CN101453165A - Summit current operated electric voltage feed forward method in switch power source - Google Patents

Abstract

The invention discloses a voltage feedforward method for controlling peak current in a switch power, which comprises a main circuit and a control circuit of the switch power, wherein power components are connected in series at the primary side of the main circuit; and the control circuit mainly comprises a sample circuit, a comparator, a voltage control delay unit and a drive device. The method comprises: performing the voltage sampling and comparing with a threshold value of the comparator, and turning the comparator if the value is larger than the threshold value of the comparator; and triggering the voltage control delay unit by a turning signal of the comparator to generate a delay voltage signal to the drive device according to a specific arithmetic, to control the on-off of the power components to control the peak current in the switch power. The method improves the reliability of the whole system, simplifies the design of the system and reduces the requirements on the components.

Description

Electric voltage feed forward method in the control of Switching Power Supply peak current

Technical field

The present invention relates to the method for Switching Power Supply peak current control, relate in particular to the method for electric voltage feed forward in a kind of Switching Power Supply peak current control.

Background technology

In switch power supply system, generally all comprised the peak current limit module.The reliability of system has been strengthened in the introducing of peak current limit module, has reduced the requirement to components and parts, makes the controllability of system's output be improved.

Existing peak current limit module is work like this: system passes through current sensing means real-time detecting system electric current, and compares with set point, if system power less than set point, then allows electric current to continue to increase; If system power, is then exported control signal driving power pipe greater than set point and is closed.As shown in Figure 1, at power tube 100 open periods, inductive current rises under the input voltage effect gradually, and the voltage Vcs on the sampling resistor Rcs follows rising.When Vcs voltage rises to threshold voltage V _ThThe time, comparator 101 sends control signal and gives driving element 102, and driving element 102 is closed power tube 100 according to the requirement of control signal.

In such scheme, the original intention of system design is according to following formula control peak current: $\mathrm{Ipeak}=\frac{\mathrm{Vth}}{\mathrm{Rcs}},$ This scheme has been ignored the influence of system delay time to peak current.At power tube 100 open periods, Vcs voltage rises gradually, when voltage rises to threshold voltage V _ThThe time, the output of comparator 101 is from high step-down, and driving element 102 begins GATE voltage is also moved to low level from high level after receiving the variation of input signal.In this process, comparator 101 itself has delay, and driving element 102 also has delay.Postpone during this period of time in, the grid voltage of power tube 100 does not also have enough time to change, power tube is still opened, peak electricity fails to be convened for lack of a quorum and continues to increase, up to power tube 100 grid voltages dragged down close till.

The system of setting up departments is T time of delay _D, then $\mathrm{Ipeak}=\frac{\mathrm{Vth}}{\mathrm{Rcs}}+\frac{\mathrm{Vline}*T_D}{\mathrm{Lpri}}$

Wherein, Vline is an input voltage; T _DIt is the system delay time; In the inductance value following formula of Lpri transformer, first

Be system's controlled target numerical value, second portion

Be the numerical value that peak current that system delay causes departs from controlled target.When change range of input voltage is very big, the bias of the peak current that system delay causes is also very big, with the AC/DC converter is example, usually require the input voltage range of broad, as exchange 85V to 265V, the input direct voltage excursion reaches 250V, and according to the circuit of Fig. 1, peak current will change a lot under different input voltages.Therefore, be necessary to introduce the electric voltage feed forward function and compensate the influence of input voltage variation peak current.

In the system, at system's run duration, it is constant that vdd voltage keeps substantially as shown in Figure 2, and the electric current that flows through resistance 206 is

, because Vline is much larger than VDD, this electric current can be approximated to be

Inner at controller by amplifying this electric current and, producing new threshold voltage and control peak current this electric current and the stack of existing threshold voltage.Peak current just becomes like this:

$\mathrm{Ipeak}=\frac{\mathrm{Vth}-k*\mathrm{Vline}}{\mathrm{Rcs}}+\frac{\mathrm{Vline}*T_D}{\mathrm{Lpri}}$

By following formula as seen, under different input voltages, obtain equal peak current, must regulate external circuit and make

Equal

That is to say as external electric sensibility reciprocal Lpri to change or foreign current sample resistance Rcs when changing, all must regulate penalty coefficient k.In Fig. 2, to regulate penalty coefficient k and regulate starting resistance 206 exactly, this will influence the start-up time and the stand-by power consumption of system.In addition, in the prior art,, increased a pin Vin, inevitably increased system complexity and cost in order to realize electric voltage feed forward.

