Undervoltage protection circuit of auxiliary power supply

Abstract

The utility model discloses an under-voltage protection circuit of an auxiliary power supply. The circuit comprises a voltage division circuit, a comparison circuit and a logic control circuit, the voltage division circuit is connected with the input voltage of the auxiliary power supply and is connected with the comparison circuit; the voltage division circuit is also connected with the logic control circuit, and different voltages are switched and output under different control states; the comparison circuit is connected with the logic control circuit, generates a reference voltage and a reference voltage according to the voltage division circuit, compares the reference voltage with the reference voltage, and controls the logic control circuit to switch different control states; the logic control circuit is connected with the voltage division circuit and a control circuit of the auxiliary power supply. The utility model discloses an under-voltage protection circuit for an auxiliary power supply, and aims to solve the problems that the auxiliary power supply cannot be reset in time, voltage overcharge is easy to occur and circuit elements are damaged due to the fact that a chip is repeatedly turned on and turned off due to power supply voltage fluctuation in a chip power supply voltage power-down process in an under-voltage protection circuit for the auxiliary power supply in the related technology.

Description

Technical Field

[0001] The present application relates to the technical field of power supply protection, and in particular to an undervoltage protection circuit for an auxiliary power supply. Background Art

[0002] In related technologies, the design of an auxiliary power supply is essential in energy storage inverters, and a multi-output flyback power supply is often used. For a flyback power supply, the power management chip is usually powered by its auxiliary winding.

[0003] During the power-down process of the auxiliary power supply's input voltage, since there is basically no load on its auxiliary winding, the electricity on the winding's output capacitor cannot be released in time, and the power chip cannot be turned off in time. Moreover, when the power supply voltage of the power chip is near its startup threshold, fluctuations in the supply voltage can easily cause the power chip to turn on repeatedly.

[0004] Moreover, repeated opening and closing in a short period of time makes it impossible for the auxiliary power transformer to reset in time, which easily causes output voltage overshoot and overstress to damage electronic devices.

[0005] It can be seen from this that in the undervoltage protection circuit of the auxiliary power supply in the related art, during the power-off process of the chip power supply voltage, the power supply voltage fluctuation will cause the chip to repeatedly turn on and off, making it impossible for the auxiliary power supply to be reset in time, which is prone to voltage overcharging and damage to circuit components. Utility Model Content

[0006] The main purpose of this application is to provide an undervoltage protection circuit for an auxiliary power supply to solve the problem of the undervoltage protection circuit for the auxiliary power supply in the related art. During the power-off process of the chip power supply voltage, the power supply voltage fluctuation will cause the chip to be repeatedly turned on and off, making it impossible for the auxiliary power supply to be reset in time, which is prone to voltage overcharging and damage to circuit components.

[0007] According to one aspect of the present application, an undervoltage protection circuit for an auxiliary power supply is provided, comprising a voltage divider circuit, a comparison circuit, and a logic control circuit; the input end of the voltage divider circuit is connected to the input voltage end of the auxiliary power supply, and the output end of the voltage divider circuit is connected to the input end of the comparison circuit; the voltage divider circuit is also connected to the logic control circuit, and switches the output end to output different voltages under different control states of the logic control circuit; the output end of the comparison circuit is connected to the input end of the logic control circuit, and the comparison circuit is used to generate a reference voltage and a base voltage according to the voltage divider circuit, compare the reference voltage with the base voltage, and control the logic control circuit to switch to different control states according to the comparison result; the output end of the logic control circuit is connected to the voltage divider circuit and the control circuit of the auxiliary power supply.

[0008] As an optional embodiment, the comparison circuit is a three-terminal parallel voltage regulator chip; the three-terminal parallel voltage regulator chip includes a reference voltage terminal, an input terminal and an output terminal; the reference voltage terminal is connected to the output terminal of the voltage divider circuit; the input terminal is grounded, and the output terminal is connected to the logic control circuit.

[0009] As an optional embodiment, the equivalent circuit of the three-terminal parallel voltage regulator chip includes a reference voltage source, a voltage comparator, and a switching transistor; one end of the reference voltage source is connected to the input end, and the other end is connected to one input end of the voltage comparator; the two power supply ends of the voltage comparator are respectively connected to the input end and the output end, the other input end of the voltage comparator is connected to the reference voltage end, and the output end of the voltage comparator is connected to the base of the switching transistor; the collector of the switching transistor is connected to the output end, and the emitter of the switching transistor is connected to the input end; a diode is also connected between the collector and the emitter of the switching transistor, the input end of the diode is connected to the emitter, and the output end of the diode is connected to the collector.

[0010] As an optional embodiment, the voltage divider circuit includes a first voltage divider circuit and a second voltage divider circuit; the input end of the first voltage divider circuit is connected to the input voltage end of the auxiliary power supply, and the output end of the first voltage divider circuit is connected to the input end of the comparison circuit; the input end of the second voltage divider circuit is connected to the logic control circuit, and the output end of the second voltage divider circuit is connected to the first voltage divider circuit, and the connection with the first voltage divider circuit is connected or disconnected under different control states of the logic control circuit.

