CN207083007U - An average current control circuit - Google Patents

Abstract

The utility model discloses a kind of Average Current Control circuit, the circuit includes unit gain differential amplifier circuit, low pass filter, in-phase proportion amplifying circuit, error amplifying circuit and duty cycle signals and circuit occurs, and wherein unit gain differential amplifier circuit is used for the inductive current of sampled power converter；Low pass filter is used for the high-frequency ripple components for filtering out inductor current signal；In-phase proportion amplifying circuit is used to carry out with mutually amplification the amplitude of filtered signal；Error amplifying circuit is used to produce current reference signal, and carrying out proportional integration computing after current reference signal is made the difference with the signal after amplification obtains control voltage signal；Duty cycle signals occur circuit and are used to produce sawtooth signal, and sawtooth signal is produced to the conducting dutycycle of switching tube compared with control voltage signal, to control the inductive current of power inverter.The utility model improves the control accuracy and antijamming capability of circuit, reduces current ripples and power attenuation.

Description

An average current control circuit

technical field

The utility model belongs to the technical field of power electronics application, in particular to an average current control circuit.

Background technique

In order to realize controllable output voltage and current, high frequency switching power supply usually adopts current mode control. Commonly used current mode control includes peak current control and average current control, in which the average current control directly controls the average value of the inductor current. Due to its advantages of high control precision, small current ripple, good anti-interference performance, and strong system stability, it is widely used in Boost power factor correction, battery charging control, solar power generation and other fields have important applications.

The traditional average current control circuit makes the current loop gain bandwidth achieve the best performance by designing the compensation network of the current error amplifier, but it usually causes the sawtooth ripple component of the inductor current to be proportionally amplified. The control voltage will also contain a large ripple component value, so the slope of the control voltage may exceed the slope slope of the sawtooth signal, which may cause the control voltage to intersect with the sawtooth wave more than once during each switching period, which will cause the power tube Turn on multiple times in one switching cycle. Obviously, the circuit at this time is working in an unstable state. In the current average current control research, the traditional control circuit is mainly used to design the current loop compensation network compromised, and the design effect is difficult to maintain the system stability.

Utility model content

The purpose of this utility model is to provide an average current control circuit. By introducing a low-pass filter and a proportional amplifier circuit with the same phase, the current loop gain bandwidth can achieve the best performance, and at the same time, the high-frequency components in the current sampling signal can be reduced to the greatest extent. .

The technical solution to realize the purpose of the utility model is: the utility model proposes an average current control circuit, which is used to control the inductance current of the power converter, including a unit gain differential amplifier circuit, a low-pass filter, a phase proportional amplifier circuit, an error Amplifying circuit and duty ratio signal generating circuit, wherein:

The unity gain differential amplifier circuit is used to sample the inductor current of the power converter, and transmit the inductor current to the low-pass filter;

The low-pass filter is used to filter out the high-frequency ripple component of the inductor current signal, and transmit the filtered signal to the same-phase proportional amplifier circuit;

The in-phase proportional amplifying circuit is used for in-phase amplifying the amplitude of the filtered signal, and transmitting the amplified signal to the error amplifying circuit;

The error amplification circuit is used to generate the current reference signal, and after the difference between the current reference signal and the amplified signal, the proportional-integral operation is performed to obtain the control voltage signal, and the control voltage signal is transmitted to the non-inverting input terminal of the comparator;

The duty ratio signal generation circuit is used to generate a sawtooth wave signal, and compares the sawtooth wave signal with the control voltage signal to generate a conduction duty ratio of the switch tube to control the inductor current of the power converter.

