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Subject: PhotoMOS relays-How to get a FormC configuration??

Date: 08/28/03 at 12:45 AM
Posted by: Vivien Wong
E-mail: Vivien.Wong[AT55]motorola.com (replace [AT55] with @ to reply)
Message Posted:


I'm using a PhotoMOS relay. The PhotoMOS relay has an LED at input terminals and 2 MOSFETs(open) at output terminal. When voltage is pumped into input, LED will light up and caused MOSFETs to close the circuit.This works fine.
However,I have some applications where I need to control 2 circuits, A and B. When no input voltage, circuit A is open and circuit B is close and when voltage is applied, circuit A closes and B opens.This is the FormC configuration that I need on the PhotoMOS relays.
I have tried using 2 relays to do this job.It is fine when input voltages are 5 and 0V. But when voltage drops, there'll be an intermediate stage (~2.5V) and this will turn on both the relays ie:circuit A and circuit B closes. This causes shorting and leakage problems.
Can someone suggest of a better design or another alternative to this??
Please help!!!

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