CN100525040C - Sample-taking feedback circuit of switch electric power output electric voltage - Google Patents
Sample-taking feedback circuit of switch electric power output electric voltage Download PDFInfo
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- CN100525040C CN100525040C CNB2007101339944A CN200710133994A CN100525040C CN 100525040 C CN100525040 C CN 100525040C CN B2007101339944 A CNB2007101339944 A CN B2007101339944A CN 200710133994 A CN200710133994 A CN 200710133994A CN 100525040 C CN100525040 C CN 100525040C
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Abstract
The invention proposes a sampling feedback circuit for the switching power supply output voltage applied to a switching power supply circuit, comprising separate components. The structure is simple, the system is stable and the cost is low. The invention includes a voltage sampling circuit, an error amplifying circuit and an insulating and converting circuit. The output voltage (Vo) of the switching power supply is imported through the voltage-signal input end of the voltage sampling circuit, and the sampling signal is achieved by voltage division; and the output voltage (Vo) also acts as the power supply for the error amplifying circuit; the sampling signal is imported through the sampling-signal input end of the error amplifying circuit, converted into a current-mode error-signal that is exported to the error current signal input end of the insulating and converting circuit, and a feedback signal (Vfb) is exported by electrical insulation.
Description
Technical field
The present invention relates to a kind of feedback circuit of voltage signal, relate in particular to a kind of sampling feedback circuit of switch power source output voltage.
Background technology
Power supply is that various electronic equipments must obligato part, and Switching Power Supply is occupied critical role in power technology, and modern power supply mostly adopts this technology, its advantage is to reduce raw materials consumption, miniaturization, and the system dynamics reaction is fast, the efficient height effectively suppresses noise pollution.
Current most Switching Power Supply all is to adopt the PWM pulse modulation technology, earlier civil power is carried out basic rectifying and wave-filtering, and AC signal is become direct current.Then move by the HF switch of switching device, this direct voltage is changed into the alternating voltage of high frequency, utilize the isolation and the coupling of transformer, induce a high-frequency ac voltage of isolating at the power supply outlet side, and it is carried out rectifying and wave-filtering, produce the direct voltage that load is provided.
For making output dc voltage stable, must sample and amplify to the error signal of this electric power output voltage, and feed back to input, by the PWM comparator, change the duty ratio that the switching device conducting ends, finish the stability that output voltage is regulated in a negative feedback, the size of control output voltage ripple.
The present invention is the sampling feedback circuit of a switch power source output voltage, can depart from output voltage the error signal sampling amplification of voltage stabilizing value, and pass through the isolation of light lotus root, feeds back to power input.This circuit can be widely used in the various switch power supply equipments, and the feedback signal of its generation can reflect error signal well, and then the duty ratio of switching device in the accurately controlling switch power supply, plays the effect of regulated output voltage.
Such as the power supply of a kind of single-end ortho-exciting structure among Fig. 1, Vin is the filtered direct voltage in commercial power rectification, and metal-oxide-semiconductor plays the effect of switch, and its HF switch action can make and produce a high-frequency ac voltage on the winding of the former limit of transformer.Utilize the coupling of transformer, can induce a high-frequency ac voltage,, produce a direct current voltage Vo supply load by the rectifying and wave-filtering of diode and electric capacity at secondary.If the duty ratio of metal-oxide-semiconductor switch is constant, then in Vin or load variations, Vo can not stablize, and this just need amplify the error disturbing signal of Vo and feed back to the input side of Switching Power Supply by the voltage sample feedback circuit.By the PWM modulator, the triangular wave of this feedback signal and a constant frequency and volt value is compared, export the square-wave signal that duty ratio can be regulated, pass through power driving circuit again, the duty ratio of control metal-oxide-semiconductor switch, Vo regulates to electric power output voltage, because this is a degenerative process, so Vo can be stabilized in certain claimed range.
In Switching Power Supply, output voltage sampling feedback circuit is very crucial part, and its design directly has influence on whole
The stability of origin system and performance, current switch power supply system to the requirement of its feedback circuit is substantially:
1, has fast the stability of importing, export dynamic response and height;
2, very high output voltage precision;
3, can realize the electrical isolation of input and output.