[0011] As an optional embodiment, the first voltage divider circuit includes a first resistor and a second resistor; one end of the first resistor is connected to the input voltage end of the auxiliary power supply, and the other end of the first resistor is connected to the input end of the comparison circuit; one end of the second resistor is connected to the input end of the comparison circuit, and the other end of the second resistor is grounded; the second voltage divider circuit includes a third resistor, one end of the third resistor is connected to the input end of the comparison circuit, and the other end of the third resistor is connected to the logic control circuit.

[0012] As an optional embodiment, the logic control circuit includes a voltage divider and current limiting circuit, a voltage source, a first field effect transistor, and a second field effect transistor; the voltage source is connected to the input end of the voltage divider and current limiting circuit, and the output end of the voltage divider and current limiting circuit is connected to the gates of the first field effect transistor and the second field effect transistor; the source of the first field effect transistor is grounded, and the drain is connected to the power chip of the auxiliary power supply; the source of the second field effect transistor is grounded, and the drain is connected to the second voltage divider circuit of the voltage divider circuit.

[0013] As an optional embodiment, the voltage divider and current limiting circuit includes a ninth resistor, a fourth resistor and a fifth resistor; one end of the ninth resistor is connected to the voltage source, and the other end is connected to the output end of the comparison circuit; one end of the fourth resistor is connected to the output end of the comparison circuit, and the other end is connected to the gate of the first field effect transistor and the second field effect transistor; one end of the fifth resistor is connected to the gate of the first field effect transistor and the second field effect transistor; and the other end is grounded.

[0014] As an optional embodiment, the logic control circuit also includes a multi-stage amplifier circuit; the multi-stage amplifier circuit includes multiple amplifier transistors, the base of the amplifier transistor of the first stage is connected to the common end of the fourth resistor and the fifth resistor, the emitter is grounded, and the collector is connected to the voltage source and the base of the amplifier transistor of the next stage; the base of the amplifier transistor of the intermediate stage is connected to the collector of the amplifier transistor of the previous stage, the emitter is grounded, and the collector is connected to the voltage source and the base of the amplifier transistor of the next stage; the base of the amplifier transistor of the last stage is connected to the collector of the amplifier transistor of the previous stage, the emitter is grounded, and the collector is connected to the voltage source and the base of the amplifier transistor of the next stage through the sixth resistor.

[0015] As an optional embodiment, the multi-stage amplifier circuit is a two-stage amplifier circuit, including a first amplifier transistor and a second amplifier transistor; the base of the first amplifier transistor is connected to the common end of the fourth resistor and the fifth resistor, the emitter is grounded, the collector is connected to the base of the second amplifier transistor, and the collector is also connected to the voltage source through a seventh resistor; the base of the second amplifier transistor is connected to the collector of the first amplifier transistor, the emitter is grounded, the collector is connected to the gate of the first field-effect transistor through a sixth resistor, and the collector is also connected to the voltage source through a seventh resistor.

[0016] As an optional embodiment, a first capacitor is provided between the reference voltage terminal and the input terminal of the three-terminal parallel voltage regulator chip of the comparison circuit; a second capacitor and an eighth resistor are provided between the gate and source of the first field-effect transistor and the second field-effect transistor of the logic control circuit; and a third capacitor is provided between the gate and source of the amplifying transistor of the multi-stage amplifying circuit of the logic control circuit.

[0017] In the present application, a voltage divider circuit is controlled by a logic control circuit. Different resistors are connected to provide different reference voltages for the comparison circuit under different usage states of the auxiliary power supply. By comparing the actual input voltage of the auxiliary power supply with the reference voltage, the undervoltage protection of the auxiliary power supply is turned off, and the boost recovery and restart are automatically controlled. Moreover, the comparison output result uses the logic control circuit to control the voltage divider circuit to output the corresponding reference voltage, so that when the auxiliary power supply is undervoltage protection, a smaller reference voltage is used, and when the auxiliary power supply resumes operation, a larger reference voltage is used, forming a hysteresis loop protection, effectively avoiding the problem of the auxiliary power supply input voltage fluctuating near the protection threshold and causing continuous restart, thereby improving the reliability and stability of the auxiliary power supply operation. This solves the problem of the undervoltage protection circuit of the auxiliary power supply in the related art. During the power-off process of the chip power supply voltage, the power supply voltage fluctuation causes the chip to be repeatedly turned on and off, making it impossible for the auxiliary power supply to be reset in time, prone to voltage overcharging, and causing damage to circuit components. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0019] Figure 1 A schematic diagram of an undervoltage protection circuit for an auxiliary power supply disclosed in this application;

[0020] Figure 2 A schematic diagram of another undervoltage protection circuit disclosed in this application;

[0021] Figure 3 A schematic diagram of the equivalent circuit of the three-terminal parallel voltage regulator chip disclosed in this application;

[0022] Figure 4 A schematic diagram of the test waveform of the undervoltage protection action disclosed in this application;

[0023] Figure 5 This is a schematic diagram of the test waveform of the boost recovery action disclosed in this application. DETAILED DESCRIPTION

[0024] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0025] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0026] Unless otherwise specifically stated, the relative arrangement of the parts and steps, numerical expressions and numerical values set forth in these embodiments do not limit the scope of the present application. At the same time, it should be understood that, for ease of description, the sizes of the various parts shown in the drawings are not drawn according to actual proportional relationships. The techniques, methods and equipment known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, the techniques, methods and equipment should be considered as part of the authorization specification. In all examples shown and discussed here, any specific values should be interpreted as being merely exemplary, not as limitations. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that similar numbers and letters represent similar items in the following figures, and therefore, once an item is defined in one figure, it does not need to be further discussed in subsequent figures.

