25W power inverter circuit ciagram. The two transistors drive the transformer push-pull fashion. When one transistor is biased-on, the other is cut-off. The transformer is a 120V / 18V CT unit which is connected backward, so that is steps the voltage up rather than down. Oscillator circuit U1, R1, R2 and C1 operates from about 4 to 16V with a really stable output.