Relay circuit with optocoupler without transistor

Thread Starter

szotyi

Joined Jan 14, 2016
19
Hi,

I would like to minimise my PCB components.
Is it safe to use e.g. TIL193 with some resistor, and fly-back diode to drive a FINDER 34.51.7.012.0010 without any other components? Or why every schematic show a separate transistor between the relay, and the opto?

What would be the optimal resistor values if i want to drive the opto with 3.3 V signal?

Thanks
 

kubeek

Joined Sep 20, 2005
5,795
I wouldn´t reccomend that. TIL193 has only 20% CTR, which means to get the required 14mA on the output transistor, you need to feed the LED five times that - 70mA, which is way too much. A transistor at the output will be a superior solution.
 
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