CN213693456U

CN213693456U - Filter circuit

Info

Publication number: CN213693456U
Application number: CN202022190327.3U
Authority: CN
Inventors: 吴朝勇; 吴沛; 王小亮
Original assignee: Mornsun Guangzhou Science and Technology Ltd
Current assignee: Mornsun Guangzhou Science and Technology Ltd
Priority date: 2020-09-29
Filing date: 2020-09-29
Publication date: 2021-07-13
Anticipated expiration: 2030-09-29

Abstract

The utility model discloses a filter circuit, including electric capacity C1, electric capacity C2, relay RY1, switch tube Q1, switch tube Q2, switch tube Q3, resistance R1, resistance R2, voltage detection control circuit 102 is provided with first default, when detecting that input voltage is less than first default, input voltage charges for C2 electric capacity through resistance R1 when giving electric capacity C1 charging, relay RY1 switches on simultaneously, because relay RY1 itself has the time delay, so resistance R1 and electric capacity C2 series charging when starting, the impulse current problem when starting can be solved, avoid switch tube Q1 to damage, end when relay RY1 time delay, relay RY1 actuation back, resistance R1 is by the short circuit, can reduce the consumption when the circuit maintains like this, realize energy-saving effect.

Description

Filter circuit

Technical Field

The utility model relates to a switching power supply rectification filtering field especially relates to wide voltage input's rectification filter circuit.

Background

In both industrial and civil fields, it is often necessary to rectify ac power from various power grids into dc power, and in order for a switching power supply to meet global grid standards, it is necessary to design the input voltage of the switching power supply to meet the wide-range input voltage requirement.

In general, for various electrical apparatuses with power less than 75w, the internal rectifying and filtering circuits still adopt the topology of the common rectifying circuit plus the filtering circuit, as shown in fig. 1. In many industries, such as the power industry, there is a need for a switching power supply with an input voltage as wide as 85VAC to 460VAC or even 85VAC to 850VAC, and the selection of the filter capacitor for such demanding wide-voltage input switching power supply is a problem that is confusing to designers. For products with 85VAC-850VAC input, the range of rectified direct current voltage is about 120VDC-1200VDC, and at least 3 capacitors with withstand voltage of 450V need to be connected in series to meet the circuit requirement. Since a filter capacitor with a large capacity is needed when the low voltage 85VAC is input, once the capacitor is determined, when the input voltage is high, the capacity of the capacitor is too large, which causes unnecessary waste. Therefore, for various electrical equipment used in a wide voltage input range, the internal rectifying and filtering circuits still adopt the topology of a common rectifying circuit and a filtering circuit, and the existing filtering circuit has the defects of high cost and large occupied space.

Therefore, a filter circuit capable of avoiding this problem is proposed in "a filter circuit" under publication No. 201210303821.3, and its functional block diagram is shown in fig. 2. The voltage detection control circuit 102 is provided with a first preset value, and when the direct current input voltage is detected to be smaller than the first preset value, the switch K1 is controlled to be switched on, and the capacitor C1 is connected with the capacitor C2 in parallel, so that the total capacity of the capacitor in the filter circuit is increased; when the direct current input voltage is detected to be above a first preset value, the switch K1 is controlled to be switched off, and the filter capacitor is only the capacitor C1. The capacitor C2 can be a low-voltage large-capacity capacitor, and the capacitor C1 can be a high-voltage small-capacity capacitor, so that resource waste is avoided, space is saved, and cost is saved. However, the filter circuit has the disadvantage that in the startup phase, where K1 is a switch tube, when the switch tube K1 is turned on, due to the virtual short of the startup transient capacitance, the surge current will flow through the switch tube K1, and the switch tube K1 is easily damaged, or in the case of large surge current caused by lightning surge, large input voltage fluctuation, etc., such problems will occur. Therefore, the switch tube K1 needs to select high-voltage large current, the cost of the switch tube for high-voltage large current is high, and compared with the common scheme, the filter circuit scheme has no cost advantage.

SUMMERY OF THE UTILITY MODEL

In view of this, the utility model aims at providing a filter circuit, both solved under wide pressure input range, current filter circuit exists with high costs, and occupation space is big problem can be solved again and impact current causes the insecure problem of circuit.