Specifically, the unity-gain differential amplifier circuit includes a first resistor, a second resistor, a third resistor, a fourth resistor, and a differential amplifier; one end of the first resistor is connected to the non-inverting input end of the differential amplifier, and the other end is connected to the current sampling resistor. Input terminal, one end of the second resistor is connected to the inverting input end of the differential amplifier, the other end is connected to the output end of the current sampling resistor, one end of the third resistor is connected to the non-inverting input end of the differential amplifier, the other end is connected to the circuit reference ground, one end of the fourth resistor Connect the inverting input terminal of the differential amplifier, and the other end is connected to the output terminal of the differential amplifier. The signal amplitude gain of the unity gain differential amplifier circuit is 1, and the resistance values of the first resistor, the second resistor, the third resistor, and the fourth resistor are equal;

The low-pass filter includes a fifth resistor and a filter capacitor; one end of the fifth resistor is connected to the output end of the differential amplifier, the other end is connected to one end of the filter capacitor, and the other end of the filter capacitor is connected to the circuit reference ground, and the low-pass filter The cutoff frequency is half of the switching frequency f _s , the capacitance of the filter capacitor is 1nF, and the resistance value of the fifth resistor is R _f =1/(πC _f f _s ).

Compared with the prior art, the utility model has the remarkable advantages that: the utility model optimizes the current feedback loop, filters out the high-frequency ripple in the current sampling signal, makes the current sampling signal close to direct current, and further improves the current control accuracy And the anti-interference ability of the circuit reduces the complexity of current ripple, power loss and circuit design.

Description of drawings

Fig. 1 is a structural schematic diagram of the average current control circuit of the present invention.

Fig. 2 is the average current control circuit diagram of the utility model.

FIG. 3 is a schematic structural diagram of a step-down power converter.

Fig. 4 is a schematic diagram of waveforms when the average current control circuit of the present invention operates stably, wherein Fig. (a) is a waveform diagram of the inductive current of a step-down power converter, and Fig. (b) is passed through a low-pass filter and a proportional amplifier of the same phase The waveform diagram of the final output signal, Figure (c) is the waveform diagram of the control voltage signal and the sawtooth signal.

Detailed ways

The scheme of the utility model is further described below in conjunction with the accompanying drawings and specific embodiments.

As shown in Figure 1-2, the average current control circuit includes: unity gain differential amplifier circuit 1, low-pass filter 2, same-phase proportional amplifier circuit 3, error amplifier circuit 4 and duty ratio signal generation circuit 5, wherein: unity gain The differential amplifier circuit 1 is used to sample the inductor current of the power converter, and transmit the inductor current to the low-pass filter 2; the low-pass filter 2 is used to filter out the high-frequency ripple component of the inductor current signal, and transfer the filtered The signal is transmitted to the same phase proportional amplifier circuit 3; the same phase proportional amplifier circuit 3 is used to amplify the amplitude of the filtered signal in phase, and transmits the amplified signal to the error amplifier circuit 4; the error amplifier circuit 4 is used to generate the current reference signal , make a difference between the current reference signal and the amplified signal, and then perform a proportional-integral operation to obtain a control voltage signal, and transmit the control voltage signal to the non-inverting input terminal of the comparator; the duty ratio signal generating circuit 5 is used to generate a sawtooth wave signal, and compare the sawtooth signal with the control voltage signal to generate the on-duty ratio of the switch tube to control the inductor current of the power converter.

Unity gain differential amplifier circuit 1 includes a first resistor R _d1 , a second resistor R _d2 , a third resistor R _df1 , a fourth resistor R _df2 and a differential amplifier A ₁ ; one end of the first resistor R _d1 is connected to the positive phase of the differential amplifier A ₁ Input end, the other end is connected to the input end of the current sampling resistor R _s , one end of the second resistor R _d2 is connected to the inverting input end _of the differential amplifier A1, the other end is connected to the output end of the current sampling resistor R _s , one end of the third resistor R _df1 Connect the non _- inverting input terminal of the differential amplifier A1, the other end is connected to the circuit reference ground, one end of the fourth resistor _Rdf2 is connected to the inverting input terminal _of the differential amplifier A1, and the other end is connected to the output terminal of the differential amplifier A1, the _unity gain The signal amplitude gain of the differential amplifier circuit 1 is 1, and the resistance values of the first resistor R _d1 , the second resistor R _d2 , the third resistor R _df1 , and the fourth resistor R _df2 are equal, so that the input and output signals of the unity gain differential amplifier circuit 1 Small phase shift;

The low-pass filter 2 includes a fifth resistor _Rf and a filter capacitor _Cf ; one end of the fifth resistor _Rf is connected to the output terminal of the differential amplifier A1, the other end is connected to _one end of the filter capacitor _Cf , and the other end of the filter capacitor _Cf Connect the circuit with reference ground, the cut-off frequency of the low-pass filter 2 is half of the switching frequency f _s , the capacitance of the filter capacitor C _f is 1nF, and the resistance value of the fifth resistor R _f is R _f =1/(πC _f f _s ), so that the low-pass filter 2 can filter out the high-frequency ripple component of the inductor current signal.

