CN219592383U - Active filter circuit and filter - Google Patents

Abstract

The utility model relates to an active filter circuit and a filter, wherein the active filter circuit comprises a first filter stabilizing unit, a voltage drop unit and a transistor Q; the input end of the first filtering stabilizing unit is respectively connected with a power supply and the collector electrode of the transistor Q; the output end of the first filtering stabilizing unit is connected with the input end of the voltage drop unit; the output end of the voltage drop unit is connected with the base electrode of the transistor Q; the voltage drop unit is used for increasing the voltage drop between the transistor emitter and the first filtering stabilizing unit when the voltage drop unit is in a conducting state; the emitter of the transistor Q outputs a target voltage. The utility model solves the problem of poor stability of the output target voltage, and improves the peak-peak value of the voltage harmonic wave which can be filtered by the active filter circuit, thereby enhancing the filtering effect of the active filter circuit and improving the stability of the output target voltage of the active filter circuit.

Description

Active filter circuit and filter

Technical Field

The present utility model relates to the field of voltage signal filtering technologies, and in particular, to an active filter circuit and a filter.

Background

In an actual industrial production scenario, high-power devices in the circuit can generate noise signals such as harmonic disturbance. The filter can effectively filter the noise frequency in the power line and isolate useful signals from useless noise in the circuit, so that the anti-interference performance and the signal-to-noise ratio of the circuit signals are improved.

At present, a filter circuit is typically designed by adopting a filter circuit formed by capacitance and inductance, such as a common LC type filter circuit or pi type filter circuit. However, such a filter circuit has a problem that the stability of the output target voltage is poor because of the lack of a voltage stabilizing function.

Aiming at the problem that the stability of the output target voltage is poor due to the fact that a filtering circuit in the related technology has no voltage stabilizing function, no effective solution is proposed at present.

Disclosure of Invention

In view of the foregoing, it is necessary to provide an active filter circuit and a filter for solving at least the problem of poor stability of the output target voltage in the related art.

In a first aspect, the present utility model provides an active filter circuit, including a first filter stabilizing unit, a voltage drop unit, and a transistor Q;

the input end of the first filtering stabilizing unit is respectively connected with a power supply and the collector electrode of the transistor Q; the output end of the first filtering stabilizing unit is connected with the input end of the voltage drop unit;

the output end of the voltage drop unit is connected with the base electrode of the transistor Q, and the voltage drop unit is used for providing a target resistance when the voltage drop unit is in a conducting state;

the emitter of the transistor Q outputs a target voltage.

In some of these embodiments, the first filter stabilization unit includes a resistor R and a capacitor C1;

one end of the resistor R is connected with the power supply and the collector electrode of the transistor Q respectively; the other end of the resistor R is respectively connected with one end of the capacitor C1 and the input end of the voltage drop unit;

one end of the capacitor C1 is connected with the input end of the voltage drop unit; the other end of the capacitor C1 is grounded.

In some of these embodiments, the resistor R is a variable resistor.

In some embodiments, the pressure drop unit comprises a pressure drop subunit and a pressure drop expansion unit;

the input end of the voltage drop subunit is respectively connected with the other end of the resistor R and one end of the capacitor C1; the output end of the pressure drop subunit is connected with the input end of the pressure drop expansion unit;

the other end of the voltage drop expansion unit is connected with the base electrode of the transistor Q.

In some of these embodiments, the voltage drop subunit is a diode D1;

one end of the diode D1 is respectively connected with the other end of the resistor R and one end of the capacitor C1; the other end of the diode D1 is connected with the input end of the voltage drop expansion unit.

In some of these embodiments, the voltage drop expansion unit comprises at least one diode;

in some of these embodiments, the voltage drop unit is a diode D;

one end of the diode D is respectively connected with the other end of the resistor R and one end of the capacitor C1; the other end of the diode D is connected with the base electrode of the transistor Q.

In some of these embodiments, a second filtering unit is further included;

the input end of the second filtering unit is connected with the emitter of the transistor Q; and the output end of the second filtering unit outputs target voltage.

In some of these embodiments, the second filtering unit includes a magnetic bead B and a capacitor C2;

one end of the magnetic bead B is connected with the emitter end of the transistor Q; the other end of the magnetic bead B is connected with one end of the capacitor C2 and outputs target voltage;

one end of the capacitor C2 is connected with the target voltage output end, and the other end of the capacitor C2 is grounded.