[0027] See also Figures 1 to 2 As shown, the present application provides an undervoltage protection circuit for an auxiliary power supply, including a voltage divider circuit, a comparison circuit, and a logic control circuit; the input end of the voltage divider circuit is connected to the input voltage end of the auxiliary power supply, and the output end of the voltage divider circuit is connected to the input end of the comparison circuit; the voltage divider circuit is also connected to the logic control circuit, and under different control states of the logic control circuit, the output end is switched to output different voltages; the output end of the comparison circuit is connected to the input end of the logic control circuit, and the comparison circuit is used to generate a reference voltage and a base voltage according to the voltage divider circuit, and compare the reference voltage with the base voltage, and control the logic control circuit to switch to different control states according to the comparison result; the output end of the logic control circuit is connected to the voltage divider circuit and the control circuit of the auxiliary power supply.

[0028] The voltage divider circuit is controlled by a logic control circuit. Under different usage conditions of the auxiliary power supply, different resistors are connected to provide different reference voltages for the comparison circuit. By comparing the actual input voltage of the auxiliary power supply with the reference voltage, the undervoltage protection of the auxiliary power supply is turned off, and automatic control of restart and recovery is achieved.

[0029] Moreover, the comparison output result uses a logic control circuit to control the voltage divider circuit to output the corresponding reference voltage, so that when the auxiliary power supply is undervoltage protection, a smaller reference voltage is used, and when the auxiliary power supply resumes working, a larger reference voltage is used. The reference voltages of different actions of the auxiliary power supply are distinguished and staggered to form a hysteresis protection, which effectively avoids the problem of continuous restart caused by the input voltage of the auxiliary power supply fluctuating near the protection threshold, thereby improving the reliability and stability of the auxiliary power supply.

[0030] This solves the problem of undervoltage protection circuit of the auxiliary power supply in the related technology. During the power-off process of the chip power supply voltage, the power supply voltage fluctuation will cause the chip to turn on and off repeatedly, making it impossible to reset the auxiliary power supply in time, which is prone to voltage overcharging and damage to circuit components.

[0031] The above-mentioned voltage divider circuit divides the input voltage of the auxiliary power supply and samples and monitors it to obtain a reference voltage, and inputs it into the comparison circuit. The comparison circuit compares the input voltage with the reference voltage of the action to determine whether it is necessary to control the auxiliary power supply through the auxiliary power supply control circuit through the logic control circuit, execute the corresponding undervoltage protection action to turn off the auxiliary power supply, or perform the boost recovery action to turn on the auxiliary power supply.

[0032] Specifically, the input end of the voltage divider circuit is connected to the input voltage end of the auxiliary power supply. After the input voltage passes through the voltage divider circuit, a corresponding reference voltage can be obtained. The output end of the voltage divider circuit is connected to the input end of the comparison circuit, and the reference voltage is transmitted to the comparison circuit for comparison.

[0033] The voltage divider circuit is also connected to the logic control circuit. Under different control states of the logic control circuit, the output terminal outputs different voltages. This is because this embodiment distinguishes the reference voltage for undervoltage protection from the reference voltage for boost recovery. This requires changes to the voltage divider circuit that determines the reference voltage of the comparison circuit.

[0034] like Figure 1 As shown in the figure, U1 is a TL431. During undervoltage protection, the voltage divider circuit is connected to resistors R1, R2, R3, and R4. The undervoltage protection point is calculated as Vth1 = 2.5 * (R1 + R2 + R3 + R4) / R4. During boost recovery, the voltage divider circuit is connected to resistors R1, R2, R3, R4, and R11. The undervoltage protection point is calculated as Vth2 = 2.5 * (R1 + R2 + R3 + R4 / / R11) / (R4 / / R11), where Vth2 > Vth1.

[0035] In this way, when the auxiliary power supply is under-voltage protection, a smaller reference voltage Vth1 is used, and when the auxiliary power supply resumes working, a larger reference voltage Vth2 is used. The reference voltages of different actions of the auxiliary power supply are distinguished and staggered to form a hysteresis protection, which effectively avoids the problem of continuous restart caused by the input voltage of the auxiliary power supply fluctuating near the protection threshold, thereby improving the reliability and stability of the auxiliary power supply.