The utility model aims at realizing through the following technical scheme:

the first technical scheme is that the filter circuit is applied to a switching power supply under a wide-voltage input range, and is characterized in that: the device comprises a capacitor C1, a capacitor C2, a relay RY1, a MOS tube Q1, a triode Q2, a triode Q3, a resistor R1, a resistor R2 and a voltage detection control circuit (102);

the input port Vin is connected with a first output end of a relay RY1, one end of a resistor R1 and one end of a capacitor C1, the other end of the resistor R1 is connected with a second output end of the relay RY1 and one end of a capacitor C2, the other end of the capacitor C2 is connected with a drain electrode of a MOS tube Q1, a grid electrode of the MOS tube Q1 is connected with a collector electrode of a triode Q2, a base electrode of a triode Q3 and one end of a resistor R2, the other end of the resistor R2 and a collector electrode of a triode Q3 are connected with a power supply circuit port VC, an emitter electrode of a triode Q3 is connected with an input end of the relay RY1, a base electrode of a triode Q2 is connected with a voltage detection control circuit (102), and an emitter electrode of a triode Q35.

The second technical scheme is that the filter circuit is applied to a switching power supply under a wide-voltage input range, and is characterized in that: the device comprises a capacitor C1, a capacitor C2, a relay RY1, a MOS tube Q1, a triode Q2, a triode Q3, a MOS tube Q4, a diode D1, a diode D2, a resistor R1, a resistor R2, a resistor R3 and a voltage detection control circuit (102);

the input port Vin is connected with a first output end of a relay RY1, one end of a resistor R3, one end of a resistor R1 and one end of a capacitor C1, the other end of the resistor R1 is connected with a second output end of the relay RY1 and one end of the capacitor C2, the other end of the capacitor C2 is connected with a drain electrode of a MOS tube Q4, a source electrode of the MOS tube Q4 is connected with a drain electrode of the MOS tube Q1 and an anode electrode of a diode D1, a grid electrode of the MOS tube Q1 is connected with a collector electrode of a triode Q2, a base electrode of a triode Q3 and one end of a resistor R2, the other end of the resistor R2 and a collector electrode of a triode Q3 are connected with a power supply circuit port VC, an emitter electrode of the triode Q3 is connected with an input end of the relay RY1, a base electrode of the, the cathode of the diode D1 and the gate of the MOS transistor Q4, the emitter of the transistor Q2, the anode of the diode D2, the source of the MOS transistor Q1, and the other end of the capacitor C1 are commonly grounded. According to the scheme, the main power is divided by 2 MOS tubes, so that the problem of high cost caused by the adoption of a high-voltage tube can be avoided.

The third technical scheme is that the filter circuit is applied to a switching power supply under a wide-voltage input range, and is characterized in that: the voltage detection circuit comprises a capacitor C1, a capacitor C2, a relay PY1, an MOS tube Q1, a triode Q2, a triode Q3, a resistor R1, a resistor R2, a resistor R4, a resistor R5, a resistor R6, a resistor R7, a resistor R8, a voltage-stabilizing source U1, a voltage-stabilizing source U2, a diode D3 and a voltage detection control circuit (102);

an input port Vin is connected with a first output end of a relay RY1, one end of a resistor R1 and one end of a capacitor C1, the other end of a resistor R1 is connected with a second output end of the relay RY1 and one end of a capacitor C2, the other end of a capacitor C2 is connected with a drain electrode of a MOS transistor Q1, a gate electrode of the MOS transistor Q1 is connected with an anode electrode of a diode D3, a collector electrode of a triode Q2, a base electrode of a triode Q3 and one end of a resistor R2, a source electrode of the MOS transistor Q2 is connected with one end of the resistor R2 and one end of the resistor R2, the other end of the resistor R2 is connected with a sampling end and an output end of a voltage stabilizing source U2 and one end of the resistor R2, a cathode electrode of the diode D2 is connected with one end of the resistor R2 and the output end of the voltage stabilizing source U2, the other end of the resistor R2, the, the emitter of the triode Q3 is connected with the input end of the relay RY1, the base of the triode Q2 is connected with the voltage detection control circuit (102), and the emitter of the triode Q2, the input end of the voltage stabilizing source U1, the other end of the resistor R4, the other end of the capacitor C1 are grounded and the input end of the voltage stabilizing source U2 are grounded together. The scheme can solve the problem that the MOS transistor Q1 is damaged due to large power grid voltage fluctuation.

