CN201860257U - Input overvoltage protection circuit - Google Patents

Abstract

The utility model discloses an input overvoltage protection circuit, comprising a voltage detector, a first capacitor and a second capacitor, and a first switch. The voltage detector detects a DC input voltage after rectification of an AC power source received by a power supply. When the DC input voltage exceeds a threshold value, the voltage detector outputs a switching signal to make the first switch non-conductive and the second switch conductive, so as to provide the first and second capacitors coupled in series as input filter capacitors. When the DC input voltage does not exceed the threshold value, the voltage detector does not output a switching signal to make the first switch conductive and the second switch non-conductive, so as to provide the first capacitor as an input filter capacitor. Therefore, input filter capacitors with different withstand voltages are automatically provided according to different AC power source voltages received by the power supply, so as to achieve the effect of input overvoltage protection at a relatively low cost.

Description

Input overvoltage protection circuit

technical field

The utility model relates to an input overvoltage protection circuit, in particular to an input overvoltage protection circuit for a power supply.

Background technique

FIG. 1 is a schematic circuit diagram of a conventional power supply. Referring to FIG. 1 , the power supply 1 includes an EMI filter 11 , a bridge rectifier 12 , an input filter capacitor 13 , a DC-to-DC converter 14 and an output filter capacitor 15 . After the AC power Vac is input, the noise is filtered out by the electromagnetic interference filter 11 , and then converted into a DC input voltage Vin by rectification by the bridge rectifier 12 and filtering by the input filter capacitor 13 . The non-adjustable DC input voltage Vin is converted into an adjustable DC output voltage Vout through conversion by the DC-to-DC converter 14 and filtering by the output filter capacitor 15 .

When the power supply 1 is designed to receive a lower voltage (such as 110Vrms) AC power Vac, the input filter capacitor 13 used has a lower withstand voltage, and if it is accidentally inserted into the AC plug to provide a higher voltage during use (such as 220Vrms) of the AC power supply Vac socket, the input filter capacitor 13 will explode and catch fire because the withstand voltage is not enough. Of course, the power supply 1 can use the input filter capacitor 13 with a higher withstand voltage to prevent explosion and fire due to insufficient withstand voltage, but the cost is of course higher.

Contents of the invention

The purpose of the utility model is to provide an input overvoltage protection circuit, which can automatically provide input filter capacitors with different withstand voltages according to the difference in the AC power voltage received by the power supply.

The utility model provides an input overvoltage protection circuit, which has a first terminal and a second terminal coupled in parallel to receive a DC input voltage. The input overvoltage protection circuit includes a voltage detector, a first capacitor, a first switch, a second capacitor and a second switch, wherein the voltage detector has a first terminal, a second terminal and an output terminal, and the first capacitor and the second capacitor are both It has a first terminal and a second terminal, and each of the first switch and the second switch has a first terminal, a second terminal and a control terminal. The first terminal and the second terminal of the voltage detector are respectively coupled to the first terminal and the second terminal of the input overvoltage protection circuit, and the output terminal of the voltage detector outputs a switching signal when the DC input voltage exceeds a threshold. The first end of the first capacitor is coupled to the first end of the input overvoltage protection circuit. The first terminal, the second terminal and the control terminal of the first switch are respectively coupled to the second terminal of the first capacitor, the second terminal of the input overvoltage protection circuit and the output terminal of the voltage detector. Switch does not conduct. The first end of the second capacitor is coupled to the second end of the first capacitor. The first terminal, the second terminal and the control terminal of the second switch are respectively coupled to the second terminal of the second capacitor, the second terminal of the input overvoltage protection circuit and the output terminal of the voltage detector, and the second terminal receives the switching signal The switch is turned on.

The utility model automatically switches to the first capacitor (its withstand voltage is lower) or the first and second capacitors coupled in series (its withstand voltage Higher) to provide input filter capacitors with different withstand voltages, which can prevent explosions and fires due to insufficient withstand voltages, and achieve the effect of input overvoltage protection at a lower cost.

In order to make the above and other objects, features and advantages of the present invention more comprehensible, preferred embodiments will be described in detail below together with the accompanying drawings.

