CN104143819A - A filter capacitor discharge circuit - Google Patents

Abstract

The embodiment of the invention provides a filter capacitor bleeder circuit, which comprises a control circuit and a bleeder circuit, wherein: the control circuit is used for controlling the switch state of the bleeder circuit; the bleeder circuit is used for discharging the charges accumulated on the filter capacitor. By adopting the invention, the charges accumulated on the filter capacitor can be quickly discharged after the external direct current power supply is powered off, and the safety of maintenance personnel and the circuit of the whole machine is protected.

Description

A filter capacitor discharge circuit

technical field

The invention relates to the field of electronic technology, in particular to a filter capacitor discharge circuit.

Background technique

Filter capacitor is an energy storage device used to reduce the ripple coefficient of alternating current. Almost all circuits that need to convert AC to DC will have a filter capacitor at the output of the power supply to obtain a smooth DC output. Generally, the capacitance value of the filter capacitor is very large, and a large amount of charge will accumulate on the filter capacitor in a short time after the circuit is powered off. If the circuit does not design a discharge path for the filter capacitor, maintenance personnel who do not understand the circuit structure may It will cause electric shock due to touching the filter capacitor, and the high voltage at both ends of the filter capacitor also poses a safety hazard to the entire circuit.

Contents of the invention

The technical problem to be solved by the present invention is to provide a filter capacitor discharge circuit. After the external DC power supply is cut off, the charge accumulated on the filter capacitor can be quickly discharged to protect the safety of maintenance personnel and the whole machine circuit.

In order to solve the above technical problems, an embodiment of the present invention provides a filter capacitor discharge circuit, including a control circuit and a discharge circuit, wherein:

The control circuit is used to control the switch state of the discharge circuit;

The discharge circuit is used to discharge the charge accumulated on the filter capacitor.

In some feasible implementation manners, the control circuit includes a 555 chip, a switch, a first capacitor, a second capacitor and a second resistor, wherein:

The first pin and the fifth pin of the 555 chip are grounded, the second pin is connected to the ground after the switch is connected in series, the third pin is connected to the discharge circuit, the fourth pin is connected to the eighth pin, Its common node is connected in series with the first capacitor and grounded, the sixth pin is connected to the seventh pin, and its common node is connected to an external DC power supply through the second resistor;

One end of the second capacitor is connected to the common node of the sixth pin and the seventh pin of the 555 chip, and the other end is grounded;

The common node of the second resistor and the external DC power supply is connected to the common node of the fourth pin and the eighth pin of the 555 chip.

In some feasible implementation manners, the bleeder circuit includes a third resistor, a MOS transistor and a filter capacitor, wherein:

One end of the third resistor is connected to the external DC power supply, and the other end is connected to the drain of the MOS transistor;

The gate of the MOS transistor is connected to the third pin of the 555 chip, and the source is grounded;

One end of the filter capacitor is connected to the external DC power supply, and the other end is grounded.

In some feasible implementation manners, a first resistor is connected between the second resistor and the external DC power supply.

In some feasible implementation manners, a Zener diode is connected in parallel across the first capacitor.

In some feasible implementation manners, a third capacitor is connected between the fifth pin of the 555 chip and the common node between the fifth pin and the first pin;

In some feasible implementation manners, the MOS transistor is an N-channel enhancement type MOS transistor.

Implementing the embodiment of the present invention has the following advantages or beneficial effects:

The filter capacitor discharge circuit in the embodiment of the present invention includes a control circuit and a discharge circuit, wherein the control circuit includes a 555 chip, a switch, a first capacitor, a second capacitor, and a second resistor; the discharge circuit includes a third Resistors, MOS tubes and filter capacitors. When the external DC power supply is powered off, pressing the switch can trigger the 555 chip, so that the 555 chip is in a temporary stable state, and the third pin outputs a high level, which further causes the MOS tube to be turned on. The filter capacitor can be discharged through the third resistor and the MOS transistor to release the accumulated charge. When the external DC power supply is normally powered, the 555 chip is in the reset state, and the third pin outputs a low level, so that the MOS tube is not turned on, and the discharge circuit does not work at this time, which does not affect the operation of the whole machine circuit. normal operation.

It can be seen that, by adopting the present invention, after the external DC power supply is cut off, the charge accumulated on the filter capacitor can be quickly discharged, so as to protect the safety of the maintenance personnel and the circuit of the whole machine.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. For those skilled in the art, other drawings can also be obtained according to these drawings without any creative effort.

FIG. 1 is a schematic diagram of the structural composition of an embodiment of the filter capacitor discharge circuit of the present invention.

FIG. 2 is a circuit connection schematic diagram of an embodiment of the filter capacitor discharge circuit of the present invention.

FIG. 3 is a circuit connection schematic diagram of another embodiment of the filter capacitor discharge circuit of the present invention.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

Please refer to FIG. 1 , which is a schematic structural composition diagram of an embodiment of the filter capacitor discharge circuit of the present invention. As shown in Figure 1, the filter capacitor discharge circuit of the present invention includes a control circuit 1 and a discharge circuit 2, wherein the control circuit 1 is used to control the switching state of the discharge circuit 2; the discharge circuit 2 is used to discharge The charge accumulated on the filter capacitor.

