how does inverter reverse thr polarity of the current for the AC side?

[sdowney717]

I am fixing a 3000 watt inverter.
I see the 12 volt side mosfets run outputs to transformers.
The transformers boost the voltage from 12 to 120v.
Mosfets are turned on and off, looks like 2 controls lines to the gates
16 Mosfets split into 2 groups of 8 feeding 4 transformers.

How though does the polarity get reversed?
Do they feed the 12v power in and out of the primary coils in different directions?
So the output voltage polarity changes?

Also I assume the charged coils when the mosfet turns off, the field collapses, generating a higher 120v pulse on the output side. Sort of like an automotive spark coil.

Also on the AC side is a long row of more transistors. I have not taken their rubber covers off. what do they do? Somehow modify the voltage coming off the transformer to approximate MSW steps?

 

[sdowney717]

according to this, I am right about the current flow reversing in different directions due to the connection of the mosfet one side of transformer versus other side.
fire mosfet, current flows one way, fire other mosfet, current flows other way alternating the flow inside the transformer.

When pin 10 is high Q1 conducts and current flows through the upper half of the transformer primary which accounts for the positive half of the output AC voltage. When pin 11 is high Q2 conducts and current flows through the lower half of the transformer primary in opposite direction and it accounts for the negative half of the output AC voltage.

https://www.circuitstoday.com/simple-100w-inverter-circuit

 

[betwixt]

I can't comment on the specifics of the inverter you have but the basic principle is the output changes polarity by first being connected one way around to the HV and then disconnected and reconnected the other way around.

Normally this is done at high speed using PWM signals which operate MOSFET switches.

Brian.

 

[sdowney717]

I noticed inverter uses NPN plus PNP to absolutely make sure the mosfets turn on and off.
Inverter has 2 boards which are synced together
Each Board on 12 vdc side has 16 mosfets and 2 PNP and 2NPN tied into the gates of the mosfets.

I had sent 120vac into the on-off switch by accident. So ordered many various parts and couple dip IC and 3 optical couplers to rebuild the 12v control side.

 

[Tahmid]

The NPN-PNP are used to form a totem-pole driver.

In the inverter you have, it seems like a push-pull converter is used. Perhaps, reading up a little on push-pull converters will help clear some of your doubts.

Hope this helps.
Tahmid.