Working principle: The typical circuit of power source of push-pull formula switch is shown like the graph. It belongs to circuit of the double commutation that carry type, the magnetism core job of high frequency transformer is in the two side of magnetic hysteresis loop-line. Circuit uses two switch to be in charge of VT1 and VT2, guide alternately below the control that two switch provide signal of outer and incentive square wave with end, in transformer T sub all group gets square wave tension, wave of classics commutate filter turns into the volts d.c. of a need.   

 

The advantage of this kind of circuit is two switch manage easy drive, the compression that main drawback is switch canal should achieve voltage of double circuit peak value. The output power of circuit is greater, it is commonly inside 100-500  W limits.

 

   

 

Rectification outputs principle of job of power source of switch of push-pull type transformer

Rectification outputs power source of switch of push-pull type transformer, as a result of two switch the canal works alternately by turns, be equivalent to two switch power source outputting power at the same time, double what its output power to approximate onefold switch power source to output power. Accordingly, power of output of power source of switch of push-pull type transformer is very great, work efficiency is very tall, after classics bridge-type commutate or complete wave commutate, need very small filter wave inductance and electric capacity only, its output voltage ripple to be able to be achieved very small.

 

Graph 1-30 is graph of principle of job of power source of switch of transformer of type of push-pull of bridge-type commutate output, besides circuit of rectification filter wave, the working principle of others circuit is basic as identical as graph 1-27. Bridge-type commutate circuit is comprised by D1, D2, D3, D4, c is store can filter wave capacitance, r is laden resistor, uo outputs voltage for dc, io is the electric current that sheds overload resistor.

 

 

 

The principle of job of power source of switch of push-pull type transformer that graph 1-31 is output of complete wave commutate pursues, same, besides circuit of rectification filter wave, the working principle of others circuit is mixed basically with graph 1-27 graph 1-30 is identical. But the sub need of switch transformer many winding, two winding N31, N32 outputs voltage by turns; Quan Bo rectifies galvanic road to be comprised by D1, D2, c is store can filter wave capacitance, r is laden resistor, uo outputs voltage for dc, io is the electric current that sheds overload resistor.

 

  

 

Graph 1-30 and graph 1-31 are compared, the power source of switch of push-pull type transformer that the power source of switch of push-pull type transformer that bridge-type commutate outputs outputs than complete wave commutate is multi-purpose two commutate diode, the switch transformer that the switch transformer that Dan Quanbo commutate outputs outputs than bridge-type commutate again many groups of secondary coil. Accordingly, power source of switch of transformer of type of push-pull of output of commutate of graph 1-30 bridge-type applies to the circumstance with output relatively lesser electric current quite; And power source of switch of transformer of type of push-pull of output of commutate of graph 1-31 Quan Bo applies to output electric current quite relative to bigger case. Because, cost of diode of commutate of big electric current is high, and loss power is greater also.

 

We come to commutate of bridge-type of labor graph 1-30 output power source of switch of push-pull type transformer and commutate of graph 1-31 Quan Bo to output the working principle of power source of switch of push-pull type transformer below.

 

The voltage output that because commutate of graph 1-30 bridge-type outputs power source of switch of push-pull type transformer or graph 1-31 Quan Bo,rectification exports power source of switch of push-pull type transformer is received in circuit have store can filter wave capacitance, store can filter wave capacitance reachs flowing action since can pulsatile to the input voltage, accordingly, uo of voltage of the output in graph 1-30 and graph 1-31 won’t appear the voltage of very tall extent is reactive, its output the peak value Up of voltage to basically can consider as half average Upa. Its value is more than slightly stimulating output NUi, namely: Power source of switch of transformer of type of push-pull of bridge-type commutate output or complete wave commutate output power source of switch of push-pull type transformer, the value of output voltage Uo is more than rectification filter wave to stimulating output NUi slightly, the v/LIT all over the ground number that N is winding of N3 of transformer secondary coil and winding of primary coil N1 or N2 winding is compared.

