Small-signal rectification filter circuit with low impedance output

Abstract

The utility model discloses a small-signal rectification filter circuit with low impedance output, and belongs to the technical field of analog circuits and digital circuits. The circuit comprises an operational amplifier power supply circuit powered by a single power supply; and a precise full-wave rectification circuit, a filter circuit and a voltage follower. Voltage enters the precision full-wave rectification circuit and is connected to the filter circuit after being rectified, the output end of the precision full-wave rectification circuit is connected to the in-phase input end of the filter circuit, and the output end of the filter circuit is connected to the reverse input end of the voltage follower circuit.

Description

Technical Field

[0001] The utility model relates to the technical field of analog circuits and digital circuits, in particular to a small signal rectification and filtering circuit with low impedance output. Background Art

[0002] The main function of rectification and filtering is to obtain a pulsed DC signal through rectification of the AC signal, and then use the charging and discharging principle of the capacitor to smooth the output signal. This filtering method has poor output characteristics and is greatly affected by the load. It is often used in situations where the load voltage is high and the load is stable, and cannot adapt to situations that require precise filtering and rectification. In addition, in small-signal filter circuits, considering the impact of the rectifier voltage drop on the signal, existing small-signal rectification schemes mostly use operational amplifiers to form precise rectification circuits. The output of the operational amplifier is directly connected to the filter capacitor for filtering. Due to the fact that the capacitor voltage cannot change suddenly, a large impact current will be generated when the circuit is started, which often causes damage to the operational amplifier. Utility Model Content

[0003] The purpose of the utility model is to overcome the defects of the prior art and provide a small signal rectifier and filter circuit with low impedance output. The circuit has a full-wave precision rectifier circuit, a precision filter circuit and a voltage follower circuit. The circuit only uses an operational amplifier to complete the precision rectification. In the filter circuit, only a small-capacity capacitor of nF level is used, and a large filter capacitor of uF level or above is not used. The capacitor charging time is fast, the impact current is small, and the output impedance is low, and the output signal is not affected by load changes.

[0004] In order to achieve the above purpose, the utility model provides the following technical solutions:

[0005] The utility model discloses a small signal rectification and filtering circuit with low impedance output, comprising:

[0006] Operational amplifier power supply circuit using single supply; and

[0007] Precision full-wave rectifier circuit, filter circuit and voltage follower circuit;

[0008] The voltage enters the precision full-wave rectifier circuit and is connected to the filter circuit after rectification, wherein the output end of the precision full-wave rectifier circuit is connected to the in-phase input end of the filter circuit, and the output end of the filter circuit is connected to the reverse input end of the voltage follower circuit.

[0009] Further, the precision full-wave rectifier circuit includes a second resistor, a first resistor connected in series in sequence, a first operational amplifier, and a first diode;

[0010] One end of the second resistor is connected to the inverting input end of the first operational amplifier, and the other end is connected to the output end of the first diode. The input end of the second resistor and the output end of the first resistor are connected to the inverting input end of the first operational amplifier, and the output end of the second resistor is connected to the output end of the first diode.

[0011] Furthermore, the filtering circuit includes a second operational amplifier, a fourth resistor, a second diode, and a third resistor and a capacitor connected in series to the reverse input terminal of the second operational amplifier;

[0012] The capacitor is connected to the output end of the second diode away from the third resistor end;

[0013] The third resistor is a discharge resistor;

[0014] The fourth resistor is a current limiting resistor;

[0015] The capacitor is a filter capacitor.

[0016] Furthermore, the first diode and the second diode are both feedback diodes.

[0017] Furthermore, the capacitance of the capacitor is 470nF.

[0018] Furthermore, the fourth resistor has a resistance of 10Ω, and the third resistor has a resistance of 1MΩ.

[0019] Further, the voltage follower circuit includes a third operational amplifier;

[0020] The non-inverting input terminal of the third operational amplifier is connected to the output terminal of the filter circuit;

[0021] The inverting input terminal of the third operational amplifier is connected to its output terminal, and the output terminal of the third operational amplifier is also connected in series with a fifth resistor, which is a current limiting resistor.

