of the subsequent main circuit. Field-effect transistors Q1 and Q2 are turned on, the main circuit starts up, the output voltage Vo begins to build up, the auxiliary winding circuit T1C generates a pulsating square wave voltage, which is rectified by diode VD3 and connected to VCC. At this point, VCC is no longer provided by the charging circuit, but by the auxiliary winding circuit T1C, and the flyback power supply completes the startup process.

[0057] In addition, the breakdown voltage V of the Zener diode VZ5 Z5 The base conduction voltage V of transistor VT1 t1be The sum is V cc V Z5 +V t1b =V cc When the RC charging circuit charges to V cc At the same time, transistor VT1 is turned on, thereby pulling the gate of field-effect transistor Q3 low to the input power ground HV-, and field-effect transistor Q3 is turned off, and the charging circuit is disconnected and does not work.

[0058] It should be noted that in a traditional startup circuit, after the RC charging circuit has finished charging, the power supply for the driver U1 and the PWM controller U2 is provided by the auxiliary winding T1C. However, there is still a voltage across resistor R2 in the RC charging circuit, and the voltage magnitude is (V). in -V cc In formula (1), the overpower coefficient n of resistor R2 is 1; the formula for calculating resistor power is (V in -V cc ) 2 / R2, for a resistor with a specific package, the maximum power of its resistance is fixed. For example, the maximum power that a 1210 package resistor can withstand is 0.25W. In actual use, the power usually needs to be dated by 60% to 70%, that is, the actual power of a 1210 resistor is usually less than 0.18W. Since the power that the resistor can withstand is limited, in order to ensure a small resistance power, the resistance value is very large. The charging time t1 obtained by formula (1) is long and cannot meet the fast response requirements of power supply products.

[0059] In this embodiment, after the RC charging circuit is fully charged, the transistor VT1 is turned on, the charging circuit containing resistor R2 is turned off, the voltage across resistor R2 is 0 and there is no power loss. Therefore, resistor R2 only has power loss during the startup process. Since the voltage withstand time of resistor R2 is short, resistor R2 is allowed to operate with overpower during startup. For example, the overpower coefficient n can be 4 or 5, that is, the resistance value of R2 can be regarded as 4 or 5 times the actual value. The charging time t2 of this embodiment can be obtained using formula (1). t2 can be reduced to 20%-25% of t1. That is, the startup time of the flyback DC-DC circuit in this embodiment is shortened to 20%-25% of the startup time of the traditional circuit.

[0060] It should be noted that the input startup voltage V of the power supply product th Typically, starting a power supply product above Vth will degrade its performance, including: abnormal noises, increased output voltage ripple, increased heat generation, and damage to internal components that prevent them from functioning properly. In traditional flyback DC-DC circuits, even if the input voltage is below Vth... th However, as long as the charging time of the RC charging circuit is long enough, the voltage across capacitor C2 can reach V. cc This can lead to abnormal startup of the main power circuit. This embodiment adds a threshold judgment function to prevent the main power circuit from starting up the power supply product when the voltage is below Vth.

[0061] Compared with the prior art, the flyback DC-DC power supply fast start-up circuit provided in this embodiment sets a threshold judgment on the input voltage value to avoid starting the power supply product when the input voltage is lower than the start-up voltage, thus ensuring the working performance of the power supply module; and shortens the circuit start-up time, meeting the fast response requirements of the power supply product.

[0062] Another specific embodiment of the present invention includes a power supply for the startup circuit, and further includes a main circuit and a drive control circuit; wherein,

[0063] The main circuit includes a transformer, which is used to sequentially perform power conversion, isolation transmission, rectification and filtering on the input voltage to obtain the output voltage;

[0064] The drive control circuit includes a driver and a PWM controller, both of which are powered by a startup power supply. The driver is used to control the startup of the main circuit and generate an output voltage. The PWM controller is used to generate control signals to the main circuit through the driver and adjust the output voltage of the main circuit.