In the Switching Power Supply evolution, the output voltage feedback circuit has produced multiple structure and distortion, mainly can be summed up as following several:
(1) from current application, the simplest structure adopts electric resistance partial pressure exactly, but this structure can not be accomplished electrical isolation, and precision is lower, can not change multiplication factor and carry out frequency compensation, poor stability.So this method is seldom used.
(2) have the small part power supply to adopt amplifier to carry out error now and amplify feedback, but this method still can not be accomplished electrical isolation, and amplifier is had relatively high expectations.
(3) though the circuit that adopts the auxiliary winding of transformer to carry out the voltage sample feedback can be realized electrical isolation, when the load variations of power supply greatly the time, voltage regulation result is very poor.And the reaction speed of this circuit is slower, can not adapt to the Switching Power Supply of high frequency.
(4) linear pressurizer TL431 is to adopt maximum voltage feedback circuits in the present middle low power Switching Power Supply in conjunction with light-coupled isolation.But,,, also usually can when start, be damaged by peak voltage even if adopt electric resistance partial pressure if the output voltage of Switching Power Supply is higher because t1431 is withstand voltage to be had only about 40V.So need to add the operating voltage that auxiliary winding provides light lotus root and t1431, this has just increased the complexity of transformer coiling, and can interfere with the winding of main output loop in some applications.
Summary of the invention
At above-mentioned existing in prior technology problem, the present invention proposes simple in structure, the sampling feedback circuit of the strong a kind of switch power source output voltage of stability.
The present invention adopts following technical scheme:
A kind of sampling feedback circuit of switch power source output voltage, comprise voltage sampling circuit, error amplifying circuit, isolation change-over circuit, the output voltage V o of Switching Power Supply is by the voltage signal input input of voltage sampling circuit, carry out dividing potential drop and obtain sampled signal, and the voltage input signal Vo while is as the power supply of error amplifying circuit, sampled signal is by the sampled signal input input of error amplifying circuit, be converted to the current mode error signal and output to the error current signal input part of isolating change-over circuit, carry out electrical isolation and obtain feedback loop output signal Vfb.
Described voltage sampling circuit comprises slide rheostat VR1, resistance R 5 and resistance R 6, one end of resistance R 6 is as the voltage signal input, meet voltage input signal Vo, the other end is connected with an end of slide rheostat VR1, resistance R 5, the other end ground connection of resistance R 5, the tap of slide rheostat VR1 is connected with the sampled signal input of error amplifying circuit as the sampled signal output of voltage sampling circuit.
Described error amplifying circuit comprises resistance R 1, R2, R3, R4, capacitor C 1, voltage stabilizing didoe ZD1, triode Q1; Wherein, the base stage of triode Q1 is as the sampled signal input of error amplifying circuit, resistance R 3 is connected in series with voltage-stabiliser tube ZD1, its end that links to each other links to each other with the emitter of triode Q1, the plus earth of voltage stabilizing didoe ZD1, the other end of resistance R 3 is as the output voltage V o of the power supply input termination switch power supply of error amplifying circuit, the output voltage V o of resistance R 1 one termination Switching Power Supplies, the other end is connected with the error current signal input upper end that isolates change-over circuit as the error current signal output upper end of error amplifying circuit, the collector electrode of triode Q1 is connected with the error current signal output lower end that isolates change-over circuit as the error current signal input lower end of error amplifying circuit, the collector electrode of one termination triode Q1 of resistance R 2, the other end of other end connecting resistance R1, one end of resistance R 4 is connected with an end of capacitor C 1, the base stage of another termination triode Q1 of resistance R 4, the collector electrode of another termination triode Q1 of capacitor C 1.
Described isolation change-over circuit comprises optocoupler OP1, resistance R 7, R8, R9, capacitor C 2, diode D1; Wherein, the light-emitting diodes tube anode of optocoupler OP1 is as the error current signal input upper end that isolates change-over circuit, the light-emitting diodes tube cathode of optocoupler OP1 is as the error current signal output lower end that isolates change-over circuit, the phototriode of optocoupler OP1 is connected in series with diode D1, resistance R 7, the anode of diode D1 meets power supply Vc, resistance R 9 and capacitor C 2 series connection, in parallel with the phototriode two ends of optocoupler OP1, resistance R 8 one ends are as the feedback signal output of isolating change-over circuit, output signal Vfb, other end ground connection.