The fourth technical scheme is that the filter circuit is applied to a switching power supply under a wide-voltage input range, and is characterized in that: the voltage detection circuit comprises a capacitor C1, a capacitor C2, a relay PY1, an MOS tube Q1, a triode Q2, a triode Q3, an MOS tube Q4, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a resistor R6, a resistor R7, a resistor R8, a voltage stabilizing source U1, a voltage stabilizing source U2, a diode D1, a diode D2, a diode D3 and a voltage detection control circuit (102);

an input port Vin is connected with a first output end of a relay RY1, one end of a resistor R3, one end of a resistor R1 and one end of a capacitor C1, the other end of a resistor R1 is connected with a second output end of a relay RY1 and one end of a capacitor C2, the other end of a capacitor C2 is connected with a drain electrode of a MOS tube Q4, a source electrode of the MOS tube Q4 is connected with a drain electrode of the MOS tube Q4 and an anode electrode of a diode D4, a gate electrode of the MOS tube Q4 is connected with an anode electrode of the diode D4, a collector electrode of a triode Q4, a base electrode of the triode Q4 and one end of the resistor R4, a source electrode of the MOS tube Q4 is connected with one end of the resistor R4 and one end of the resistor R4, the other end of the resistor R4 is connected with a sampling end of a voltage stabilizing source U4 and one end of the resistor R4, a cathode electrode of the diode D4 is connected with one end of the voltage stabilizing source R4 and one end of the voltage, The other end of the resistor R8, the other end of the resistor R2 and the collector of the triode Q3 are connected with a power supply circuit port VC, the emitter of the triode Q3 is connected with the input end of the relay RY1, the base of the triode Q2 is connected with the voltage detection control circuit (102), the other end of the resistor R3 is connected with the cathode of the diode D2, the cathode of the diode D1 and the grid of the MOS tube Q4, the emitter of the triode Q2, the input end of the voltage stabilizing source U1, the anode of the diode D2, the other end of the resistor R4, the other end of the capacitor C1, and the input end of the voltage stabilizing source U2. The scheme can solve the problem that the MOS transistor Q1 is damaged due to large voltage fluctuation of a power grid, and can use the low-voltage tube to save cost.

Preferably, in the above technical solution, the diode D1 and the diode D2 are zener diodes.

The utility model discloses a theory of operation can combine specific embodiment to carry out the detailed description at the back, and the here is not repeated, compares with prior art, the utility model discloses following beneficial effect has:

1. the capacity of a filter capacitor in the access circuit can be adjusted by controlling the on and off of the MOS transistor Q1, and the appropriate filter capacity can be provided for input voltages in different voltage ranges, so that the circuit is suitable for wide-voltage input of alternating current or photovoltaic direct current input occasions, and the circuit cost is effectively reduced;

2. the resistor R1 is connected in series in the branch of the MOS transistor Q1, so that the problem caused by impact current can be effectively solved, and the resistor R1 is short-circuited by the relay RY1 after the start is finished, so that the efficiency of the circuit is ensured, and the circuit has higher practicability;

3. through the utility model discloses the circuit can reduce input filter capacitance's quantity to reduce the circuit volume, practiced thrift the area of circuit board.

Drawings

FIG. 1 is a circuit diagram of a conventional bridge rectifier filter;

FIG. 2 is a block diagram of a filter circuit suitable for wide voltage input;

fig. 3 is a schematic diagram of a first embodiment of a filter circuit according to the present invention;

fig. 4 is a schematic diagram of a second embodiment of a filter circuit according to the present invention;

fig. 5 is a schematic diagram of a third embodiment of a filter circuit according to the present invention;

fig. 6 is a schematic diagram of a fourth embodiment of the filter circuit of the present invention.

Detailed Description

First embodiment

Fig. 3 is a schematic diagram of a filter circuit according to a first embodiment of the present invention, the circuit of which includes a capacitor C1, a capacitor C2, a relay RY1, a MOS transistor Q1, a transistor Q2, a transistor Q3, a resistor R1, a resistor R2, and a voltage detection control circuit 102;

the connection relationship is as follows:

the input port Vin is connected with a first output end of a relay RY1, one end of a resistor R1 and one end of a capacitor C1, the other end of the resistor R1 is connected with a second output end of the relay RY1 and one end of a capacitor C2, the other end of the capacitor C2 is connected with a drain electrode of an MOS tube Q1, a grid electrode of the MOS tube Q1 is connected with a collector electrode of a triode Q2, a base electrode of a triode Q3 and one end of a resistor R2, the other end of the resistor R2 and a collector electrode of a triode Q3 are connected with a power supply circuit port VC, an emitter electrode of a triode Q3 is connected with an input end of the relay RY1, a base electrode of a triode Q2 is connected with the voltage detection control circuit 102, and an emitter electrode of a triode Q35.

