A foreword

Because switching power supply energy-conservation also brings the huge economic benefits, cause the attention of the various circles of society to be popularized rapidly. With the technical development at full speed of power, high frequency, becoming the development trend of stabilized voltage supply of switch miniaturizedly, integratedly. Single-end anti exciting type switching power supply not merely has small, the circuit is succinct, advantage that reliability is high with high efficiency, and there is automatic equalization from various places that outputs loaded ability, are often used for designing the accessory power supply of high-frequency switching power supply of high-power or drive power of the power switch ^{[1-2]. PSPICE software is the common circuit analogue simulation software that EDA company ORCAD with most well-known domain developed. }

Compared with miscellaneous simulation software, PSPICE has a lot of advantages: Having increased the kinds of model and components and parts, the components and parts in user’s all right direct call model base, also can revise the parameter of the model according to the needs of reality, or set up one’s own model; Use the model set up of PSPICE to be more accurate, the real circuit of simulation that it can be better; Because analyze to the circuit that does not need actual components and parts with PSPICE, so, will not be influenced by quantity and type of the components and parts in emulation; The operation of PSPICE is simpler, practicability is strong, utilizing its user will pay emulation to the complicated circuit, reduce the cycle sum expenses of circuit design. PSPICE has good man-machine interface and control mode, pass the waveform analysis window, users can be convenient to observe and output corrugate properties, have important directive significance on design of the circuit.

Basic principle of anti exciting type switching power supply of 2 single-end

Switching power supply ac input ‘ Single-phase or three phases The voltage is turned into a device of the required direct-current volts. The circuit is mainly input the smoothing circuit of electromagnetic disturbance, input and commutated the smoothing circuit, inverter of power, exported and commutated the smoothing circuit etc. to make up. The basic principle of switching power supply is shown as in Fig. 1, the controlling circuit is a piece of one pair of closed loop control systems outputted the control loop of voltage feedback and the inductor current feedback control loop makes up. Among them, the electric current loop can make the change of the input voltage of tracing of input current close to the sine, output of making the voltage stable of the voltage ring. Its basic principle is: Exchanging the input voltage is filter, commutates and filters and gets the direct-current volts U1 by the electric wire netting, after stepping down through the power gas switching tube VT or MOSFET chopping, high-frequency voltage transformer T, output the required voltage of high-frequency square wave, commutate the smoothing circuit the output composed of VD, C2 finally, receive required high quality, high-quality direct-current volts UO to export. Utilize the sense resistor of electric current to transform the electric current of the gas switching tube into the feedback signal of the voltage, then compare with detected voltage of control loop of the voltage, produce PWM wave, and then control the magnitude of the output voltage.

Basic schematic diagram of anti exciting type switching power supply of the single-end of Fig. 1

Design of the anti exciting type power supply circuit of switch of 3 single-end

This text only concentrates on high-frequency voltage transformer and design of the control circuit to the design of the anti exciting type power supply circuit of switch of multi-functional single-end. The control method is as follows, crest current control pattern, it is the control method that a fixed clock is turned on, the crest current shuts off, it does not directly control PWM pulse width with the error signal of the voltage, but use the indirect control PWM pulse width of inductive current of the crest value; The control pattern of the average current, it is a kind of constant frequency that is controlled too, its advantage is that the anti-interference is good, the shortcoming is that the circuit is more complicated, will shake when it is unreasonable to be designed; The electric current control pattern of the hysteresis, it is that a kind of frequency conversion is modulated, its advantage is working good stability, anti-interference is good, difficult to shake, the shortcoming is to need to carry on overall detection and control to the inductive current. Compare the above three kinds of control methods, originally design adopting the crest current control pattern. The performance index of multi-functional switching power supply is:

Input the direct-current volts: 170V-700V;

The frequency of input voltage: 100kHz;

Power rating: 70W;

The duty ratio of maximum: 48%;

Operating temperature: -10 – 70 ;

The electric current of output voltage: 5V/1A, 24V/2A, 15V/0.2A, 15V * 3/0.15A, 15V/0.3A;

Regulation factor of the voltage and load regulation are smaller than 3%, and have higher efficiency.