In a second aspect, in this embodiment, there is provided an active filter, including the active filter circuit described in the first aspect;

the active filter outputs a stabilized target voltage when the voltage passes through the active filter circuit.

Compared with the related art, the active filter circuit and the filter provided in the embodiment comprise a first filter stabilizing unit, a voltage drop unit and a transistor Q; the input end of the first filtering stabilizing unit is respectively connected with a power supply and the collector electrode of the transistor Q; the output end of the first filtering stabilizing unit is connected with the input end of the voltage drop unit; the output end of the voltage drop unit is connected with the base electrode of the transistor Q; the voltage drop unit is used for providing voltage drop when the voltage drop unit is in conduction and providing stable voltage for the base electrode of the transistor Q; the emitter of the transistor Q outputs a target voltage. Through the cooperation of the first filtering stabilizing unit and the voltage drop unit, the peak-peak value of the voltage harmonic wave which can be filtered by the active filtering circuit is improved, so that the filtering effect of the active filtering circuit is enhanced, the stability of the output target voltage of the active filtering circuit is improved, and the problem of poor stability of the output target voltage is solved.

The details of one or more embodiments of the utility model are set forth in the accompanying drawings and the description below to provide a more thorough understanding of the other features, objects, and advantages of the utility model.

Drawings

The accompanying drawings, which are included to provide a further understanding of the utility model and are incorporated in and constitute a part of this specification, illustrate embodiments of the utility model and together with the description serve to explain the utility model and do not constitute a limitation on the utility model. In the drawings:

fig. 1 is a block diagram of an active filter circuit according to an embodiment of the present utility model;

fig. 2 is a schematic structural diagram of an active filter circuit according to an embodiment of the present utility model;

fig. 3 is a schematic structural diagram of an active filter circuit according to an embodiment of the present utility model;

fig. 4 is a schematic structural diagram of an active filter circuit according to an embodiment of the present utility model;

FIG. 5 is a block diagram of an active filter circuit according to an embodiment of the present utility model;

fig. 6 is a schematic structural diagram of an active filter circuit according to an embodiment of the present utility model;

fig. 7 is a schematic structural diagram of an active filter circuit applied to an analog op-amp circuit according to an embodiment of the present utility model;

fig. 8 is a schematic structural diagram of an active filter circuit applied to an ADC analog-to-digital sampling conversion circuit according to an embodiment of the present utility model;

fig. 9 is a schematic diagram of an active filter circuit applied to a radio receiving circuit according to an embodiment of the present utility model.

Fig. 10 is a schematic diagram of an active filter circuit applied to an analog op-amp circuit according to an embodiment of the present utility model;

fig. 11 is a schematic structural diagram of an active filter circuit applied to an ADC analog-to-digital sampling conversion circuit according to an embodiment of the present utility model;

fig. 12 is a schematic diagram of an active filter circuit applied to a radio receiving circuit according to an embodiment of the present utility model.

Reference numerals: 10. an active filter circuit; 11. a first filtering stabilization unit; 12. a pressure drop unit; 13. a second filtering unit; 20. an analog operational amplifier circuit; 30. an ADC analog-to-digital sampling conversion circuit; 40. a radio receiving circuit.

Detailed Description

The present utility model will be described and illustrated with reference to the accompanying drawings and examples in order to make the objects, technical solutions and advantages of the present utility model more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the utility model. All other embodiments, which can be made by a person of ordinary skill in the art based on the embodiments provided by the present utility model without making any inventive effort, are intended to fall within the scope of the present utility model. Moreover, it should be appreciated that while such a development effort might be complex and lengthy, it would nevertheless be a routine undertaking of design, fabrication, or manufacture for those of ordinary skill having the benefit of this disclosure, and thus should not be construed as having the benefit of this disclosure.

Reference in the specification to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the utility model. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. It is to be expressly and implicitly understood by those of ordinary skill in the art that the described embodiments of the utility model can be combined with other embodiments without conflict.

Unless defined otherwise, technical or scientific terms used herein should be given the ordinary meaning as understood by one of ordinary skill in the art to which this utility model belongs. When an element is referred to as being "disposed" on another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "disposed on" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "secured to" another element, it can be directly secured to the other element or intervening elements may also be present. The terms "first," "second," "third," and the like, as used herein, are merely distinguishing between similar objects and not representing a particular ordering of objects. The terminology used in the description of the utility model herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the utility model. The term "and/or" as used herein includes any and all combinations of one or more of the associated listed items.

