Electronics > Beginners

Driving LED with Solid State Relay?

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ryanmills:
I seem to be missing something fundamental with solid state relays. I'm trying to use a AQY211EHAX thats rated for 1 amp but I'm shorting out the transistor side trying to drive a tiny LED. Am i just implementing the transistor side wrong? Or am I missing something basic?

jmelson:
You need current limiting resistors on both the input and output of the SSR. 

Jon

ryanmills:
Forgive me, I'm feeling like kind of an idiot today. Are the resistors to actually limit current or like a pulldown resistors. Examples that may or may not be correct below.



TheHolyHorse:
The first image is the correct one, the other one is the same as your first design except it wastes power for no reason.

You want a resistor in series with a LED to limit the current, since the LED is just a diode so it's gonna start conducting if the voltage is higher than the forward voltage, basically just a short circuit and the LED blows. 
The LED should have a forward current(IF) parameter in the datasheet, chose a resistor to achieve that current.

ryanmills:
Thank you, the wrinkle I have is that the input voltage varies from 1.5 to 3 volts. I picked that SSR because it has a reverse voltage of 5 volts so I had hoped I would not need a resistor on the input. Would something small like 27 Ohm on the input and output be enough?

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