1. The utility model provides a switching power supply input voltage overvoltage under-voltage detection circuit which characterized in that: the voltage divider circuit divides the input voltage of the switching power supply, and the divided voltage is used as a signal for detecting undervoltage, normal and overvoltage of the input voltage; the overvoltage and undervoltage detection circuit outputs a first path of detection signal and a second path of detection signal according to the input divided voltage, when the input voltage is undervoltage, the first path of detection signal and the second path of detection signal both output low levels, when the input voltage is normal, the first path of detection signal outputs high levels, the second path of detection signal outputs low levels, and when the input voltage is overvoltage, the first detection signal and the second detection signal both output high levels;

the amplifying circuit amplifies the first detection signal and the second detection signal and converts the first detection signal and the second detection signal into level signals; the signal output circuit converts the output signal of the amplifying circuit into a level signal output, outputs a high level signal when the input voltage is under-voltage or over-voltage, and outputs a low level signal when the input voltage is normal so as to identify the over-voltage and under-voltage states of the input voltage.

2. The input voltage over-voltage and under-voltage detection circuit of the switching power supply according to claim 1, wherein: the voltage dividing circuit consists of a resistor R1 and a resistor R2, two ends of the resistor R1 and the resistor R2 which are connected in series are respectively connected with the anode of the input voltage of the switching power supply and the power ground, and the connection part of the R1 and the R2 forms divided voltage; the threshold of overvoltage and undervoltage detection is adjusted by changing the resistance values of the resistor R1 and the resistor R2.

3. The input voltage over-voltage and under-voltage detection circuit of the switching power supply according to claim 2, wherein: the overvoltage and undervoltage detection circuit consists of a first voltage-stabilizing diode Z1 (1), a second voltage-stabilizing diode Z2 (2), a resistor R4 and a resistor R5, wherein the cathode of the Z1 is connected with the joint of the resistor R1 and the resistor R2, the anode of the Z1 is connected with the cathode of the Z2, the two ends of the resistor R4 are respectively connected with the power ground and the anode of the Z1, and the two ends of the R5 are respectively connected with the power ground and the anode of the Z2; the positive pole of Z1 forms the first path of detection signal, and the positive pole of Z2 forms the second path of detection signal.

4. The input voltage over-voltage and under-voltage detection circuit of the switching power supply according to claim 3, wherein: the discharging circuit is composed of a first triode T1 (3), a second triode T2 (4), a third triode T3 (5) and a fourth triode T4 (6), the triode T1 and the triode T3 are both NPN type triodes, and the triode T2 and the triode T4 are both PNP type triodes; the base electrode of T1 is connected to the positive electrode of a first voltage-stabilizing diode Z1 (1) through a resistor R3, the emitter electrode is connected to the power ground, and the collector electrode is connected with the base electrode of T2; the collector of T2 is connected to the power ground, the emitter is connected to the power ground and the positive power VDD via resistors R6 and R7;

the base electrode of T3 is connected with the anode of the second voltage-stabilizing diode Z2 (2), the emitter electrode is connected with the power ground, and the collector electrode is connected with the base electrode of T4; an emitter of the T4 is connected with a power supply positive electrode VDD through a resistor R8, and a collector is connected with a power supply ground through a resistor R9; the amplitude of the level signal converted from the undervoltage signal is adjusted by changing the resistance values of the resistor R6 and the resistor R7, and the amplitude of the level signal converted from the overvoltage signal is adjusted by changing the resistance values of the resistor R8 and the resistor R9.

5. The input voltage over-voltage and under-voltage detection circuit of the switching power supply according to claim 4, wherein: the signal output circuit consists of a first diode D1 (7), a second diode D2 (8) and a resistor R10, wherein the anode of the D1 is connected with the joint of the resistor R6 and the resistor R7, the D2 is connected with the collector of a fourth triode T4 (6), and the cathode of the D1 is connected with the cathode of the D2; the connection between the cathode of D1 and the cathode of D2 forms an overvoltage/undervoltage level signal through resistor R10.

