CN101741224B - Voltage-drop compensation method for power output lines and switch power supply - Google Patents

Abstract

The invention discloses a voltage-drop compensation method for power output lines and a switch power supply, and the key points of the technical scheme are as follows: the circuit at the feedback part of the switch power supply comprises a sampling resister 04, a reference source 03, a photoelectric coupler 02, an output capacitor 05, a power output line resister 06 and a current-limiting resister 01, wherein one end of the current-limiting resister 01 is connected with the output resister 05, and the other end thereof is connected with the photoelectric coupler 02; the photoelectric coupler 02 is connected with the cathode of the reference source 03, the anode of the reference source 03 is set as a reference ground, and the reference end of the reference source 03 is connected with the common ports of R2 and R3 of the sampling resister 04; R2 end of R2 and R3 of the serial sampling circuit 04 is connected with the output capacitor 05, and R3 end is connected with the reference ground of the reference source 03; and a compensation resister Rd is added between the reference ground of the reference source 03 and R3 of the sampling resister 04. The invention has the advantages of saving wires and improving load regulation. The invention can be used in the feedback parts of various power supplies, and comprises but is not limited to the following devices such as a flyback converter, a forward converter, a half-bridge converter, a full-bridge converter, a quasi-resonant converter and the like.

Description

A kind of method of power output lines and switch power supply voltage-drop compensation

Technical field

The present invention relates to fields such as simulation electronic, power electronics, digital and electronic, automatic control, more particularly, relate to the power supply output line voltage-drop compensation method for designing of Switching Power Supply.

Background technology

In the design of Switching Power Supply, load regulation is a crucial design objective, and it is defined as: under unloaded and fully loaded situation, and the changing value of power output end voltage and the ratio of rated output voltage.If the output point on the PCB of power supply is measured this numerical value, then this parameter depends primarily on the gain of error amplifier in the feedback control loop.Be smaller generally speaking, can reach below 0.1%.

But for the pressure drop on the power supply output line, for example the output lead of power supply adaptor then is difficult to handle.Because the resistance on the power supply output line is positioned at outside the feedback control loop, if the power supply output line of output is long, perhaps the cabling of output line on PCB is long, and output current is bigger, and then the pressure drop on the power supply output line will be very considerable.For example for the Switching Power Supply of a 5V/10A, the resistance of supposing power supply output line is 0.02 ohm, and then under fully loaded situation, the pressure drop on the line will reach 0.2V, and the pressure drop on no-load condition rolls off the production line is 0V.Then load regulation is (0.2-0)/5*100%=4%.The index of such power supply load regulation rate is underproof.

At this problem, utilize prior art, three kinds of solutions are arranged:

The one, have a mind to improve the output voltage of power supply, make that load end can access specified voltage under the situation of band full load.

Two are to use the output in parallel of many power supply output lines, reduce the resistance on the output lead.

Three are to use the teletransmission function.This is a kind of method that generally adopts.This method can compensate the voltage drop that produces in the distributed system to a certain extent, make and on load end or certain test point, to regulate output voltage, the teletransmission line only carries very little electric current, does not need very big sectional area to carry big electric current.But, when on user's printed circuit board, using the teletransmission function, very high: the teletransmission line closely plane of should trying one's best to the requirement of teletransmission line.When using discrete power supply output line to be used as the teletransmission line, need to use twisted-pair feeder to reduce interference of noise as teletransmission line or use additive method.The voltage that the teletransmission circuit can compensate at most is 10% rated output voltage, needs the voltage drop of compensation to be created between the voltage of the voltage of sampling and output.This method is that essence is taken at load-side with sampling point exactly, thereby realizes the purpose of compensation.

Though above-mentioned three kinds of methods all are used, the shortcoming of its existence is conspicuous:

Method one voltage in zero load is higher, just can drop to normal value when having only the band full load, and load regulation is without any improvement.

Method two has reduced the resistance on the out-put supply output line, produces effect for improving load regulation, but the effect that improves and not clear, the loss on the power supply output line still is not compensated.

The regulation of scheme three can be significantly improved, but needs extra power supply output line, and need do special processing to power supply output line, and it is convenient inadequately to use.

In addition, in case open fault appears in the teletransmission line, then voltage feedback loop will disconnect, and output voltage is uncontrollable, will cause load equipment to damage.

Summary of the invention

The objective of the invention is to overcome deficiency of the prior art, a kind of method of power output lines and switch power supply voltage-drop compensation is provided, no matter output current is zero load or fully loaded, and it is invariable that the voltage of power source loads end keeps, and do not need extra wire compensation.

