Input voltage control circuit of linear voltage regulator circuit

Abstract

An input voltage control circuit for a linear voltage regulator includes a power input terminal, a chopper circuit, a startup control circuit, a voltage comparator circuit, and a capacitor C1. The power input terminal is connected to the chopper circuit and the startup control circuit. The first input terminal of the voltage comparator circuit is connected to a reference voltage, the second input terminal is connected to the common junction of the startup control circuit, capacitor C1, and the input terminals of the linear voltage regulator circuit, and the output terminal is connected to the chopper circuit. The voltage comparator circuit outputs first and second voltages respectively when the voltage at the first input terminal is greater than and less than the voltage at the second input terminal. The chopper circuit is connected to the startup control circuit and controls the startup control circuit to establish a charging circuit between the power input terminal and capacitor C1 when the first voltage is received, and controls the startup control circuit to cut off the charging circuit when the second voltage is received, so that capacitor C1 supplies power to the linear voltage regulator circuit. This invention can provide a stable input voltage for the linear voltage regulator circuit when the external operating voltage range is large.

Description

Technical Field

[0001] This utility model relates to power supply circuits, and more particularly to an input voltage control circuit for a linear voltage regulator circuit. Background Technology

[0002] As electronic devices become increasingly sophisticated, the demands for power supply stability are also rising. While traditional linear regulators can provide high-precision output voltage, their efficiency is low and they tend to generate a lot of heat when there are large differences in input voltage or high current. Summary of the Invention

[0003] The technical problem to be solved by this utility model is to provide an input voltage control circuit for a linear voltage regulator circuit, which can provide a stable input voltage for the linear voltage regulator circuit under a wide external operating voltage range, thereby improving the efficiency of the linear voltage regulator circuit and reducing its power consumption.

[0004] An embodiment of this utility model discloses an input voltage control circuit for a linear voltage regulator, comprising a power input terminal VIN, a chopper circuit, a startup control circuit, a voltage comparator circuit, and a capacitor C1. The power input terminal VIN is connected to both the chopper circuit and the startup control circuit. The first input terminal of the voltage comparator circuit is connected to a reference voltage, and the second input terminal of the voltage comparator circuit is connected to the common junction of the startup control circuit, the first terminal of capacitor C1, and the input terminal of the linear voltage regulator circuit. The second terminal of capacitor C1 is grounded, and the output terminal of the voltage comparator circuit is connected to the chopper circuit. The voltage comparator circuit outputs a first voltage to the chopper circuit when the voltage at the first input terminal is greater than the voltage at the second input terminal, and outputs a second voltage to the chopper circuit when the voltage at the first input terminal is less than the voltage at the second input terminal. The chopper circuit is connected to the control terminal of the startup control circuit. When the chopper circuit receives the first voltage, it controls the startup control circuit to establish a charging circuit between the power input terminal VIN and the capacitor C1, allowing the voltage at the power input terminal VIN to charge the capacitor C1 through the charging circuit. When the second voltage is received, the chopper circuit controls the startup control circuit to cut off the charging circuit, allowing the capacitor C1 to supply power to the linear voltage regulator circuit.

[0005] This embodiment of the invention regulates the input voltage of the linear voltage regulator circuit by periodically controlling the charging and discharging of capacitor C1. When the external operating voltage range is large, it provides a stable input voltage for the linear voltage regulator circuit, thereby improving the efficiency of the linear voltage regulator circuit, reducing the power consumption of the linear voltage regulator circuit, and preventing the linear voltage regulator circuit from overheating. Attached Figure Description

[0006] Figure 1 A circuit diagram of the input voltage control circuit of the linear voltage regulator circuit according to the first embodiment of the present invention is shown. Detailed Implementation

[0007] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0008] Please refer to Figure 1 According to the first embodiment of the present invention, the input voltage control circuit of a linear voltage regulator circuit includes a power input terminal VIN, a chopper circuit 1, a start-up control circuit 2, a voltage comparison circuit 3, a reference voltage generation circuit 4, and a capacitor C1.

[0009] The power input terminal VIN is connected to the chopper circuit 1, the start-up control circuit 2, and the reference voltage generation circuit 4, respectively.

[0010] Reference voltage generation circuit 4 is used to generate a reference voltage.

