# optocoupler input voltage ranges

#### dswartz2

Joined May 19, 2009
31
hello.

I am currently trying to figure out what range of input ranges, both AC and DC, that I can use for the circuit that I have built (attached is the circuit).

I'm trying to use a wide range of high voltages and isolate them. The 24 Vdc on the output of the opto gives the my load a constant input of 24V. The load is a LOW ACTIVE input, so when the opto turns on, it will take the 24V to ground, and send a low signal to my load.

I have tested the circuit from 90 Vdc to 120 Vdc and it works. I was wondering if this circuit can be also used for AC voltage as well. I think it can, because I have inputed the extra diode in parallel to the LED in the Opto to take on the AC voltage and also the 51V zener.

If anyone can take a look at my circuit and give me some feedback, that would be great. Let me know if you have any other questions to try and help me.

Thanks!

#### Attachments

• 23.5 KB Views: 215

#### dswartz2

Joined May 19, 2009
31
The ranges I was hoping to be able to use is as high as 230 Vac and low as 90Vdc

#### bertus

Joined Apr 5, 2008
20,314
Hello,

When using the circuit on AC the output will be pulsed.
The frequency will be the same as the applied AC frequency.
The led in the optocoupler is most times an IR led.
An IR led has a forward voltage of about 1.2 Volts (depending on type, see datasheet for the excact value).

Greetings,
Bertus

#### dswartz2

Joined May 19, 2009
31
Yes, the datasheet says that the forward voltage is 1.25/1.64 max.

But how will the output be pulsed, if all the AC voltage is doing is turning the opto on, which will then just ground my 24 Vdc source on the collector?

#### bertus

Joined Apr 5, 2008
20,314
Hello,

Each time the led burns (positive cycle) the 24 Volts is switched.
Each negative cycle the led will do nothing and the 24 Volts is NOT switched.

Greetings,
Bertus

#### dswartz2

Joined May 19, 2009
31
OK I understand now.

What would you recommend to do to not have the pulse?

#### bertus

Joined Apr 5, 2008
20,314
Hello,

If you do want the pulses, rectify (a bridge will shorten the gaps) and use a capacitor.
This will slowdown the reaction time, depending on the size of the capacitor.

Greetings,
Bertus

#### dswartz2

Joined May 19, 2009
31
hi,

I put the diode right before the input of the opto in parallel with the LED pointing upward to take on the negative voltage for the AC input.

I thought that this would make my circuit to be able to take AC. Am I wrong?

#### bertus

Joined Apr 5, 2008
20,314
Hello,

Here I have an idea for the opto coupler.

Perhaps the capacitor needs some tuning for speed.

Greetings,
Bertus

#### Attachments

• 9 KB Views: 1,104