Help choosing correct opto isolator.

I'm relatively new to electronics, and although I can hook stuff up well if I know the right components, learning to choose the correct ones for myself by trying to search through the thousands out there, reading datasheets, etc has been a massive challenge.

I'm trying to find out if there is a single opto isolator that can be triggered by the arduino, but able to pass 200-400volts on its output, and operate extremely fast (like a fraction of a millisecond or less). The purpose is for triggering a old vivitar 283 camera flash, and triggering it instantly within less than a millisecond, for high speed photography. When I measured the flash it was only putting out about 120-150 volts, but I always hear 400v as a common number when talking about similar flashes, so potentially passing 150 volts could be fine, but might be good to go with 400v for a good safety margin.

Right now I've got a goofy setup with an underrated optocoupler, linked to spare batteries to trigger an scr, etc. I'm having many issues with it (right now an issue of having a very considerable delay). I'm hoping to simplify this and just use a single optocoupler, but the problem is I've spent hours upon hours reading through all sorts of different datasheets, most of which I barely understand, and can hardly tell if any are even close to what I need.

Can anyone help suggest one that has an input current low enough for arduino, and output current high enough for the flash, the speed to operate as fast as possible (less than a millisecond), and hopefully not too hard to find or expensive? Thanks.

Triac opto-isolators are often used to trigger a bigger triac, as the triac in the little DIL package is not usually up to much.

The LED side of the isolator usually doesn't need more than 10mA to trigger it, and your Arduino can put out 40mA per pin, so just use a series resistor, as you would any other LED.

My usual approach is to go to Farnell and find some reasonably priced devices that look hopeful then look at the datasheets (especially the example applications bits).


How about a Toshiba TLP372?

Switching time depends strongly on load current but the datasheet definitely suggests it's less than 50 microseconds.

Are you sure you need an optoisolator? A 400V MOSFET would work just as well. With some circuit protection you could make sure that 150V doesn't make its way to the Arduino.

-- The Aussie Shield: breakout all 28 pins to quick-connect terminals

Most remote trigger things use the optoisolator to trigger an SCR and IT handles the voltage and current of an older flash unit.

So you get optoisolation AND high voltage/current cheaply.

You need a voltage divider from the high voltage to charge a small capacitor to several volts, and use the Optoisolator to switch THAT into the SCR gate..

Gotta get an easy schematic drawer.....

Personally, I would use a relay as opose to an opto-istolator, but that's just me. Using a transistor, you could use a higher power relay.

I've just found this on the playground:

Replace the solenoid with a relay, and it should work. Remember to check if the relay is quick enough though!

Hopefully I've been some help! Onions.

The problem is that a relay is not fast enough for this application by the order of several hundred times.

I looked up that TLP372 that was suggested, a tad pricey at around $10 shipped for a single one, but I'd consider it if it will solve all the issues I'm having, and work as a single component without needing any additional stuff.

I'd consider a mosfet too if it would work, although you said it could need additional current protection. I've heard of using only SCR's too, but I also heard of someone frying their arduino pins with an scr, so I'm a little nervous. Just trying to find the simplest solution, hoping for a single optocoupler that works without any extra parts (or don't they exist)?

My current buggy setup is using a cny17 opto isolator, and a MAC97A8 600V SCR, but I've just been having all sorts of trouble with it (I have another thread on here trying to figure it out, but still haven't), so hoping to get rid of all that junk and use a single optoisolator, if that's possible.

Bumping the thread. Its been a few weeks, and still haven't got a suitable optocoupler.

Can anyone confirm the TLP372 should work by itself? Or have a different one to recommend?

I've been reading over the datasheet, trying to make sense of it all, but I just don't know enough to understand most of the details, and if it will let through enough volts and current, with a low enough input voltage.

No, TLP372 is only 300 V at max., so if there is a chance to get 400 it's definitely should be mark out. Don't even consider using MOSFET, if flash camera has a plug to AC outlet - optoisolation is mandatory, not an option in this case. I will vote, as someone already recommend, opto SCR, for example: VO4257. Look on: Cheers.

Thanks for that advice, I did not know that there was such a thing as an opto-scr.

I'm pretty sure my flash doesn't go above 300v, my multimeter says 160, I've just heard rumors they could go up to 400, so perhaps the TLP372 could work, but I am leaning towards theVO4257. One thing I don't know for sure is the current requirement of the flash, since my multimeter doesn't trigger the flash when measuring the voltage, it must not let through enough current. So the higher the capable current the better.

One thing that would help big time is can anyone help explain exactly what variables I should be looking for on a datasheet? I mean, I wish it was more simple like max input voltage, and max output voltage, and speed. But instead there are so many more complex terms, such as input always contains "reverse voltage", "forward current", "breakdown voltage", "collector emitter voltage" and many other cryptic terms. Which one simply means the input voltage? And when you try to figure out the amount it can pass through the output, they are always full of cryptic terms like "off state voltage", "continuous power dissipation", "breakdown voltage", "dark current", "isolation voltage", "rms on state current", and many others, how to I simply figure out how much voltage and current can pass? Also the speed, on occasion I think I find speed listed on datasheets, usually in "us" microseconds, but many times I don't find it at all. I'm not too picky about speed, but as long as its within the microsecond range it should be fine, but I'd still like to know, and can't always find it.

If anyone could simplify which are the important fields to look at, it would really help in being able to figure this stuff out on my own. I've tried looking up datasheet reading tutorials before without much luck.

All of this parameters you’ve meet in data sheet were bring on stage from science.
I’m afraid it’d be impossible to explain 2-4 years university course on this forum.
Name of the subject:
“Physics of semiconductor devices”, try to find a book or look on i-net
Good things, 99% of this parameters you can just ignore, as not related to project.
For this particular case, you should be caution on:
• High input sensitivity IFT = 1.6, 2, and 3 mA
• 700 and 800 V blocking voltage
• Isolation test voltage 5300 VRMS


timing, “Fig. 8 - Trigger Current vs. Turn-On Time” - in chart section of the document.

Did you make a search, if there is a project posted, that someone build and explain details in his blog?

Perhaps go for an opto-triac - then the high voltage polarity doesn't matter and they are usually good to 600V or more....