Please refer to FIG. 2 , which is a circuit connection schematic diagram of an embodiment of the filter capacitor discharge circuit of the present invention. As shown in Figure 2, the control circuit 1 includes a 555 chip, a switch S1, a first capacitor C1, a second capacitor C2 and a second resistor R2, wherein: the first pin and the fifth pin of the 555 chip are grounded, and the second pin The pin is connected in series with the switch S1 and grounded, the third pin is connected to the discharge circuit 2, the fourth pin is connected to the eighth pin, its common node is connected in series with the first capacitor C1 and then grounded, the sixth pin is connected to the seventh pin The common node is connected to the external DC power supply VCC through the second resistor R2; one end of the second capacitor C2 is connected to the common node of the sixth pin and the seventh pin of the 555 chip, and the other end is grounded; the second resistor R2 is connected to the external DC power supply. The common node of the power supply VCC is connected to the common node of the fourth pin and the eighth pin of the 555 chip. Specifically, the first pin, the second pin, the third pin, the fourth pin, the fifth pin, the sixth pin, the seventh pin and the eighth pin of the 555 chip are respectively Pin 1, Pin 2, Pin 3, Pin 4, Pin 5, Pin 6, Pin 7, Pin 8. The discharge circuit 2 includes a third resistor R3, a MOS transistor Q1 and a filter capacitor C4, wherein: one end of the third resistor R3 is connected to the external DC power supply VCC, and the other end is connected to the drain of the MOS transistor Q1; the gate of the MOS transistor Q1 is connected to the 555 Pin 3 of the chip, the source is grounded; one end of the filter capacitor C4 is connected to the external DC power supply VCC, and the other end is grounded.

In a specific implementation, the MOS transistor Q1 is an N-channel enhancement type MOS transistor. In order to be able to withstand the large current from the filter capacitor C4, the third resistor R3 should be a high-power resistor, and the MOS transistor Q1 should be a MOS transistor with a larger maximum withstand current.

Please refer further to FIG. 3 , which is a circuit connection schematic diagram of an embodiment of the filter capacitor discharge circuit of the present invention. As shown in FIG. 3 , in some feasible implementation manners, on the basis of the circuit in FIG. 2 , one or more of the following circuit structures may also be included.

1. A first resistor R1 is connected between the second resistor R2 and the external DC power supply VCC. The first resistor R1 is used for voltage division, so that the 555 chip can work at a suitable voltage.

2. A Zener diode D1 is connected in parallel with both ends of the first capacitor C1; the Zener diode D1 is used to control the voltage at both ends of the first capacitor C1, so that the pin 4 and pin 8 of the 555 chip work at an appropriate voltage.

3. A third capacitor C3 is connected between pin 5 of the 555 chip and the common node between pin 5 and pin 1; the third capacitor C3 is a filter capacitor for preventing the 555 chip from being interfered by clutter.

In specific implementation, the working principle of the circuit in the embodiment of the present invention is roughly as follows:

When the external DC power supply VCC is powered off, press the switch S1 to trigger the 555 chip, so that the 555 chip is in a temporary steady state, and the pin 3 of the 555 chip outputs a high level, which further leads to the conduction of the MOS transistor Q1. At this time, the filter The capacitor C4 can be discharged through the third resistor R3 and the MOS transistor Q1 to discharge the accumulated charge.

When the external DC power supply VCC is normally powered, the 555 chip is in the reset state, and the pin 3 outputs a low level, so that the MOS transistor Q1 is not turned on, and the discharge circuit 2 does not work at this time, which does not affect the normal operation of the whole circuit.

The implementation methods described above do not limit the protection scope of the technical solution. Any modifications, equivalent replacements and improvements made within the spirit and principles of the above embodiments shall be included in the protection scope of the technical solution.

Claims (7)

1. A filter capacitor discharge circuit, characterized in that, comprises a control circuit and a discharge circuit, wherein: The control circuit is used to control the switch state of the discharge circuit; The discharge circuit is used to discharge the charge accumulated on the filter capacitor. 2. The filter capacitor discharge circuit according to claim 1, wherein the control circuit comprises a 555 chip, a switch, a first capacitor, a second capacitor and a second resistor, wherein: The first pin and the fifth pin of the 555 chip are grounded, the second pin is connected to the ground after the switch is connected in series, the third pin is connected to the discharge circuit, the fourth pin is connected to the eighth pin, Its common node is connected in series with the first capacitor and grounded, the sixth pin is connected to the seventh pin, and its common node is connected to an external DC power supply through the second resistor; One end of the second capacitor is connected to the common node of the sixth pin and the seventh pin of the 555 chip, and the other end is grounded; The common node of the second resistor and the external DC power supply is connected to the common node of the fourth pin and the eighth pin of the 555 chip. 3. The filter capacitor discharge circuit according to claim 1, wherein the discharge circuit comprises a third resistor, a MOS tube and a filter capacitor, wherein: One end of the third resistor is connected to the external DC power supply, and the other end is connected to the drain of the MOS transistor; The gate of the MOS transistor is connected to the third pin of the 555 chip, and the source is grounded; One end of the filter capacitor is connected to the external DC power supply, and the other end is grounded. 4. The filter capacitor discharge circuit according to claim 1, wherein a first resistor is connected between the second resistor and the external DC power supply. 5 . The filter capacitor discharge circuit according to claim 1 , wherein a Zener diode is connected in parallel at both ends of the first capacitor. 5 . 6. The filter capacitor discharge circuit according to claim 1, wherein a third capacitor is connected between the fifth pin of the 555 chip and the common node between the fifth pin and the first pin. 7. The filter capacitor discharge circuit according to claim 1-6, wherein the MOS transistor is an N-channel enhancement type MOS transistor.