DC to AC power

[dns1764]

have a design project an need help. we are taking 120v 60hz and trying to make that 120v with a variable frequency. our end goal is to build a variable speed control for an induction motor.

right now our idea is to take our original ac and switch it to dc. then use some sort of converter (555 timer or hartley oscillator) to make an adjustable pulse width ac. problem is these only work on the small scale. any suggestions?

[wilkin250r]

My first thought would be to generate a small variable frequency, and then amplify it with the 120V DC source.

Problem is, 120V is pretty high voltage for most transistors, especially when you consider that just a few milliamps is going to result in several watts of power dissipation. The GOOD thing about a strategy like this is the small 0.7V offset voltages around your zero are going to be so negligible that you can probably ignore them completely.

[TheLane]

Lightning power......thats how they did it in back to the future at least.