Forward baised photodiode

It's certainly not a healthy modus operandi. What does the datasheet say under abs max?

Once, I hooked up the Tripplet 630 to check out a large diode and it blew. I could see the wire that fused. Was expensive too. I just measured that meter to a ma. meter and was about 200 ma at RX1.

greg

Depends on the PD. Some have really thin epi for good blue response, which leads to a lot of current crowding near the contact, so that they die with an applied forward bias but easily survive the same size photocurrent. If it doesn't die right away, and the leakage doesn't get degraded by the experience, you should be fine.

Cheers

Phil Hobbs

Why 250 mA? Well the power supply can used for other things also. The biggest power hog is running a light bulb.

nt the forward

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Data sheet says nothing... Some list a maxiumum short circuit photo current but that's sure to be much less than 250 mA. At full light I can only get about 10mA from the diode.

George H.

(Hmm I guess I could ask the manufacturer)

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Thanks, I'll measure the leakage current after the abuse. Perhaps I should 'test' a few more and measure leakage before and after.

George H.

You can't add a current limiter to the PD? Like a polyfuse or a depletion fet? Or even a resistor?

It is a big chip, lots of wire bonds, so maybe it's OK.

John

Could they connect the PD backwards with the power supply already turned on? There may be enough capacitance on the output side of the current limiting to sauté la jonction toute de suite.

I'd add an angst resistor towards the PD, especially when dealing with students. Or at least a fast 50mA fuse.

Good idea :-)

I was thinking I might have to add some sort of current limit. It would just be much easier if I didn't have to. OK I just tried adding a bit of R in series. 50 ohms limited the current to 150 mA with a

I'm going to try Phil's idea of measuring the leakage currents on Monday.

George H.

Yeah there is a switch and indicator LED, so hoepfully they turn things off before screwing around... But of course some will forget to turn it off.

But I'll do a bit of live swtiching and see.... Well that might have cooked it. After several rapid forward biases something has changed. The forward voltage drop is now less than it was before...Hmm

George H.

It depends on the photodiode, but some of the precautions against aging and surface dirt (photodiodes have a LOT of surface) are field-dependent. So forward bias can turn photodiodes leaky and noisy. Maybe reverse bias/heat/time will fix, maybe not.

ey

Yeah I think a bit of R will be a good idea.

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Opps sorry, that's only 1 mA and in fact a bit less than that. (700uA??)

George H.

Thanks Whit3rd, I'll check it out. To be honest I made this mistake myself a month or so ago. (I hooked up the PD backwards.) I took me a few minutes to figure out what was wrong and afterwards the PD worked just fine. (But I didn't look at the leakage current!)

George H.

Glad to be of help. ;-)

Can you incorporate a current limiting resistor into the circuit?

Even if the R degrades the ckt operation, put it together, verify that its at least the right way around and then swap the resistor for a jumper.

Nice going. Sneaking feminine French nouns into what used to be a polite thread. Who are you working for? Have you no shame?

mike

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Yeah, If I put in a current limiting resistor and the PD still 'faults' because of hot switching, I'm not going to worry about it. Everyone has to make mistakes, a double mistake is a learning experience.

George H.

Yeah, I think that may work. Have them hook it up first with a series resistor to check the polarity. I've got this floating terminal block that can be used. Thanks, George H.

Have you read the manual for that meter? It, and others designed for troubleshooting tube electronics had a warning not to use it to measure resistance in solid state circuits.