Compared with prior art, the present invention has following advantage:
1, the present invention adopts discrete component to form fully, and simple in structure, cost is low.In error amplifying circuit, utilized the signal of telecommunication amplification principle of triode, guarantee the transistor emitter voltage constant with voltage-stabiliser tube, the voltage error signal that reflects between Base-Emitter, be enlarged into the collector current signal of triode, feed back.So just do not need to adopt the linear regulator chip of TL431 and so on or operational amplifier chip to carry out the amplification of error signal, simplified circuit structure, saved cost.
2, stability of the present invention is high, adopt in this circuit that light-emitting diode carries out current limliting in 1 pair of optocoupler of resistance R, when triode turn-offs, utilize 2 pairs of light-emitting diodes of resistance R to carry out bypass, prevent the false triggering of light-emitting diode and produced bigger anti-phase bias voltage thereon.Therefore, only need to select withstand voltage suitable triode, just can directly utilize the output voltage V o of Switching Power Supply operating voltage to be provided for optocoupler and triode, and not need to adopt the mode of the auxiliary winding of transformer that voltage is provided separately, particularly under output voltage V o condition with higher.This also makes this circuit structure further simplify, and has improved the stability of a system, and wide adaptability, can both be suitable for exporting ten volts of Switching Power Supplies to several hectovolts.
3, the present invention uses the frequency compensated circuit of capacitor C 1 and resistance R 4 composition error amplifiers in the feedback circuit of the present invention, adopts different values just can change the amplitude-frequency and the phase-frequency characteristic of error amplifying circuit.Can guarantee that by reasonable value the transfer function of circuit has enough phase margins, make the switch power supply system that adopts this feedback circuit significantly reduce the generation of oscillatory occurences, further improve system's operation stability.
4, input and output side of the present invention adopts photoelectrical coupler to carry out the transmission of signal, is the conversion of electricity-light-electricity, is not electrically connected so two ends have directly, disturbs to reduce greatly, makes the operation of system more stable.
5, the present invention's bleed off path of adopting resistance R 9 and capacitor C 2 to form high-frequency signal at the optocoupler output, filtering High-frequency Interference effectively strengthens the stability of feedback signal.
6, the present invention adopt resistance R 8 can limit feedback the maximum of output Vfb.When electric current was bigger, its resistance is much larger than the phototriode equivalent resistance, and was by bypass, inoperative; When electric current was less, its resistance was less than the phototriode equivalent resistance, and electric current mainly flows through from resistance R 8, and the maximum output valve of feedback output Vfb is exactly the value that resistance R 8 and resistance R 7 dividing potential drops obtain.Make circuit of the present invention to be complementary with whole switch power supply system more neatly by limiting this value, the maximum duty cycle of restriction pulse-width signal.In addition, realize that this function only needs a resistance, circuit structure is simple.
Description of drawings
Fig. 1 is a kind of circuit structure diagram of Switching Power Supply.
Fig. 2 is a structured flowchart of the present invention.
Fig. 3 is an electrical schematic diagram of the present invention.
Fig. 4 is the circuit diagram of one embodiment of the invention.
Fig. 5 is in one embodiment of the invention, the waveform testing figure of key node when Vo has positive and negative 6V nominal error to fluctuate.
Fig. 6 is in another embodiment of the present invention, and Vo has the significantly waveform testing figure of key node during fluctuating error of positive and negative 50V.
Embodiment
Below by specific embodiments of the invention also in conjunction with the accompanying drawings, purpose of the present invention, circuit structure and advantage are further described.
As shown in Figure 1 be the basic circuit structure of the positive activation type Switching Power Supply of an extensive use, the VD that this Switching Power Supply produces is voltage input signal Vo.This voltage input signal Vo inputs to sampling feedback circuit of the present invention, obtains voltage feedback signal Vfb through handling, and as the output signal of circuit of the present invention, feeds back to PWM (pulse-width modulation) module of Switching Power Supply.
