# Need help analysing pushpull circuit

#### ozair29

Joined Mar 26, 2017
1
Hi i need help regarding analysing push pull circuit attached
it is push pull circuit with voltage doubler after transfomer
Following are the parameters
Vin = 30 volts
Vout = 380-400 volts
Pout = 100 watts
Duty cycles greater than 0.5
with isolated transformer
i want help in modes of operation of this circuit and equations when switch is open and closed
Any kind of help regarding output voltage equation and determining transformer parameters like how much isolation voltage and what turns ratio would be perfect would be great

#### WBahn

Joined Mar 31, 2012
26,398
It doesn't sound much like you want "help" as much as it does that you want someone to answer your homework for you.

You need to show your best effort to work YOUR homework -- we can then make suggestions to help guide you to go from where you are to where you are trying to get to.

#### Motanache

Joined Mar 2, 2015
511
After the transformer is simple-
C2 is charged through D2 at the maximum positive voltage of transformer output.
C3 is charged through D1 at the maximum negative voltage of transformer output.

But C2 and C3 are in series. Their voltage is added and C4 will have double the output "transformer" voltage.

In Proteus you can see this animated. How does electricity "flow".
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Before the transformer we again have a voltage rise.

I do not know the values of L1 and L2. But if they are large enough they change the input voltage (see boost SMPS).

Eg. MOS1 ON and MOS2 OFF
L1 is charging through MOS1.

Next MOS1 OFF and MOS2 ON
L1 is discharged and can cause overvoltages.

#### Motanache

Joined Mar 2, 2015
511
L1 tries to keep the intensity of current constant through him. While the primary of transformer is trying to block the current increase.

The solution that L1 "will find" is to increase the voltage at its terminals.
See Faraday low e=-d Magnetic flux /d Time
L=d Magnetic flux /di(t)