Description of drawings

FIG. 1 is a schematic circuit diagram of an existing power supply;

Fig. 2 is a schematic circuit diagram of a power supply adopting the input overvoltage protection circuit of the present invention;

Fig. 3 is the circuit diagram of the input overvoltage protection circuit of the utility model;

FIG. 4 is a circuit diagram of a preferred embodiment of the input overvoltage protection circuit of the present invention.

Description of reference signs: 1, 2-power supply; 11, 21-electromagnetic interference filter; 12, 22-bridge rectifier; 13-input filter capacitor; 14, 24-DC to DC converter; 15, 25- Output filter capacitor; 23, 43-input overvoltage protection circuit; 231, 431-first end of input overvoltage protection circuit; 232, 432-second end of input overvoltage protection circuit; C1-first capacitor; C2- The second capacitor; C3-the third capacitor; DET-voltage detector; IN1-the first terminal of the voltage detector; IN2-the second terminal of the voltage detector; OUT-the output terminal of the voltage detector; Dz1-zener diode ; Q1, Q3-N channel field effect transistor; Q2-P channel field effect transistor; R1-resistor; Rb1-first bias resistor; Rb2-second bias resistor; Re1-first voltage equalizing resistor ; Re2- the second voltage equalizing resistor; Rs1- the first detection resistor; Rs2- the second detection resistor; - DC input voltage; Vout - DC output voltage.

Detailed ways

FIG. 2 is a schematic circuit diagram of a power supply adopting the input overvoltage protection circuit of the present invention. Referring to FIG. 2 , the power supply 2 includes an EMI filter 21 , a bridge rectifier 22 , an input overvoltage protection circuit 23 , a DC-to-DC converter 24 and an output filter capacitor 25 . After the AC power Vac is input, the noise is filtered out by the electromagnetic interference filter 21 , and then converted into a DC input voltage Vin by rectification by the bridge rectifier 22 and filtering by the input overvoltage protection circuit 23 . The non-adjustable DC input voltage Vin is converted into an adjustable DC output voltage Vout through conversion by the DC-to-DC converter 24 and filtering by the output filter capacitor 25 . The input overvoltage protection circuit 23 can automatically provide input filter capacitors with different withstand voltages according to the different voltages of the AC power Vac received by the power supply 2 , so as to achieve the effect of input overvoltage protection at a lower cost.

FIG. 3 is a schematic circuit diagram of the input overvoltage protection circuit of the present invention. Referring to FIG. 3 , the input overvoltage protection circuit 23 has a first terminal 231 and a second terminal 232 and is coupled in parallel to the output terminal of the bridge rectifier 22 shown in FIG. 2 to receive the DC input voltage Vin. The input overvoltage protection circuit 23 includes a voltage detector DET, a first capacitor C1, a first switch S1, a second capacitor C2 and a second switch S2, wherein the voltage detector DET has a first terminal IN1, a second terminal IN2 and an output terminal OUT, the first capacitor C1 and the second capacitor C2 both have a first terminal and a second terminal, and both the first switch S1 and the second switch S2 have a first terminal, a second terminal and a control terminal.

The first terminal IN1 and the second terminal IN2 of the voltage detector DET are respectively coupled to the first terminal 231 and the second terminal 232 of the input overvoltage protection circuit 23, and the output terminal OUT of the voltage detector DET is when the DC input voltage Vin exceeds the threshold outputting a switching signal; otherwise, when the DC input voltage Vin does not exceed the threshold, of course no switching signal is outputted. The first terminal of the first capacitor C1 is coupled to the first terminal 231 of the input overvoltage protection circuit 23 . The first terminal, the second terminal and the control terminal of the first switch S1 are respectively coupled to the second terminal of the first capacitor C1, the second terminal 232 of the input overvoltage protection circuit 23 and the output terminal OUT of the voltage detector DET. The first switch S1 is not turned on when the switching signal is received; otherwise, the first switch S1 is of course turned on when the switching signal is not received. A first terminal of the second capacitor C2 is coupled to a second terminal of the first capacitor C1. The first terminal, the second terminal and the control terminal of the second switch S2 are respectively coupled to the second terminal of the second capacitor C2, the second terminal 232 of the input overvoltage protection circuit 23 and the output terminal OUT of the voltage detector DET. The second switch S2 is turned on when the switching signal is received; otherwise, the second switch S2 is of course not turned on when the switching signal is not received.