As shown in Figure 2, a kind of sampling feedback circuit of switch power source output voltage comprises voltage sampling circuit 1, error amplifying circuit 2, isolates change-over circuit 3;
The effect of described voltage sampling circuit 1 is that voltage input signal Vo is carried out the dividing potential drop sampling.Voltage input signal Vo is by the voltage signal input input of voltage sampling circuit 1, and the sampled signal that obtains Vo by electric resistance partial pressure exports error amplifying circuit 2 to.It comprises slide rheostat VR1, resistance R 5 and resistance R 6; One end of resistance R 6 is as the voltage signal input of voltage sampling circuit 1, insert voltage input signal Vo, the other end is connected with an end of slide rheostat VR1, resistance R 5, the other end ground connection of resistance R 5, the tap of slide rheostat VR1 as the sampled signal input of the sampled signal output of voltage sampling circuit 1 and error amplifying circuit 2 just the base stage of triode Q1 be connected;
The effect of described error amplifying circuit 2 is sampled signal to be carried out error amplify.Voltage input signal Vo is as the power supply of error amplifying circuit 2, be connected with its power supply input, sampled signal is converted to the current mode error signal outputs to isolation change-over circuit 3 from the error current signal output upper end of error amplifying circuit 2 error current signal input upper end by the sampled signal input input of error amplifying circuit 2.This error amplifying circuit 2 comprises resistance R 1, R2, R3, R4, capacitor C 1, voltage stabilizing didoe ZD1, triode Q1; Resistance R 3 is connected in series with voltage-stabiliser tube ZD1, its end that links to each other links to each other with the emitter of triode Q1, the plus earth of voltage stabilizing didoe ZD1, the other end of resistance R 3 is as the output voltage V o of the power supply input termination switch power supply of error amplifying circuit 2, the output voltage V o of resistance R 1 one termination Switching Power Supplies, the other end is connected with the light-emitting diodes tube anode as the optocoupler OP1 on the input of error current signal of isolating change-over circuit 3 as the error current signal output upper end of error amplifying circuit 2, the collector electrode of triode Q1 is connected with the light-emitting diodes tube cathode as the optocoupler OP1 of error current signal output lower end of isolating change-over circuit 3 as the error current signal of error amplifying circuit 2 input lower end, with the formation current circuit; The collector electrode of one termination triode Q1 of resistance R 2, the other end of other end connecting resistance R1; One end of resistance R 4 is connected with an end of capacitor C 1, the base stage of another termination triode Q1 of resistance R 4, the collector electrode of another termination triode Q1 of capacitor C 1.
The effect of described isolation change-over circuit 3 is that the current mode error signal of error amplifying circuit 2 outputs is carried out electrical isolation, is converted to voltage feedback signal Vfb, the output of self feed back signal output part.It comprises optocoupler OP1, resistance R 7, R8, R9, capacitor C 2, diode D1; The phototriode of optocoupler OP1 is connected in series with diode D1, resistance R 7, the anode of diode D1 meets power supply Vc, resistance R 9 and capacitor C 2 series connection, in parallel with the phototriode two ends of optocoupler OP1, resistance R 8 one ends are as the feedback signal output of isolating change-over circuit 3, output signal Vfb, other end ground connection.
The course of work of circuit of the present invention and principle:
During Switching Power Supply work, its VD is Vo.Make output voltage V o stable, must sample to its error signal that departs from the voltage stabilizing value and amplify, feed back to the prime control end of Switching Power Supply again, carry out PWM (pulse-width modulation), utilize negative feedback to carry out voltage stabilizing again and control through the sampling feedback circuit.
The voltage sampling circuit that resistance R 5, resistance R 6, slide rheostat VR1 form is with the sampling of voltage input signal Vo dividing potential drop, and the fluctuation that this sampled voltage is followed voltage input signal Vo changes, thus the base voltage of control triode Q1.Because the emitter of triode Q1 meets a voltage stabilizing didoe ZD1, make the emitter of triode Q1 be stabilized in a comparatively fixing current potential.So the Base-Emitter junction voltage of triode Q1 changes with its base voltage, promptly the variable quantity with voltage input signal Vo is directly proportional.
