# Best way to power a photo interrupter from 12V

#### Dritech

Joined Sep 21, 2011
901
Hi all,

I am using HY301-07 which I need to power from 12V. What will be the best / simplest way to power the IR ?

To use a current limiting resistor in series, that would cause a low of power drop (i.e. will require high power resistor). Also tried experimenting with voltage divider, but this does not seem to work well, presumably as the IR is a current driven device, not a voltage powered device.

Also suggestions of how I can do this effectively and in the simplest way?

#### ericgibbs

Joined Jan 29, 2010
16,784
hi Dri,
Is it a continuous 50mA current drive.?
E

If Yes, a 220R 1.5Watt would be fine, it only dissipates approx 0.53Watt.

or use a 100R + 120R rated at 1Watt each.

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#### Jerry-Hat-Trick

Joined Aug 31, 2022
208
The data sheet says a max 50mA current but you should get by with 20mA, maybe even 10mA. The voltage drop across an IR diode is typically about 1.2V at 20mA so a series resistor of 1K ohms will give more than 10mA, reduce the resistor value to increase the current if it doesn’t switch sufficiently for your application. What are you asking the collector pin to do?

#### Dritech

Joined Sep 21, 2011
901
Hi @ericgibbs
I was considering driving it at lower current, as long as it works.

#### ericgibbs

Joined Jan 29, 2010
16,784
Hi Dri,
I quoted the maximum current rating, any current lower will of course run cooler.
E

20mA approx 0.22Watt , say 560R

#### Dritech

Joined Sep 21, 2011
901
The data sheet says a max 50mA current but you should get by with 20mA, maybe even 10mA. The voltage drop across an IR diode is typically about 1.2V at 20mA so a series resistor of 1K ohms will give more than 10mA, reduce the resistor value to increase the current if it doesn’t switch sufficiently for your application. What are you asking the collector pin to do?
The collector will drive an ASR-04DD solid state relay.

#### ericgibbs

Joined Jan 29, 2010
16,784
hi Dri,
The SSR is a 3Vmin to 32V Control voltage.
E

#### Jerry-Hat-Trick

Joined Aug 31, 2022
208
The collector will drive an ASR-04DD solid state relay.
Wow, I've never used a solid state relay. I looked quickly at the datasheet but I'd need to study a bit more. I do wonder if the opto interrupter can manage the collector current you will need. If you need light interruption to switch the relay then the relay could be turned on by another transistor where it's base is fed from the 12V line (via a resistor to turn it hard on) but you connect the collector of opto interrupter to the base of the driving transistor to turn it off when the opto transistor is on. If you need light to turn the relay on. the emitter of the opto can go to the base of the switching transistor rather like a darlington pair.

#### Dritech

Joined Sep 21, 2011
901
Hi both. It worked as intended with a 1K resistor in series with the IR and a 3.3K with the collector. Thanks a lot.
Below is how I wired everything.

#### Jerry-Hat-Trick

Joined Aug 31, 2022
208
Great, always nice to get feedback when the thread starter gets a result!