[0036] The output end of the comparison circuit is connected to the input end of the logic control circuit. The comparison circuit is used to generate a reference voltage and a base voltage according to the voltage divider circuit. That is, the reference voltage Vref and the reference voltages Vth1 and Vth2 are calculated according to the voltage divider circuit, and compared to determine whether to trigger the corresponding undervoltage protection action or boost recovery action.

[0037] The comparison circuit can also control the logic control circuit to switch to different control states according to the comparison result, so that the voltage divider circuit switches to the corresponding state and connects the corresponding voltage divider resistor to prepare for subsequent actions.

[0038] The logic control circuit is connected to the voltage divider circuit to change the voltage divider circuit according to different control states to achieve changes in the reference voltage. The logic control circuit is also connected to the auxiliary power supply control circuit to achieve corresponding action control of the auxiliary power supply based on the comparison result of the comparator.

[0039] The control circuit of the auxiliary power supply may be a power chip of the auxiliary power supply. The feedback signal voltage VFB of the power chip may control the PWM output of the power chip, thereby controlling the start and stop of the auxiliary power supply.

[0040] As an optional embodiment, the comparison circuit is a three-terminal parallel voltage regulator chip; the three-terminal parallel voltage regulator chip includes a reference voltage terminal, an input terminal and an output terminal; the reference voltage terminal is connected to the output terminal of the voltage divider circuit; the input terminal is grounded, and the output terminal is connected to the logic control circuit.

[0041] The three-terminal parallel voltage regulator chip can be a TL431 chip, such as Figure 3 As shown, REF is the reference voltage terminal, the anode ANODE is the input terminal and the cathode CATHODE is the output terminal. Figure 1 As shown, U1 is TL431, the reference voltage terminal REF is connected to the output terminal Vref of the voltage divider circuit, the input terminal is grounded, and the output terminal is connected to the logic control circuit.

[0042] As an optional embodiment, the equivalent circuit of the three-terminal parallel voltage regulator chip includes a reference voltage source of 2.5V, a voltage comparator, and a switching transistor; one end of the reference voltage source is connected to the input terminal ANODE, and the other end is connected to one input terminal of the voltage comparator; the two power supply terminals of the voltage comparator are respectively connected to the input terminal ANODE and the output terminal CATHODE, the other input terminal of the voltage comparator is connected to the reference voltage terminal REF, and the output terminal of the voltage comparator is connected to the base of the switching transistor; the collector of the switching transistor is connected to the output terminal CATHODE, and the emitter of the switching transistor is connected to the input terminal ANODE; a diode is also connected between the collector and the emitter of the switching transistor, the input terminal of the diode is connected to the emitter, and the output terminal of the diode is connected to the collector.

[0043] like Figure 3 As shown in the figure, the TL431 is a common three-terminal adjustable shunt regulator. Its equivalent circuit consists of a 2.5V precision reference voltage source, a voltage comparator, and a switching transistor. When the input voltage V>2.5V, the TL431 turns on, and vice versa. Using the TL431 chip's comparison function to build a hysteresis undervoltage protection circuit is low-cost and simple, achieving the comparison function and replacing more expensive comparators.

[0044] As an optional embodiment, the voltage divider circuit includes a first voltage divider circuit and a second voltage divider circuit; the input end of the first voltage divider circuit is connected to the input voltage end of the auxiliary power supply, and the output end of the first voltage divider circuit is connected to the input end of the comparison circuit; the input end of the second voltage divider circuit is connected to the logic control circuit, and the output end of the second voltage divider circuit is connected to the first voltage divider circuit, and the connection with the first voltage divider circuit is connected or disconnected under different control states of the logic control circuit.

[0045] like Figure 2 As shown, the first voltage divider circuit includes R1, R2, R3, and R4, and the second voltage divider circuit includes R11. The input end of the first voltage divider circuit is connected to the input voltage terminal Vin of the auxiliary power supply, and the output end of the first voltage divider circuit is connected to the input terminal Vref of the comparison circuit.

[0046] The input end of R11 of the second voltage divider circuit is connected to Q1 of the logic control circuit, and the output end of R11 of the second voltage divider circuit is connected to the first voltage divider circuit. Under different control states of the logic control circuit, the connection with the first voltage divider circuit is connected or disconnected, thereby changing the voltage divider circuit and changing the reference voltage of the comparison circuit U1.

[0047] As an optional embodiment, the first voltage divider circuit includes a first resistor and a second resistor; one end of the first resistor is connected to the input voltage terminal of the auxiliary power supply, and the other end of the first resistor is connected to the input terminal of the comparison circuit; one end of the second resistor is connected to the input terminal of the comparison circuit, and the other end of the second resistor is grounded; the second voltage divider circuit includes a third resistor, one end of the third resistor is connected to the input terminal of the comparison circuit, and the other end of the third resistor is connected to the logic control circuit.

[0048] The first voltage divider circuit includes first resistors, such as R1, R2, and R3, and a second resistor, such as R4. The output end of the first voltage divider circuit is set between the first resistors and the second resistors. The first resistor is connected to the input voltage terminal Vin of the auxiliary power supply, and the second resistor is grounded to form an effective reference voltage in U1.