The working principle of the filter circuit of the embodiment is as follows:

the input port Vin is connected with the rectified input positive voltage, the voltage detection control circuit 102 is provided with a first preset value, and when the input voltage is smaller than the first preset value, the voltage detection control circuit 102 outputs a low level, namely the base of the triode Q2 is at the low level, which is not enough to conduct the triode Q2; meanwhile, the power supply circuit supplies power to the MOS tube Q1 and the triode Q3, the MOS tube Q1 and the triode Q3 are conducted, and when the MOS tube Q1 is conducted, due to the fact that the conducting resistance of the MOS tube Q1 is small, the resistor R1 is connected with the capacitor C2 in series and then connected with the capacitor C1 in parallel to filter the rectifying circuit. At this time, the existence of the resistor R1 is important, so that the impact current can be suppressed, and the MOS transistor Q1 is prevented from being damaged, but if the resistor R1 exists for a long time, the loss of the circuit is serious, so that the branch of the relay RY1 is added, and the resistor R1 can be short-circuited; the triode Q3 and the MOS tube Q1 are conducted almost simultaneously, the input end of the relay RY1 is in a high level, the time delay is generally more than 1ms due to the fact that the attraction of the relay RY1 exists, after the time delay, the relay RY1 attracts, the resistor R1 is in a short circuit, and the power consumption of the circuit is reduced.

When the input voltage is greater than the first preset value, the voltage detection control circuit 102 outputs a high level, the triode Q2 is switched on, the gate voltage of the MOS transistor Q1 is pulled low, the MOS transistor Q1 is cut off, meanwhile, the base voltage of the triode Q3 is also pulled low, and the triode Q3 is cut off; when the MOS transistor Q1 is turned off, the capacitor C2 does not function in the circuit, and only the capacitor C1 filters the rectifier circuit.

The capacitor C1 is a small-capacity high-withstand-voltage capacitor, and is generally composed of a plurality of capacitors connected in series. For example, assuming that the input voltage is up to 1200VDC, the capacitor C1 needs to be composed of 3 capacitors of 450V in series, and the capacitor C2 has a large capacity and a lower withstand voltage than the capacitor C1. In general, the first preset value is set to be slightly lower than the nominal withstand voltage of the capacitor C2.

Generally, a port Vc of a power supply circuit is connected with a relatively low-voltage point of a starting circuit, the input voltage is less than the withstand voltage of a grid electrode of an MOS tube Q1 and a base electrode of a triode Q3, if the voltage of the port Vc of the power supply circuit is greater than the withstand voltage of the grid electrode of an MOS tube Q1 and the base electrode of the triode Q3, a voltage stabilizing tube needs to be added to the base electrode of the triode Q3 to be connected to the negative end of a filter circuit, and the MOS tube Q1 and the triode Q3.

Second embodiment

As shown in fig. 4, a schematic diagram of a filter circuit according to a second embodiment of the present invention is different from the first embodiment in that: MOS pipe Q4, resistance R3, diode D1, diode D2 have been increased.

The connection relationship is as follows:

the input port Vin is connected with a first output end of a relay RY1, one end of a resistor R3, one end of a resistor R1 and one end of a capacitor C1, the other end of the resistor R1 is connected with a second output end of the relay RY1 and one end of the capacitor C2, the other end of the capacitor C2 is connected with a drain electrode of a MOS tube Q4, a source electrode of the MOS tube Q4 is connected with a drain electrode of the MOS tube Q1 and an anode electrode of a diode D1, a grid electrode of the MOS tube Q1 is connected with a collector electrode of a triode Q2, a base electrode of a triode Q3 and one end of a resistor R2, the other end of the resistor R2 and a collector electrode of a triode Q3 are connected with a power supply circuit port VC, an emitter electrode of the triode Q3 is connected with an input end of the relay RY1, a base electrode of the, the cathode of the diode D1 and the gate of the MOS transistor Q4, the emitter of the transistor Q2, the anode of the diode D2, the source of the MOS transistor Q1, and the other end of the capacitor C1 are commonly grounded.