 

Accordingly, the output voltage Uo of power source of switch of push-pull type transformer, still basically be by (1-131) mood will decide. Namely: The output voltage Uo of power source of switch of push-pull type transformer (during K1 or K2 put through) , the stimulating type to output voltage Up or Up- half average Upa that approximates generation of winding of N3 of switch transformer secondary coil or Upa- :

 

Uo = Upa = NUi ——During K1 puts through (1-134)

 

Or Uo = Upa- = – NUi ——During K2 puts through (1-135)

 

Go up in type, uo is push

 

Pull type transformation

 

Implement the output voltage of switch power source, the v/LIT all over the ground number that N is winding of N3 of transformer secondary coil and winding of primary coil N1 or N2 winding is compared, ui is switch transformer the input voltage of winding of primary coil N1 or N2 winding.

 

Graph 1-32 is power source of switch of transformer of type of push-pull of bridge-type commutate output or output of complete wave commutate, in two control switch K1 and K2 put through alternately and disconnect, and occupy sky comparing D to all be equal to 0.5 when, the voltage of each main job place, electric current is undee.

 

Graph 1-32-a) with graph 1-32-b) when expressing to control switch K1 to put through respectively, switch transformer is primary coil N1 winding the weaveform of the voltage U1 of two end, and had shed transformer winding of primary coil N1 the voltaic I1 of two end is undee; Graph 1-32-c) with graph 1-32-d) when expressing to control switch K2 to put through respectively, switch transformer is primary coil N2 winding the weaveform of the voltage U2 of two end, and had shed switch transformer winding of primary coil N2 the weaveform of the voltaic I2 of two end; Graph 1-32-e) with graph 1-32-f) when expressing to control switch K1 and K2 to put through by turns respectively, two end output winding of N3 of switch transformer secondary coil the weaveform of voltage Uo, and had shed winding of N3 of switch transformer secondary coil the electric current of two end is undee.

 

Graph 1-32-f) in, dotted line arrowhead expresses to stimulate type to export electricity instead is begin by maximum, reduce the smallest cost gradually next; And solid line arrowhead expresses to stimulating type to export electricity is begin by the least value, raise maximum gradually next; Accordingly, both at the same time the result of action, as it happens outputs a rectangular wave.

 

 

From graph 1-32-e) can see, although output voltage Uo still is comprised by two parts, one part passes transformer to input voltage Ui winding of primary coil N1 or N2 induction arrive of winding of secondary coil N3 stimulating type to output voltage (Uo) ; Another part sheds the energy that through transformer winding of primary coil N1 or N2 winding store to arise for excitation report stimulate type to output voltage instead [Uo] ; Type is stimulated to output voltage instead here [Uo] won’t make weaveform produces recoil again, because,be store can filter wave capacitance is met a reactive voltage sponge, make its are become fill electric current.

 

Because power source of switch of push-pull type transformer exports half average of voltage,Upa amplitude basically is stable, it won’t resemble stimulating type to output switch power source instead in that way, output the amplitude of voltage to occupy sky comparing as control switch change and change. Accordingly, if need to adjust power source of switch of push-pull type transformer to output voltage, can pass those who change two control switch to occupy sky comparing only, will change the average that exports voltage. Accordingly, in the circuit of power source of switch of push-pull type transformer with output adjustable voltage, must want to be added at the back of rectification output circuit receive a LC store can filter wave circuit, ability extracts average to output from inside the pulsatile volts d.c. that rectification outputs.

 

Graph 1-33 is the circuit of power source of switch of push-pull type transformer with output adjustable voltage. Actually graph 1-33 is namely on the foundation of circuit of power source of switch of transformer of type of push-pull of output of commutate of graph 1-31 Quan Bo, add at the back of rectification output circuit received a LC store can filter wave circuit. LC store can in the working principle of filter wave circuit and power source of switch of formula of graph 1-2 series connection store can principle of job of filter wave circuit is basic and same. Nevertheless, the LC that outputs in complete wave commutate store can in filter wave circuit can leave out diode of a follow on current, because be used at two diode of complete wave commutate,can act as by turns the action of diode of follow on current. About LC store can the detailed work principle of filter wave circuit, consult please ” 1-2-2. Circuit of wave of filter of voltage of output of power source of switch of series connection formula ” paragraphic.