3.1. The high-frequency voltage transformer is designed

There are many kinds of design methods of the voltage transformer, such as the literature ^{[3]Unidirectional design law and literature that China introduces [4]The simple and convenient design method to introduce, a simple and convenient design method after can be adopted as to the high-frequency voltage transformer in the anti exciting type switching power supply of single-end. Its flow block diagram of design is shown as in Fig. 2. }

Flow block diagram of the anti exciting type simple and convenient design method of voltage transformer of medium high frequency of switching power supply of the single-end of Fig. 2

Calculate the parameter of the voltage transformer according to the procedure above.

1 Confirm the output power of the voltage transformer

Within the range of direct-flow input 170V 700V, export a route of 5V/1A, 24V/2A of No. 1, 15V/0.2A of No. 1, No. 1 – 15V/0.2A, 15V/0.15A of No. 3, the voltage of 15V/0.3A of No. 1. General output power Po =70.25W, so the output power of the high-frequency voltage transformer fetches 70W.

2 Calculate the crest current of the first rear axle winding

In the type: Us fetches the minimum, Dmax is a maximum duty ratio of the anti exciting voltage transformer, fetch 0.45. Calculate IP =1.83A.

3 Calculate the inductance of the first rear axle winding

The inductance of the first rear axle winding is shown by the following formulae:

In the type: Usmin It is a minimum of the input current, Dmax is a maximum duty ratio of the anti exciting voltage transformer, fetch 0.45, calculate LP =0.42mH.

4 Calculate Dmin

Act as Us max Occasionally minimum duty ratio Dmin. So when the input voltage go from maximum value change to the minimum, the duty ratio goes from minimum change to maximum value. The relation between them can be represented as follows:

In the type: It is a fluctuating range coefficient of the voltage. Bring into every numerical calculation and get Dmin =0.166.

5 Choice of the magnetic core specification

Suppose the first rear axle winding thread diameter is dw, then the area of the magnetic core window that the first rear axle winding accounts for is by following formula computing:

In the type: B – -The change value of working magnetic induction intensity, generally fetch half of the magnetic induction intensity of the saturation, namely ; dw – -Diameter of the wire. Calculate APP =0.246cm4, fetches AP =4APP=4* 0.246 =0.984cm4 .

6 Calculate the length of the air gap

In the type: Ae is the effective area of the magnetic core, inserts numerical calculation and gets lg =0.06cm. Namely polish the air gap with length of 0.06cm out in the central cylinder of the magnetic core, or the magnetic pinch each polishes the air gap of 0.03cm outside the magnetic core.

7 Calculate the turn of the first rear axle winding

The calculation of the number of turns of winding of primary side has two formulae: Formula 6 , formula 7 ,The turn that usually chooses the first rear axle winding is that two formulae differentiate the mean value of the number of turns of winding of assumed primary side.

The turn of calculating first rear axle winding is 52 circles.

8 Calculate the turn of the secondary coil

The number of turns of winding of secondary is according to inputting the minimum voltage, the duty ratio maximum turned on is calculated. Because of

In the type: Ns – -Turn of the secondary coil; UD – -The forward voltage drop of the kenotron, fetch 1V; Uo – -Output voltage of the secondary coil.

Put the formula 8 in order Can get:

Through calculating:

When the output voltage is 24V, Circle, fetch Ns =10 circles;

When the output voltage is 15V, Circle, fetch Ns =6 circles;

When the output voltage is 5V, Circle, fetch Ns =3 circles.

Cyclical design of 3.2 voltage feedback

There are four kinds of fundamental types in the backfeed loop of voltage: Basic backfeed loop; Basic backfeed loop of modified version; Mix the backfeed loop of photosensitive resister of the regulator tube; Mix the backfeed loop of accurate photosensitive resister of TL431. The analysis of four kinds of basic backfeed loop is relatively shown in Table 1.