In the present embodiment, an active filter circuit is provided, and fig. 1 is a circuit block diagram of the active filter circuit of the present embodiment, and as shown in fig. 1, the block diagram includes a first filter stabilizing unit 11, a voltage drop unit 12, and a transistor Q;

the input end of the first filtering stabilizing unit 11 is respectively connected with a power supply and the collector electrode of the transistor Q; the output end of the first filtering stabilizing unit 11 is connected with the input end of the voltage drop unit 12;

the output end of the voltage drop unit 12 is connected with the base electrode of the transistor Q, and the voltage drop unit 12 is used for increasing the voltage drop between the transistor emitter and the first filter stabilizing unit when the voltage drop unit 12 is in a conducting state;

the emitter of the transistor Q outputs a target voltage.

The power supply may be a built-in power supply or an external power supply. Preferably, the power supply may be a dc power supply, providing an input voltage to the active filter circuit. The first filtering stabilization unit 11 may be an RC filter circuit including a resistor and a capacitor, and the filtering function of the active filter circuit is mainly implemented by the unit; in other embodiments, the first filter stabilization unit 11 may be an LC type filter circuit, a pi type filter circuit, a multi-stage filter circuit, or the like, which is not limited thereto. The voltage drop unit 12 may include at least one diode or a diode combined with other voltage drop components to increase the voltage drop between the transistor emitter and the first filter stabilization unit and to increase the reverse voltage resistance of the active filter circuit; the transistor Q may be a triode or a field effect transistor, and the filtering effect of the active filtering circuit may be improved by using the current amplification characteristic of the triode or the voltage amplification characteristic of the field effect transistor.

If the first filter stabilization unit 11 is an RC filter circuit; the resistor provides charging current for the capacitor, the RC circuit has a low-pass filtering function by utilizing the characteristic of isolation and intersection of the capacitor, the filtering effect of the RC filtering circuit is related to the capacity of the capacitor, the capacitance is inversely related to the capacitance reactance, the capacity of the capacitor is higher when the capacitance reactance is smaller, and therefore the filtering effect is better when the capacitance is larger. When the current amplification coefficient of the transistor Q is beta, the current taken by the load from the capacitor C is 1/beta times of the load current by utilizing the current amplification characteristic of the transistor, which is equivalent to that the circuit amplifies the capacitor C by beta times, so that the filtering effect of the active filter circuit is improved.

In the prior art, the filter circuit consists of a capacitor and an inductor, and has no voltage stabilizing function. In this embodiment, by adding the voltage drop unit 12, a voltage drop of at least 0.4V-0.6V is provided, so that the peak-peak value of the voltage harmonic that can be filtered by the active filter circuit is improved, and the stability of the output target voltage of the active filter circuit is improved, thereby solving the problem of poor stability of the output target voltage.

The following describes the implementation of the first filter stabilization unit 11 in detail:

as shown in fig. 2, a schematic structural diagram of an active filter circuit according to a second embodiment of the present utility model is shown, wherein the first filter stabilizing unit 11 includes a resistor R and a capacitor C1;

one end of the resistor R is connected with a power supply and the collector electrode of the transistor Q respectively; the other end of the resistor R is respectively connected with one end of the capacitor C1 and the input end of the voltage drop unit 12;

one end of the capacitor C1 is connected with the input end of the voltage drop unit 12; the other end of the capacitor C1 is grounded.

It should be noted that the resistor R and the voltage drop unit 12 provide the base bias current for the transistor Q, and the resistor R is also a filter resistor. In other embodiments, R may be a variable resistor, and the filtering effect of the active filtering circuit is controlled by adjusting the resistance value of the variable resistor R. The capacitor C1 has a "cut-off ac" characteristic, with which a high-frequency signal can be filtered.

The current flowing through the resistor R is the base bias current of the transistor Q, and when the current passes through the capacitor C1, the capacitor C1 is equivalent to an open circuit for direct current, so that a direct current voltage signal in the active filter circuit cannot pass through the capacitor C1 to the ground and can only be applied to the resistor R and the voltage drop unit 12, and a high-frequency alternating current voltage signal can flow to the ground through the capacitor C1, so that the filtering function of the capacitor C1 is realized, and the bias current is small, so that the filtering effect of the active filter circuit can be controlled by adjusting the resistance value of the resistor R.

