Make sure that the free wheeling diodes are able to carry the current flowing.
Why not change to MOSFETs?
It seems your Diodes are not able to carry the current. 1N5408 is not a fast type, and BA 159 has low forward current.
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Isn't it depend on the kind of the winding. if it's a EI type transformer, and primary winding is just a winding with a middle connection I am agree with FvM.
You are of course right.Only one small thing is that i expect 22V instead of 20V.
Find a new irfz44n MOSFET, remove the output of SG3524 ic and ground the gate of the two MOSFETs and power the inverter. Then give me a feedback, I am suspecting that the two sides are at one time being switched ON the same time.
Hi,
FvM is right
Read post#5.
Only one small thing is that i expect 22V instead of 20V.
Onother thing is your output stage. Are you sure to connect the capacitors directely to the transformer output...without a series inductor?
I expect high current peak on the 12V side and through the capacitors but about no benefit in output voltage waveform.
Klaus
If the transformer is well designed, the coupling between the two halves of the primary will be very tight, so as explained when one end is "earthed" the other end will swing to 2 X Vcc. The only problem will be the leakage inductance which will generate an EMF = Di/Dt X L. So there will be a short high voltage pulse which needs to be suppressed. As the level and duration of this pulse is dependent on the transformer's leakage inductance it is not easily calculated. Feed the output stage from a variable supply, reduce it to zero. Remove your diodes. monitor the end of the transformer with a CRO. Set the inverter going and gradually increase the voltage to the output stage. Look out for the high voltage ring at the start of the voltage. See how bad it is and if present and of a high amplitude when the Vcc is 12V. Try putting a snubbing network (1 ohm +.01MF in series) across the transformer.Select the components for maximum risetime with minimum over voltage.
Frank
The problem is about understanding transformer operation in push-pull output stage
This is a new idea for me, so forgive my ignorance if I am asking anything foolish,
are these back emf voltages actually getting applied across that diode without any load but the total diode resistance ?
can this be solved by adding rc elements in the loop ?
Hi,
Read about LC filters.
With switching signals you get very high voltage rise. Capacitors are low ohmic for high voltage rise. High current is the consequence. You need a device to become high ohmic with high voltage rise, these are inductivities. Capacitors and inductivities combine to a low pass filter, reducing overtones and making signal smooth and sinusoid.
Klaus
yes now understand,so where should I add an inductor in series ?
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