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Circuit Isolation

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Lighty

New Member
Hi All

I've got a circuit that has a 12V output from a ULN2803A for driving a relay, how ever I would like to opto couple it for extra safety.

Could you please advise if this circuit will work?

The optocoupler I thought of using is a TLP521-1, which has a input voltage 1.15V, probably not the best? wanting to use a DIP4 package for a easier board.

Thanks
 

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smanches

New Member
No need to isolate it further. The relay itself provides the isolation.

An optocoupler would be unnecessarily redundant.
 

Externet

Well-Known Member
Add a <~10K resistor between base and emitter ; the optocoupler should be fine.
 

crutschow

Well-Known Member
Most Helpful Member
Obviously a belt + suspenders type.
 

mneary

New Member
Won't work as drawn.

ULN2803 is open collector. You need to hook resistor to +V and cathode to ULN2803 output.
 

Lighty

New Member
No need to isolate it further. The relay itself provides the isolation.

An optocoupler would be unnecessarily redundant.

I do realise that, just thought I would make it "safer" but seem to be too much of a problem

Obviously a belt + suspenders type.

:confused:

Won't work as drawn.

ULN2803 is open collector. You need to hook resistor to +V and cathode to ULN2803 output.

Like this? (attached)
 

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