Everlight EL357N NPN Phototransister eBay

[Falcon69]

So, I bought some of these EL357N NPN Phototransisters off eBay.

http://www.mouser.com/ds/2/143/201407061738295695-365680.pdf

And they are working for what I need them to do.  Which will save me quite abit $ over what I am using now (.06 vs .85 per), which is a Vishay VO1400EAFR.

http://www.mouser.com/ds/2/427/vo1400aeftr-244774.pdf

Now, my question is, currently I am using a TVS diode and a 3000kV Capacitor on the input/output of the mosFET side of the Vishay chip to help protect it from the possibly ESD of plugging in and unplugging of a connector wired to those outputs. It is needed because the Vishay chip is a mosFET and prone to those ESDs, from what I understand.

Now, with this new EL357N chip, do you think that the TVS diode and Capacitor are still needed, seeing how it is NOT a mosFET nor a CMOS device?  The connector will not be plugged/unplugged very often. Most likely it will be connected, and then never touched again.

But because the Vishay chip was a mosFET, I wanted protection for the initial plug in, in case there was ESD.

Thanks in advance.

[danadak]

Since you are in a cabled environment might be prudent to still
provide some protection. A simple zener should suffice, its fast,
protects from HV in one direction, is a diode clamp in the other.

Just a thought.

[Falcon69]

So, something like this with maybe a 24v zener?
The optocoupler accepts up to 80V, but I think only 24V will ever go through it, but should I put like an 80v zener in it or something, to allow up to the 80V, just in case?

[danadak]

Thats correct, and I would use 60V jsut to give some margin.
Note if you have a situation where reverse V can occur on the
cable might want a series r from top of Zener/coupler to cable
to limit current thru zener. Like 100 ohms, something like that.

Regards, Dana.

[Falcon69]

okay, but if someone plugs in 72V (some of the power supplies used, may be 72V, but NEVER above), then it won't work because Zener will allow current to flow through at 60V, correct?

So, something like this with the resistor? What size resistor? 1/8w? 1/4w? 1/2w? I'm really not sure on the current going through the transistor of the optocoupler.  I'm assuming it won't be anymore then 50mA (as that is all the optocoupler can handle anyway, with a Peak of 1A quickly)

If this works, it will still be alot cheaper then the TVS diode and that Cap.

[Falcon69]

This isn't going to work.

72v going through a 100ohm resistor at a max of 50mA = 3.6watt resistor. that's going to be WAY to big. That's too big of a footprint for my little circuit board.

Not to mention, the 75V zener diodes I'm finding have a max of 500mW rating.

[Falcon69]

Found this one.

http://www.mouser.com/ds/2/302/BZX84J_SER-841066.pdf

Peak Reverse Watts is 40W, and 200mA Peak Amps for the 75V version.

But the resistor still has me stumped.

[Falcon69]

How about these two, wired like in the picture...

http://www.mouser.com/ds/2/302/BZX884_SERIES-840822.pdf
http://www.mouser.com/ds/2/427/rcse3-884122.pdf

Resistor is 0603 1/4w.

Will this work?  I really doubt that the 72volts will be more then even 10mA switching. It will probably be switching on another Optocoupler from another product. The majority of the external connection will most likely be only 12v to switch, and not the 72volts.  But I would like the availability.

If this will work, it would give me a really great configuration of footprints for my PCB.

[danadak]

I might be a bit confused, what is at the far end of the cable, V and DC Z ?

And when you switch on the opto coupler what is the max I you have to switch ?

Yes, as you see, you can trade off Pdiss of the R for Vz.

Your other tradeoff is where the R goes, if in series with cable that changes noise
margin, if in series with Vz and that net in parallel with coupler output, less protection
results, due to speed affected by stray C and R, and of course effective clamping Z.

Regards, Dana.

[Falcon69]

the output of the optocoupler, (the transister side, pins 3 and 4), will be connected to an external circuit which can vary depending on application.

That voltage can be anywhere from 3.3v to 72v DC (maybe AC, but I doubt it).

I don't think it will have anymore than 50mA. It will most likely be switching on/off another Optocoupler from the external circuit.

The diode side of the optocoupler will be switched on via a uC or a logic gate.