According to the triode characteristic, collector current is directly proportional with the Base-Emitter junction voltage, and then the collector current of triode Q1 also is directly proportional with the variable quantity of voltage input signal Vo.The light-emitting diode of optocoupler OP1 is connected with the collector electrode of triode Q1, and the electric current that flows through is the same substantially, and hence one can see that, and the electric current on the light-emitting diode of optocoupler OP1 is directly proportional with the variable quantity of Vo.In the circuit of the present invention, resistance R 1 is an optocoupler OP1 current limliting, and resistance R 3 is a voltage-stabiliser tube ZD1 current limliting.Resistance R 2 shields, and when triode Q1 conducting, the impedance ratio resistance R 2 of light-emitting diode is much smaller, and resistance R 2 is by bypass, and is inoperative; When triode Q1 turn-offs, the impedance ratio resistance R 2 of light-emitting diode is much bigger, resistance R 2 bypasses light-emitting diode, less leakage current mainly flows through from resistance R 2, guaranteed that the light-emitting diode both end voltage is near 0V, make its not conducting, prevent false triggering and the bigger anti-phase bias voltage on diode.This electric circuit characteristic is triode Q1 to be used as an error amplifier use, and its emitter is equivalent to the anode of amplifier, and base stage is equivalent to negative terminal, and emitter current is equivalent to error and amplifies output.Between the collector electrode of triode Q1 and base stage, add resistance R 4 and capacitor C 1, just be equivalent between the output of error amplifier and input, add negative feedback, play the frequency compensation effect, can set corresponding value according to the transfer function of different electrical power main structure, make that whole Switching Power Supply regulating system is more stable, if be provided with improper or this frequency compensation network not, system may be unstable, vibration occurs.
Because can there be very big electromagnetic interference in the input/output terminal of Switching Power Supply, is starved of and carries out electrical isolation, circuit of the present invention adopts photoelectrical coupler, is that light signal goes back to the signal of telecommunication again with electrical signal conversion, finishes the electrical isolation at two ends.Under the power supply of Vc, the phototriode of optocoupler OP1 can flow through and the directly proportional electric current of light-emitting diode.7 metering functions of resistance R, diode D1 irritates for preventing that voltage is counter.When the electric current difference that flows through, the voltage drop of resistance R 7 is just different, and the pressure drop substantially constant of Vc and diode D1, then the small signal variable quantity of the error of output amplification feedback signal Vfb is directly proportional with the current change quantity that phototriode flows through.As from the foregoing, feedback signal Vfb is directly proportional with the disturbance quantity of switch power source output voltage Vo, can reflect the error of switch power source output voltage well and amplifies, and plays the effect of switch power source output voltage Vo error signal feedback.Resistance R 9 and capacitor C 2 play considers the effect that removes High-frequency Interference.Resistance R 8 is connected between Vfb and the ground, and when electric current was bigger, its resistance is much larger than the phototriode equivalent resistance, and was by bypass, inoperative; When electric current was less, its resistance was less than the phototriode equivalent resistance, and electric current mainly flows through from resistance R 8, can make Vfb be no more than a certain set point, the output duty cycle of restriction back level PWM controller.
With a specific embodiment advantage of the present invention is described below:
1, input is set:
The stationary value of the output dc voltage Vo of Switching Power Supply is 195V;
Ripple voltage: in 3%, promptly the normal fluctuation range of Vo is the positive and negative 6V of 195V.
2, parameter is selected:
(1) the voltage stabilizing value of voltage-stabiliser tube ZD1 can be got the arbitrary value between 2V-10V, and other component parameters calculate according to this value.Choose the voltage-stabiliser tube that the voltage stabilizing value is 6.2V in this example.
If the voltage stabilizing value of voltage-stabiliser tube ZD1 is Vz, then Vo just often, resistance R 5, R6, the sampling dividing potential drop of slide rheostat VR1 will be Vz+0.7V, promptly than the pressure drop of the high triode emitter junction of Vz.The Standard resistance range of resistance R 5 is generally got 1K～10K ohm (free setting), and resistance R 6 will be calculated according to the resistance of resistance R 5 with slide rheostat VR1.Resistance R 5 is got 5K ohm in this example.Getting voltage for the circuit that resistance resistance R 5, R6 and slide rheostat VR1 are formed is 6.9V, promptly than the high 0.7V of voltage stabilizing value of 6.2V voltage-stabiliser tube, power taking resistance R6 is 250K ohm in this example, slide rheostat VR1 is the slide rheostat of 20K ohm, by regulating slide rheostat VR1, can make dividing potential drop is 6.9V.
(2) select the β value of triode Q1 according to the requirement of error multiplication factor, be typically chosen in about 100, the withstand voltage of triode Q1 wants the maximum of specific output voltage Vo high by 20% in addition.Choosing model in this example is the NPN pipe of q2n3439.
(3) current-limiting resistance R1, R3 choose according to the size of output voltage, generally get 500 times of ohms of Vo value.Get 100K ohm in this example.