[0011] The first input terminal of voltage comparator circuit 3 is connected to a reference voltage. The second input terminal of voltage comparator circuit 3 is connected to the common junction of the start-up control circuit 2, the first terminal of capacitor C1, and the input terminal of linear voltage regulator circuit 5. The second terminal of capacitor C1 is grounded. The output terminal of voltage comparator circuit 3 is connected to chopper circuit 1. Voltage comparator circuit 3 outputs a first voltage to chopper circuit 1 when the voltage at the first input terminal is greater than the voltage at the second input terminal, and outputs a second voltage to chopper circuit 1 when the voltage at the first input terminal is less than the voltage at the second input terminal.

[0012] The chopper circuit 1 is connected to the control terminal of the start-up control circuit 2. When the first voltage is received, the chopper circuit 1 controls the start-up control circuit 2 to establish a charging circuit between the power input terminal VIN and the capacitor C1, so that the voltage of the power input terminal VIN can charge the capacitor C1 through the charging circuit. When the second voltage is received, the start-up control circuit 2 controls the start-up control circuit 2 to cut off the charging circuit, so that the capacitor C1 supplies power to the linear voltage regulator circuit 5.

[0013] In this embodiment, the start-up control circuit 2 includes a switching transistor, a switching transistor control circuit, and a unidirectional conducting element. The first conducting terminal of the switching transistor is connected to the power input terminal VIN, and the second conducting terminal of the switching transistor is connected to the first terminal of the unidirectional conducting element. The second terminal of the unidirectional conducting element is connected to the second input terminal of the voltage comparator circuit 3 and the first terminal of the capacitor C1, respectively. The unidirectional conducting element allows current to flow from the first terminal to the second terminal. The input terminal of the switching transistor control circuit is connected to the chopper circuit 1, and the output terminal of the switching transistor control circuit is connected to the controlled terminal of the switching transistor. The chopper circuit 1 is used to control the switching transistor control circuit to close the switching transistor when a first voltage is received, and to control the switching transistor control circuit to open the switching transistor when a second voltage is received.

[0014] Specifically, the aforementioned switching transistor is a PNP transistor Q1. The base, emitter, and collector of the PNP transistor Q1 constitute the controlled terminal, the first conducting terminal, and the second conducting terminal of the switching transistor, respectively. The aforementioned switching transistor control circuit includes an NPN transistor Q5, resistors R17, R18, R19, and R21. The first terminal of resistor R18 is connected to the power input terminal VIN. The common junction of the second terminal of resistor R18 and the first terminal of resistor R19 constitutes the control terminal of the start-up control circuit 2. The common junction of the second terminal of resistor R19 and the first terminal of resistor R21 is connected to the base of NPN transistor Q5. The collector of NPN transistor Q5 is connected to the base of PNP transistor Q1 via resistor R17. The emitter of NPN transistor Q5 and the second terminal of resistor R21 are both grounded. The aforementioned unidirectional conducting element is a diode D2. The anode and cathode of diode D2 constitute the first and second terminals of the unidirectional conducting element, respectively.

[0015] Furthermore, the start-up control circuit includes resistors R1, R3, and R13. Resistor R1 is connected to the base and emitter of the PNP transistor Q1, respectively. The first terminal of resistor R3 is connected to the common junction of the second conducting terminal of the switching transistor and the first terminal of the unidirectional conducting element; the second terminal of resistor R3 is grounded. Resistor R13 is connected in parallel with capacitor C1. The function of resistor R1 is to ensure stable switching of the switching transistor. Resistors R3 and R13 act as dummy loads.

[0016] In this embodiment, the chopper circuit 1 includes a first voltage divider circuit, a voltage regulator U1, a PNP transistor Q2, an NPN transistor Q4, resistors R2, R4, R20, R22, and R23. The input terminal of the first voltage divider circuit is connected to the output terminal of the voltage comparator circuit 3, and the output terminal of the first voltage divider circuit is connected to the reference terminal of the voltage regulator U1. The anode of the voltage regulator U1 is grounded, and the cathode of the voltage regulator U1 is connected to the power input terminal VIN via resistor R2. The first voltage divider circuit includes resistors R8 and R10. The first terminal of resistor R8 is connected to the output terminal of the voltage comparator circuit 3, and the common junction of the second terminal of resistor R8 and the first terminal of resistor R10 is connected to the reference terminal of the voltage regulator U1. The second terminal of resistor R10 is grounded. The emitter of PNP transistor Q2 is connected to the power input terminal VIN. The base of PNP transistor Q2 is connected via resistor R4 to the common junction of resistor R2 and the cathode of voltage regulator U1. The collector of PNP transistor Q2 is grounded via resistor R22. The base of NPN transistor Q4 is connected to the common junction of the first terminals of resistors R20 and R23. The collector of NPN transistor Q4 is connected to the control terminal of startup control circuit 2. The emitter of NPN transistor Q4 and the second terminal of resistor R23 are grounded. The second terminal of resistor R20 is connected to the common junction of PNP transistor Q2 and resistor R22.