 

What occupy sky comparing D as a result of switch of two control in graph 1-33 is adjustable scope is very little (be less than 0.5) , and two are in inside a cycle control switch to all need to put through and close

 

Break,

 

Accordingly, those who output voltage is adjustable limits is opposite for what should stimulate formula switch power source to output voltage than sheet is adjustable scope is a lot of less; But power source of the double switch that stimulate type stimulates formula switch power source than sheet, have output power small, voltage outputs ripple of big, voltage character is good wait for an advantage.

 

 

 

Graph 1-34 is the power source of switch of push-pull type transformer with output adjustable voltage the voltage of each main job place, electric current is undee.

 

Graph 1-34-a) when expressing to control switch K1 to put through, switch transformer is primary coil N1 winding the voltage of two end is undee; Graph 1-34-b) when expressing to control switch K2 to put through, switch transformer is primary coil N2 winding the voltage of two end is undee; Graph 1-34-c) when expressing to control switch K1 and K2 to put through by turns, two end output winding of N3 of switch transformer secondary coil the weaveform of voltage Uo. Graph 1-34-d) express winding of N3 of switch transformer secondary coil the voltage after two end output commutate of voltage classics complete wave is undee.

 

Graph 1-34-c) in, up, Up- expresses winding of N3 of switch transformer secondary coil respectively two end output voltage Uo maximum (half average) with negative maximum (half average) , [Up] , [Up- ] express those who output voltage to two end stimulate winding of N3 of switch transformer secondary coil instead respectively maximum (half average) with negative maximum (half average) .

 

 

Here still needs to explain again, stimulate output voltage instead actually [Up] and [Up- ] pulse extent is very tall, just its energy is very small, namely width is very narrow, its extent is restricted a peace all become very low later. In rectification output circuit, stimulate output voltage instead [Up] , [Up- ] range is general won’t the extent of prep above Up, Up- , up of its extent prep above, Up- will by filter wave capacitance the voltage of two end is restricted, or through transformer the mutual inductance action of two primary coil is restricted by voltage of input power source.

 

Graph 1-34-d) in, when correspondence of solid line weaveform controls switch K1 to put through, two end output winding of N3 of switch transformer secondary coil the weaveform after voltage classics bridge-type or complete wave commutate; When correspondence of dotted line weaveform controls switch K2 to put through, two end output winding of N3 of switch transformer secondary coil the weaveform after voltage classics bridge-type or complete wave commutate. Ua states rectification exports the average of voltage.

 

From graph 1-34-d) can see, use only store can capacitance has filter wave to rectification output voltage, it is very difficult take out the average that exports voltage from inside pulsatile dc, must use at the same time store can the average that ability of filter wave inductance takes out output voltage.

 

In graph 1-33, store can filter wave inductance and store can the computation of parameter of filter wave capacitance, in the power source of switch of series connection formula with graph 1-2 store can filter wave inductance and store can the computational method of parameter of filter wave capacitance is very similar. According to graph 1-33 and graph 1-34, we output rectification picture of IL of the voltage Uc of voltage Uo and circuit of LC filter wave, electric current gives the 1-35 that be like a graph, so that use,will calculate power source of switch of push-pull type transformer store can the parameter of filter wave inductance, capacitance.

 

 

Graph 1-35-a) the undee graph that is Uo of rectification output voltage. When solid line expresses to control switch K1 to put through, winding of N3 of secondary coil of transformer of mains switch of switch of push-pull type transformer outputs the weaveform after voltage classics commutate; When dotted line expresses to control switch K2 to put through, winding of N3 of secondary coil of transformer of mains switch of switch of push-pull type transformer outputs the weaveform after voltage classics commutate. Up states rectification outputs peak value voltage (stimulating output voltage) , up- states rectification outputs lowermost voltage (stimulate output voltage instead) , ua states rectification exports the average of voltage.

 

Graph 1-35-b) it is filter wave capacitor the undee graph of two upright voltage, or the undee graph of voltage of output of filter wave circuit. Uo expresses to output voltage, or

 

Filter wave capacitance

Implement the average of two upright voltage; ΔUc states capacitance charges voltage increment, 2ΔUc is equal to output voltage ripple.

