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Anonymous Poster #1

Optocoupler Question

02/12/2012 11:42 PM

Hi everyone.

I've managed to get my TL494 (PWM controller) working giving me wide ranges of frequency and duty cycle.

But I'm having problem with the next part: Connecting it to the optocoupler. I'm using HCPL3140 http://parts.digikey.com/1/parts/501798-optocoupler-igbt-drive-0-4a-8dip-hcpl-3140-000e.html . I tried connecting the PWM signal (from TL494) straight to the input of HCPL 3140 (cathode and anode) of the optocoupler, but it's not giving any output. (I did added caps and zener diode to the HCPL3140)

What have i done wrong?

Thanks :)
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redfred
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Engineering Fields - Electrical Engineering - Been there, done that. Engineering Fields - Control Engineering - New Member

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#1

Re: optocoupler

02/12/2012 11:50 PM

How did you limit the input current to the LED to be less than the 25 mA maximum?

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fifahaywire
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Join Date: Nov 2011
Posts: 20
#2
In reply to #1

Re: optocoupler

02/12/2012 11:55 PM

i place a series 10 ohm resistor...is that sufficient?
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redfred
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Engineering Fields - Electrical Engineering - Been there, done that. Engineering Fields - Control Engineering - New Member

Join Date: Dec 2008
Location: Long Island NY
Posts: 15600
Good Answers: 981
#3
In reply to #2

Re: optocoupler

02/13/2012 12:08 AM

Well the recommended forward current by Avago is only 10 mA with the LED having a forward voltage drop of 1.5 V. So a 10 ohm resistor will be perfect if your PWM driver circuit is switching between 0 & 1.6 V.

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fifahaywire
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Join Date: Nov 2011
Posts: 20
#4
In reply to #3

Re: optocoupler

02/13/2012 11:46 PM

thanks for your reply! i got the output already

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