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OptoCoupler's NPN output to drive my gate driver circuit...

 
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shifanyroma
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Joined: 12 Jul 2009
Posts: 2
Location: Kuwait

PostPosted: Wed Jul 15, 2009 3:16 am    Post subject: OptoCoupler's NPN output to drive my gate driver circuit... Reply with quote

Hi. I have a PWM that i'd like to isolate from the business end of the dc motor. i bought some cheap 4n25 optocouplers for starts and I can't figure out how to get them to work for my situation.

I don't know how to explain this well so let me give you a scenario.

Lets say my optocoupler has a PNP photo-transistor on the output side. To drive my gate driver circuit, I would connect the collector pin to Vcc and the emitter pin to the gate driver input to source current. Correct?

Well the problem I have is that my optocoupler has an npn phototransistor on the output side and npn transistors sink current, right? Meaning I can't use it to pulse current to my gate driver because the load has to go between the collector and Vcc?

I'm not sure if that made any sense but here's a graphical representation of what I mean:

I know I could buy the pnp version to solve my problem but it there any way I could make this work for what I have?

bare in mind I'm really new to electronics so it could just be that I have no idea what I'm talking about, so go easy on me
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Alan
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Joined: 29 Jan 2006
Posts: 1399
Location: Winnipeg, MB

PostPosted: Tue Jul 21, 2009 12:11 pm    Post subject: Reply with quote

Either should work fine. You may have to switch you high and low logic on the microcontroller (or whatever is driving the PWM circuit though.

I would also connect a resistor up to VCC though as in this picture.


Picture source:
http://www.mech.uwa.edu.au/NWS/How_to_do_stuff/micro_crash_course/optocoupler/
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