 

1-8-1-3-1. Power source of switch of push-pull type transformer store can the computation of parameter of filter wave inductance

 

In graph 1-33, when control switch K1 puts through, input voltage Ui adds the two end of winding of N1 of switch transformer coil through controlling switch K1, in control switch K1 puts through during Ton, winding of N3 of switch transformer coil outputs an extent to be Up (half average) stimulating voltage Uo, add next store can L of filter wave inductance and store can on the filter wave circuit that C of filter wave capacitance comprises, during this store can the voltage EL of two end is L of filter wave inductance:

 

EL = Ldi/dt = Up–Uo ——During K1 puts through (1-136)

 

In type: Ui is input voltage, uo outputs voltage for dc, namely: Uo is filter wave capacitance the average of Uc of two upright voltage.

 

Explain incidentally here: As a result of capacitance the voltage of two end changes increment ΔU is opposite at outputting voltage Uo for very small, for simple, regard Uo as here constant will handle.

 

Right (1-136) type undertakes integral gets:

 

The I in type (0) for initiative electric current (the electric current that hour of T = 0 has shed inductance L) , namely: Control switch K1 just put through the instant, had shed the electric current of inductance L, or the initiative electric current that says to had shed inductance L. Can see I from inside graph 1-35 (0) = Ix.

 

Should control switch K by during putting through, Ton is changed suddenly during closing the instant of Toff, the voltaic IL that has shed inductance L reachs maximum:

 

 

(1-139) and (1-140) the expression that type is voltage of output of power source of switch of transformer of computational push-pull type. In type, uo outputs voltage for power source of switch of push-pull type transformer, ui inputs voltage for power source of switch of push-pull type transformer, up is winding of N3 of secondary coil of transformer of mains switch of switch of push-pull type transformer stimulating output voltage, up- is winding of N3 of secondary coil of transformer of mains switch of switch of push-pull type transformer stimulate output voltage instead, the v/LIT all over the ground number that N is winding of N3 of secondary coil of switch power source and winding of primary coil N1 or N2 winding is compared.

 

The result is analysed above the basis, (1-138) type can write for:

 

 

 

By (1-75) type is knowable, occupy sky comparing to all be when what control switch K1, K2 0.5 when, upa and Upa- are basic and equal, from this we also can think Up and Up- are basic and equal.

 

As a result of, occupy sky comparing to all be when what control switch K1, K2 0.5 when, (1-141) type and (1-142) the computational eventuate of type 0. Accordingly, occupy sky comparing to all be when what control switch K1, K2 0.5 when, the voltage weaveform that outputs after commutate of classics of power source of switch of push-pull type transformer basically is pure dc, did not exchange part, output voltage Uo is equal to maximum Up, accordingly, need not need store can inductance filter wave.

 

But, if ask output voltage is adjustable, of the K1 of two control switch of power source of switch of push-pull type transformer, K2 occupy sky comparing to must want to be less than 0.5; Because positive and negative of power source of switch of push-pull type transformer stimulates two kinds of condition to have voltage output, be in so same output voltage (average) below the circumstance, of K1 of two control switch, K2 occupy sky is one times smaller than be equivalent to wanting. From this knowable, should ask output voltage is adjustable limits is the biggest when, occupy sky comparing to had better take a cost for 0.25.

 

Control switch K1, K2 when two occupy sky comparing to take a value to all be 0.25 when, upa = 3Upa- , from this we also can think Up is equal to 3Up- . Above foregone condition takes the place of (1-1

 

42) type,

 

Can get:

 

 

 

(1-143) , (1-144) , (1-145) type is power source of switch of transformer of computational push-pull type store can filter wave inductance and the expression that filter wave outputs voltage (D is 0.25 when) . The Uo in type outputs voltage for power source of switch of push-pull type transformer, ui inputs voltage for power source of switch of push-pull type transformer, t is the working cycle that controls switch, f is the working frequency that controls switch, the v/LIT all over the ground number that N is winding of N3 of secondary coil of switch power source and winding of primary coil N1 or N2 winding is compared.

 

Manage together, (1-143) , (1-144) , (1-145) the computational result of type, gave out only power source of switch of transformer of computational push-pull type store can the intermediate value of L of filter wave inductance, or average, can be in to extreme circumstance the computation of average is multiplied again on the result be more than the coefficient of 1 with.