My application is controlling home lights. I want to use relays to switch lights on and off. My circuit should work on all kind of lights such as neon lights, halogen lights, strobe lights and others. I should decide what kind of relay I have to use, EMR or SSR. I have read about solid state relays and I encountered two issues.

First, I know one of the limitations of the SSR is the leakage current. If it is 5 mA for example, the neon light my not turn completely off. The leakage current may be sufficient to keep the light on. Right?

Second, some types of strobe lights incorporate a diode in series with the coil or filament. This causes the light to behave as a half-wave rectifier. There is an RC circuit in parallel with the output of SSR. The capacitor in this circuit cannot discharge through the series diode, causing a voltage to appear across the SSR terminals. I know that SSR must see a zero voltage across the terminals to come on, it can’t turn on again in this situation. Right?

what is your final recommendation for my specific application. I am not really concerned about the life time because typically the number of contacts may not exceed 10 per day


1 Answer 1


This sounds like a good application for regular old mechanical relays. They won't care about the direction of current, won't have a offset voltage, and their off leakage is zero in a practical sense.

Relays that can switch house power are common and available in a variety of coil voltages. Since you say you want to switch "lights", it seems like the current will be low. Relays that can do this will be small and available in coils meant to be driven from 5 V. This means you can run them from the same power supply as the processor doing the controlling, but not that the relays can be run directly from a digital output. You will need a transistor controlled by the digital output that in turn controls the larger relay coil current. Don't forget the reverse diode accross the relay coil, else you'll end up with fried transistors.


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