Help on 12V DC to 230V AC INVERTER Phenomina.........

[KRYCHEK]

Hi Guys need some help.........

I have repaired loads of Chinese sine wave inverters , i keep coming across this one same problem........

After replacing the DC TO DC Stage push- pull Mosfets, and then Pressing the ON button,Yes i get about 350Vdc on the bulk capacitor..........

Occasionally or should i say randomly, after power cycling the inverter... if i press the ON button again... The Dc to Dc stage Mosfets go BANG BANG BANG.....................

Can somebody please tell me whats could be the cause, it is very random and its not something you can simulate or put a scope to it, not knowing when its gonna happen, any help appreciated, Thanks

 

[KlausST]

Hi,

My crystal ball says Q7 is defective.

Klaus

 

[mrinalmani]

If the capacitor is preceded by a diode, then it is NOT unexpected for the capacitor voltage to reach 350V
The peak of 230V RMS is already about 325V and the extra 25V can be added due to transient overshoot due to parasitic inductances. The diode will "trap" this voltage in the capacitor.

 

[KRYCHEK]

Hi,

My crystal ball says Q7 is defective.

Klaus

Your Crystal ball is wrong, all Mosfets are brand new and were checked beforehand

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If the capacitor is preceded by a diode, then it is NOT unexpected for the capacitor voltage to reach 350V
The peak of 230V RMS is already about 325V and the extra 25V can be added due to transient overshoot due to parasitic inductances. The diode will "trap" this voltage in the capacitor.

I think that extra 25v is due to the winding configuration ........

I think that for some reason the gate drives is being switched hard on, or both pos and neg are being switched on at same time, or transformer saturation..........

Again its very rare this happens , its more of a shock