[0065] Specifically, such as Figure 2As shown, the main circuit 5 of the power supply includes: field-effect transistors Q1 and Q2, diodes D1, D2, and VD1, capacitor C1, primary winding T1A of the transformer, and secondary winding T1B of the transformer; the input voltage is connected to the drain of field-effect transistor Q1 and the cathode of diode D1, the gate of field-effect transistor Q1 is connected to the first output port of the driver, and the source of field-effect transistor Q1 is connected to one end of the primary winding T1A and the cathode of diode D2; the other end of the primary winding T1A is connected to... The drain of MOSFET Q2 is connected to the anode of diode D1. The gate of MOSFET Q2 is connected to the second output port of the driver. The source of MOSFET Q2 is connected to the anode of diode D2 and the negative terminal of the input voltage. One end of the secondary winding T1B is connected to the positive terminal of diode VD1. The other end of the secondary winding T1B is connected to one end of capacitor C1 and the negative terminal of the output voltage. The negative terminal of diode VD1 is connected to the other end of capacitor C1. The connection point is the output voltage Vo+, which is used by the subsequent load.

[0066] Specifically, such as Figure 2 As shown, the power supply drive control circuit 6 includes: resistors R6-10, capacitors C3 and C4, optocoupler BO1, PWM controller U2, driver U1, and reference source VZ4; the startup power supply supplies power to PWM controller U2 and driver U1, the negative terminal of the input voltage is connected to the ground of optocoupler BO1, PWM controller U2, and driver U1, the signal output terminal of PWM controller U2 is connected to the signal input terminal of driver U1, and the modulation voltage output terminal of optocoupler BO1 is connected to the input terminal of PWM controller U2; the output voltage Vo+ of the main circuit is... One end of resistor R6 and one end of resistor R7 are connected. The other end of resistor R6 is connected to the anode of the input diode of optocoupler BO1. The other end of resistor R7 is connected to one end of capacitor C3, one end of resistor R9, one end of resistor R10, and the reference voltage pin of reference source VZ4. The other end of capacitor C3 is connected to the cathode of the input diode of optocoupler BO1, one end of capacitor C4, and the cathode of reference source VZ4. The other end of capacitor C4 is connected to the other end of resistor R9. The other end of resistor R10 is connected to the anode of reference source VZ4 and the negative terminal Vo- of the output voltage.

[0067] Specifically, the input DC voltage is converted into a high-frequency switching component using the combined power conversion of MOSFETs Q1 and Q2, diodes D1 and D2, and the primary winding T1A of the transformer. The secondary winding T1B of the transformer isolates and transmits the energy of the high-frequency switching component. After rectification by diode VD1 and DC ripple filtering by capacitor C1, the DC output voltage Vo+ is obtained and regulated for use by the subsequent load. The output of Vo+ employs the classic control method of optocoupler BO1 and reference source TL431, including:

[0068] The output voltage is sampled using resistors R7 and R10 and fed into a reference source TL431 for compensation. Capacitors C3 and C4 and resistor R9 near the reference source TL431 form a PI compensation circuit. The compensation signal is isolated and transmitted to the input of the PWM controller U2 through the modulation voltage output terminal of the optocoupler BO1 to generate a PWM control signal. The PWM control signal is transmitted from the signal output terminal of the PWM controller U2 to the signal input terminal of the driver U1. The driver U1 amplifies the power of the PWM control signal and then connects it to the gate of the field-effect transistor Q1 through the first output port and to the gate of the field-effect transistor Q2 through the second output port. This controls the on / off state of the field-effect transistors Q1 and Q2 respectively, thereby controlling the output voltage value and realizing closed-loop control of the output voltage.

[0069] Those skilled in the art will understand that all or part of the processes of the methods described in the above embodiments can be implemented by a computer program instructing related hardware, and the program can be stored in a computer-readable storage medium. The computer-readable storage medium may be a disk, optical disk, read-only memory, or random access memory, etc.

[0070] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A DC-DC power supply fast start-up circuit with threshold judgment, characterized in that, Includes charging circuit, threshold start circuit, shutdown circuit, and auxiliary winding circuit; A switch is provided on the charging circuit. The threshold start-up circuit is used to turn the switch on when the input voltage is greater than or equal to the threshold voltage, so as to charge the start-up power supply using the charging circuit. The shutdown circuit is used to turn off the switch when the charging circuit is charged to the starting power supply voltage, so that the starting power supply is powered by the auxiliary winding circuit.

