Octopart found them for $1.42 right off the bat...
AD8036 found at around $5 so that means somewhat cheaper than that for a manufacturer.
boB
tion is
own.
precisely,
of mV
comparator in
that's
ched set,
better.
ED.JPG
rc_d...
rc_b...
bout 4000
A little difficult. I'm in Christchurch, New Zealand, at the moment, and my electronic gear - such as it is - is out of reach.
You were interested eniugh to measure the temperature stability of the circuits you'd put together. Why weren't you interested enough to work out where the temperature variation was coming from?
-- Bill Sloman, Sydney (but in Christchurch, New Zealand at the moment)
(PDT),BillSloman
is
precisely,
comparator in
that's
set,
better.
4000Because I was designing a real product, a fast laser driver, and the LED current source was plenty good enough. 100 PPM/K is down where the power supply, the resistors, the capacitors, and beta variations all matter. If I wanted a more precise current source, which I often do, it would be closed-loop. I didn't have need or room for that on this little board, and the LED thing was fun. But not fun enough to spend a full day on it.
Here's the board:
-- John Larkin Highland Technology Inc www.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
(PDT),BillSloman
is
precisely,
comparator in
that's
set,
better.
4000Larkin can't handle the math >:-} ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
(PDT),BillSloman
saturation is
own.
precisely,
mV
comparator in
that's
set,
better.
about 4000
It's plain that this circuit will never be a really good current source, for several reasons, so why bother doing a lot of math? Some of us don't need to do pages of algebra or a Spice sim to see the obvious.
Power supply rejection can be greatly improved, and I bet you can't tell us how, without looking up my old posts.
Design some *real* electronics, you obsolete old geezer:
-- John Larkin Highland Technology Inc www.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
turation is
my own.
ore precisely,
10s of mVor comparator in
ay, that's
matched set,
do better.
rc_LED.JPG
D_Isrc_d...
D_Isrc_b...
the
ply
of about 4000
e l ...Jim Thompsonfor
to do
It can't be perfect, but it could have been better than you achieved with fairly minor modifications, none of which demand pages of algebra or a Spice sim - though it's often quicker (if less reliable) to run a Spice sim than it is to solder in the extra/differemt components.
us how,
The obvious technique is to make it a "ring of two" circuit, and use the LED voltage to set up a current source to bias the LED at a more nearly constant current. The traditional way would add three more transistors - two of them in a current mirror.
-- Bill Sloman, Sydney
30 (fast and
ive
amplifier
tios. The
pre- and
up using a
rt of like
real
er 100 GHz
ting,
.board
But ground loops put noise on the power supply rails.
You called it oscillation, rather than electromagnetic interference, so the implication is that the extra feedback paths through the supply rails (including the ground connection) were creating the instability.
-- Bill Sloman, Sydney
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