# Using a Optocoupler - Determining Parameters

by jsinglet   Last Updated October 09, 2019 13:25 PM

I'm looking at possibly using an optocoupler to drive a higher powered circuit from a lower powered one.

This is the device I am looking at: http://www.vishay.com/docs/83641/il755.pdf

The circuit I am switching is a 30V @ .5A circuit. Am I reading this correctly?

• V_CEO = 60V, meaning the circuit on the output side can handle a voltage of up to 60 volts

• V_F = 1.2, meaning, if I apply 1.2 volts, the output should be fully on.

• How much current will it draw? Under the forward voltage condition of 1.2 V it pulls 10mA.

• Where in the data sheet does it state the max current the switching side of the coupler can handle?

So then, if I supply 5V to this thing, how much resistance to I need to put in front of it to get the required 1.2 V? (5 - 1.2)/.01 = 380 ohms.

Am I reading this all correctly? Especially with regard to the last point. Is it suffient to place a resistor in front of it to induce a voltage drop of 3.8V (leaving the 1.2 to supply to the transistor)? Or do I need a dedicated supply like a LDO?

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