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### Topic: Using an optoisolator to control a 12V 5A DC Power supply? (Read 3992 times)previous topic - next topic

#### xberg

##### Sep 26, 2011, 11:59 am
Hi,

Can I use a 4N25 optoisolator to control on/off of a 12V 5A DC Power Supply? I'm thinking of cutting in 2 the wire of  the +12V of the power supply and connecting both bits to the emitter and collector of the opto and having a parallel connection of the ground to the arduino's ground.

Problem is that I have doubts that the opto can stand such current (5A). The data sheet (http://www.vishay.com/docs/83725/4n25.pdf ) says: Absolute Max Collector Current 50 mA / 100 mA - so I'm nowhere near the 5A.

Further down in the datasheet I also read:
CURRENT TRANSFER RATIO
DC current transfer ratio VCE = 10 V, IF = 10 mA
4N25 CTRDC 20 50 %

So does that mean that the opto reduces the current by 50%???

Should I forget about the opto and go the relay route?

thanks!

#### Noorman

#1
##### Sep 26, 2011, 01:31 pm
You can use the 4N25 to drive a circuit that can handle the requested current.
It cannot handle that of itself.
Depending on what you want to achive, just on/off or somekind of regulation, you need  FET(s) or transistor(s) to do the job.
If you need "high" speed switching you cannot go around FET or Transistors.

A relais is possible but is slow and only two state.

Regards,

#### Grumpy_Mike

#2
##### Sep 26, 2011, 04:10 pm
Quote
So does that mean that the opto reduces the current by 50%???

It doesn't actually reduce the current because it isolates the current in one circuit, it in effect transfer 50% of the current to the output but it is not the same current, it is just that it causes 50% of the current to flow in the isolated circuit.
Yes 5A will kill an opto isolator stone dead.

#### dc42

#3
##### Sep 26, 2011, 04:41 pm
Either use a relay, or use the optoisolator and a pullup resistor to control a P-channel mosfet (e.g. IRF9540) to do the switching
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

#### terryking228

#4
##### Sep 26, 2011, 10:17 pm
I would suggest you use a relay unless you need some high-speed on -off??

Here's an example of an opto-controlled relay with the schematic.  The isolator used is electrically similar to the 4N25.

http://arduino-direct.com/sunshop/index.php?l=product_detail&p=201

DISCLAIMER: Mentioned stuff from my own shop...
Regards, Terry King terry@yourduino.com  - Check great prices, devices and Arduino-related boards at http://YourDuino.com
HOW-TO: http://ArduinoInfo.Info

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