[0049] The second voltage divider circuit includes a third resistor, such as R11, one end of which is connected to the input of the comparison circuit, and the other end of which is connected to the logic control circuit. This allows the second voltage divider circuit to be incorporated into or separated from the first voltage divider circuit based on the state of Q1 in the logic control circuit.

[0050] As an optional embodiment, the logic control circuit includes a voltage divider and current limiting circuit, a voltage source, a first field effect transistor, and a second field effect transistor; the voltage source is connected to the input end of the voltage divider and current limiting circuit, and the output end of the voltage divider and current limiting circuit is connected to the gates of the first field effect transistor and the second field effect transistor; the source of the first field effect transistor is grounded, and the drain is connected to the power chip of the auxiliary power supply; the source of the second field effect transistor is grounded, and the drain is connected to the second voltage divider circuit of the voltage divider circuit.

[0051] The voltage-divider and current-limiting circuit includes R5, R6, and R7. R5 acts as both a voltage-divider and current-limiting resistor, limiting the current flowing from voltage source Vaux into U1. R6 and R7 act as voltage-divider resistors, transmitting the voltage from voltage source Vaux to the first and second FETs, Q4 and Q1. Vaux is typically the auxiliary power system's built-in voltage source, typically 3.3V.

[0052] The voltage source Vaux is connected to the input end of the voltage divider and current limiting circuit, and the output end of the voltage divider and current limiting circuit is connected to the gate of the first field effect transistor Q4 and the second field effect transistor Q1. Through the voltage divider and current limiting circuit, on the one hand, the comparison circuit is protected, and on the other hand, the field effect transistor of the control logic circuit is driven to operate.

[0053] The source of the first field effect transistor Q4 is grounded, and the drain is connected to the feedback signal terminal VFB of the power chip of the auxiliary power supply to control the lowering or restoration of VFB according to different conduction states to control the shutdown or opening of the auxiliary power supply.

[0054] The source of the second field effect transistor Q1 is grounded, and the drain is connected to the second voltage divider circuit of the voltage divider circuit, so as to control the second voltage divider circuit according to different conduction states and connect or disconnect the first voltage divider circuit.

[0055] As an optional embodiment, the voltage divider and current limiting circuit includes a ninth resistor, a fourth resistor and a fifth resistor; one end of the ninth resistor is connected to the voltage source, and the other end is connected to the output end of the comparison circuit; one end of the fourth resistor is connected to the output end of the comparison circuit, and the other end is connected to the gate of the first field effect transistor and the second field effect transistor; one end of the fifth resistor is connected to the gate of the first field effect transistor and the second field effect transistor; and the other end is grounded.

[0056] The voltage divider and current limiting circuit includes a ninth resistor, such as R5, which can not only limit the current of U1 but also realize voltage division. The fourth resistor, such as R6, and the fifth resistor R7 are simply used to realize voltage division. The output of the voltage divider and current limiting circuit is set between the fourth resistor and the fifth resistor. Figure 1 In the embodiment, the output voltage of the voltage divider and current limiting circuit is Vg4=Vaux*R7 / (R5+R6+R7).

[0057] As an optional embodiment, the logic control circuit also includes a multi-stage amplifier circuit; the multi-stage amplifier circuit includes multiple amplifier transistors, the base of the amplifier transistor of the first stage is connected to the common end of the fourth resistor and the fifth resistor, the emitter is grounded, and the collector is connected to the voltage source and the base of the amplifier transistor of the next stage; the base of the amplifier transistor of the intermediate stage is connected to the collector of the amplifier transistor of the previous stage, the emitter is grounded, and the collector is connected to the voltage source and the base of the amplifier transistor of the next stage; the base of the amplifier transistor of the last stage is connected to the collector of the amplifier transistor of the previous stage, the emitter is grounded, and the collector is connected to the voltage source and the base of the amplifier transistor of the next stage through the sixth resistor.

[0058] In other embodiments, the output of the voltage-divider current-limiting circuit may not be able to directly drive the field-effect transistor, but may be amplified by a multi-stage amplifier circuit to achieve driving of the field-effect transistor. The multi-stage amplifier circuit includes multiple amplifier transistors, each amplifier transistor forming an amplifier stage.

[0059] The first-stage amplifying transistor needs to be connected to the current limiting and voltage divider circuit. The base of the amplifying transistor is connected to the common end of the fourth resistor and the fifth resistor, that is, connected to the output end of the current limiting and voltage divider circuit. The emitter is grounded, and the collector is connected to the voltage source and the base of the next-stage amplifying transistor to achieve primary amplification.

[0060] The base of the intermediate stage amplifying transistor is connected to the collector of the previous stage amplifying transistor, the emitter is grounded, and the collector is connected to the voltage source and the base of the next stage amplifying transistor to achieve step-by-step amplification.

[0061] The amplifier transistor of the last stage is connected to the final first field effect transistor Q4, the base of the amplifier transistor is connected to the collector of the amplifier transistor of the previous stage, the emitter is grounded, and the collector is connected to the gate of the first field effect transistor through the sixth resistor.