There are various implementations of the pressure drop unit 12, which are described in detail below:

the first scheme is that the pressure drop unit 12 includes a pressure drop subunit and a pressure drop expansion unit;

the input end of the voltage drop subunit is respectively connected with the other end of the resistor R and one end of the capacitor C1; the output end of the pressure drop subunit is connected with the input end of the pressure drop expansion unit;

the other end of the voltage drop expansion unit is connected with the base electrode of the transistor Q.

The beneficial effects in the embodiment are as follows:

as shown in fig. 3, a schematic structural diagram of an active filter circuit according to a third embodiment of the present utility model is shown, the voltage drop subunit is a diode D1, and the voltage drop expansion unit includes at least one diode;

one end of the diode D1 is respectively connected with the other end of the resistor R and one end of the capacitor C1; the other end of the diode D1 is connected with the input end of the voltage drop expansion unit;

the output end of the voltage drop expansion unit is connected with the base electrode of the transistor Q.

The following describes the operation principle of the circuit of this embodiment:

the diode D1 generates voltage drop when the active filter circuit is in a conducting state, and the voltage drop expansion unit also provides voltage drop of at least 0.4V-0.6V when the circuit is in a conducting state; the voltage drop expansion unit has reverse voltage resistance and can play a role of a protection circuit when the power supply is reversely connected.

The diode D1 generates voltage drop when the active filter circuit is in a conducting state, and the voltage drop of the voltage drop expansion unit and the voltage drop of the transistor Q are added up by 0.4V-0.6V, so that the peak-peak value capable of filtering the power supply ripple wave is improved.

When the active filter circuit is in a conducting state, the diode D1 and the voltage drop expansion unit increase the voltage drop between the transistor emission stage and the first filter stabilizing unit, and the current amplification coefficient of the transistor Q is beta, so that the current amplification characteristic of the transistor Q is utilized to know that the active filter circuit is equivalent to amplifying the capacitor C1 by beta times, and the filter capability is greatly improved.

When the emitter voltage of the transistor Q increases, the base of the transistor Q and its emitter voltage drop and cause a decrease in the current flowing into the base of the transistor Q; the reduction of the base current of the transistor Q causes the reduction of the output current of the emitter thereof, and the voltage of the emitter thereof also decreases with the reduction of the current as the load internal resistance of the transistor Q is unchanged. Similarly, when the emitter voltage of the transistor Q is reduced, the base electrode and the emitter voltage thereof are increased, so that the current flowing into the base electrode of the transistor Q is increased, the output current of the emitter is increased, and the voltage of the emitter is increased along with the increase of the current because the internal resistance of the load of the transistor Q is unchanged, and the emitter voltage of the transistor Q has the characteristic of following the voltage of the base electrode of the transistor Q by utilizing the negative feedback principle of the transistor.

Therefore, the voltage drop unit 12 composed of the diode D1 and the voltage drop expansion unit and the stabilized voltage is provided by the first filter stabilizing unit, so that the voltage drop between the emitter of the transistor and the first filter stabilizing unit is increased, and the function of stabilizing the output voltage of the emitter of the transistor Q is realized according to the negative feedback principle of the transistor.

In a second scheme, as shown in fig. 4, a schematic structural diagram of an active filter circuit according to a fourth embodiment of the present utility model is shown, and the voltage drop unit 12 is a diode D;

one end of the diode D is respectively connected with the other end of the resistor R and one end of the capacitor C1; the other end of the diode D is connected to the base of the transistor Q.

The following describes the operation principle of the circuit of this embodiment:

diode D provides a voltage drop of 0.4V-0.6V when the circuit is in the on state; the diode D has reverse voltage resistance and can play a role of a protection circuit when the power supply is reversely connected.

When the active filter circuit is in a conducting state, the diode D in the circuit carries out voltage drop of 0.4V-0.6V on the reference voltage, namely the voltage drop between the base voltage and the emitter voltage of the transistor Q is improved from the original 0.4V-0.6V to about 0.8V-1.2V, and the peak-peak value of the filterable power supply ripple is improved.

As in the first implementation of the voltage drop unit 12, when the active filter circuit is in the on state, the diode D provides a voltage drop of 0.4V to 0.6V between the transistor emitter and the first filter stabilization unit, and the current amplification characteristic of the transistor Q is utilized to improve the filtering capability; according to the negative feedback principle of the transistor, the stability of the output voltage of the emitter electrode of the transistor Q is realized.