(4) protective resistance R2 generally gets about 10K ohm.
(5) frequency compensation resistance R 4 and capacitor C 1 are generally determined by the desired phase margin of system, and the span of resistance R 4 is 200K～500K ohm, and capacitor C 1 is 2nF～10nF.Resistance R 4 is got 270K ohm in this example, and capacitor C 1 is got 6.8nF.
(6) optocoupler OP1 selection current transfer ratio is about 1.Selecting model in this example is PC817B.
(7) diode D1 selects general-purpose diode to get final product.In this example 1N4007.
(8) can select different current-limiting resistance R7 according to the difference of Vc, be generally 1000 times of ohms of the value of Vc.Get 4.3K ohm in this example.
(9) resistance R 9 and capacitor C 2 are considered the frequency range that removes High-frequency Interference as required and are required to select, general resistance R 9 at hundreds of to several kilohms, capacitor C 2 at several nF between the 1uF.Resistance R 9 is got 2.2K ohm in this example, and capacitor C 2 is got 47nF.
(10) selection of resistance R 8 will require according to the maximum of Vfb to select, and the maximum of establishing Vfb is Vfbmax, then Vc * R7/ (R7+R8)=Vfbmax, the value of formula selection resistance R 8 thus.Get 12K ohm in this example, can limit the Vfb maximum and be no more than 2.5V.
Concrete parameter gathers as follows:
Resistance R 1:100K ohm; Resistance R 2:10K ohm;
Resistance R 3:100K ohm; Resistance R 4:270K ohm;
Resistance R 5:5K ohm; Resistance R 6:250K ohm;
Resistance R 7:4.3K ohm; Resistance R 8:12K ohm;
Resistance R 9:2.2K ohm; Slide rheostat VR1:20K slide rheostat;
Capacitor C 1:6.8nF/400V; Capacitor C 2:0.047uF/100V;
Diode D1:1n4007; Voltage stabilizing didoe ZD1:6.2V voltage-stabiliser tube;
Triode Q1:NPN manages q2n3439;
Optocoupler OP1:PC817B.
3, interpretation of result
The waveform testing figure of key node when Fig. 5 has the fluctuation of positive and negative 6V nominal error for input voltage Vo (195V); Wherein, Vo is the output voltage of Switching Power Supply; Vbe is the basic emitter voltage on the triode Q1; Id is the electric current that flows through on the light-emitting diode; Ic is the electric current of sensing on the phototriode; Vfb is the error amplification signal of voltage feedback circuit output.
As seen from Figure 5, when Vo under near the situation of positive and negative 6V fluctuation its voltage stabilizing value 195V, Vfb can follow disturbance well, phase place is opposite, is negative feedback, responds very fast, almost do not postpone, its fluctuation range is 1.5V～2V, is fit to the input requirement of its back PWM comparator.
Situation when this situation is the power supply operate as normal.As seen from Figure 5, when Vo under near the situation of positive and negative 6V fluctuation its voltage stabilizing value 195V, Vfb can follow the disturbing signal of Vo well, and phase place is opposite, is negative feedback, respond very fast, almost do not postpone, amplitude fluctuates in 1.5V～2V scope, changes comparatively level and smooth, do not have spike or burr, these test waveforms illustrate that all this circuit has the advantage of high stability.
Fig. 6 has the significantly waveform testing figure of key point during fluctuating error of positive and negative 50V for input voltage Vo (195V); Wherein each signal definition such as Fig. 5.
Situation shown in Figure 6 is near positive and negative 50V fluctuation Vo voltage stabilizing value 195V, belongs to the large-signal response, the situation when being generally power supply start, shutdown or improper running.
As seen from Figure 6, Vfb still can follow the fluctuation of Vo well and change, and has higher response speed.
When Vo crosses when low, triode Q1 ends, electric current reduces to 0 in the light-emitting diode, phototriode does not induce electric current yet, Vfb output is saturated to be maximum voltage, because the effect of resistance R 8 is arranged, makes Vfb be 2.5V to the maximum, rather than the 4V of Vc, play the effect of restriction back level PWM comparator output maximum pulse width.
When Vo was too high, led current was bigger, and phototriode is in saturation condition, and collection emitter-base bandgap grading saturation voltage drop probably is 0.3V, and Vfb exports minimum voltage 0.3V, is lower than the volt value of PWM comparator forward end sawtooth waveforms, and making its output waveform duty ratio is 0.Can stopcock metal-oxide-semiconductor a period of time, wait Vo to drop in the normal 195V voltage stabilized range and modulate again.