[0062] The sixth resistor, such as R10, is used to perform voltage division, converting the collector output of the last-stage amplifier transistor into a voltage to drive the first field effect transistor Q4 and the second field effect transistor Q1.

[0063] As an optional embodiment, the multi-stage amplifier circuit is a two-stage amplifier circuit, including a first amplifier transistor and a second amplifier transistor; the base of the first amplifier transistor is connected to the common end of the fourth resistor and the fifth resistor, the emitter is grounded, the collector is connected to the base of the second amplifier transistor, and the collector is also connected to the voltage source through the seventh resistor; the base of the second amplifier transistor is connected to the collector of the first amplifier transistor, the emitter is grounded, the collector is connected to the gate of the first field-effect transistor through the sixth resistor, and the collector is also connected to the voltage source through the seventh resistor.

[0064] This embodiment provides two amplification stages, such as Figure 2 As shown, they are a first amplifying transistor Q2 and a second amplifying transistor Q3. The base of the first amplifying transistor Q2 is connected to the common terminal of the fourth resistor R6 and the fifth resistor R7, the emitter is grounded, and the collector is connected to the base of the second amplifying transistor Q3. The collector is also connected to a voltage source via a seventh resistor, such as R8, to achieve primary amplification of the output voltage Vg2 of the current limiting voltage divider circuit.

[0065] The base of the second amplifying transistor Q3 is connected to the collector of the first amplifying transistor Q2, the emitter is grounded, the collector is connected to the gate of the first field effect transistor through the sixth resistor R10, and the collector is also connected to the voltage source through the seventh resistor, such as R9, to achieve secondary amplification of the primary amplified voltage Vg3.

[0066] As an optional embodiment, a first capacitor is arranged between the reference voltage terminal and the input terminal of the three-terminal parallel voltage regulator chip of the comparison circuit; a second capacitor and an eighth resistor are arranged between the gate and source of the first field-effect transistor and the second field-effect transistor of the logic control circuit; and a third capacitor is arranged between the gate and source of the amplifying transistor of the multi-stage amplifying circuit of the logic control circuit.

[0067] A first capacitor is provided between the reference voltage terminal and the input terminal of the three-terminal parallel voltage regulator chip of the comparison circuit to achieve the functions of voltage stabilization and circuit protection, which is not shown in the figure.

[0068] A second capacitor and an eighth resistor are placed between the gate and source of the first and second field-effect transistors in the logic control circuit, also for voltage regulation and field-effect transistor protection. A third capacitor is placed between the gate and source of the transistors in the multi-stage amplifier circuit of the logic control circuit to protect the transistors. These capacitors and resistors are not shown in the figure.

[0069] It should be noted that this embodiment also provides an optional implementation, which is described in detail below.

[0070] This embodiment provides a hysteresis undervoltage protection circuit consisting of a three-terminal shunt voltage regulator chip and a field-effect transistor (MOSFET). This circuit implements a hysteresis undervoltage protection function. Specifically, when the auxiliary power supply input voltage Vin drops below a threshold voltage Vth1, the auxiliary power supply chip's feedback signal voltage VFB is pulled low, and the PWM signal output immediately stops. At this point, the auxiliary power supply performs undervoltage protection, shutting down the auxiliary power supply. When the auxiliary power supply input voltage Vin rises above a threshold voltage Vth2, the power supply chip feedback function resumes, the PWM signal begins outputting, and the auxiliary power supply performs a voltage boost recovery action, turning the auxiliary power supply back on. Vth2 > Vth1, effectively avoiding the problem of constant restarts caused by input voltage fluctuations near the protection threshold, thereby improving the reliability of the auxiliary power supply system.

[0071] TL431 is a common three-terminal adjustable shunt regulator. Its equivalent schematic is as follows Figure 3 As shown in the figure, it consists of a 2.5V precision reference voltage source, a voltage comparator, and a switching tube. When V > 2.5V, the TL431 turns on and turns off. This function of the TL431 chip is used to build a hysteresis undervoltage protection circuit.

[0072] like Figure 2 The figure shows a schematic diagram of an auxiliary power supply with hysteresis undervoltage protection circuit for this embodiment. R1, R2, R3, R4, R6, R7, and R10 are voltage-dividing resistors; R5, R9, and R11 are both voltage-dividing and current-limiting resistors; and R8 is a current-limiting resistor. Q1 and Q4 are identical logic switching MOSFETs, and Q2 and Q3 are identical transistors. U1 is a TL431.

[0073] The detailed working principle is as follows: When the input voltage Vin of the auxiliary power supply drops and loses power, Vref is divided by R1, R2, R3, and R4. The formula is Vref = Vin*R4 / (R1+R2+R3+R4). When Vref is less than 2.5V, U1 is cut off.

[0074] There is a formula Vg2 = Vaux*R7 / (R5+R6+R7). When Vg2>Vth_Q2 (Vth_Q2 is the threshold voltage for Q2 to turn on), Q2 is turned on, Vg3 = 0V, and Q3 is turned off.

