Zero Crossing Using Optocoupler

Mojalco · Nov 19, 2003

I am currently designing a zero crossing detector using an 4N25 optocoupler. I have a series resistor which is valued at 33Kilo Ohms 5watts, in series with it is a 1N4007 diode, which normally have a greater breakdown voltage than that of the light emitting diode inside of the 4N25. It works fine.

The problem is that the resistor that Im using gets too hot. Could anyone give me an advice on how I could dissipate this heat on the resistor.

Thanks in advance!!!

Isotope · Nov 20, 2003

Hi Mojalco,
I used this same circuit before but in different value. that is, a 47Kohms in series with a 1N4007 and 4n37. The high voltage of about 230V is injected to this circuit but the resistor didnt emitted any heat or even i cant fell it. the resistor rated at 1/4W.

I used this circuit to detect an appliance status.

Roff · Nov 20, 2003

Mojalco said:
I am currently designing a zero crossing detector using an 4N25 optocoupler. I have a series resistor which is valued at 33Kilo Ohms 5watts, in series with it is a 1N4007 diode, which normally have a greater breakdown voltage than that of the light emitting diode inside of the 4N25. It works fine.

The problem is that the resistor that Im using gets too hot. Could anyone give me an advice on how I could dissipate this heat on the resistor.

Thanks in advance!!!

I think you should check your resistor value. Are you sure it's not 3.3k? A 33k resistor, even across 220 volts, should only dissipate (V^2/R)=1.5 watts. With a diode in series, it should dissipate 0.74 watts. If you're using 120v, it should only dissipate 218 mw.

Zero Crossing Using Optocoupler

Mojalco

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Isotope

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Roff

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Zero Crossing Using Optocoupler

Mojalco

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