The difference between the operating principle of the filter circuit of this embodiment and the first embodiment is:

because of the existence of the diode D2, the gate potential of the MOS transistor Q4 remains unchanged, when the MOS transistor Q1 is turned on, the anode voltage of the diode D1 is pulled low, which causes the gate-source voltage of the MOS transistor Q4 to gradually increase, and when the voltage increases to the conduction threshold of the MOS transistor Q4, the MOS transistor Q4 is turned on, and the resistor R1 is connected in series with the capacitor C2 and then connected in parallel with the capacitor C1, so as to filter the rectifier circuit together. When the MOS transistor Q1 is turned off, the voltage at the anode of the diode D1 is raised, and the gate potential of the MOS transistor Q4 is unchanged, so that the gate-source voltage of the MOS transistor Q4 is reduced, and when the gate-source voltage is reduced to the turn-off threshold of the MOS transistor Q4, the MOS transistor Q4 is turned off.

In general, the diodes D1 and D2 are zener diodes.

The second embodiment is the improved circuit of the first embodiment, can realize soft start, soft shutoff, and the make-and-break process is smooth and transitional to can let MOS pipe Q1's lectotype easier, for the product of 1200VDC input, MOS pipe Q1 and MOS pipe Q4 can select for use the ordinary 650V withstand voltage MOS pipe on the market, can solve the high-voltage tube problem with high costs. The operation principle of the other circuits is the same as that of the first embodiment, and will not be described repeatedly.

Third embodiment

As shown in fig. 5, a schematic diagram of a filter circuit according to a third embodiment of the present invention is different from the first embodiment in that: an over-current detection circuit is additionally arranged and comprises a resistor R4, a resistor R5, a resistor R6, a resistor R7, a resistor R8, a voltage regulator U1, a voltage regulator U2 and a diode D3.

The connection relationship is as follows:

an input port Vin is connected with a first output end of a relay RY1, one end of a resistor R1 and one end of a capacitor C1, the other end of a resistor R1 is connected with a second output end of the relay RY1 and one end of a capacitor C2, the other end of a capacitor C2 is connected with a drain electrode of a MOS transistor Q1, a gate electrode of the MOS transistor Q1 is connected with an anode electrode of a diode D3, a collector electrode of a triode Q2, a base electrode of a triode Q3 and one end of a resistor R2, a source electrode of the MOS transistor Q2 is connected with one end of the resistor R2 and one end of the resistor R2, the other end of the resistor R2 is connected with a sampling end and an output end of a voltage stabilizing source U2 and one end of the resistor R2, a cathode electrode of the diode D2 is connected with one end of the resistor R2 and the output end of the voltage stabilizing source U2, the other end of the resistor R2, the, the emitter of the triode Q3 is connected with the input end of the relay RY1, the base of the triode Q2 is connected with the voltage detection control circuit (102), and the emitter of the triode Q2, the input end of the voltage stabilizing source U1, the other end of the resistor R4, the other end of the capacitor C1 are grounded and the input end of the voltage stabilizing source U2 are grounded together.

typically, voltage regulator U1 and voltage regulator U2 are both TL 431. Since the regulator U2 is equivalent to providing a bias voltage to the regulator U1, the reference voltage value set by the regulator U2 is higher than the reference voltage value set by the regulator U1.

When the input voltage Vin of the filter circuit is switched from a lower voltage to a lower voltage, the input voltage does not reach the first preset value of the voltage detection control circuit, the MOS transistor Q1 is in a conducting state, and voltages at two ends of the capacitor C1 and the capacitor C2 rise along with the rise of the input voltage, so that the charging current flowing into the capacitor C2 is increased, the current of the MOS transistor Q1 connected in series is increased, and the thermal breakdown of the MOS transistor Q1 may be caused. Therefore, the overcurrent detection circuit is added in the embodiment, the current value of the overcurrent detection circuit can be set by adjusting the reference values set by the resistor R4, the resistor R5, the resistor R6 and the resistor R7 and matching with the chip U1 and the voltage regulator U2, and the value is generally set to be close to the maximum impact current value of the MOS tube Q1. When the current value flowing through the MOS tube Q1 is larger than the value set by the overcurrent detection circuit, the source voltage of the MOS tube Q1 is increased, so that the voltage of the sampling end of the voltage-stabilizing source U1 is higher than the reference voltage value of the voltage-stabilizing source U1, according to the characteristics of TL431, the voltage of the output end of the voltage-stabilizing source U1 is pulled down, therefore, the diode D3 is conducted, the grid voltage of the MOS tube Q1 is pulled down, the MOS tube Q1 is cut off, and the MOS tube Q1 is prevented from being damaged due to overlarge current.