[0075] There is a formula Vg4 = Vaux*R10 / (R9+R10). When Vg4>Vth_Q4 (Vth_Q4 is the threshold voltage for Q4 to turn on), the Q4 switch tube is turned on. At this moment, the feedback signal VFB is pulled down to 0 potential, the PWM port of the power chip outputs a low level, and the undervoltage protection of the entire auxiliary power supply system is turned off. The undervoltage protection point calculation formula at this time is Vth1 = 2.5*(R1+R2+R3+R4) / R4.

[0076] When the input voltage is boosted and powered on, Q4 is in the on state because the undervoltage protection has just been activated, Vg1 = Vg4, Vg1 > Vth_Q1 (Vth_Q1 is the threshold voltage for Q1 to turn on), Q1 is also in the on state, R11 and R4 are connected in parallel, at this time the formula Vref = Vin*(R4 / / R11) / (R1+R2+R3+R4 / / R11), when Vref > 2.5V, U1 is turned on.

[0077] There is a formula Vg2 = 2*R7 / (R6+R7). When Vg2 < Vth_Q2 (Vth_Q2 is the threshold voltage for Q2 to turn on), the Q2 switch is cut off, Vg3 = Vaux, and the Q3 switch is turned on.

[0078] The formula Vg4=0V, Q1 and Q4 switches are turned off, the feedback signal VFB returns to normal, the power chip PWM outputs normally, and the entire auxiliary power system resumes work. The formula for calculating the undervoltage recovery point at this time is Vth2=

[0079] 2.5*(R1+R2+R3+R4 / / R11) / (R4 / / R11), Vth2>Vth1.

[0080] Due to the cutoff of Q1, when the next undervoltage protection occurs, R11 does not participate in the calculation of the Vref value, so the undervoltage point is still Vth1.

[0081] From the above analysis, it can be seen that the above-mentioned hysteresis undervoltage protection circuit can realize undervoltage protection for the auxiliary power supply when Vin<Vth1; when Vin>Vth2, the auxiliary power supply resumes operation, and Vth2>Vth1, realizing the hysteresis protection function, and the voltage range of the hysteresis can be adjusted by adjusting the resistance value of R11, that is, △V=Vth2-Vth1.

[0082] The solution of this embodiment staggers the protection voltage point and the recovery voltage point, and the range is adjustable, which effectively avoids the problem of continuous restart caused by the input voltage jittering near the protection threshold and improves the reliability of the auxiliary power supply system.

[0083] according to Figure 2 The circuit diagram shown is constructed and simulated Figure 4 and Figure 5 The simulation test results of . Figure 4 This is a schematic diagram of the test waveform of the undervoltage protection action disclosed in this application, such as Figure 4 As shown in FIG, when the input voltage Vin is less than 170V and Vref is less than 2.5V, the undervoltage protection circuit is activated, VFB is pulled down to 0 potential, the drive signal Vgs is at 0 level, the auxiliary source is turned off, and the Vout output drops to 0V.

[0084] Figure 5 This is a schematic diagram of the test waveform of the boost recovery action disclosed in this application. When the input voltage Vin>190V, Vref>2.5V, the undervoltage protection circuit is turned off, VFB recovers the output, the drive signal Vgs recovers the output, the auxiliary source is turned on, and Vout recovers the output.

[0085] from Figure 4 and Figure 5 It can be seen that whether it is the undervoltage protection action to shut down the auxiliary power supply or the boost recovery action to turn on the auxiliary power supply, it can be achieved only once, and there is no situation where the auxiliary power supply is frequently turned on and off due to the jitter of the input voltage. Therefore, the circuit of this embodiment can make the control of the auxiliary power supply more stable and effective, and the working stability is higher.

[0086] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used herein to describe the spatial positional relationship of a device or feature to other devices or features as shown in the figures. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figures. For example, if the device in the drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0087] In addition, it should be noted that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of this application.

[0088] The above are merely preferred embodiments of the present application and are not intended to limit the present application. Those skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. An undervoltage protection circuit for an auxiliary power supply, characterized in that: Including voltage divider circuit, comparison circuit, logic control circuit; The input end of the voltage divider circuit is connected to the input voltage end of the auxiliary power supply, and the output end of the voltage divider circuit is connected to the input end of the comparison circuit; the voltage divider circuit is also connected to the logic control circuit, and switches the output end to output different voltages under different control states of the logic control circuit; The output end of the comparison circuit is connected to the input end of the logic control circuit, and the comparison circuit is used to generate a reference voltage and a base voltage according to the voltage divider circuit, compare the reference voltage with the base voltage, and control the logic control circuit to switch to different control states according to the comparison result; The logic control circuit is connected to the voltage divider circuit and the control circuit of the auxiliary power supply.

2. The undervoltage protection circuit according to claim 1, characterized in that: The comparison circuit is a three-terminal parallel voltage stabilization chip; The three-terminal parallel voltage stabilizing chip includes a reference voltage terminal, an input terminal and an output terminal; the reference voltage terminal is connected to the output terminal of the voltage divider circuit; The input end is grounded, and the output end is connected to the logic control circuit.