Summary of the invention

Technical problem to be solved by this invention provides the electric voltage feed forward method of the control of peak current in a kind of Switching Power Supply, in peak current limit accurately, improves the reliability of system, the simplified system design.

For solving the problems of the technologies described above, the electric voltage feed forward method of peak current control in the Switching Power Supply of the present invention, comprise Switching Power Supply main circuit and control circuit, be serially connected with power component in the main circuit primary side, control circuit mainly contains sample circuit, comparator, voltage-controlled delay unit and driving element to be formed, and this method comprises the steps:

Step 1, Switching Power Supply are opened, and the main circuit power component flows through electric current, and this electric current sample circuit of flowing through forms a sampled voltage Vcs;

Step 2, along with the main circuit power component flows through the increase of electric current, sampled voltage Vcs constantly raises, as sampled voltage Vcs during greater than the threshold voltage of comparator, the comparator output switching activity, output one controls signal to the voltage-controlled delay unit;

After step 3, voltage-controlled delay unit are controlled signal triggering, press the T in the following formula _VCDProduce and postpone

$\mathrm{Ipeak}=\frac{\mathrm{Vth}}{\mathrm{Rcs}}+\frac{\mathrm{Vline}*T_D}{\mathrm{Lpri}}+\frac{\mathrm{Vline}*T_{\mathrm{VCD}}}{\mathrm{Lpri}}$

Wherein,

$T_{\mathrm{VCD}}=\frac{\mathrm{Lpri}*I_{\mathrm{FIX}}}{\mathrm{Vline}}-T_{\mathrm{FIX}}$

I _FIXBe fixed current value T _FIXBe that fixed delay time Rcs is a sample circuit resistance

Vline is an input voltage; T _DIt is the system delay time; The inductance value of Lpri transformer

Ipeak is the main circuit peak current;

Step 4, the output of the voltage-controlled delay unit after step 3 postpones one control signal to driving element, and driving element control main circuit power component cuts out, to realize the control of peak current in the Switching Power Supply.

Because the present invention has adopted technique scheme, promptly in the control circuit of Switching Power Supply, add the voltage-controlled delay unit, and by certain algorithm realization electric voltage feed forward delay, to reach the purpose of peak current control in the Switching Power Supply, improved the reliability of whole system, simplified the design of system, reduced requirement components and parts.

Description of drawings

The present invention is described in further detail below in conjunction with drawings and embodiments:

Fig. 1 is the schematic diagram of existing Switching Power Supply peak current control,

Fig. 2 is the schematic diagram of another kind of existing Switching Power Supply peak current control,

Fig. 3 is the schematic diagram of Switching Power Supply peak current control of the present invention.

Embodiment

As shown in Figure 3, electric voltage feed forward method in the Switching Power Supply peak current control of the present invention, comprise Switching Power Supply main circuit and control circuit, be serially connected with power component 300 in the main circuit primary side, control circuit mainly contains sample circuit, comparator 301, voltage-controlled delay unit 302 and driving element 303 to be formed, and this method comprises the steps:

Step 1, Switching Power Supply are opened, and main circuit power component 300 flows through electric current, and this electric current sample circuit of flowing through forms a sampled voltage Vcs;

Step 2, along with main circuit power component 300 flows through the increase of electric current, sampled voltage Vcs constantly raises, as sampled voltage Vcs during greater than the threshold voltage of comparator 301, comparator 301 output switching activities, output one controls signal to voltage-controlled delay unit 302;

