Problems with the NTE 3083 (4N32) Optoisolator

Jag Man · 2004-11-19T08:04:24+00:00

I am using a pair of these as the output stage in my dual pulse generatordiscussedin several recent threads. When breadboarded, it worked. If I connected a10kresistor between +12 and the optoisolator collector, and grounded theemitter,I could see the optoisolator switch from open to conducting. When openthe collector was at +12 and when it conducted this voltage droped to 0almostinstantaneously. When it opened again it went back up to +12, albeit alittleslower than I had expected.Now, after moving the circuit over to a PCB and soldering it up theoptoisolatordoesn't seem to be working. The diode section (between pins 1 and 2)is getting switched, as I can see on a scope and by means of an LED I haveinits circuit. However, the Darlington section doesn't switch. It seems tobe closed all the time. That is, when I power up the board the voltage atthe collector stays at nearly zero all the time.I've checked and double checked my connections and joints and see noproblem there (famous last words, I know).Only thing I can think of is maybe I cooked the Darlington while soldering.I was careful to do most of the soldering before inserting the chips in thesockets, butI put them in to do some preliminary tests and did not remove beforesolderingthe connections to pins 4 and 5. However, the data sheet says it should beable towithstand 260C for 10 seconds. I'm no pro put don't think I exceeded that.Any other thoughts?TIAEd

Nov 19, 2004 21 Replies

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Jag Man 21 years ago

causing

*before*

Yes, I now see that. I have now replaced the base-to-ground resistor with

1.5K. Circuit works very well now! Thanks!

Don't know...

yourself

While I have reasonable training (engineering/Comp sci) and good basic understanding of circuits I have little practical experience. I'm afraid I've been accepting proposed designs here without full understanding. By and large, it's been very helpful. The baisc disign of my circuit is due to Chris Foley. I think it's very clever. Mistakes in implementations are often my own!

Thanks much

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Jag Man 21 years ago

I think this was the problem. See my reply to peterken.

I've wondered about that. Chris Foley proposed them and I thought why not. Still have not tried to drive actual circuit (the ECU on my Jag), so don't even know if the optos will provide the needed current. Since the ECU is normally driven by a pair of tiny Hall effect transistors on a circuit board in the distributor, I expect the 125 mA max of the optos will suffice.

Thanks. That's very kind. I'll let you know if I need them.

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