3. The undervoltage protection circuit according to claim 2, characterized in that: The equivalent circuit of the three-terminal parallel voltage stabilizing chip includes a reference voltage source, a voltage comparator, and a switching transistor; One end of the reference voltage source is connected to the input end, and the other end is connected to an input end of the voltage comparator; The two power supply terminals of the voltage comparator are connected to the input terminal and the output terminal respectively, the other input terminal of the voltage comparator is connected to the reference voltage terminal, and the output terminal of the voltage comparator is connected to the base of the switching transistor; The collector of the switching transistor is connected to the output end, and the emitter of the switching transistor is connected to the input end; A diode is further connected between the collector and the emitter of the switching transistor, the input end of the diode is connected to the emitter, and the output end of the diode is connected to the collector.

4. The undervoltage protection circuit according to claim 1, wherein: The voltage divider circuit includes a first voltage divider circuit and a second voltage divider circuit; The input end of the first voltage divider circuit is connected to the input voltage end of the auxiliary power supply, and the output end of the first voltage divider circuit is connected to the input end of the comparison circuit; The input end of the second voltage divider circuit is connected to the logic control circuit, and the output end of the second voltage divider circuit is connected to the first voltage divider circuit. Under different control states of the logic control circuit, the connection with the first voltage divider circuit is connected or disconnected.

5. The undervoltage protection circuit according to claim 4, characterized in that: The first voltage divider circuit includes a first resistor and a second resistor; One end of the first resistor is connected to the input voltage terminal of the auxiliary power supply, and the other end of the first resistor is connected to the input terminal of the comparison circuit; One end of the second resistor is connected to the input end of the comparison circuit, and the other end of the second resistor is grounded; The second voltage divider circuit includes a third resistor, one end of the third resistor is connected to the input end of the comparison circuit, and the other end of the third resistor is connected to the logic control circuit.

6. The undervoltage protection circuit according to claim 1, characterized in that: The logic control circuit includes a voltage-dividing and current-limiting circuit, a voltage source, a first field-effect transistor, and a second field-effect transistor; The voltage source is connected to the input end of the voltage-dividing and current-limiting circuit, and the output end of the voltage-dividing and current-limiting circuit is connected to the gates of the first field-effect transistor and the second field-effect transistor; The source of the first field effect transistor is grounded, and the drain is connected to the power chip of the auxiliary power supply; The source of the second field effect transistor is grounded, and the drain is connected to the second voltage divider circuit of the voltage divider circuit.

7. The undervoltage protection circuit according to claim 6, characterized in that: The voltage-dividing and current-limiting circuit includes a ninth resistor, a fourth resistor, and a fifth resistor; One end of the ninth resistor is connected to the voltage source, and the other end is connected to the output end of the comparison circuit; One end of the fourth resistor is connected to the output end of the comparison circuit, and the other end is connected to the gates of the first field effect transistor and the second field effect transistor; One end of the fifth resistor is connected to the gates of the first field effect transistor and the second field effect transistor; the other end is grounded.

8. The undervoltage protection circuit according to claim 7, characterized in that: The logic control circuit also includes a multi-stage amplifier circuit; The multi-stage amplifier circuit includes a plurality of amplifier transistors, wherein the base of the amplifier transistor of the first stage is connected to the common end of the fourth resistor and the fifth resistor, the emitter is grounded, and the collector is connected to the voltage source and the base of the amplifier transistor of the next stage; The base of the amplifying transistor of the intermediate stage is connected to the collector of the amplifying transistor of the previous stage, the emitter is grounded, and the collector is connected to the voltage source and the base of the amplifying transistor of the next stage; The base of the amplifier transistor of the last stage is connected to the collector of the amplifier transistor of the previous stage, the emitter is grounded, and the collector is connected to the gate of the first field effect transistor through a sixth resistor.

9. The undervoltage protection circuit according to claim 8, characterized in that: The multi-stage amplifier circuit is a two-stage amplifier circuit, comprising a first amplifier triode and a second amplifier triode; The base of the first amplifying transistor is connected to the common end of the fourth resistor and the fifth resistor, the emitter is grounded, the collector is connected to the base of the second amplifying transistor, and the collector is further connected to the voltage source via a seventh resistor; The base of the second amplifying transistor is connected to the collector of the first amplifying transistor, the emitter is grounded, the collector is connected to the gate of the first field effect transistor through a sixth resistor, and the collector is further connected to the voltage source through a seventh resistor.

10. The undervoltage protection circuit according to any one of claims 1 to 9, characterized in that: A first capacitor is provided between the reference voltage terminal and the input terminal of the three-terminal parallel voltage stabilizing chip of the comparison circuit; A second capacitor and an eighth resistor are provided between the gate and source of the first field effect transistor and the second field effect transistor of the logic control circuit; A third capacitor is provided between the gate and source of the amplifying transistor of the multi-stage amplifying circuit of the logic control circuit.

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