Power supply games

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Hey, I was reading the LM337 spec sheet.. looking for the maximum input voltage. (none listed...) And it struck me, It's only the voltage difference (Vin to Vout) that the chip knows about... I could use this to regulate -100 Volts down to -90. (Sorry I'm brain dead some days.)

George H.

As long as you don't bring up the input too fast, or short-circuit the output, or put a big bypass on the adjustment pin with no protection diode.

Cheers

Phil Hobbs

Make sure you put a Zener across it to clamp the maximum voltage to a safe level.

Why the 723 lives on...

I have an old vacuum-tube HF signal generator that I use in my lab. I made a regulator for the oscillator plate supply using a couple of high- voltage transistors and a neon bulb for the reference.

It's probably noisy as hell, but it works better than unregulated.

maybe

e.

t -

Thanks Phil... I'd forgotten about the protection diode! (It's always the simple circuits that I seem to screw up (but only a little :^) I can add some resistance in the power lead to slow down the turn on. The Phihong 48 volt supply is listed as +/-5% load line regualtion. Does that mean I'll see output voltages from 45.5V to 50.5? (unit to unit variation.)

That looks to make the design a bit 'tight' on the Vminus side.

George H.

Why do you want to zener an LED?

ybe

.highlandtechnology.com  jlarkin at highlandtechnology dot com

This one LED turns into a single photon avalanche photodiode. (Here's a plot of the statistics.. I've got some better data but this will do,)

A colleague?s built a counter - timer that was mostly made to go on the end of a PMT experiment. But this is a much cheaper way to count single photons. (I wish I could get some solid state expert interested in it.. I?d love to understand what going on in this one LED.)

George H.

Incwww.highlandtechnology.com  jlarkin at highlandtechnology dot com

Ok, OK. What sort of tests do you do to prove it detects single photons?

Looks like all you need is a resistor in parallel with the pseudo-APD. If y ou want the OA IN(+) at nominal 3V above GND at V+ of 20V then that's a div ider ratio of 3/20, then to get a 100K resistance that would be a a 750K in parallel with APD and 120K from APD||120K junction to GND. Then IN(+) is 0 .14 x V+ ranges from 2.8V -> 4.2V as V+ ranges 20V->30V. If the V+ is varia ble and you don't like the IN(+) junction variation then inject a constant current into the 100K, or ac-couple the OA output.

Hmm, the output is an RC pulse response. RC recharging determined by the 100k ohm resistor and LED capacitance. The count rate is proportinal to the light intensity. (I haven't looked over a lot of the bias range. At higher bias voltage there are more 'dark' counts but also more 'signal' I haven't plotted any of that out.) So I guess the strongest evidence is the histogram of the time between pulses. (The graph I posted.) The number of occurences of any time difference exponentially decreases from zero time, with a slope that relates to the average count rate. So it's some random process. If you want to suggest something other than photons then I'm all ears (or eyes). At some point this is just a random pulse generator to do the statistics with.

There is some 'after pulsing' More counts at a few microseconds than you'd expect from just the count rate. Apparently this is also common in other SPAD's. Here's some better data that shows the 'after pulsing' in the first bin.

I'd like to look at the spectral response too, but at that point it's alomst a research paper.

I've offered to send these to a bunch of physics types and anyone on the SED or SEB.. Send me your name and address or order your own from Newark/Allied AND114R. I'm pretty sure you have the 100k ohm resistor :^)

The circuit's up and running I'll spend the rest of the day getting some dark count vs bais voltage numbers.

Oh I measrued some (11) 12V Phihong supplies, they had a nice tight spread of voltages. min was 12.08 V max was 12.14 V (50 ohm load)

George H.

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Alternative CCS if you need that:

Please view in a fixed-width font such as Courier.

. . . . . . 20V-30V . 317 OUT--------------+-----------+-----> V+ . | | . | | . [220] APD . | | . 317 ADJ--------------+ +-----> IN(+) . | | . [2.7K] [100K] . | | . | _ | . | /| | . [2K] | . /| | . | | . +-----------' . | . [560] . | . | . --- . /// . . . .

you want the OA IN(+) at nominal 3V above GND at V+ of 20V then that's a d ivider ratio of 3/20, then to get a 100K resistance that would be a a 750K in parallel with APD and 120K from APD||120K junction to GND. Then IN(+) is 0.14 x V+ ranges from 2.8V -> 4.2V as V+ ranges 20V->30V. If the V+ is var iable and you don't like the IN(+) junction variation then inject a constan t current into the 100K, or ac-couple the OA output.- Hide quoted text -

Thanks Fred. I need the OA in(+) at 'ground'. The output signal goes into a counter that's got a 0 to 1 Volt comapartor on the input. I guess an opamp that went down to the negative rail would work. (I don't know a lot of those) but something ~8-10 MHz, with Cin ~3-10pF might be worth a look see. Oh it should have ~36V supply voltage.

George H.

This is not a precision analog application, this will be more than enough, no need for exotic OAs or dual PS: Please view in a fixed-width font such as Courier.

. . . . . . 20V-30V . 317 OUT----+-----------+-----> V+ . | | . | | . [220] APD . | | | \ 2N3906 . 317 ADJ----+ +-------|+ \ . | | | >--+--[Re]--E C----+-->TRIG . [2.7K] [100K] .-|- / | | . | | | | / | B | . | _ | | | | [Rpd] . | /| | '--------' | | . [2K] | | | . /| | | --- . | | | /// . +-----------' | . | | . | | . [72] | . | | . +-------------------------------------' . | . [510] . | . --- . /// . . .

diode.

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Cannonically that means that the output will change no more that 5% over the entire range on input, or no more that 5% of the line change, whichever is largest.

?-)

On Feb 15, 4:55 pm, snipped-for-privacy@gmail.com wrot e:

ation, this will be more than enough, no need for exotic OAs or dual PS:

nt such as Courier.

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Hmm Thanks Fred... I'm not sure I get how all the bits of that circuit are working. So the 510 ohm resistor puts t he base about 3 volts above ground... and the 72 ohm keep s the emitter ~0.4 volts above this (at idle). Maybe I'll just have to build it.

I hope you won't be too offended if I stick with the current version that has a LM317 and LM337.

George H.

LOL_ not at all...