[0017] PNP transistors Q2 and Q4 act as switching transistors. Resistor R22 provides a DC path for PNP transistor Q2 and limits the current of voltage regulator U1. Optionally, voltage regulator U1 is a TL431.

[0018] In this embodiment, the voltage comparison circuit 3 includes a comparator U2A, a second voltage divider circuit, and a third voltage divider circuit. The input terminal of the second voltage divider circuit constitutes the first input terminal of the voltage comparison circuit 3, and the output terminal of the second voltage divider circuit is connected to the inverting input of the comparator U2A. The input terminal of the third voltage divider circuit constitutes the second input terminal of the voltage comparison circuit, and the output terminal of the third voltage divider circuit is connected to the non-inverting input of the comparator U2A. The output terminal of the comparator U2A constitutes the output terminal of the voltage comparison circuit.

[0019] Specifically, the second voltage divider circuit includes resistors R5 and R6. The first terminal of resistor R6 forms the input terminal of the second voltage divider circuit, and the common junction of the second terminal of resistor R6 and the first terminal of resistor R5 forms the output terminal of the second voltage divider circuit. The second terminal of resistor R5 is grounded. The third voltage divider circuit includes resistors R9 and R12. The first terminal of resistor R9 forms the input terminal of the third voltage divider circuit, and the common junction of the second terminal of resistor R9 and the first terminal of resistor R12 forms the output terminal of the third voltage divider circuit. The second terminal of resistor R12 is grounded.

[0020] Furthermore, voltage comparator circuit 3 includes a comparator power supply circuit and resistor R11. The comparator power supply circuit includes a filter circuit and a Zener diode D3. The input terminal of the filter circuit is connected to the power input terminal VIN, and the output terminal of the filter circuit is connected to the common junction of the cathode of Zener diode D3, the power supply terminal of comparator U2A, and the first terminal of resistor R11. The anode of Zener diode D3 is grounded, and the second terminal of resistor R11 is connected to the output terminal of comparator U2A. The above-mentioned filter circuit is an RC filter circuit, including resistor R16 and capacitor C3. Resistor R16 serves as a current limiter, and resistor R11 serves as a pull-up resistor.

[0021] In this embodiment, the reference voltage generating circuit 4 includes a Zener diode D1 and a resistor R7. The first end of the resistor R7 is connected to the power input terminal VIN, and the second end of the resistor R7 is connected to the common junction of the cathode of the Zener diode D1 and the input terminal of the aforementioned second voltage divider circuit. The anode of the Zener diode D1 is grounded. The resistor R7 serves to limit current.

[0022] In this embodiment, the linear voltage regulator circuit 5 includes an NPN transistor Q3, a resistor R14, and a Zener diode D4. The collector of the NPN transistor Q3 is connected to the common junction of the first terminal of the resistor R14 and the first terminal of the capacitor C1. The base of the NPN transistor Q3 is connected to the common junction of the second terminal of the resistor R14 and the cathode of the Zener diode D4. The anode of the Zener diode D4 is grounded, and the emitter of the NPN transistor Q3 constitutes the output terminal of the linear voltage regulator circuit. The resistor R14 limits the current of the Zener diode D4.

[0023] Furthermore, the linear voltage regulator circuit 5 includes a capacitor C4, which is connected in parallel with the Zener diode D4. The capacitor C4 acts as a filter capacitor.

[0024] Figure 1 The diagram also shows capacitor C2 and resistor R15. The common junction of the first terminal of capacitor C2 and the first terminal of resistor R15 is connected to the output terminal of the linear voltage regulator circuit 5, and the second terminals of capacitor C2 and resistor R15 are grounded. Capacitor C2 is a filter capacitor, and resistor R15 is an analog load.

[0025] The following combination Figure 1 and one A specific application example provides a more detailed explanation of the working principle and process of the input voltage control circuit of the linear voltage regulator circuit of this invention. In this specific application example, the power input terminal VIN of the input voltage control circuit is connected to the power supply V1. The standard output voltage of the power supply V1 is 20V, and its operating voltage range is 10V to 20V. The resistance values ​​of resistors R5, R6, R9, and R12 are all 10kΩ, the resistance value of resistor R10 is 100kΩ, and the resistance value of resistor R8 is 200kΩ. The working process of the input voltage control circuit of the linear voltage regulator circuit is roughly as follows.

