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'[OT}: Fast optoisolator with totem pole output??'
2003\07\31@165329 by Art

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Greetings,

I'm looking for a fast opto device that will switch ~150v dc in less than a
microsecond. If it can do it in 250 nanoseconds, I'd be a happy camper, but
can settle for a microsecond:>:

The devices I've found handle the voltage ok, but they seem to be based on
phototransistors and they just don't switch fast enough.

I did a bench test with a small photodiode driving an mpsa42/mpsa92
transistor(s) and it worked ok, but I'd like a prepackaged chip rather than
a homebrewed solution:>:

Any ideas??

Thanks,

Art

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2003\07\31@171646 by Bob Axtell

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You'll need to look at HP Optoelectronics. They sell very fast optical
switches, although 1uS is pretty fast, in my book.

--Bob

At 04:49 PM 7/31/2003 -0400, you wrote:
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2003\07\31@174414 by Art

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Thanks Bob!

I have used their VCSEL laser diodes, and a high end optoisolator (rated at
10 Mhz analog using a photodiode and a high speed transistor). I know the
high speed device I used DOES NOT have the voltage rating I need however
and it was not a totem pole type output.

I'll swing by HP and do some searches!

Regards,

Art



At 02:16 PM 7/31/03 -0700, you wrote:
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'Fast optoisolator with totem pole output??'
2003\08\01@061330 by Alan B. Pearce
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>I'm looking for a fast opto device that will switch ~150v dc
>in less than a microsecond. If it can do it in 250 nanoseconds,
>I'd be a happy camper, but can settle for a microsecond:>:

Is that switch it on, or both off and on? The only ones I can think of that
would approach this sort of voltage rating would be designed to drive mains
SCR's and Triacs (thinking of devices like the MOC series here). Everything
else with phototransistors or photodiodes is limited to about 30V and much
slower rise and fall times, plus quite significant transfer delay times.
Anything with fast rise and fall times has an internal amplifier optimally
matched to the photo transistor or diode.

A device I suggest you look at is the Agilent (HP) HCPL-2300 or similar
series. These require a 5V supply for the receive side amplifier, are open
collector (but there is a 1k pull up resistor available on chip) but have a
transfer delay in the double digit nanoseconds. Then hang some sort of high
voltage switching transitory totem pole on the output of this.

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2003\08\01@104319 by Chris Loiacono

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The catch with this is the opto's fall time with such high voltage. To my
best recall, high rate devices are rated at logic level voltages. If you get
tempted to try a voltage divider, it will slow the rise time significantly.
Using a single current limit resistor, the opto's emitter is going to hang
on a long slope on the way down. The best I have been able to do is to use a
part rated for 5300 - 7000V (MCT62, I think), limit the led current and
amplify the output to bring the CTR up. Of course there's a need to bias
this carefully so the transistor switches off quickest. I have gotten this
down in the 1 - 3 uS range for a single transition.
Again, IIRC, there is no single device that will acocmplish this in less
than 4 or 5 uS.

If you find a new or overlooked device or method, please let us know!!!

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2003\08\02@192139 by Charles Craft

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When HP split up a few years ago the chips went to Agilent:
http://www.semiconductor.agilent.com/

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