How to change AC balance?

[mrbuell]

Anyone know of an ic or circuit that will modify the balance of an AC wave? I want to be able to manipulate the percentage of positive cycle relative to the negative cycle. I've been searching for hours...

 

[pico]

Pure AC +/- DC = Shifted level AC => change AC balance (in your meaning).

 

[mrbuell]

I actually want to change the AC wave itself by varying the lenth of the positive or negative part of the wave. I want to chage the pulse width of either the negative or positive portion of a square wave. Am I making any sense?

 

[Orson Cart]

Sounds like you need to balance the output of an inverter? Usual practice is to measure and integrate and average either the o/p current or voltage and use the resultant signal to offset the demand signal going into the PWM generator.
Regards, Orson Cart.

 

[mrbuell]

When welding aluminum, some welders have the ability to control the ac balance to best suit the job. If you were to look at a square ac wave, the positive portion would be normal width, but the negative would be quite narrow. or visa versa.

 

[Orson Cart]

Thank you for the clarification, it is fairly easy to do this using a triangle wave reference and a comparator to generate the PWM o/p. As you change the reference level away from halfway of the triangle wave the comparator o/p will become a-symmetric, this is the technique used in a lot of PWM audio amplifiers.
Regards, Orson Cart.

 

[mrbuell]

Thanks for your reply, Orson. Would you get the same effect biasing the ac wave pos or neg as you would increasing the pulse width of the just the pos or neg portion of the wave?
COlin

 

[Orson Cart]

Indeed the net effect is very similar, Regards, Orson Cart.