PWM Variac

[Leftyretro]

Well I don't have any specific circuit in mind but it would seem to me that it (an active variac) would be pretty straight forward. There are class D audio amplifiers designs available today and that is a form of PWM and of course audio amps can cover 60/50hz.

So it would seem to me just a matter of a putting together a precision low level audio oscillator followed by a variable gain stage followed by an audio class D power amp stage. Make sense?

 

[Ubergeek63]

Well I don't have any specific circuit in mind but it would seem to me that it (an active variac) would be pretty straight forward. There are class D audio amplifiers designs available today and that is a form of PWM and of course audio amps can cover 60/50hz.

So it would seem to me just a matter of a putting together a precision low level audio oscillator followed by a variable gain stage followed by an audio class D power amp stage. Make sense?

Very inefficient, overly complicated and power limited.

This thread had scrolled out of sight...

 

[Hero999]

Alright it's probably less efficient than a variac but class D amplifiers are used in power converters which change the frequency.

Suppose the power supply is 400V 50Hz three phase and you want 115V 400Hz three phase supply to test some aircraft electronics.

A transformer and rectifier or SMPs converts the 400V 50Hz to a DC voltage just above the peak voltage required at the output and a class D inverter converts it to 115V 400Hz.

 

[Ubergeek63]

Alright it's probably less efficient than a variac but class D amplifiers are used in power converters which change the frequency.

Suppose the power supply is 400V 50Hz three phase and you want 115V 400Hz three phase supply to test some aircraft electronics.

A transformer and rectifier or SMPs converts the 400V 50Hz to a DC voltage just above the peak voltage required at the output and a class D inverter converts it to 115V 400Hz.

True, I have done that as well, but that is not what we were talking about. We were talking about simply changing the voltage of the existing powerline frequency with out a transformer.

Dan