After step 3, voltage-controlled delay unit 302 are controlled signal triggering, press the T in the following formula _VCDProduce and postpone

$\mathrm{Ipeak}=\frac{\mathrm{Vth}}{\mathrm{Rcs}}+\frac{\mathrm{Vline}*T_D}{\mathrm{Lpri}}+\frac{\mathrm{Vline}*T_{\mathrm{VCD}}}{\mathrm{Lpri}}$

Wherein,

$T_{\mathrm{VCD}}=\frac{\mathrm{Lpri}*I_{\mathrm{FIX}}}{\mathrm{Vline}}-T_{\mathrm{FIX}}$

I _FIXBe fixed current value T _FIXBe that fixed delay time Rcs is a sample circuit resistance

Vline is an input voltage; T _DIt is the system delay time; The inductance value of Lpri transformer

Ipeak is the main circuit peak current;

With T _VCDThe expression formula of expression formula substitution Ipeak in, then obtain

$\mathrm{Ipeak}=\frac{\mathrm{Vth}}{\mathrm{Rcs}}+\frac{\mathrm{Vline}*T_D}{\mathrm{Lpri}}+\frac{\mathrm{Vline}*T_{\mathrm{VCD}}}{\mathrm{Lpri}}=\frac{\mathrm{Vth}}{\mathrm{Rcs}}+\frac{\mathrm{Vline}*T_D}{\mathrm{Lpri}}-\frac{\mathrm{Vline}*T_{\mathrm{FIX}}}{\mathrm{Lpri}}+I_{\mathrm{FIX}}$ , in design with T _FIXBe designed to equal T _D, so $\mathrm{Ipeak}=\frac{\mathrm{Vth}}{\mathrm{Rcs}}+I_{\mathrm{FIX}}$ To no longer relation be arranged, change with input voltage with regard to having solved peak current like this, the problem that also changes simultaneously with the primary electrical sensibility reciprocal with input voltage Vline and primary electrical sensibility reciprocal Lpri;

Step 4,302 outputs one of the voltage-controlled delay unit after step 3 postpones control signal to driving element 303, and driving element 303 control main circuit power components 300 cut out, to realize the control of peak current in the Switching Power Supply.

Claims (1)

1, the electric voltage feed forward method in a kind of Switching Power Supply peak current control, comprise Switching Power Supply main circuit and control circuit, be serially connected with power component in the main circuit primary side, control circuit mainly contains sample circuit, comparator, voltage-controlled delay unit and driving element to be formed, and it is characterized in that: this method comprises the steps:

Step 1, Switching Power Supply are opened, and the main circuit power component flows through electric current, and this electric current sample circuit of flowing through forms a sampled voltage Vcs;

Step 2, along with the main circuit power component flows through the increase of electric current, sampled voltage Vcs constantly raises, as sampled voltage Vcs during greater than the threshold voltage of comparator, the comparator output switching activity, output one controls signal to the voltage-controlled delay unit;

After step 3, voltage-controlled delay unit are controlled signal triggering, press the T in the following formula _VCDProduce and postpone

$\mathrm{Ipeak}=\frac{\mathrm{Vth}}{\mathrm{Rcs}}+\frac{\mathrm{Vline}*T_D}{\mathrm{Lpri}}+\frac{\mathrm{Vline}*T_{\mathrm{VCD}}}{\mathrm{Lpri}}$

Wherein, $T_{\mathrm{VCD}}=\frac{\mathrm{Lpri}*I_{\mathrm{FIX}}}{\mathrm{Vline}}-T_{\mathrm{FIX}}$

I _FIXBe fixed current value T _FIXBe that fixed delay time Rcs is a sample circuit resistance

Vline is an input voltage; T _DIt is the system delay time; The inductance value Ipeak of Lpri transformer is the main circuit peak current;

Step 4, the output of the voltage-controlled delay unit after step 3 postpones one control signal to driving element, and driving element control main circuit power component cuts out, to realize the control of peak current in the Switching Power Supply.

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