When the voltage of the AC power supply Vac is high and the DC input voltage Vin exceeds the threshold, the output terminal OUT of the voltage detector DET outputs a switching signal, so that the first switch S1 is not turned on and the second switch S2 is turned on. At this time, the first capacitor C1 and the second capacitor C2 are coupled in series between the first terminal 231 and the second terminal 232 of the input overvoltage protection circuit 23 to serve as an input filter capacitor, which has a higher withstand voltage. When the voltage of the AC power supply Vac is low and the DC input voltage Vin does not exceed the threshold value, the output terminal OUT of the voltage detector DET does not output a switching signal, so that the first switch S1 is turned on and the second switch S2 is not turned on. Only the first capacitor C1 is coupled between the first terminal 231 and the second terminal 232 of the input overvoltage protection circuit 23 as an input filter capacitor, and its withstand voltage is relatively low.

FIG. 4 is a circuit diagram of a preferred embodiment of the input overvoltage protection circuit of the present invention. Referring to FIG. 4 , the input overvoltage protection circuit 43 has a first terminal 431 and a second terminal 432 coupled in parallel to receive the DC input voltage Vin. The input overvoltage protection circuit 43 includes a voltage detector DET, a first capacitor C1, a first switch S1, a second capacitor C2 and a second switch S2, wherein the voltage detector DET has a first terminal IN1, a second terminal IN2 and an output terminal OUT, the first capacitor C1 and the second capacitor C2 both have a first terminal and a second terminal, and both the first switch S1 and the second switch S2 have a first terminal, a second terminal and a control terminal.

The input overvoltage protection circuit 43 further includes a first voltage sharing resistor Re1 and a second voltage sharing resistor Re2, wherein both the first voltage sharing resistor Re1 and the second voltage sharing resistor Re2 have a first terminal and a second terminal. The first terminal and the second terminal of the first equalizing resistor Re1 are respectively coupled to the first terminal and the second terminal of the first capacitor C1. The first terminal and the second terminal of the second equalizing resistor Re2 are respectively coupled to the first terminal and the second terminal of the second capacitor C2. The first voltage equalizing resistor Re1 and the second voltage equalizing resistor Re2 are used to equalize the voltages falling on the first capacitor C1 and the second capacitor C2, so as to prevent voltage unevenness from causing the voltage falling on a certain capacitor to be too high. is broken down, and then the other capacitor is also broken down soon.

In this embodiment, the first switch S1 includes an N-channel field effect transistor Q1, and the N-channel field effect transistor Q1 has a drain terminal, a source terminal and a gate terminal and is respectively coupled to the first terminal and the second terminal of the first switch S1 and control terminal. The second switch S2 includes a P-channel field effect transistor Q2, which has a source terminal, a drain terminal and a gate terminal and is respectively coupled to the first terminal, the second terminal and the control terminal of the second switch S2. At this time, the input overvoltage protection circuit 43 further includes a first bias resistor Rb1 and a second bias resistor Rb2, wherein both the first bias resistor Rb1 and the second bias resistor Rb2 have a first terminal and a second terminal. Two ends. The first terminal and the second terminal of the first bias resistor Rb1 are respectively coupled to the first terminal 431 of the input overvoltage protection circuit 43 and the output terminal OUT of the voltage detector DET. The first terminal and the second terminal of the second bias resistor Rb2 are respectively coupled to the second terminal of the first bias resistor Rb1 and the second terminal 432 of the input overvoltage protection circuit 43 . The first bias resistor Rb1 and the second bias resistor Rb2 are used to provide a bias voltage so that the N-channel field effect transistor Q1 is turned on and the P-channel field effect transistor is turned on when the output terminal OUT of the voltage detector DET does not output a switching signal. Q2 does not conduct.

