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# Transformer ratings to convert 12v p-p to 220v in a full bridge inverter

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#### mazhara

##### Junior Member level 1
Can someone help me: I am building a 1000W full bridge inverter using 2 self oscillating full bridge drivers IRS2453D. The first irs2453d converts 12v dc at high frequency of 10kHz to 12v peak to peak, then a transformer to step it to 220v then a rectifier to get 310v dc, and finally another urs2453d to get 220v ac.
1. What are the step up transformer ratings transformer ratings
2. or you can help me with coming with the circuit diagram
i am using IRF720 Mosfets
You can see datasheet and typical connection for IRS2453D at International Rectifier Home Page - Flash Detection and search the part number

You can find the minimum relationship (number representing n1/n2) this way:
n1/n2 > (220×√2)/12 = 25,9.

Other than that, it's important that transformer core does NOT saturate when feed with 12V@50Hz input.

I would have choosen n1/n2 ≈30.

If you want 1000 W output max then you'll have to be able to supply upwards of 1200 W going in. Expect 20 percent loss.

12 VAC P-P converts to 4.24 VAC nominal.

The current going into your transformer will be 1000 / 4.24. Which makes 236 amps max.
This will not be easy to accomplish. You'll need double-0 gauge cable and very clean connections.

Or did you mean your first driver stage will have 12 V peak at positive polarity and 12V on at negative?
24V peak to peak?
Then you're talking 8.5 nominal VAC. I can picture this working much easier.

Then current going into your transformer will be 1000 / 8.5. Which makes 117 amps max.

The lower the ohmic resistance in your coils, the easier they'll pass current.
Your primary circuit must admit 117 amps at 8.5VAC. This sets a max ohmic resistance at .07 ohms in your primary circuit.
Your full bridge driver mosfets can total as much as .03 ohms total and your primary coil can add up to .03 ohms.

You'll need some hefty wire in your primary coil. Possibly 2 AWG to handle that current. Not more than 200 ft. for .03 ohm (consulting an electrician's table).

Your step-up ratio is 220 / 8.5, or 26x. Maybe use 27 or 28.

The current coming out of the transformer will be 1/26 of the current going in.

So 117 amps going in, 4.5 amps available coming out. (More like 4.1 due to losses.)

Consider making your secondary from 14 gauge wire or thicker.

Your secondary coil and its related circuitry cannot have ohmic resistance more than 220 / 4.5 ohms. Equals 49 ohms. But wait.

Remember your load has resistance too. Drawing 1000 W at 220 VAC means your load pulls 4.5 amps. So you want to allow the load to be 49 ohms.

So you need to minimize resistance in your output stages. Under one ohm. This should be possible if you drive your mosfets properly.

All the above is just the theoretical easy part.

I'm not taking into account coil reactance. This affects the calculations.
I don't know what length of wire you need in the coils. I believe the more metal you put in the transformer, the fewer turns of wire you need. Just so the turns ration stays 1:26.

At a freq of 10khz you won't need as big a transformer as you'd need for 50 hz. Nevertheless it will need sufficient metal in it to avoid heating up too much.

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