A kind of method of power output lines and switch power supply voltage-drop compensation, Switching Power Supply feedback fraction circuit comprises sample resistance 04, a reference source 03, photoelectrical coupler 02, output capacitance 05, power supply output line resistance 06, current-limiting resistance 01; Current-limiting resistance 01 1 ends are connected with output capacitance 05, and the other end is connected with photoelectrical coupler 02, and photoelectrical coupler 02 is connected with the cathode of a reference source 03, and the anode of a reference source 03 is made as with reference to ground, the reference edge of a reference source 03 and the sample resistance of connecting 04 R ₂, R ₃Common port be connected; Sample resistance 04 R of series connection ₂, R ₃Circuit R ₂End is connected with output capacitance 05, R ₃End is connected with the reference ground of a reference source 03; Reference ground and sample resistance 04 R in a reference source 03 ₃Between add compensating resistance R _d

Compensating resistance R _dSize multiply by sample resistance R for power supply output line resistance ₃With R ₂Ratio, formula is: $R_d=R_l\frac{R_3}{R_2}.$

A reference source 03 adopts three-terminal shunt regulator TL431.

The invention has the beneficial effects as follows: after the feedback reference loop of Switching Power Supply adds compensating resistance Rd, make the pressure drop on the original power supply output line obtain equivalent compensation, the load regulation of measuring output voltage at load end will be 0 substantially, and irrelevant with the size of output current.Overcome the inherent shortcoming of traditional solution.Save wire rod, improved load regulation.The adaptable occasion of this circuit comprises the feedback fraction of various Switching Power Supplies, includes but not limited to: anti exciting converter, forward converter, half-bridge converter, full-bridge converter, quasi resonant convertor etc.

Description of drawings

The Switching Power Supply feedback fraction circuit diagram that Fig. 1 is traditional;

The improved Switching Power Supply feedback fraction of Fig. 2 circuit diagram;

The improved Switching Power Supply feedback fraction of Fig. 3 circuit application instance graph.

Embodiment

The invention will be further described below in conjunction with accompanying drawing.

Fig. 1 has indicated traditional Switching Power Supply feedback fraction circuit diagram; Sample resistance 04: determine output voltage; A reference source 03: produce reference voltage; Photoelectrical coupler 02: secondary feedback signal is delivered to primary side; Conductor resistance 06: feedback sample is put the actual impedance that exists in the section lead of load end in the practical power; Current-limiting resistance 01: the electric current in the restriction optocoupler is provided with the feedback control loop working point.

In the Feedback Design of Switching Power Supply, traditional method is the sample resistance 04R of the reference of a reference source 03 ground and series connection ₂, R ₃Circuit R ₃Link together, like this, output voltage depends on equation:

$V_1=V_{\mathrm{ref}}(1+\frac{R_2}{R_3}),$ The pressure drop that produces on the lead can't be compensated.

Fig. 2 has indicated improved Switching Power Supply feedback fraction circuit diagram; Compensating resistance R _d: the pressure drop on the lead is compensated.Suppose that the resistance on the every power supply output line is R _l/ 2, then the resistance sum on two output lines is R _l, the resistance of compensating resistance is R _d, the resistance of divider resistance is R ₂, R ₃, the anode of getting a reference source 03 is 0V with reference to ground, and establishing load current is I, and then the pressure drop through compensating resistance is IR _dReference voltage is Vref, and sampling point voltage is V ₁, output loading end port voltage is V _o, according to the characteristic of a reference source, following proportion expression is arranged:

$\frac{R_2}{R_3}=\frac{V_1-V_{\mathrm{ref}}}{V_{\mathrm{ref}}-\left({-\mathrm{IR}}_d\right)}$

$\frac{R_2}{R_3}=\frac{V_1-V_{\mathrm{ref}}}{V_{\mathrm{ref}}+{\mathrm{IR}}_d}$

By the above Output Voltage Formula of deriving after the improvement be: $V_1=V_{\mathrm{ref}}+\frac{R_2}{R_3}{V}_{\mathrm{ref}}+\frac{{\mathrm{IR}}_2{R}_d}{R_3}=V_{\mathrm{ref}}(1+\frac{R_2}{R_3})+\frac{{\mathrm{IR}}_2{R}_d}{R_3},$

As seen, along with the increase of output current I, V ₁Also can increase gradually;

Pressure drop on the power supply output line is: $2\×\frac{R_l}{2}\×I={\mathrm{IR}}_l,$ If make the pressure drop on the line obtain full remuneration, as long as make $\frac{{\mathrm{IR}}_2{R}_d}{R_3}={\mathrm{IR}}_l$ Get final product;

Draw thus: $R_d=R_l\frac{R_3}{R_2}.$

Fig. 3 has indicated improved Switching Power Supply feedback fraction circuit application instance graph; For the system of the Switching Power Supply of DC24V/10A, the reference voltage V of TL431 _Ref=2.5V, Vo are the voltage that load end measures.Suppose the resistance R of every lead _l/ 2 is 0.01 ohm, and then the all-in resistance on the lead is R _l=0.02 ohm.

