A/C positive clipping circuit??

James Long

Ok guys....I have a voltage that swings over a wide range,

I would like to use a clipping circuit to keep the voltage in a range that an optoisolator can see.

The frequency is what I'm trying to read....it changes.

Can I just use an optoisolator with·a resistor and a zener?

I don't see this as being complicated....but wanted to know before designing a board to house the surface mount parts.

I don't have the item the board will read, so I really can't test this. I'll have to travel some distance to install it.

Thanks,

James L

LilDi

If you are talking about an A/C voltage that swings negative and then positive say at 60 cycles and you want to clip the negative voltage swing, then all you need is a diode in series with the optoisolator. You will need a resistor in series with the optoisolator as well, to limit the current to be within the maximum rating of you optoisolator.

James Long

Lildi,

I'm talking about an ac voltage (most ac voltages swing positive and negative) that I want to clip off the negative totally....and the clip off the top of the positive wave to be flat at a certain voltage.

Clipping and clamping....I guess.


James L

JonnyMac

You can use the circuit that's attached; it gives a quick pulse out starting at the zero cross of each cycle -- measure from leading edge to leading edge to get frequency. Adjust the resistors for your voltage (as shown works for 120 VAC).

James Long

JonnyMac,

Unfortunately......the voltage changes.....and the frequency......that is why I require the zener clipping circuit. I'm going to use a regular diode for half wave clipping, and another zener to clip the positive voltage. Then just add a resistor to limit the current for the opto.

James L

Phil Pilgrim (PhiPi)

James,

What kind of voltages and frequencies are we talking about here (min to max)?

-Phil

James Long

Phil,

The voltage will change from about 18 volts to about 70 volts. The frequency will go from 120 Hz to about 400 Hz.

James L