As seen, Vfb still can follow the fluctuation of Vo well and change under improper situation, have higher response speed, can't influence job stability because of significantly sharply changing of Vo.
Claims (3)
1, a kind of sampling feedback circuit of switch power source output voltage, comprise voltage sampling circuit (1), error amplifying circuit (2), isolate change-over circuit (3), the output voltage V o of Switching Power Supply is by the voltage signal input input of voltage sampling circuit (1), carry out dividing potential drop and obtain sampled signal, and the voltage input signal Vo while is as the power supply of error amplifying circuit (2), sampled signal is by the sampled signal input input of error amplifying circuit (2), be converted to the current mode error signal and output to the error current signal input part of isolating change-over circuit (3), carry out electrical isolation and obtain feedback loop output signal Vfb, it is characterized in that: described isolation change-over circuit (3) comprises optocoupler (OP1), resistance R 7, resistance R 8, resistance R 9, electric capacity (C2), diode (D1); Wherein, the light-emitting diodes tube anode of optocoupler (OP1) is as the error current signal input upper end that isolates change-over circuit (3), the light-emitting diodes tube cathode of optocoupler (OP1) is as the error current signal output lower end that isolates change-over circuit (3), the collector electrode of the phototriode of optocoupler (OP1) respectively with resistance R 7, resistance R 8, one end of resistance R 9 connects the back and constitutes the feedback output end of isolating change-over circuit (3), isolate change-over circuit (3) output feedback loop output signal Vfb, the other end of resistance R 7 is connected with the negative electrode of diode (D1), the anode of diode (D1) meets power supply Vc, the other end of resistance R 9 with after electric capacity (C2) is connected respectively with the other end of resistance R 8, the emitter of the phototriode of optocoupler (OP1) connects ground connection.
2, the sampling feedback circuit of a kind of switch power source output voltage according to claim 1, it is characterized in that: described voltage sampling circuit (1) comprises slide rheostat (VR1), resistance R 5 and resistance R 6, one end of resistance R 6 is as the voltage signal input, meet voltage input signal Vo, the other end is connected with an end of slide rheostat (VR1), resistance R 5, the other end ground connection of resistance R 5, the tap of slide rheostat (VR1) is connected with the sampled signal input of error amplifying circuit (2) as the sampled signal output of voltage sampling circuit (1).
3, the sampling feedback circuit of a kind of switch power source output voltage according to claim 1, it is characterized in that: described error amplifying circuit (2) comprises resistance R 1, resistance R 2, resistance R 3, resistance R 4, electric capacity (C1), voltage stabilizing didoe (ZD1), triode (Q1); Wherein, the base stage of triode (Q1) is as the sampled signal input of error amplifying circuit (2), resistance R 3 is connected in series with voltage-stabiliser tube (ZD1), its end that links to each other links to each other with the emitter of triode (Q1), the plus earth of voltage stabilizing didoe (ZD1), the other end of resistance R 3 is as the output voltage V o of the power supply input termination switch power supply of error amplifying circuit (2), the output voltage V o of resistance R 1 one termination Switching Power Supplies, the other end is connected with the error current signal input upper end that isolates change-over circuit (3) as the error current signal output upper end of error amplifying circuit (2), the collector electrode of triode (Q1) is connected with the error current signal output lower end that isolates change-over circuit (3) as the error current signal input lower end of error amplifying circuit (2), the collector electrode of one termination triode (Q1) of resistance R 2, the other end of other end connecting resistance R1, one end of resistance R 4 is connected with an end of electric capacity (C1), the base stage of another termination triode (Q1) of resistance R 4, the collector electrode of another termination triode (Q1) of electric capacity (C1).
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|---|---|---|---|---|
| JP2009291006A (en) * | 2008-05-29 | 2009-12-10 | Fujitsu Ltd | Device and method for converting voltage, and program for determining duty ratio |
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| CN112886807B (en) * | 2021-02-07 | 2023-06-20 | 上海空间电源研究所 | Device and method for realizing soft start |
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2007
- 2007-10-26 CN CNB2007101339944A patent/CN100525040C/en not_active Expired - Fee Related
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