[0026] a. When the power is first turned on, the power supply V1 supplies power to the comparator U2A through the comparator power supply circuit. The supply voltage of the comparator U2A is clamped at 10V by the Zener diode D3, and the comparator U2A starts to work. b. The voltage supplied by power supply V1 to reference voltage generation circuit 4 is clamped at 6.8V by Zener diode D1 (that is, the reference voltage generated by reference voltage circuit 4 is 6.8V). After the 6.8V is divided by the second voltage divider circuit, the output voltage is 3.4V, that is, the input voltage of the inverting terminal of comparator U2A is 3.4V. c. In the initial state, the voltage across capacitor C1 is 0V. After being divided by the third voltage divider circuit, the output voltage is 0V, that is, the input voltage of the non-inverting input of comparator U2A is 0V. d. Since the voltage at the inverting input of comparator U2A is greater than the voltage at the non-inverting input, the output of comparator U2A is a low potential V2_low (approximately 0V). After being divided by the first voltage divider circuit, it is compared with the reference voltage Vref inside the regulator U1 (Vref=2.5V). V2_low*(R10 / (R8+R10)) is less than Vref. Since resistor R2 is pulled up to the power supply V1, the cathode output of regulator U1 is high level U1_high≈V1. e. The emitter of PNP transistor Q2 is connected to the power supply V1, and the base is connected to a high level U1_high. U1_high-V1≈0V<Vq2_pn, where Vq2_pn is the PN junction voltage of PNP transistor Q2. Therefore, PNP transistor Q2 is in the cutoff state. f. Because PNP transistor Q2 is in the off state, the base of NPN transistor Q4 is pulled down to ground by resistor R22. The base voltage of NPN transistor Q4 is V4_b≈0V, V4_b<Vq4_pn, and Vq4_pn is the PN junction voltage of NPN transistor Q4. Therefore, NPN transistor Q4 is also in the off state. g. The output current of power supply V1 flows into the base of NPN transistor Q5 through resistors R18 and R19. The base current of NPN transistor Q5 is iq5_b≈(V1-Vq5_pn) / (R18+R19)-Vq5_pn / R21, where Vq5_pn is the PN junction voltage of NPN transistor Q5. The collector current of NPN transistor Q5 when it is saturated is iq5_c_sat≈(V1-Vq1_pn-Vq5_sat) / R17, where Vq1_pn is the PN junction voltage of PNP transistor Q1, and Vq5_sat is the saturation voltage of NPN transistor Q5. iq5_b*β5 >> iq5_c_sat, indicating that NPN transistor Q5 is operating in saturation. β5 is the amplification factor of NPN transistor Q5. h. When PNP transistor Q1 is pulled down to Vq5_sat≈0.1V~0.2V through resistor R17, PNP transistor Q1 operates in saturation conduction state. Power supply V1 charges capacitor C1 instantaneously through PNP transistor Q1 and diode D2. When the voltage Uc1 of capacitor C1 is charged to greater than 6.8V, the voltage division of resistors R9 and R12 is 1 / 2 * Uc1, that is, the voltage at the inverting input of comparator U2A is less than the voltage at the non-inverting input. Therefore, comparator U2A outputs a high potential voltage. The voltage Ur8_r10 after being divided by resistors R8 and R10 is compared with the reference voltage Vref (2.5V) inside regulator U1. Ur8_r10 > Vref. Therefore, the cathode of regulator U1 outputs a low level U1_low≈1V. i. The emitter of PNP transistor Q2 is connected to the power supply V1, and the base is connected to a low level U1_low. V1 - U1_low >> Vq2_pn, where Vq2_pn is the PN junction voltage of PNP transistor Q2, meaning that PNP transistor Q2 is operating in saturation. j. The base of NPN transistor Q4 is connected to a high potential because PNP transistor Q2 is in saturation. NPN transistor Q4 is in saturation. Resistor R18 is pulled down to Vq4_sat because NPN transistor Q4 is saturated and conducting. Vq4_sat is the saturation voltage of NPN transistor Q4, Vq4_sat≈0.1V~0.2V, Vq4_sat< Vq5_pn, Vq5_pn is the PN junction voltage of NPN transistor Q5. NPN transistor Q5 is turned off because the PN junction is reverse-biased. k. PNP transistor Q1 is turned off because NPN transistor Q5 is cut off. Capacitor C1 cannot discharge in reverse because of diode D2, thus supplying power to the downstream linear voltage regulator circuit 5. When the voltage of capacitor C1 is lower than 6.8V, the system will repeat the above process b to k.