In this embodiment, the voltage detector DET includes a first detection resistor Rs1, a second detection resistor Rs2, a Zener diode Dz1, a third capacitor C3, a resistor R1 and a third switch S3, wherein the first detection resistor Rs1, the second detection resistor Rs2, the third capacitor C3 and the resistor R1 all have a first end and a second end, the zener diode Dz1 has a cathode end and an anode end, and the third switch S3 has a first end, a second end and control terminal. A first terminal of the first detection resistor Rs1 is coupled to a first terminal IN1 of the voltage detector DET. The first terminal and the second terminal of the second detection resistor Rs2 are respectively coupled to the second terminal of the first detection resistor Rs1 and the second terminal IN2 of the voltage detector DET. A cathode terminal of the Zener diode Dz1 is coupled to a first terminal of the second detection resistor Rs2 . The first terminal and the second terminal of the third capacitor C3 are respectively coupled to the anode terminal of the Zener diode Dz1 and the second terminal IN2 of the voltage detector DET. The first terminal and the second terminal of the resistor R1 are respectively coupled to the anode terminal of the Zener diode Dz1 and the second terminal IN2 of the voltage detector DET. The first terminal, the second terminal and the control terminal of the third switch S3 are respectively coupled to the output terminal OUT of the voltage detector DET, the second terminal IN2 of the voltage detector DET and the anode terminal of the Zener diode Dz1. When the threshold is exceeded, the third switch S3 is turned on; otherwise, when the DC input voltage Vin does not exceed the threshold, the third switch S3 is of course not turned on. In addition, the third switch S3 includes an N-channel field effect transistor Q3, which has a drain terminal, a source terminal and a gate terminal and is respectively coupled to the first terminal, the second terminal and the control terminal of the third switch S3.

Wherein, the first detection resistor Rs1 and the second detection resistor Rs2 are used to divide and sample the DC input voltage Vin. The third capacitor C3 is used for filtering and stabilizing the voltage divided by the DC input voltage Vin through the first detection resistor Rs1 and the second detection resistor Rs2 when the Zener diode Dz1 breaks down and conducts. The resistor R1 is used to discharge the third capacitor C3 when the Zener diode Dz1 is not broken down and provides a path for the gate terminal of the N-channel field effect transistor Q3 to be coupled to the second terminal 432 of the input overvoltage protection circuit 43 and grounded.

The design of the utility model is that when the DC input voltage Vin exceeds the threshold, the DC input voltage Vin passes through the voltage divided by the first detection resistor Rs1 and the second detection resistor Rs2 to make the Zener diode Dz1 collapse and turn on, and the N-channel field effect The transistor Q3 is turned on, and the output terminal OUT of the voltage detector DET is coupled to the second terminal 432 of the input overvoltage protection circuit 43 through the turned-on N-channel field effect transistor Q3 and grounded. At this time, the output terminal OUT of the voltage detector DET is Grounding and outputting a switching signal (that is, a low-level signal) can make the N-channel field effect transistor Q1 non-conductive and the P-channel field effect transistor Q2 conduction. When the DC input voltage Vin does not exceed the threshold value, the voltage divided by the DC input voltage Vin through the first detection resistor Rs1 and the second detection resistor Rs2 cannot cause the Zener diode Dz1 to collapse and conduct, so the N-channel field effect transistor Q3 is not conducting, at this time the output terminal OUT of the voltage detector DET is equivalent to an open circuit, and the bias voltage is provided by the first bias resistor Rb1 and the second bias resistor Rb2 so that the N-channel field effect transistor Q1 is turned on and the P-channel field effect transistor Q1 is turned on. The effect transistor Q2 is not turned on.

In summary, the input overvoltage protection circuit of the utility model detects the rectified DC input voltage of the AC power received by the power supply through the voltage detector. When the AC power voltage is high and the DC input voltage exceeds the threshold, the voltage detector Outputting a switching signal to make the first switch non-conductive and the second switch conductive, so as to provide the first capacitor and the second capacitor coupled in series as an input filter capacitor, and its withstand voltage is relatively high. When the DC input voltage does not exceed the threshold, the voltage detector does not output a switching signal, so that the first switch is turned on and the second switch is not turned on, so as to provide the first capacitor as an input filter capacitor with a relatively low withstand voltage. Therefore, the input overvoltage protection circuit of the present invention automatically provides input filter capacitors with different withstand voltages according to the different AC power voltages received by the power supply, which can prevent explosions and fires due to insufficient withstand voltage, and achieve input overvoltage at a lower cost. protective effect.