In this embodiment, the added overcurrent detection circuit can better protect the MOS transistor Q1, and avoid the increase of the current flowing through the MOS transistor Q1 due to the large fluctuation of the grid voltage, so that the circuit has higher practicability, and the working principle of other circuits is consistent with that of the first embodiment and will not be described in detail.

In practical use, the filter circuit may be used in combination with the second embodiment and the present embodiment.

Fourth embodiment

Fig. 6 is a schematic diagram of a filter circuit according to a fourth embodiment of the present invention. The circuit of the second embodiment and the circuit of the third embodiment are combined in this embodiment, and the working principle is the same as that of the previous embodiment, which is not described in detail. This implementation both can use the low-voltage switch tube to practice thrift the cost, also can solve because of the grid voltage undulant great problem that causes MOS pipe Q1 to damage.

The above is only a preferred embodiment of the present invention, and it should be noted that the above preferred embodiment should not be considered as limiting the present invention, and the protection scope of the present invention should be subject to the scope defined by the claims. It will be apparent to those skilled in the art that various modifications and enhancements can be made without departing from the spirit and scope of the invention, and such modifications and enhancements are intended to be within the scope of the invention.

Claims

1. A filter circuit is applied to a switching power supply under a wide voltage input range, and is characterized in that: the device comprises a capacitor C1, a capacitor C2, a relay RY1, a MOS tube Q1, a triode Q2, a triode Q3, a resistor R1, a resistor R2 and a voltage detection control circuit (102);

2. A filter circuit is applied to a switching power supply under a wide voltage input range, and is characterized in that: the device comprises a capacitor C1, a capacitor C2, a relay RY1, a MOS tube Q1, a triode Q2, a triode Q3, a MOS tube Q4, a diode D1, a diode D2, a resistor R1, a resistor R2, a resistor R3 and a voltage detection control circuit (102);

3. A filter circuit is applied to a switching power supply under a wide voltage input range, and is characterized in that: the voltage detection circuit comprises a capacitor C1, a capacitor C2, a relay PY1, an MOS tube Q1, a triode Q2, a triode Q3, a resistor R1, a resistor R2, a resistor R4, a resistor R5, a resistor R6, a resistor R7, a resistor R8, a voltage-stabilizing source U1, a voltage-stabilizing source U2, a diode D3 and a voltage detection control circuit (102);

4. A filter circuit is applied to a switching power supply under a wide voltage input range, and is characterized in that: the voltage detection circuit comprises a capacitor C1, a capacitor C2, a relay PY1, an MOS tube Q1, a triode Q2, a triode Q3, an MOS tube Q4, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a resistor R6, a resistor R7, a resistor R8, a voltage stabilizing source U1, a voltage stabilizing source U2, a diode D1, a diode D2, a diode D3 and a voltage detection control circuit (102);

an input port Vin is connected with a first output end of a relay RY1, one end of a resistor R3, one end of a resistor R1 and one end of a capacitor C1, the other end of a resistor R1 is connected with a second output end of a relay RY1 and one end of a capacitor C2, the other end of the capacitor C2 is connected with a drain electrode of a MOS tube Q2, a source electrode of the MOS tube Q2 is connected with a drain electrode of the MOS tube Q2 and an anode electrode of a diode D2, a gate electrode of the MOS tube Q2 is connected with an anode electrode of the diode D2, a collector electrode of a triode Q2, a base electrode of the triode Q2 and one end of the resistor R2, a source electrode of the MOS tube Q2 is connected with one end of the resistor R2 and one end of the resistor R2, the other end of the resistor R2 is connected with a sampling end of a voltage stabilizing source U2 and one end of the resistor R2, a cathode electrode of the diode D2 is connected with one end of the voltage stabilizing source R2 and one end of the voltage stabilizing source U2, and, The other end of the resistor R2 and the collector of the triode Q3 are connected with a power supply circuit port VC, the emitter of the triode Q3 is connected with the input end of the relay RY1, the base of the triode Q2 is connected with the voltage detection control circuit (102), the other end of the resistor R3 is connected with the cathode of the diode D2, the cathode of the diode D1 and the grid of the MOS tube Q4, the emitter of the triode Q2, the input end of the voltage stabilizing source U1, the anode of the diode D2, the other end of the resistor R4, the other end of the capacitor C1 and the input end of the voltage stabilizing source U2 are grounded together.

5. A filter circuit according to claim 2 or 4, wherein: the diode D1 and the diode D2 are voltage stabilizing diodes.