2. The DC-DC power supply fast start-up circuit with threshold judgment according to claim 1, characterized in that, The switch installed on the charging circuit is a field-effect transistor Q3; the drain and source of the field-effect transistor Q3 are connected to the charging circuit.

3. The DC-DC power supply fast start-up circuit with threshold judgment according to claim 2, characterized in that, The threshold start-up circuit includes Zener diodes VZ1 and VZ2, and resistors R1, R3, and R4. The cathode of the Zener diode VZ1 is connected to the positive terminal of the input voltage through a resistor R1, and the anode is connected to one end of a resistor R3 and the cathode of the Zener diode VZ2. The other end of the resistor R3 is connected to the gate of the field-effect transistor Q3. The anode of the Zener diode VZ2 is connected to the gate of the field-effect transistor Q3. The resistor R4 is connected between the gate and the source of the field-effect transistor Q3.

4. The DC-DC power supply fast start-up circuit with threshold judgment according to claim 3, characterized in that, The breakdown voltage of the Zener diode VZ1 is equal to the input startup voltage V of the power supply product to be started. th The breakdown voltage of the Zener diode VZ2 is equal to the gate drive voltage of the field-effect transistor Q3.

5. The DC-DC power supply fast start-up circuit with threshold judgment according to claim 3 or 4, characterized in that, The shutdown circuit includes: transistor VT1, resistor R5, Zener diode VZ5, resistor R8, and capacitor C5. The base of transistor VT1 is connected to one end of resistor R5, one end of resistor R8, and one end of capacitor C5. The collector is connected to the gate of field-effect transistor Q3 through resistor R3, and the emitter is connected to the negative terminal of the input voltage. The other end of resistor R5 is connected to the anode of Zener diode VZ5, and the cathode of Zener diode VZ5 is connected to the power supply. The other ends of resistor R8 and capacitor C5 are respectively connected to the negative terminal of the input voltage.

6. The DC-DC power supply fast start-up circuit with threshold judgment according to claim 5, characterized in that, The breakdown voltage of the Zener diode VZ5 and the base turn-on voltage of the transistor VT1 satisfy the following relationship: V Z5 =V CC -V t1be Among them, V Z5 This represents the breakdown voltage of the Zener diode, V. CC This indicates the voltage value of the starting power supply, V. t1be This represents the base conduction voltage of transistor VT1.

7. The DC-DC power supply fast start-up circuit with threshold judgment according to claim 6, characterized in that, The charging circuit also includes a resistor R2, a diode VD2, and a capacitor C2; One end of the resistor R2 is connected to the positive terminal of the input voltage, and the other end is connected to the drain of the field-effect transistor Q3; the anode of the diode VD2 is connected to the source of the field-effect transistor Q3, and the cathode is connected to the power supply and one end of the capacitor C2; the other end of the capacitor C2 is connected to the negative terminal of the input voltage.

8. The DC-DC power supply fast start-up circuit with threshold judgment according to claim 7, characterized in that, The auxiliary winding circuit includes an auxiliary winding T1C and a diode VD3; one end of the auxiliary winding T1C is connected to the anode of the diode VD3; the cathode of the diode VD3 is connected to the starting power supply, and the other end of the auxiliary winding T1C is connected to the negative terminal of the input voltage.

9. The DC-DC power supply fast start-up circuit with threshold judgment according to claim 7, characterized in that, It also includes a Zener diode VZ3, the cathode of which is connected to the power supply and the anode of which is connected to the negative terminal of the input voltage.

10. A power supply comprising the startup circuit according to any one of claims 1-9, characterized in that: It also includes the main circuit and the drive control circuit; among which, The main circuit includes a transformer, which is used to sequentially perform power conversion, isolation transmission, rectification and filtering on the input voltage to obtain the output voltage; The drive control circuit includes a driver and a PWM controller, both of which are powered by a startup power supply. The driver is used to control the startup of the main circuit and generate an output voltage. The PWM controller is used to generate control signals to the main circuit through the driver and adjust the output voltage of the main circuit.

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