Comparison of different backfeed loop of voltage of Table 1

In this design, because expecting relatively much to regulation factor of the voltage and load regulation, so adopt the backfeed loop of accurate photosensitive resister which mixes TL431. Mix the backfeed loop of accurate photosensitive resister of TL431 and is shown as in Fig. 3. In mixing the backfeed loop of accurate photosensitive resister of TL431, replace the regulator tube with accurate shunt regulator of TL431 -type variable type, thus form the external error amplifier and adjust the output voltage. Though the circuit of this circuit is more complicated, the voltage regulation characteristic of this circuit is the best. For having one piece switching power supply of the multileaving, besides regarding primary output as the master feedback signal, other from various places to assist outputting it to 2.5V basic reference end of TL431 according to certain proportional feedback too, this has great meanings in improving the global stability of multileaving type switching power supply.

Fig. 3 mixes the backfeed loop of voltage of the accurate photosensitive resister of TL431

Cyclical design of 3.3 current feedback

The electric current loop, through transforming the electric current of the gas switching tube into the feedback signal of the voltage with the electric current sense resistor, then is comparing with detected voltage of control loop of the voltage, produce PWM wave, control the voltage outputted. The change to the input voltage and variation on load are fast in response, the good stability of the loop, the interference-free characteristic is strong, the advantage such as being small of regulation factor of the voltage ^{[5]. }

Current feedback circuit of Fig. 4

4.Artificial experiment test

On the basis of the above-mentioned analysis and research, set up simulation model, use ORCAD/PSPICE to carry on the whole circuit of this switching power supply on the foundation of the artificial experiment, key parameters of different components and parts in corrector circuit, make the characteristic of the circuit give play to the best.

In order to optimize the systematic cipher scheme of multi-functional switching power supply, reduce the blindness, complexity of the development process, shortened development cycle, the low cost very much, this text carried on emulation to the whole circuit of multi-functional switching power supply. Use ORCAD/PSPICE to set up the simulation model of the integrated system of multi-functional switching power supply, then carry on the steady state, dynamical analysis to the system and seek to meet the component parameter of designing performance requirement ^{[6-7]. The test chart of the whole circuit is shown as in Fig. 5. }

Test chart of the whole circuit of Fig. 5

Will often meet the astringent question in the artificial course. What has been disappeared question in various forms, appear, be related to factors such as the topological structure, modeling of device, arrangement of simulator of the circuit,etc. usually at scale and false appearance. The fast method which solves the astringent problem is: Some options of setting up OPTION while setting up.

ABSTOL =0.01 Default =1p

VNTOL =10 Default =1

GMIN =0.1nDefault =1p

RELTOL =0.05Default =0.001

ITL4 =500Default =10

Arrangement the can it solves to be mostly astringent problem, certainly if mistake in the circuit, it can not solve. If the model is not accurate enough, the arrangement above needs real-time steering to receive the desired result.

In the multi-functional switching power supply, the output waveform of 5V output circuit is shown as in Fig. 6. Be able to find out to pursue, 5V power that this text designs meets regulation factor of voltage and requirement of the load regulation.

Test oscillogram of Fig. 65V power

The output waveform of 15V output circuit is shown as in Fig. 7. Be able to find out to pursue, 15V power that this text designs meets regulation factor of voltage and requirement of the load regulation.

Test oscillogram of Fig. 715V power

The output waveform of 24V output circuit is shown as in Fig. 8. Be able to find out to pursue, 24V power that this text designs meets regulation factor of voltage and requirement of the load regulation.

Test oscillogram of Fig. 824V power

5.Conclusion

Using ORCAD/PSPICE to show the artificial experimental result to the whole circuit of switching power supply, the total power of regulation factor of voltage, load regulation and switching power supply that outputted from various places of this multi-functional switching power supply has met requirements for ones that expect. On condition that change on a large scale in load, export stable, such characteristics as the voltage ripple is little, simple in construction, with high efficiency.

Bibliographical reference

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