The same phase proportional amplifying circuit 3 includes the sixth resistor _Raf1 , the seventh resistor _Raf2 and the first operational amplifier A2 _; the non _- inverting input terminal of the first operational amplifier A2 is connected to the output terminal of the fifth resistor _Rf , and the first operation _The inverting input end of the amplifier A2 is connected to one end of the sixth resistor _Raf1 , the other end of the sixth resistor _Raf1 is connected to the circuit reference ground, and one end of the seventh resistor _Raf2 is connected to the _inverting input end of the first operational amplifier A2, _The other end is connected to the output end of the first operational amplifier A2.

The error amplification circuit 4 includes an eighth resistor _Ref1 , a ninth resistor _Ref2 , an integrating capacitor _Cef , a current reference signal generator V _RI and a second operational amplifier A ₃ ; the anode of the current reference signal generator V _RI is connected to the first The positive phase input terminal of the second operational amplifier A ₃ , the negative pole of the current reference signal generator V _RI is connected to the circuit reference ground, one end of the eighth resistor _Ref1 is connected to the inverting input terminal of the second operational amplifier A ₃ , and the other end is connected to the ninth One end of the resistor _Ref2 and the other end of the ninth resistor _Ref2 are connected to one end of the integrating capacitor C _ef , and the other end of the integrating capacitor C _ef is connected to the output end _of the second operational amplifier A3. _The second operational amplifier A3 is used to make the positive and negative input terminal voltages consistent through negative feedback control.

_Described duty cycle signal generation circuit ₅ comprises _sawtooth signal source V _saw and comparator A ₄ ; It is connected to the circuit reference ground, the non _- inverting input terminal of the comparator A4 is connected to the output terminal _of the second operational amplifier A3, the output terminal of the comparator A4 is connected to the power switch S of the power converter, and the output control switch tube S is turned _on duty cycle signal V _GS .

The average current control method based on the above average current control circuit comprises the following steps:

Step 1, the unity gain differential amplifier circuit 1 samples the inductor current of the power converter;

Step 2, the low-pass filter 2 filters out the high-frequency ripple component of the inductor current signal;

Step 3, in-phase proportional amplification circuit 3 performs in-phase amplification on the amplitude of the filtered signal;

Step 4, the error amplification circuit 4 generates a current reference signal, and after making a difference with the amplified signal, a proportional-integral operation is performed to obtain a control voltage signal;

Step 5, the duty ratio signal generation circuit 5 generates a sawtooth wave signal, and compares it with the control voltage signal to generate the conduction duty ratio of the switch tube to control the inductor current of the power converter. When the control voltage signal value is higher than the sawtooth wave signal When the value is high, the output high level turns on the power switch; when the control voltage signal value is lower than the sawtooth signal value, the output low level turns off the power switch.

The working principle is analyzed as follows:

The unity-gain differential amplifier circuit detects the inductor current of the power converter. The magnitude of the inductor current can be reflected by the sampling resistor voltage R _s i _L , and the sampling resistor voltage is expressed as:

V _Rs ＝R _s i _L ＝R _s (I _L +Δi _L +i _l )

Among them, I _L is the DC component of the inductor current, Δi _L is the high frequency AC component of the inductor current, and i _l is the low frequency AC component of the inductor current.