6. The input voltage over-voltage and under-voltage detection circuit of the switching power supply according to claim 5, wherein: the overvoltage and undervoltage protection circuit comprises a driving chip (9), a field effect tube (10) and a transformer (11), wherein an overvoltage and undervoltage level signal output by a resistor R10 is connected with the input end of the driving chip, a primary side winding of the transformer is connected to the input voltage of a switching power supply, the field effect tube is connected in series with the primary side winding of the transformer, and the output of the driving chip is connected with the grid electrode of the field effect tube; the secondary winding of the transformer supplies power to an oscillator in the switching power supply.

Background

The switching power supply is widely applied to high-voltage frequency converters, high-voltage SVG and energy storage products at present, is used as a power supply of a control system, and provides stable and reliable direct-current voltage for the power supply.

In industrial applications, the input voltage of the switching power supply is generally taken from the bus voltage inside the unit, and is limited by the fluctuation of the bus voltage, and the input voltage of the switching power supply also fluctuates in a large range. When the switching power supply works below the lowest working voltage or above the highest working voltage, the switching power supply is easily damaged. Therefore, overvoltage protection and undervoltage protection are necessary to be considered in the design process of the switching power supply. When the input voltage of the switching power supply is overvoltage or undervoltage, the oscillator circuit is ensured to stop oscillating, the driving pulse is closed, the switching power supply stops working, and when the undervoltage or overvoltage fault disappears, the switching power supply resumes working again.

An input overvoltage and undervoltage detection circuit is integrated in part of the switching power supply driving chip, and for the driving chip without the integrated overvoltage and undervoltage detection circuit, a specific protection circuit needs to be built to realize the detection of overvoltage and undervoltage of input voltage.

Therefore, the invention provides a switch power supply input voltage overvoltage and undervoltage detection circuit, which converts undervoltage and overvoltage states of input voltage into level signals and transmits the level signals to a power supply driving chip, can change the threshold value of overvoltage and undervoltage detection by adjusting circuit parameters, and can adjust the amplitude values of the overvoltage and undervoltage level signals so as to adapt to the requirements of different driving chips on pin voltage.

Disclosure of Invention

In order to overcome the defects of the technical problems, the invention provides an overvoltage and undervoltage detection circuit for the input voltage of a switching power supply.

The invention discloses a switch power supply input voltage overvoltage and undervoltage detection circuit, which is characterized in that: the voltage divider circuit divides the input voltage of the switching power supply, and the divided voltage is used as a signal for detecting undervoltage, normal and overvoltage of the input voltage; the overvoltage and undervoltage detection circuit outputs a first path of detection signal and a second path of detection signal according to the input divided voltage, when the input voltage is undervoltage, the first path of detection signal and the second path of detection signal both output low levels, when the input voltage is normal, the first path of detection signal outputs high levels, the second path of detection signal outputs low levels, and when the input voltage is overvoltage, the first detection signal and the second detection signal both output high levels;

the amplifying circuit amplifies the first detection signal and the second detection signal and converts the first detection signal and the second detection signal into level signals; the signal output circuit converts the output signal of the amplifying circuit into a level signal output, outputs a high level signal when the input voltage is under-voltage or over-voltage, and outputs a low level signal when the input voltage is normal so as to identify the over-voltage and under-voltage states of the input voltage.

The overvoltage and undervoltage detection circuit for the input voltage of the switching power supply comprises a voltage division circuit, wherein the voltage division circuit consists of a resistor R1 and a resistor R2, two ends of the resistor R1 and the resistor R2 which are connected in series are respectively connected to the positive electrode of the input voltage of the switching power supply and a power ground, and the connection part of R1 and R2 forms voltage after voltage division; the threshold of overvoltage and undervoltage detection is adjusted by changing the resistance values of the resistor R1 and the resistor R2.