As shown in fig. 5, a block diagram of an active filter circuit according to a fifth embodiment of the present utility model is provided, and in some embodiments, the active filter circuit further includes a second filter unit 13;

an input end of the second filtering unit 13 is connected with an emitter of the transistor Q; the output terminal of the second filter unit 13 outputs a target voltage.

The second filter unit 13 will further filter the output voltage of the emitter of the transistor Q.

Wherein the second filter unit 13 comprises a magnetic bead B and a capacitor C2;

one end of the magnetic bead B is connected with the emitter end of the transistor Q; the other end of the magnetic bead B is connected with one end of the capacitor C2 and outputs target voltage;

one end of the capacitor C2 is connected with the target voltage output end, and the other end of the capacitor C2 is grounded.

The magnetic bead B is a ferrite magnetic bead, and an equivalent circuit of the magnetic bead B is an inductor and a resistor which are connected in series, when low-frequency current passes through the magnetic bead B, the resistance value of the generated resistor is small, but the resistance value of the magnetic bead B for high-frequency current is large, so that the high-frequency current can radiate out in a heat energy mode, and the high-frequency filtering function is realized.

The capacitor C2 has a very high impedance to the dc power, and has a lower impedance for the ac power at a higher frequency, so that the ac component in the dc power can be filtered out, thereby realizing a filtering function.

In the second filtering unit 13, the combination of the magnetic bead B and the capacitor C2 can further filter the output target voltage of the active filter circuit, thereby further improving the stability of the target voltage.

The present embodiment is described and illustrated below by way of preferred embodiments.

FIG. 6 is a schematic diagram of the structure of the active filter circuit of the preferred embodiment; as shown in fig. 6, the active filter circuit includes a first filter stabilization unit 11, a voltage drop unit 12, a transistor Q, and a second filter unit 13. The first filter stabilizing unit 11 includes a resistor R and a capacitor C1, the voltage drop unit 12 is a diode D, and the second filter unit 13 includes a magnetic bead B and a capacitor C2. One end of the resistor R is connected with a power supply and the collector electrode of the transistor Q respectively; the other end of the resistor R is respectively connected with one end of the capacitor C1 and one end of the diode D; one end of the capacitor C1 is connected with one end of the diode D; the other end of the capacitor C1 is grounded; the other end of the diode D is connected with the base electrode of the transistor Q; the emitter of the transistor Q is connected with one end of the magnetic bead B; the other end of the magnetic bead B is respectively connected with the voltage output end and one end of the capacitor C2; one end of the capacitor C2 is connected with the voltage output end; the other end of the voltage C2 is grounded.

It should be noted that the voltage drop of 0.4V-0.6V is performed on the reference voltage by using the diode D, that is, the voltage drop between the base voltage and the emitter voltage of the transistor Q is increased from 0.4V-0.6V to 0.8V-1.2V, so that the peak-peak value of the power supply ripple wave can be filtered; the utility model can realize good filtering from low frequency to high frequency without expensive inductance with large inductance and large capacitance with large volume and extremely low cost of the device, thereby being beneficial to reducing the cost of the circuit device and reducing the volume space of the circuit device; the utility model utilizes the high reverse bias voltage withstand characteristic of the diode D to improve the reverse bias voltage withstand value of the transistor Q, thereby realizing the high voltage withstand and reverse connection preventing function of the integral active filter circuit; the utility model has no LC resonance risk and is easy to design and integrate.

In some of these embodiments, in combination with the active filter circuit in the above embodiments, embodiments of the present utility model may provide a filter to be implemented. The filter includes any of the active filter circuits of the above embodiments. Such as: the active filter circuit comprises a first filter stabilizing unit 11, a voltage drop unit 12, a transistor Q and a second filter unit 13; the input end of the first filtering stabilizing unit 11 is respectively connected with a power supply and the collector electrode of the transistor Q; the output end of the first filtering stabilizing unit 11 is connected with the input end of the voltage drop unit 12; the output end of the voltage drop unit 12 is connected with the base electrode of the transistor Q; the emitter of the transistor Q is connected to the input of the second filter unit 13, the output of which outputs the target voltage. The form of the other active filter circuits in the filter is not illustrated here.

According to the active filter circuit in the filter, the first filter stabilizing unit 11 is matched with the voltage drop unit 12, so that the filtering effect of the active filter circuit is enhanced, and the stability of the output target voltage of the active filter circuit is improved.

