Inverter 500-W 12volt to 220volt By 2N3055 +4047 Citcuit schematic with explanation

Using this circuit you can convert the 12V dc in to the 220V Ac. In this
circuit 4047 is use to generate the square wave of 50hz and amplify the
current and then amplify the voltage by using the step transformer.

How to calculate transformer rating

The basic formula is P=VI and between input output of the
transformer we have 
Power input = Power output

For example if we want a 220W output at 220V then we need 1A at the output.
Then at the input we must have at least 18.3V at 12V because: 12V*18.3 =
220v*1

So you have to wind the step up transformer 12v to 220v but input winding
must be capable to bear 20A.

author: Ashad Mustufa
Source: electronic-lab.com