The overvoltage and undervoltage detection circuit for the input voltage of the switching power supply comprises a first voltage stabilizing diode Z1, a second voltage stabilizing diode Z2, a resistor R4 and a resistor R5, wherein the cathode of the Z1 is connected to the joint of a resistor R1 and a resistor R2, the anode of the Z1 is connected with the cathode of the Z2, two ends of a resistor R4 are respectively connected to the power ground and the anode of the Z1, and two ends of the R5 are respectively connected to the power ground and the anode of the Z2; the positive pole of Z1 forms the first path of detection signal, and the positive pole of Z2 forms the second path of detection signal.

The overvoltage and undervoltage detection circuit for the input voltage of the switching power supply comprises a discharge circuit, a first triode T1, a second triode T2, a third triode T3 and a fourth triode T4, wherein the triode T1 and the triode T3 are both NPN type triodes, and the triode T2 and the triode T4 are both PNP type triodes; the base electrode of T1 is connected to the positive electrode of a first voltage-stabilizing diode Z1 through a resistor R3, the emitter electrode is connected to the power ground, and the collector electrode is connected with the base electrode of T2; the collector of T2 is connected to the power ground, the emitter is connected to the power ground and the positive power VDD via resistors R6 and R7;

the base electrode of the T3 is connected with the anode of the second voltage-stabilizing diode Z2, the emitter electrode is connected with the power ground, and the collector electrode is connected with the base electrode of the T4; an emitter of the T4 is connected with a power supply positive electrode VDD through a resistor R8, and a collector is connected with a power supply ground through a resistor R9; the amplitude of the level signal converted from the undervoltage signal is adjusted by changing the resistance values of the resistor R6 and the resistor R7, and the amplitude of the level signal converted from the overvoltage signal is adjusted by changing the resistance values of the resistor R8 and the resistor R9.

The invention discloses an overvoltage and undervoltage detection circuit for input voltage of a switching power supply, wherein a signal output circuit consists of a first diode D1, a second diode D2 and a resistor R10, the anode of D1 is connected with the joint of the resistor R6 and a resistor R7, D2 is connected with the collector of a fourth triode T4, and the cathode of D1 is connected with the cathode of D2; the connection between the cathode of D1 and the cathode of D2 forms an overvoltage/undervoltage level signal through resistor R10.

The overvoltage and undervoltage detection circuit of the input voltage of the switching power supply comprises a driving chip, a field-effect tube and a transformer, wherein an overvoltage and undervoltage level signal output by a resistor R10 is connected with the input end of the driving chip; the secondary winding of the transformer supplies power to an oscillator in the switching power supply.

The invention has the beneficial effects that: the overvoltage and undervoltage detection circuit is provided with a voltage division circuit, an overvoltage and undervoltage detection circuit, an amplification circuit and a signal output circuit, wherein the overvoltage and undervoltage detection circuit outputs different high and low level combination modes of a first path of detection signal and a second path of detection signal according to the undervoltage, normal and overvoltage states of the divided voltage output by the voltage division circuit, the amplification circuit amplifies and converts the level of the first path of detection signal and the second path of detection signal, and finally the signal output circuit outputs high level and normal low level when undervoltage or overvoltage occurs. The overvoltage and undervoltage states of the input voltage are converted into signals of the same level to be output, and hardware resources required by overvoltage and undervoltage detection are reduced; the threshold value of overvoltage and undervoltage detection can be realized by selecting proper voltage dividing circuit parameters and voltage stabilizing diode parameters, and the method is widely suitable for overvoltage and undervoltage detection of input voltages of various switching power supplies; the overvoltage and undervoltage level signal amplitude can be adjusted by adjusting the resistance value of the resistor, and the requirements of various driving chips on signal levels are met.

Drawings

FIG. 1 is a circuit diagram of an input voltage over-voltage and under-voltage detection circuit of a switching power supply according to the present invention;

fig. 2 is a diagram illustrating an application example of the input voltage over-voltage and under-voltage detection circuit of the switching power supply of the present invention.

