Opto Isolator Question

[mark30504]

Hello

I have an application were I need 24V DC Plus out

I want to use an opto isolator but all seem to be NPN.

Any Thoughs ?

thanks

Mark

 

[fsmyth]

Tie the collector of the output transistor to the
+24v rail. It IS isolated, after all.
<als>

 

[joozwa]

Hi, you may simply add external PNP transistor which will be driven from that NPN inside optoisolator. In this way you will avoid placing a load in emitter circiut.

 

[mark30504]

Hello

Thanks for the replys

I would like to do it without adding componets if possible. So,

Are you saying the opto acts more like a switch. that is,

By connecting the Collector to 24 V Plus and using the emitter to drive my circuit ?

So that the emitter goes low when the transistor in the opto is off, should I add a resistor to 0V DC to the emitter pin ?

I have always seen the opto drawn as NPN working. That is,

The emitter tied to 0V and a resistor on the collector to Plus DC and the signal taken at the collector juction of resistor and collector pin.

Are you saying it will work either way ? Collector to Plus and resistor to OV on Emitter ? Signal taken at the Emitter pin ?

Thanks

Mark

 

[laktronics]

Hi,
Yes, sure it works, but check the Vceo specs of the output transistor. Also use a high resistor from its base to ground. The collector resistor should be large enough to limit the current to ensure that the transistor enters into saturation for a given input diode current.

Regards,
Laktronics