Calculate R _d:

$V_1=V_{\mathrm{ref}}(1+\frac{R_2}{R_3})$

$24=2.5(1+\frac{R_2}{R_3})$

$\frac{R_2}{R_3}=8.6$

$\frac{R_3}{R_2}=\frac{1}{8.6}$

$R_d=R_l\frac{R_3}{R_2}=0.02\×\frac{1}{8.6}=\frac{0.02}{8.6}.$

(1) work as Rd=0, during I=0, promptly adopt conventional Feedback Design Method:

$V_o=V1-{\mathrm{IR}}_l=(1+\frac{R_2}{R_3})\×V_{\mathrm{ref}}+\frac{{\mathrm{IR}}_2{R}_d}{R_3}-{\mathrm{IR}}_l$

$=(1+8.6)*2.5-0=24V.$

(2) work as Rd=0, during I=10A, promptly adopt conventional Feedback Design Method:

$V_o=V1-{\mathrm{IR}}_l=(1+\frac{R_2}{R_3})\×V_{\mathrm{ref}}+\frac{{\mathrm{IR}}_2{R}_d}{R_3}-{\mathrm{IR}}_l$

$=(1+8.6)*2.5+0-10*0.02=23.8V$

Load regulation is: $\frac{24-23.8}{24}\×100\%=0.83\%.$

(3) when $R_d=R_l\frac{R_3}{R_2}=0.02\×\frac{1}{8.6}=\frac{0.02}{8.6},$ During I=0, promptly adopt the Feedback Design Method after compensating, output voltage:

$V_o=V1-{\mathrm{IR}}_l=(1+\frac{R_2}{R_3})\×V_{\mathrm{ref}}+\frac{{\mathrm{IR}}_2{R}_d}{R_3}-{\mathrm{IR}}_l$

$=(1+8.6)*2.5+0-0=24V.$

(4) when $R_d=R_l\frac{R_3}{R_2}=0.02\×\frac{1}{8.6}=\frac{0.02}{8.6},$ During I=10A, promptly adopt the Feedback Design Method after compensating, output voltage:

$V_o=V1-{\mathrm{IR}}_l=(1+\frac{R_2}{R_3})\×V_{\mathrm{ref}}+\frac{{IR}_2{R}_d}{R_3}-{\mathrm{IR}}_l$

$=(1+8.6)*2.5+10*0.02-10*0.02=24V$

Load regulation is:

$\frac{24-24}{24}\×100\%=0\%.$

As seen, increased compensating resistance Rd after, load regulation has obtained essential raising.This method does not increase extra lead, and the loss pressure drop on the compensating wire, the index of the load regulation of Ti Gaoing greatly accurately.

The above only is process of the present invention and method embodiment, in order to restriction the present invention, all any modifications of being made, is not equal to replacement, improvement etc. within spirit of the present invention and essence, all should be included within the protection range of the present invention.

Claims (1)

1. the method for a power output lines and switch power supply voltage-drop compensation, Switching Power Supply feedback fraction circuit comprises sample resistance (04), a reference source (03), photoelectrical coupler (02), output capacitance (05), power supply output line resistance (06), current-limiting resistance (01); Current-limiting resistance (01) one end is connected with output capacitance (05), the other end is connected with photoelectrical coupler (02), photoelectrical coupler (02) is connected with the cathode of a reference source (03), and the anode of a reference source (03) is made as with reference to ground, the reference edge of a reference source (03) and the sample resistance of connecting (04) R ₂, R ₃Common port be connected; Sample resistance (04) R of series connection ₂, R ₃Circuit R ₂Non-common port is connected with output capacitance (05), R ₃Non-common port is connected with the reference ground of a reference source (03); It is characterized in that, at the reference ground and sample resistance (04) R of a reference source (03) ₃Between add compensating resistance R _d, compensating resistance R _dSize be the power supply output line resistance R _lMultiply by sample resistance R ₃With R ₂Ratio, formula is:

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