In the figure: the power supply comprises a first voltage stabilizing diode Z1, a second voltage stabilizing diode Z2, a first triode T1, a second triode T2, a third triode T3, a fourth triode T4, a first diode D1, a second diode D2, a driving chip 9, a field effect transistor 10 and a transformer 11, wherein the first triode T2, the third triode T3, the fourth triode T4, the first diode D1, the second diode D2 and the driving chip 9 are connected in series.

Detailed Description

The invention is further described with reference to the following figures and examples.

As shown in fig. 1 and fig. 2, a circuit diagram of an input voltage overvoltage and undervoltage detection circuit of a switching power supply and an exemplary application diagram thereof are respectively provided, the overvoltage and undervoltage detection circuit of the invention is composed of a voltage division circuit, an overvoltage and undervoltage detection circuit, an amplification circuit and a signal output circuit, and the voltage division circuit is used for dividing an input voltage of the switching power supply to generate a divided voltage. The overvoltage and undervoltage detection circuit is used for detecting the divided voltage and generating a first path of detection signal and a second path of detection signal according to the size of the divided voltage; when the voltage is low, the first and second detection signals output low level, when the voltage is normal, the first detection signal outputs high level, the second detection signal outputs low level, when the voltage is over, the first and second detection signals output high level. The amplifying circuit amplifies the signal output by the overvoltage and undervoltage detection circuit and converts the signal into a level signal; the signal output circuit converts the output signal of the amplifying circuit into a path of level signal for output.

The voltage division circuit comprises a resistor R1 and a resistor R2, one end of the resistor R1 is connected to the positive electrode VIN of the input voltage of the switching power supply, the other end of the resistor R2 is connected to the power ground, and the resistor R1 and the resistor R2 divide the input voltage of the switching power supply and output the divided voltage through the connection part of the resistor R1 and the resistor R2. It can be seen that the threshold for over-voltage and under-voltage detection can be adjusted by adjusting the resistance values of the resistor R1 and the resistor R2.

The overvoltage and undervoltage detection circuit is composed of a first voltage stabilizing diode Z1, a second voltage stabilizing diode Z2, a resistor R4 and a resistor R5, wherein the cathode of the Z1 is connected with the connection position of the resistor R1 and the resistor R2, the anode of the Z1 is connected with the cathode of the Z2, two ends of the resistor R4 are respectively connected with a power ground and the anode of the Z1, and two ends of the R5 are respectively connected with the power ground and the anode of the Z2. When the divided voltage is under-voltage, Z1 can not be conducted and is in a cut-off state due to small voltage; when the voltage division voltage is normal, the voltage value is large, Z1 is switched on, and Z2 is switched off; when the divided voltage is over-voltage, the voltage value is larger, and Z1 and Z2 are both conducted. Therefore, the overvoltage and undervoltage states of the input voltage can be judged according to the breakdown state of the voltage stabilizing diode, and the threshold values of overvoltage and undervoltage detection are adjusted by selecting the voltage stabilizing diodes with different voltage stabilizing parameters.

The amplification circuit shown comprises a first triode T1, a second triode T2, a third triode T3 and a fourth triode T4, wherein the triode T1 and the triode T3 are both NPN type triodes, and the triode T2 and the triode T4 are both PNP type triodes. The base electrode of T1 is connected to the positive electrode of a first voltage-stabilizing diode Z1 through a resistor R3, the emitter electrode is connected to the power ground, and the collector electrode is connected with the base electrode of T2; the collector of T2 is connected to the power ground, the emitter is connected to the power ground and the positive power VDD via resistors R6 and R7; the base electrode of the T3 is connected with the anode of the second voltage-stabilizing diode Z2, the emitter electrode is connected with the power ground, and the collector electrode is connected with the base electrode of the T4; the emitter of T4 is connected to the positive power supply VDD via resistor R8, and the collector is connected to ground via resistor R9.