In some embodiments, the active filter circuit in the filter of the utility model has wide application field and can be applied to a high-precision analog operational amplifier circuit, a high-precision ADC analog-to-digital sampling conversion circuit, a radio transceiver circuit and the like. The circuit structure diagram is shown in fig. 7, and the specific analog operational amplifier circuit 20 is shown in fig. 10; the circuit structure diagram is shown in fig. 8, and the specific ADC analog-to-digital sampling conversion circuit 30 is shown in fig. 11; wherein, applied to the transceiver circuit 40, the circuit structure schematic diagram is shown in fig. 9, and the specific transceiver circuit 40 is shown in fig. 12; and the power supply part of other active circuits provides clean, stable and burr-free power supply for the subsequent power receiving circuit.

It should be understood that the specific embodiments described herein are merely illustrative of this active filter circuit and are not intended to be limiting. All other embodiments, which can be made by one of ordinary skill in the art without undue burden from the present disclosure, are within the scope of the present disclosure in accordance with the embodiments provided herein.

The term "embodiment" in this disclosure means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the utility model. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive. It will be clear or implicitly understood by those of ordinary skill in the art that the embodiments described in the present utility model can be combined with other embodiments without conflict.

The above examples merely represent a few embodiments of the present utility model, which are described in more detail and are not to be construed as limiting the scope of the patent claims. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the utility model, which are all within the scope of the utility model. Accordingly, the scope of the utility model should be assessed as that of the appended claims.

Claims (10)

1. An active filter circuit is characterized by comprising a first filter stabilizing unit, a voltage drop unit and a transistor Q;

the input end of the first filtering stabilizing unit is respectively connected with a power supply and the collector electrode of the transistor Q; the output end of the first filtering stabilizing unit is connected with the input end of the voltage drop unit;

the output end of the voltage drop unit is connected with the base electrode of the transistor Q, and the voltage drop unit is used for increasing the voltage drop between the transistor emitter and the first filtering stabilizing unit when the voltage drop unit is in a conducting state;

the emitter of the transistor Q outputs a target voltage.

2. The active filter circuit of claim 1, wherein the first filter stabilization unit comprises a resistor R and a capacitor C1;

one end of the resistor R is connected with the power supply and the collector electrode of the transistor Q respectively; the other end of the resistor R is respectively connected with one end of the capacitor C1 and the input end of the voltage drop unit;

one end of the capacitor C1 is connected with the input end of the voltage drop unit; the other end of the capacitor C1 is grounded.

3. The active filter circuit of claim 2, wherein the resistor R is a variable resistor.

4. The active filter circuit of claim 2, wherein the voltage drop unit comprises a voltage drop sub-unit and a voltage drop expansion unit;

the input end of the voltage drop subunit is respectively connected with the other end of the resistor R and one end of the capacitor C1; the output end of the pressure drop subunit is connected with the input end of the pressure drop expansion unit;

the other end of the voltage drop expansion unit is connected with the base electrode of the transistor Q.

5. The active filter circuit of claim 4, wherein the voltage drop subunit is a diode D1;

one end of the diode D1 is respectively connected with the other end of the resistor R and one end of the capacitor C1; the other end of the diode D1 is connected with the input end of the voltage drop expansion unit.

6. The active filter circuit of claim 4, wherein the voltage drop expansion unit comprises at least one diode.

7. The active filter circuit of claim 2, wherein the voltage drop unit is a diode D;

one end of the diode D is respectively connected with the other end of the resistor R and one end of the capacitor C1; the other end of the diode D is connected with the base electrode of the transistor Q.

8. The active filter circuit of claim 1, further comprising a second filter unit;

the input end of the second filtering unit is connected with the emitter of the transistor Q; and the output end of the second filtering unit outputs target voltage.

9. The active filter circuit of claim 8, wherein the second filter unit comprises a magnetic bead B and a capacitor C2;

one end of the magnetic bead B is connected with the emitter end of the transistor Q; the other end of the magnetic bead B is connected with one end of the capacitor C2 and outputs target voltage;

one end of the capacitor C2 is connected with the target voltage output end, and the other end of the capacitor C2 is grounded.

10. An active filter comprising an active filter circuit as claimed in any one of claims 1 to 9;

the active filter outputs a stabilized target voltage when the voltage passes through the active filter circuit.