Power supply games

[George Herold]

Hi guys, Doing a simple circuit.


V(+)------+------+
20-30V _ |
^ LED|\|
+----|+\
| | >-+--out
R +-|-/ |
| | |/| |
| +---)--+
GND |
Vminus

The LED is a GaP one that avalanches at ~25V*
R is 100k
I need V minus to be 3 or so volts below ground.
(V+ to the opamp will get the usual 0.1 bypass cap and some R between
it and the led.)

I thought I'd power it from a Phihong 48 volt wall wart.
With a LM317HV for the 20-30 (+Vminus) side.
I first drew it up with another lm317 to make the ground above
Vminus. Duh... it can't sink any current.
An LM337HV would work.. but it looks to "be no more".

Any ideas for making my ground? At the moment I'm thinking I could
just use another opamp. (a dual opamp is easy.)

George H.

*So the LED is an AND114R, I ordered some other GaP LEDs from the same
company to see if I could get them to break down. There's these
AND113R's that have very similar specs.
(same wavelength 700nm but a bit more light output.)
I cranked 'em up to 50V... no breakdown, another supply,
100V.. no breakdown, another supply... finally at ~125 V the
AND113R's avalanched. The avalanche was also photosensitive. maybe
more so... But 125V is way too scary! And WTF is going on in the
AND114r's?

 

[George Herold]

Hi guys, Doing a simple circuit.

V(+)------+------+
20-30V    _      |
          ^ LED|\|
          +----|+\
          |    |  >-+--out
          R  +-|-/  |
          |  | |/|  |
          |  +---)--+
         GND     |
              Vminus

The LED is a GaP one that avalanches at ~25V*
R is 100k
I need V minus to be  3 or so volts below ground.
(V+ to the opamp will get the usual 0.1 bypass cap and some R between
it and the led.)

I thought I'd power it from a Phihong 48 volt wall wart.
With a LM317HV for the 20-30 (+Vminus) side.
I first drew it up with another lm317 to make the ground above
Vminus.  Duh... it can't sink any current.
An LM337HV would work.. but it looks to "be no more".

Any ideas for making my ground?  At the moment I'm thinking I could
just use another opamp. (a dual opamp is easy.)

George H.

*So the LED is an AND114R, I ordered some other GaP LEDs from the same
company to see if I could get them to break down.  There's these
AND113R's that have very similar specs.
(same wavelength 700nm but a bit more light output.)
I cranked 'em up to 50V... no breakdown, another supply,
100V.. no breakdown, another supply... finally at ~125 V the
AND113R's  avalanched.  The avalanche was also photosensitive.  maybe
more so... But 125V is way too scary!  And WTF is going on in the
AND114r's?

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.

 

[George Herold]

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

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot nethttp://electrooptical.net- Hide quoted text -

- Show quoted text -

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.

 

[George Herold]

Why do you want to zener an LED?

--

John Larkin                  Highland Technology Incwww..highlandtechnology.com  jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME  analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators- Hide quoted text -

- Show quoted text -

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,)

http://bayimg.com/fajaJaAEk

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.

 

[[email protected]]

Hi guys, Doing a simple circuit.

The LED is a GaP one that avalanches at ~25V*

R is 100k

I need V minus to be 3 or so volts below ground.

(V+ to the opamp will get the usual 0.1 bypass cap and some R between

it and the led.)



I thought I'd power it from a Phihong 48 volt wall wart.

With a LM317HV for the 20-30 (+Vminus) side.

Looks like all you need is a resistor in parallel with the pseudo-APD. If you want the OA IN(+) at nominal 3V above GND at V+ of 20V then that's a divider ratio of 3/20, then to get a 100K resistance that would be a a 750K inparallel 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 variable and you don't like the IN(+) junction variation then inject a constant current into the 100K, or ac-couple the OA output.

 

[George Herold]

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

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.
http://bayimg.com/CaJdMaaEk

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.

 

[[email protected]]

On Thursday, February 14, 2013 6:56:54 PM UTC-5, George Herold wrote:

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]
.. |
.. |
.. ---
.. ///
..
..
..
..

 

[George Herold]

Looks like all you need is a resistor in parallel with the pseudo-APD. Ifyou want the OA IN(+) at nominal 3V above GND at V+ of 20V then that's a divider 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(+) is0.14 x V+ ranges from 2.8V -> 4.2V as V+ ranges 20V->30V. If the V+ is variable and you don't like the IN(+) junction variation then inject a constant current into the 100K, or ac-couple the OA output.- Hide quoted text -

- Show 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.

 

[[email protected]]

On Friday, February 15, 2013 4:13:56 PM UTC-5, George Herold wrote:

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]
.. |
.. ---
.. ///
..
..
..

 

[josephkk]

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.

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.

?-)

 

[[email protected]]

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...