Need help on Voltage detector design

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Gracie

Joined: 03 Jul 2006
Posts: 15

06 Feb 2007 17:15 Need help on Voltage detector design

Hello everyone:

Here is my problem: the power supply of my circuit is a AC Power( From -100V to 100V), I need to detect the polarity of this AC signal and use it to choose the control signals for my circuit.

There are two reqirements for the voltage detector:
(1) It can't affect the operation of the main circuit;
(2) The speed of the detector should be fast. In another word, it can track the variation of te AC signal very fast.

Can anybody help me with this?

Thank you very much!

bbbb

Joined: 24 Apr 2006
Posts: 47
Helped: 11

06 Feb 2007 17:27 Need help on Voltage detector design

1. Using an opto coupler if isolation required
2. use a resistive divider , apply the divided voltage to BASE of a BJT.

Gracie

Joined: 03 Jul 2006
Posts: 15

06 Feb 2007 17:33 Need help on Voltage detector design

Dear bbbb:

Thank you for your help!

I'm not familiar with this kind of design. Could you please draw a schematic for me?

Thank you!

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bbbb

Joined: 24 Apr 2006
Posts: 47
Helped: 11

06 Feb 2007 17:43 Need help on Voltage detector design

what you need seems similar to ring detection circuits of the modems, see this as an example:
http://www.epanorama.net/circuits/elephone_ringer.html

hakeen

Joined: 16 Jun 2005
Posts: 153
Helped: 16

04 Jul 2007 13:39 Re: Need help on Voltage detector design

Hi

Use a voltage divider connected to input LED ports. When + cycle is ON, optocoupler puts output low. A simple DC input photoransistor optocupler can do it.

Also I saw there is a special part for AC sensing. it looks nice.. You can check at

http://www.avagotech.com/products/product-detail.jsp?navId=H0,C1,C7189,C4982,P93603

Regards
Hakeen