[0027] Based on the above analysis, the PNP transistor Q1 operates from saturation to cutoff, meaning it operates at a certain switching frequency. Through rectification by diode D2, the voltage of capacitor C1 is ultimately stabilized at the target set voltage of 6.8V. When the input voltage increases, the switching process is the same as analyzed above, except that the voltage rise rate of capacitor C1 becomes faster, the time to reach the target set voltage is shorter, and the duty cycle of the PWM signal becomes narrower. However, through rectification by diode D2, the voltage of capacitor C1 is also ultimately stabilized at the target set voltage of 6.8V.

[0028] The linear voltage regulator circuit of this embodiment can automatically adjust the duty cycle of the PWM signal according to the input voltage during the entire operation process to make the input voltage of the linear voltage regulator circuit 5 reach the set voltage value, without causing the NPN transistor Q3 to overheat. It solves the problems of high power loss, difficult heat dissipation and low efficiency that are common in existing linear voltage regulator circuits. It is especially suitable for scenarios with a large input voltage range, high drive current capability requirements and requirements that the linear components cannot generate too much heat.

Claims

1. An input voltage control circuit for a linear voltage regulator, characterized in that, This includes the power input terminal VIN, chopper circuit, startup control circuit, voltage comparator circuit, and capacitor C1; The power input terminal VIN is connected to both the chopper circuit and the start-up control circuit. The first input terminal of the voltage comparator circuit is connected to a reference voltage. The second input terminal of the voltage comparator circuit is connected to the common junction of the start-up control circuit, the first terminal of capacitor C1, and the input terminal of the linear voltage regulator circuit. The second terminal of capacitor C1 is grounded. The output terminal of the voltage comparator circuit is connected to a chopper circuit. The voltage comparator circuit is used to output a first voltage to the chopper circuit when the voltage at the first input terminal is greater than the voltage at the second input terminal, and to output a second voltage to the chopper circuit when the voltage at the first input terminal is less than the voltage at the second input terminal. The chopper circuit is connected to the control terminal of the startup control circuit. When the first voltage is received, the chopper circuit controls the startup control circuit to establish a charging circuit between the power input terminal VIN and the capacitor C1, so that the voltage of the power input terminal VIN can charge the capacitor C1 through the charging circuit. When the second voltage is received, the startup control circuit controls the startup control circuit to cut off the charging circuit, so that the capacitor C1 supplies power to the linear voltage regulator circuit.

2. The input voltage control circuit of the linear voltage regulator circuit according to claim 1, characterized in that, The start-up control circuit includes a switching transistor, a switching transistor control circuit, and a unidirectional conducting element; The first conducting terminal of the switching transistor is connected to the power input terminal VIN. The second conducting terminal of the switching transistor is connected to the first terminal of the unidirectional conducting element. The second terminal of the unidirectional conducting element is connected to the second input terminal of the voltage comparator circuit and the first terminal of the capacitor C1. The unidirectional conducting element allows current to flow from the first terminal to the second terminal. The input terminal of the switching transistor control circuit is connected to the chopper circuit, and the output terminal of the switching transistor control circuit is connected to the controlled terminal of the switching transistor. The chopper circuit is used to control the switching transistor control circuit to close the switching transistor when a first voltage is received, and to control the switching transistor control circuit to open the switching transistor when a second voltage is received.

3. The input voltage control circuit of the linear voltage regulator circuit according to claim 2, characterized in that, The switching transistor is a PNP transistor Q1. The base, emitter, and collector of the PNP transistor Q1 constitute the controlled terminal, the first conducting terminal, and the second conducting terminal of the switching transistor, respectively. The switching control circuit includes an NPN transistor Q5, resistors R17, R18, R19, and R21. The first end of resistor R18 is connected to the power input terminal VIN. The common connection point of the second end of resistor R18 and the first end of resistor R19 constitutes the control terminal of the start-up control circuit. The common connection point of the second end of resistor R19 and the first end of resistor R21 is connected to the base of NPN transistor Q5. The collector of NPN transistor Q5 is connected to the base of PNP transistor Q1 via resistor R17. The emitter of NPN transistor Q5 and the second end of resistor R21 are both grounded.