When the base of the T1 is a low-level signal input, the T1 and the T2 are both cut off, and the high level is output at the connection part of the R6 and the R7; when the base of the T1 is a high-level signal input, the T1 and the T2 are both conducted, and the connection position of the R6 and the R7 is low level; it can be seen that the amplification circuit formed by T1 and T2 has an inverting action. When the base of the T3 is a low-level signal input, the T3 and the T4 are both cut off, and the collector of the T4 is at a low level; when the base of the T3 is a high-level signal input, the T3 and the T4 are conducted, and the collector of the T4 is at a high level; it can be seen that the amplifying circuit composed of T3 and T4 has a following function.

The signal output circuit is composed of a first diode D1, a second diode D2 and a resistor R10, wherein the anode of D1 is connected with the joint of the resistor R6 and the resistor R7, D2 is connected with the collector of a fourth triode T4, and the cathode of D1 is connected with the cathode of D2; the connection between the cathode of D1 and the cathode of D2 forms an overvoltage/undervoltage level signal through resistor R10. The amplitude of the under-voltage signal level can be adjusted by adjusting the resistance values of the resistor R6 and the resistor R7, and the amplitude of the over-voltage signal level can be adjusted by adjusting the resistance values of the resistor R8 and the resistor R9.

The working principle of the overvoltage and undervoltage detection circuit is as follows:

when the input voltage of the switching power supply is in an undervoltage state, the resistor R1 and the resistor R2 are connected in series for voltage division, at the moment, the voltage at the joint of the resistor R1 and the resistor R2 is smaller than the reverse breakdown voltage of the first voltage-stabilizing diode Z1, the first voltage-stabilizing diode Z1 and the second voltage-stabilizing diode Z2 are both in a cut-off state, the voltages at the upper ends of the resistor R4 and the resistor R5 are both 0, the base voltages of the triode T1 and the triode T3 are 0, the triodes T1 and T3 are both in a cut-off state, the triode T2 is in a cut-off state, the resistor R6 and the resistor R7 are connected in series for voltage division, and the voltage at two ends of the resistor R7 is in a high level; the transistor T4 is in an off state, the voltage across the resistor R9 is 0, at this time, the diode D1 is turned on, the diode D2 is turned off in the reverse direction, and a high level signal is output.

When the input voltage of the switching power supply is in a normal state between undervoltage and overvoltage, the voltage of two ends of the resistor R2 is increased to reach the reverse breakdown voltage of the first voltage stabilizing diode, and at the moment, the leakage current of the first voltage stabilizing diode flows through the resistor R4, so that the voltage of two ends of the resistor R4 is increased but does not reach the reverse breakdown voltage of the second voltage stabilizing diode. At this time, the emitter junction of the transistor T1 is biased in the forward direction, the transistor T1 is conducted, the emitter junction of the transistor T2 is biased in the forward direction, the transistor T2 is conducted, and the voltage at the two ends of the resistor R7 is at a low level. The transistor T3 and the transistor T4 are kept in an off state, the voltage across the resistor R9 is 0, and the diode D1 and the diode D2 are both in an off state, outputting a low level signal.

When the input voltage of the switching power supply is increased to an overvoltage state, the leakage current of the first voltage stabilizing diode is continuously increased, the voltage at two ends of the resistor R4 reaches the reverse breakdown voltage of the second voltage stabilizing diode, the leakage current of the second voltage stabilizing diode flows through the resistor R5, the voltage at two ends of the resistor R5 is increased, the triode T3 and the triode T4 are conducted, the resistor R8 and the resistor R9 are connected in series for voltage division, the two ends of the resistor R9 are in a high level, and the diode D2 is conducted. The transistor T1 and the transistor T2 are kept in a conducting state, two ends of the resistor R7 are at a low level, the diode D1 is turned off in the reverse direction, and the output level signal is a high level signal.