Although the utility model has been disclosed in the above-mentioned preferred embodiments, it is not used to limit the utility model, and any person skilled in the art can make some modifications and embellishments without departing from the spirit and scope of the utility model, so The scope of protection of the utility model should be defined by the appended scope of patent application as the criterion.

Claims (7)

1. An input overvoltage protection circuit having a first terminal and a second terminal coupled in parallel to receive a DC input voltage, characterized in that the input overvoltage protection circuit comprises: A voltage detector has a first terminal, a second terminal and an output terminal, the first terminal and the second terminal of the voltage detector are respectively coupled to the first terminal and the second terminal of the input overvoltage protection circuit, The output terminal of the voltage detector outputs a switching signal when the DC input voltage exceeds a threshold; a first capacitor, the first end of which is coupled to the first end of the input overvoltage protection circuit; A first switch, having a first terminal, a second terminal and a control terminal, respectively coupled to the second terminal of the first capacitor, the second terminal of the input overvoltage protection circuit and the output terminal of the voltage detector , the first switch is not turned on when receiving the switching signal; a second capacitor, the first end of which is coupled to the second end of the first capacitor; A second switch, having a first terminal, a second terminal and a control terminal, respectively coupled to the second terminal of the second capacitor, the second terminal of the input overvoltage protection circuit and the output terminal of the voltage detector , the second switch is turned on when receiving the switching signal. 2. The input overvoltage protection circuit according to claim 1, wherein the input overvoltage protection circuit further comprises: a first equalizing resistor, the first terminal and the second terminal of which are respectively coupled to the first terminal and the second terminal of the first capacitor; A second equalizing resistor, the first terminal and the second terminal of which are respectively coupled to the first terminal and the second terminal of the second capacitor. 3. The input overvoltage protection circuit according to claim 1, wherein the first switch comprises an N-channel field effect transistor, and the drain terminal, the source terminal and the gate terminal of the N-channel field effect transistor are respectively coupled to the The first terminal, the second terminal and the control terminal of the first switch. 4. The input overvoltage protection circuit according to claim 1, wherein the second switch comprises a P-channel field effect transistor, and the source terminal, the drain terminal and the gate terminal of the P-channel field effect transistor are respectively coupled to the The first terminal, the second terminal and the control terminal of the second switch. 5. The input overvoltage protection circuit according to claim 3 or 4, wherein the input overvoltage protection circuit further comprises: a first bias resistor, the first terminal and the second terminal of which are respectively coupled to the first terminal of the input overvoltage protection circuit and the output terminal of the voltage detector; A second bias resistor, the first terminal and the second terminal of which are respectively coupled to the second terminal of the first bias resistor and the second terminal of the input overvoltage protection circuit. 6. The input overvoltage protection circuit according to claim 1, wherein the voltage detector comprises: a first detection resistor, the first end of which is coupled to the first end of the voltage detector; a second detection resistor, the first terminal and the second terminal of which are respectively coupled to the second terminal of the first detection resistor and the second terminal of the voltage detector; a zener diode, the cathode end of which is coupled to the first end of the second detection resistor; a third capacitor, the first terminal and the second terminal of which are respectively coupled to the anode terminal of the Zener diode and the second terminal of the voltage detector; a resistor, the first terminal and the second terminal of which are respectively coupled to the anode terminal of the Zener diode and the second terminal of the voltage detector; A third switch, having a first terminal, a second terminal and a control terminal, respectively coupled to the output terminal of the voltage detector, the second terminal of the voltage detector and the anode terminal of the Zener diode, at the The third switch is turned on when the DC input voltage exceeds the threshold. 7. The input overvoltage protection circuit according to claim 6, wherein the third switch comprises an N-channel field effect transistor, and the drain terminal, the source terminal and the gate terminal of the N-channel field effect transistor are respectively coupled to the The first terminal, the second terminal and the control terminal of the third switch.

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