The low-pass filter has the characteristics of passing low-frequency and blocking high-frequency. The sampling resistor voltage V _Rs passes through the low-pass filter, and the high-frequency AC component R _s Δi _L of the obtained signal has been filtered out, and except for a small amount of low-frequency AC component, The rest are DC components, that is, output a DC signal V _Cf with less low-frequency AC components, expressed as:

V _Cf ＝R _s (I _L +i _l )≈R _s I _L

The same-phase proportional amplifier circuit amplifies the DC component R _s I _L by a corresponding multiple through the resistance network value to obtain the current feedback signal V _fi to match the amplitude of the positive and negative phase input signals of the post-stage error amplifier, that is, the current feedback signal during steady-state operation V _fi will track the current reference voltage signal V _ri , V _fi is expressed as follows:

So far, the high-frequency AC component from the inductor current has been attenuated to the greatest extent, so V _fi can be regarded as a DC signal. The current error amplifier circuit makes a difference between the DC voltage signal output by the proportional amplifier circuit of the same phase and the current reference voltage signal, and performs a proportional-integral operation. The high-frequency AC component of the obtained control voltage signal V _ci has been filtered by the low-pass filter and the current error amplifier circuit. There is little left to decay.

The control voltage signal is sent to the positive-phase input terminal of the comparator, and the comparator compares the signals at the positive-phase input terminal and the negative-phase input terminal: when the value of the control voltage signal is higher than the value of the sawtooth wave signal, the comparator flips and outputs a high level, generating The power switch turns on the pulse signal; when the value of the control voltage signal is lower than the value of the sawtooth wave signal, the comparator flips and outputs a low level to generate a power switch off pulse signal. Reciprocating in this way can obtain a stable or adjustable load current value.

The above-mentioned average current control circuit and method can be widely used in DC-DC power converters, and the utility model is illustrated by taking a step-down power converter as an example. The step-down power converter shown in Fig. 3 includes: input DC power supply V _in , power switch S, power diode D, filter inductor L, current sampling resistor R _s , filter capacitor C and load resistor R _L . Based on the average current control circuit and method, the inductor current of the power converter can be effectively controlled in a constant current state or an adjustable state.

Fig. 4 is a main waveform diagram of the control loop in a steady state after applying the circuit and method of the utility model to the step-down power converter of Fig. 3 . As shown in Figure 4(a), the high-frequency ripple contained in the power converter inductor current i _L has a large amplitude. If it is directly introduced into the current error amplifier after sampling, it is bound to fail to take into account the system stability and the optimal loop bandwidth. As shown in Figure 4(b), due to the existence of the low-pass filter, the output signal V _fi signal of the non-inverting proportional amplifier is close to DC, which makes the high-frequency ripple component from the inductor current no longer fed into the current error amplifier, ensuring the current The loop gain bandwidth can be designed in an optimal state. As shown in Figure 4(c), the high-frequency ripple component of the control voltage signal V _ci is greatly reduced, and its slope is very small compared with the slope of the sawtooth wave, and V _ci is approximately constant throughout the switching cycle. Obviously, by decoupling the filtered high-frequency ripple component and the gain bandwidth design, the current control accuracy is improved, the current ripple is reduced, and the anti-interference ability of the control circuit is greatly enhanced, that is, the utility model can reduce the control voltage ripple. The purpose of the wave size.

Claims (4)

