Author Topic: Very fast optocouplers/optoisolators. Wanted freq ~ 20kHz  (Read 2343 times)

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Offline TrickyNekroTopic starter

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Very fast optocouplers/optoisolators. Wanted freq ~ 20kHz
« on: March 08, 2011, 05:52:55 PM »
Hello guys.

For once again I'm in need of your expertize. I'm building an H-Bridge and I want all components to be N channel, for that reason I need to use optocouples for at least high side mosfets.

So far I used a CYN17 - 3 with some success at 10kHz.
I really don't know if I need to go beyond the hearing range for optimum PWM, still I need a faster optocoupler.
It's not that the CYN17 isn't working but it's introducing me a phase delay, cause of it's rising and falling time, which is just not good...

Before telling me that a N-channel H-bridge is an over kill and so on, please guys I got everything else covered, and everything else seems to work fine, at least on multisim...

So I just need a easy commercially, fast switching (rising/falling times negligible at 20kHz) optocoupler. Have anything to suggest?

Thanks in advance, please let me know, cause I'm really in a hurry.

Best Regards, Lefteris
Greece
For whom the interrupts toll...


P.S. I've been inactive for almost a year... Don't give promises but I'll try to complete my tutorials. I'll let you know when..

Cheers!

Offline Soeren

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Re: Very fast optocouplers/optoisolators. Wanted freq ~ 20kHz
« Reply #1 on: March 08, 2011, 11:48:35 PM »
Hi,

So far I used a CYN17 - 3 with some success at 10kHz.
I really don't know if I need to go beyond the hearing range for optimum PWM, still I need a faster optocoupler.
Quite the opposite, but the optimum frequency depends on your motor.


So I just need a easy commercially, fast switching (rising/falling times negligible at 20kHz) optocoupler. Have anything to suggest?
CNY17-3 (as I believe you meant?) is rubbish. Any of the 4Nxx or 6Nxx should do and Vishay (who don't like standard numbers) makes some fast ones too.

Or why not do it right (not saying a word on P-ch. devices here ;D) and use a dedicated MOSFET driver optocoupler able to supply the needed power surge - like eg. PS9552 from Renesas?

Despite the "MOSFETs are voltage driven devices", they do need a lot of "start" current for fast switching and the current used for this will be more than gained by the lower switching losses in the MOSFETs
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline TrickyNekroTopic starter

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Re: Very fast optocouplers/optoisolators. Wanted freq ~ 20kHz
« Reply #2 on: March 09, 2011, 02:11:24 PM »
I solved my problem with some borrowed H11L1, they work fine up to 30kHz as far my oscilloscope says testing them with a Ne555 (isn't just bad to just lack proper equipment...)

I'll post the circuit to get the idea of what I'm doing, I got almost everything covered.
They circuit doesn't account for dead time and starting sequence, for it's just a proof of concept, but hell I know what I'm doing.... :P :P :P
I upload only for educational purposes... (how you shouldn't design it :-p)

And don't you just love the smell of burned transistors in the morning... IC smoke just doesn't do it...

For whom the interrupts toll...


P.S. I've been inactive for almost a year... Don't give promises but I'll try to complete my tutorials. I'll let you know when..

Cheers!

 


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