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I am trying to design a circuit to get a 50-110 Ac as output and a maximum of 5W power from a 5V power bank. I am using IC3525 for oscillator , but I have no idea to choose transformer. Hope someone will help me?
When you say you would like an output voltage of 50V to 110V [RMS], do you mean that you would like the output to be variable between 50V and 110V RMS or do you mean that you would be happy with any fixed voltage between 50V and 110V RMS?
Having said that, a 5W inverter operating from 5V should be good fun and not too difficult to design and make. You ask about suitable transformers: off the top of my head, a standard 10W to 20W 50Hz mains transformer, with a 110V RMS primary and two 3.3V secondaries, should do the job. A couple of power NMOSFETs or possibly a couple of NPN power BJTs should drive the two primaries nicely. The transformer secondary would then provide the 110V output. The frequency drive could be provided by an LM555 timer configured as a free running oscillator set to either 50Hz or 60 Hz depending on your requirements.
You don't say if you need a sine wave output or if a square wave will do. If you need a sine wave you could connect a suitable capacitor across the primaries to resonate with the inductance of the transformer.
Alternatively, if you fancy doing a little programing, a microcontroller could drive the two transistors and possibly generate a sine wave by pulse width modulation techniques.
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