1. A mean current control circuit is used to control the inductance current of power converter, it is characterized in that, comprises unity gain differential amplifier circuit (1), low-pass filter (2), same-phase proportional amplifier circuit (3), error Amplifying circuit (4) and duty cycle signal generating circuit (5), wherein: The unity gain differential amplifier circuit (1) is used to sample the inductor current of the power converter, and transmit the inductor current to the low-pass filter (2); The low-pass filter (2) is used to filter out the high-frequency ripple component of the inductor current signal, and transmit the filtered signal to the same-phase proportional amplifier circuit (3); The in-phase proportional amplifying circuit (3) is used for in-phase amplifying the amplitude of the filtered signal, and transmitting the amplified signal to the error amplifying circuit (4); The error amplification circuit (4) is used to generate a current reference signal, and perform a proportional-integral operation after the difference between the current reference signal and the amplified signal to obtain a control voltage signal, and transmit the control voltage signal to the non-inverting input terminal of the comparator; The duty ratio signal generation circuit (5) is used to generate a sawtooth wave signal, and compares the sawtooth wave signal with the control voltage signal to generate a conduction duty ratio of the switch tube, so as to control the inductor current of the power converter; Specifically, the unity gain differential amplifier circuit (1) includes a first resistor (R _d1 ), a second resistor (R _d2 ), a third resistor (R _df1 ), a fourth resistor (R _df2 ) and a differential amplifier (A ₁ ); one end of the first resistor (R _d1 ) is connected to the non-inverting input end of the differential amplifier (A ₁ ), the other end is connected to the input end of the current sampling resistor (R _s ), and one end of the second resistor (R _d2 ) is connected to the differential amplifier ( The inverting input end of A ₁ ), the other end is connected to the output end of the current sampling resistor (R _s ), one end of the third resistor (R _df1 ) is connected to the non-inverting input end of the differential amplifier (A ₁ ), and the other end is connected to the circuit reference ground , one end of the fourth resistor (R _df2 ) is connected to the inverting input end of the differential amplifier (A ₁ ), and the other end is connected to the output end of the differential amplifier (A ₁ ), the signal amplitude gain of the unity gain differential amplifier circuit (1) is 1, the resistance values of the first resistor (R _d1 ), the second resistor (R _d2 ), the third resistor (R _df1 ), and the fourth resistor (R _df2 ) are equal; The low-pass filter (2) includes a fifth resistor (R _f ) and a filter capacitor (C _f ); one end of the fifth resistor (R _f ) is connected to the output end of the differential amplifier (A ₁ ), and the other end is connected to the filter capacitor One end of (C _f ), the other end of the filter capacitor (C _f ) is connected to the circuit reference ground, the cutoff frequency of the low-pass filter (2) is half of the switching frequency f _s , and the capacitance of the filter capacitor (C _f ) is 1nF, the resistance of the fifth resistor (R _f ) is R _f =1/(πC _f f _s ). 2. The average current control circuit according to claim 1, characterized in that, the same-phase proportional amplifier circuit (3) comprises the sixth resistor (R _af1 ), the seventh resistor (R _af2 ) and the first operational amplifier (A ₂ ); the non-inverting input terminal of the first operational amplifier (A ₂ ) is connected to the output terminal of the fifth resistor (R _f ), and the inverting input terminal of the first operational amplifier (A ₂ ) is connected to the sixth resistor (R _af1 ) One end of the sixth resistor (R _af1 ) is connected to the circuit reference ground, one end of the seventh resistor (R _af2 ) is connected to the inverting input end of the first operational amplifier (A ₂ ), and the other end is connected to the first operational amplifier ( A ₂ ) output terminal. 3. The average current control circuit according to claim 1, characterized in that, the error amplifier circuit (4) comprises an eighth resistor (Re _ef1 ), a ninth resistor (Re _ef2 ), an integrating capacitor (C _ef ), Current reference signal generator (V _RI ) and the second operational amplifier (A ₃ ); the positive pole of the current reference signal generator (V _RI ) is connected to the non-inverting input terminal of the second operational amplifier (A ₃ ), and the current reference signal generator The negative pole of (V _RI ) is connected to the circuit reference ground, one end of the eighth resistor (Re _ef1 ) is connected to the inverting input end of the second operational amplifier (A ₃ ), the other end is connected to one end of the ninth resistor (Re _ef2 ), the ninth The other end of the resistor (Re _ef2 ) is connected to one end of the integrating capacitor (C _ef ), and the other end of the integrating capacitor (C _ef ) is connected to the output end of the second operational amplifier (A ₃ ). 4. The average current control circuit according to claim 1, characterized in that, the duty ratio signal generating circuit (5) comprises a sawtooth signal source (V _saw ) and a comparator (A ₄ ); the sawtooth signal source The positive pole of (V _saw ) is connected to the inverting input terminal of the comparator (A ₄ ), the negative pole of the sawtooth signal source (V _saw ) is connected to the circuit reference ground, and the non-inverting input terminal of the comparator (A ₄ ) is connected to the second The output terminal of the operational amplifier (A ₃ ) is connected, and the output terminal of the comparator (A ₄ ) is connected with the power switch (S) of the power converter.