[0022] Furthermore, the resistance of the fifth resistor is 10Ω.

[0023] In the above technical solution, the utility model provides a small signal rectifier filter circuit with low impedance output, which has the following beneficial effects:

[0024] The circuit has a full-wave precision rectifier circuit, a precision filter circuit and a voltage follower circuit. It only uses one operational amplifier to complete the precision rectification. In the filter circuit, only one nF-level small-capacity capacitor is used. The capacitor has a fast charging time, a small impact current, and a low output impedance. The output signal is not affected by load changes. In the voltage follower circuit, resistor R5 is a current-limiting resistor, which effectively prevents the downstream circuit from short-circuiting and burning the operational amplifier. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present utility model. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0026] Figure 1 This is a small signal rectification and filtering circuit diagram with low impedance output disclosed by the utility model;

[0027] Figure 2 The utility model discloses a waveform diagram of a small signal rectification and filtering circuit with low impedance output after rectification.

[0028] Description of reference numerals:

[0029] 1. Operational amplifier power supply circuit; 2. Precision full-wave rectifier circuit; 3. Filter circuit; 4. Voltage follower circuit. DETAILED DESCRIPTION

[0030] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below in conjunction with the accompanying drawings.

[0031] See also Figure 1 As shown;

[0032] The utility model discloses a small signal rectifier filter circuit with low impedance output, comprising: the circuit mainly comprises four circuits, an operational amplifier power supply circuit 1, a precision full-wave rectifier circuit 2, a filter circuit 3, and a voltage follower circuit 4;

[0033] The operational amplifier power supply circuit 1 is powered by a single power supply and supplies power to a precision full-wave rectifier circuit 2, a filter circuit 3 and a voltage follower circuit 4;

[0034] The voltage UI enters the precision full-wave rectifier circuit 2 and is connected to the filter circuit 3 after rectification. The output end of the precision full-wave rectifier circuit 2 is connected to the in-phase input end of the filter circuit 3, and the output end of the filter circuit 3 is connected to the reverse input end of the voltage follower circuit 4.

[0035] In the precision full-wave rectifier circuit 2, the first diode D1 is a feedback diode;

[0036] When the diode is turned on, the resistors R1, R2, and U1-A form an inverting operational amplifier circuit, U1o = -UI*R2 / R1, and R1 = R2, then U1o = -UI;

[0037] When the diode is cut off, it is equivalent to UI connected to the in-phase input terminal of U1-B through R1 and R2 in series. Due to the "virtual cut-off" characteristic of the operational amplifier, the input impedance of the operational amplifier is infinite, and U1 o = UI*∞ / (∞

[0038] + R1 + R2) = UI;

[0039] During the negative half cycle of UI, UI<0, the diode is turned on, U1o=-UI, and the negative half cycle is reversed.

[0040] When UI is in the positive half cycle, UI>0, the op amp cannot output negative voltage, the diode is cut off, U1o=UI, and the positive half cycle is maintained. The waveform after rectification is as follows Figure 2 As shown:

[0041] The fourth resistor R4 connected to the filter circuit 3 is a current limiting resistor with a resistance value of 10Ω, C1 is a filter capacitor with a capacitance of 470nF, R3 is a discharge resistor with a resistance value of 1MΩ, and D2 is a feedback diode.

[0042] After rectification, UI becomes U1o and is connected to the non-inverting input terminal of the second operational amplifier U1-B. Due to the existence of capacitor C1, the voltage at the inverting input terminal of the second operational amplifier U1-B cannot change suddenly, and the initial voltage is 0V; after U1o passes through the zero point, the voltage rise is greater than the inverting voltage, and the operational amplifier outputs a high level, and charges the capacitor C1 through the fourth resistor R4 and D2. The charging time constant τ=R4*C1. Since the parameters of the fourth resistor R4 and capacitor C1 are relatively small, the inverting voltage can be charged to the same level as the positive voltage after 15-20us, and the inverting voltage can be charged to the peak value U2o after half a cycle (5ms) of the pulsed DC signal.