4. The input voltage control circuit of the linear voltage regulator circuit according to claim 3, characterized in that, The start-up control circuit includes resistors R1, R3, and R13; the two ends of resistor R1 are connected to the base and emitter of PNP transistor Q1, respectively; the first end of resistor R3 is connected to the common junction of the second conducting end of the switching transistor and the first end of the unidirectional conducting element, and the second end of resistor R3 is grounded; resistor R13 is connected in parallel with capacitor C1.

5. The input voltage control circuit of the linear voltage regulator circuit according to claim 2, characterized in that, The unidirectional conducting element is a diode D2, and the anode and cathode of the diode D2 constitute the first and second terminals of the unidirectional conducting element, respectively.

6. The input voltage control circuit of the linear voltage regulator circuit according to claim 1, characterized in that, The chopper circuit includes a first voltage divider circuit, a voltage regulator U1, a PNP transistor Q2, an NPN transistor Q4, resistors R2, R4, R20, R22, and R23. The input terminal of the first voltage divider circuit is connected to the output terminal of the voltage comparator circuit, the output terminal of the first voltage divider circuit is connected to the reference terminal of the voltage regulator U1, the anode of the voltage regulator U1 is grounded, and the cathode of the voltage regulator U1 is connected to the power input terminal VIN through resistor R2. The emitter of PNP transistor Q2 is connected to the power input terminal VIN. The base of PNP transistor Q2 is connected to the common junction of resistor R2 and the cathode of voltage regulator U1 via resistor R4. The collector of PNP transistor Q2 is grounded via resistor R22. The base of NPN transistor Q4 is connected to the common junction of the first terminal of resistor R20 and the first terminal of resistor R23. The collector of NPN transistor Q4 is connected to the control terminal of the start-up control circuit. The emitter of NPN transistor Q4 and the second terminal of resistor R23 are grounded. The second terminal of resistor R20 is connected to the common junction of PNP transistor Q2 and resistor R22.

7. The input voltage control circuit of the linear voltage regulator circuit according to claim 1, characterized in that, The voltage comparison circuit includes a comparator U2A, a second voltage divider circuit, and a third voltage divider circuit; The input terminal of the second voltage divider circuit forms the first input terminal of the voltage comparator circuit, and the output terminal of the second voltage divider circuit is connected to the inverting terminal of comparator U2A. The input terminal of the third voltage divider circuit forms the second input terminal of the voltage comparator circuit, and the output terminal of the third voltage divider circuit is connected to the non-inverting input of the comparator U2A. The output terminal of comparator U2A constitutes the output terminal of the voltage comparison circuit.

8. The input voltage control circuit of the linear voltage regulator circuit according to claim 7, characterized in that, The input voltage control circuit of the linear voltage regulator circuit includes a reference voltage generation circuit, which is used to generate the reference voltage. The reference voltage generation circuit includes a Zener diode D1 and a resistor R7. The first end of the resistor R7 is connected to the power input terminal VIN, and the second end of the resistor R7 is connected to the common junction of the cathode of the Zener diode D1 and the input terminal of the second voltage divider circuit. The anode of the Zener diode D1 is grounded.

9. The input voltage control circuit of the linear voltage regulator circuit according to claim 7, characterized in that, The voltage comparison circuit includes a comparator power supply circuit and a resistor R11; The comparator power supply circuit includes a filter circuit and a Zener diode D3. The input terminal of the filter circuit is connected to the power input terminal VIN. The output terminal of the filter circuit is connected to the common junction of the cathode of the Zener diode D3, the power supply terminal of the comparator U2A, and the first terminal of the resistor R11. The anode of the Zener diode D3 is grounded, and the second terminal of the resistor R11 is connected to the output terminal of the comparator U2A.

10. The input voltage control circuit of the linear voltage regulator circuit according to claim 1, characterized in that, The linear voltage regulator circuit includes an NPN transistor Q3, a resistor R14, and a Zener diode D4. The collector of the NPN transistor Q3 is connected to the common junction of the first end of the resistor R14 and the first end of the capacitor C1. The base of the NPN transistor Q3 is connected to the common junction of the second end of the resistor R14 and the cathode of the Zener diode D4. The anode of the Zener diode D4 is grounded. The emitter of the NPN transistor Q3 constitutes the output terminal of the linear voltage regulator circuit.

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