The inverter output (output of T2) is tapped from point’s labelled b, c and supplied to the primary of the transformer T2.

The output voltage regulation section of the inverter circuit works as follows. Current flows from the +12V source (marked with label a) through the lower half of the transformer primary and sinks to the ground through transistors Q7, Q8, Q9 and the resultant voltage induced at the T2 secondary contributes to the lower half cycle of the 220V output wave form. When 11 of the IC pin goes high Q3 gets switched ON and as result Q7, Q8 and Q9 will be also switched ON. During this period pin 11 will be low and its succeeding stages will be inactive. As a result a voltage is induced in the transformer secondary (due to electromagnetic induction) and this voltage contributes to the upper half cycle of the 220V output waveform. When signal at pin 14 is high, transistor Q2 is switched on which in turn makes transistor Q4, Q5, Q6 ON are current flows from the +12V source (battery) connected at point a (marked with label a) through the upper half of the transformer (T1) primary and sinks to ground through the transistors Q4, Q5 and Q6. These are the signals which drive the subsequent transistor stages. Two 50Hz pulse trains which are 180 degree out of phase are available at pin 14 and 15 of the IC. The collector terminals of the driver transistors (pin 13 and 12) are tied together and connected to the +8V rail (output of the 7808).

Pin 14 and pin 11 are the emitter terminals of the internal driver transistor of the IC. Preset R1 can be used for fine tuning of the oscillator frequency. Resistor R2 and capacitor C1 sets the frequency of the ICs internal oscillator.

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