[0043] After that, U1 o drops, the inverting input of the second operational amplifier U1-B is greater than the non-inverting input, and the output of the operational amplifier is low. Since the second diode D2 cannot be reversed, the capacitor C1 can only discharge through the resistor R3, and the discharge time constant τ = R3*C1. Since the DC pulse signal period is much smaller than the discharge time constant τ, the inverting voltage fluctuation does not exceed 2% before the next peak arrives.

[0044] When the input voltage UI drops, the positive voltage of the second operational amplifier U1-B is lower than the negative voltage, and the capacitor C1 is in a discharge state until it drops to the peak voltage of U1o and remains stable:

[0045] In the voltage follower circuit 4, the inverting input of the third operational amplifier U2-A is connected to the inverting input terminal of the second operational amplifier U1-B. The voltage follower has the characteristics of high input impedance, no influence on the previous stage circuit, low output impedance, no influence on the output load fluctuation, high linearity, and the output is equal to the inverting input, UO=U2o;

[0046] R5 is a current limiting resistor with a resistance of 10Ω to prevent the downstream circuit from short-circuiting and burning the operational amplifier.

[0047] The above only describes some exemplary embodiments of the present invention by way of illustration. It is undoubted that those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A small signal rectifier filter circuit with low impedance output, characterized in that: include: An operational amplifier power supply circuit using a single power supply (1); as well as A precision full-wave rectifier circuit (2), a filter circuit (3) and a voltage follower circuit (4); The voltage (UI) enters the precision full-wave rectifier circuit (2) and is connected to the filter circuit (3) after rectification, wherein the output end of the precision full-wave rectifier circuit (2) is connected to the in-phase input end of the filter circuit (3), and the output end of the filter circuit (3) is connected to the reverse input end of the voltage follower circuit (4).

2. A small signal rectifier filter circuit with low impedance output according to claim 1, characterized in that ； The precision full-wave rectification circuit (2) comprises a second resistor (R2), a first resistor (R1) connected in series, a first operational amplifier (U1-A), and a first diode (D1); One end of the second resistor (R2) is connected to the reverse input end of the first operational amplifier (U1-A), and the other end is connected to the output end of the first diode (D1), and the input end of the second resistor (R2) and the output end of the first resistor (R1) are connected to the reverse input end of the first operational amplifier (U1-A), and the output end of the second resistor (R2) is connected to the output end of the first diode (D1).

3. A small signal rectifier filter circuit with low impedance output according to claim 1, characterized in that ； The filter circuit (3) comprises a second operational amplifier (U1-B), a fourth resistor (R4), a second diode (D2) connected in series in sequence, and a third resistor (R3) and a capacitor (C1) connected in sequence to the reverse input terminal of the second operational amplifier (U1-B); The capacitor (C1) is connected to the output end of the second diode (D2) away from the end of the third resistor (R3); The third resistor (R3) is a discharge resistor; The fourth resistor (R4) is a current limiting resistor; Capacitor (C1) is a filter capacitor.

4. A small signal rectifier filter circuit with low impedance output according to claim 2 or 3, characterized in that ； The first diode (D1) and the second diode (D2) are both feedback diodes.

5. The small signal rectifier filter circuit with low impedance output according to claim 3, characterized in that ； The capacitance of the capacitor (C1) is 470nF.

6. The small signal rectifier filter circuit with low impedance output according to claim 3, characterized in that ； The fourth resistor (R4) has a resistance of 10Ω, and the third resistor (R3) has a resistance of 1MΩ.

7. The small signal rectifier filter circuit with low impedance output according to claim 1, characterized in that ； The voltage follower circuit (4) includes a third operational amplifier (U2-A); The non-inverting input terminal of the third operational amplifier (U2-A) is connected to the output terminal of the filter circuit (3); The inverting input terminal of the third operational amplifier (U2-A) is connected to its output terminal, and the output terminal of the third operational amplifier (U2-A) is also connected in series with a fifth resistor (R5), which is a current limiting resistor.

8. A small signal rectifier filter circuit with low impedance output according to claim 7, characterized in that ； The resistance of the fifth resistor (R5) is 10Ω.

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