Regulated Current Source for High Powered laser diodes.
Joshua Dickerson
and 18 hours of classes, but I managed to put a little info on a
simple, yet effective diode laser power supply. I designed and
frabricated the unit a few days ago for an emergency in the lab. Sam,
if you're out there, I'de like to know what you think. ;) I've seen
your Electronics and Laser FAQ and I'm most impressed.
http://home.satx.rr.com/worpjr/
Best Regards,
- Joshua.
Christoph Bollig
Interesting, thanks for posting.
Did you ever try how fast you can modulate it?
Christoph
FlingPlasma
You might find it very helpful to use FETs. You won't get that nasty
thermal runaway problem, and some of the new ones can drive MASSIVE loads
(their Impedence is 0.1 Ohms as opposed to a bipolar at several Ohms).
Also, for an LD, it's best to set the threshold on one FET driver, and
modulation on another FET driver. And for perfection, cool the little dude
with a Peltier / thermistor loop.
"Joshua Dickerson" <TheSu...@yahoo.com> wrote in message
news:f3b87972.04012...@posting.google.com...
Sam Goldwasser
I think it's nice and simple and obviously could be extended to more than
two transistors.
Since there is feedback, you could go to much smaller emitter resistors
and cut way down on the power dissipation. Then, run the supply from
a 5 VDC source rather than 12 or 13 VDC.
However, it's what's missing that is most important: issues relating to
behavior upon power cycling. Vref can be controlled nicely but you must
make sure that the op-amps behave or that any transients are smoothed out.
Operator error is just as likely to kill diodes as poor circuit design! :)
And, of course if it's to be for general use, then things like variable
current limit, power up only at zero current, etc.
Note that for many low power laser diodes, optical feedback is essential
due to the narrow operating range and drift with temperature.
--- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Site Info: http://www.repairfaq.org/REPAIR/F_mirror.html
Important: The email address in this message header may no longer work. To
contact me, please use the feedback form on the S.E.R FAQ Web sites.
Joshua Dickerson
aspect was completely neglected. We are only using the laser diode
for obtaining fluorescence spectra of rare-earth doped crystals and
HEMA Polymers, so a modulation is not required. I am assuming that my
final circuit is not suitable for high speed modulation or data
transfer. To know for sure will take further design and analysis, for
which I may or may not have the time. Hopefully someday I can get
around to that. ;) Thanks for your response!
Best Regards,
- Joshua.
Christoph Bollig <laser...@gmx.net> wrote in message news:<elbs00tugou5t9hff...@4ax.com>...
Michael Anton
news:f3b87972.04012...@posting.google.com...
One thing I would suggest is to not use the TL082 opamp for this
application, as its common mode input range only extends to about
2-3 volts from either supply, so technically your input at some output
currents will fall outside the common mode range, which will obviously
cause you many problems. Though the typical spec indicates that the
common mode voltage extends to the positive supply, the minimum spec
states that it is 4V from the positive supply, so you may have just been
lucky. I'm sure that over a wider temperature range, you will run into
greater regulation problems. Pick a rail to rail input and output part
instead.
Mike Anton
Joshua Dickerson
op-amps behave? I don't need schematics or details, just a general
idea. Being a physics major has helped me design a few electronic
ciruits, but I am by no means an electrical engineer ;)
Best Regards,
- Joshua.
Sam Goldwasser <s...@saul.cis.upenn.edu> wrote in message news:<6woesxj...@saul.cis.upenn.edu>...
Rick
"Joshua Dickerson" <TheSu...@yahoo.com> wrote in message
news:f3b87972.04012...@posting.google.com...
I made some attempt at simulating a laser diode supply in ltspice. You can
get ltspice free at http://www.linear.com/software/ It is pretty sweet and
easily worth the price :-)
Here is the spice file (cut and save it as a .asc file and it will load
right up in ltspice). The basic part of the current source is from some
discussions with Win Hill (co-author of Art of Electronics) on s.e.d. a year
or two ago. I am still trying to decide the best way to modulate a current
source between sub-threshold current and operating current (for the 315M
specifically, so I want the current to swing from about 500mA to programmed
current).
Version 4
SHEET 1 1160 1300
WIRE -16 304 32 304
WIRE 32 304 32 144
WIRE 32 304 64 304
WIRE 32 144 -16 144
WIRE -80 144 -128 144
WIRE -128 144 -128 288
WIRE -128 288 -80 288
WIRE -48 272 -48 256
WIRE -48 464 -48 336
WIRE 752 512 752 480
WIRE 240 80 128 80
WIRE 48 80 -128 80
WIRE -128 80 -128 144
WIRE 240 80 240 64
WIRE 240 -80 -528 -80
WIRE -704 64 -704 32
WIRE -704 -80 -704 -48
WIRE -704 -80 -704 -96
WIRE 240 -32 -208 -32
WIRE -208 -32 -208 224
WIRE -208 304 -208 320
WIRE -208 320 -80 320
WIRE -400 448 -368 448
WIRE -368 448 -368 272
WIRE -368 448 -256 448
WIRE -496 272 -496 432
WIRE -496 432 -464 432
WIRE -464 464 -624 464
WIRE -496 432 -496 576
WIRE -496 576 -336 576
WIRE -256 576 -208 576
WIRE -208 576 -208 464
WIRE -432 528 -432 480
WIRE -432 416 -432 400
WIRE -368 272 -400 272
WIRE -464 272 -496 272
WIRE -208 608 -208 576
WIRE -208 720 -208 688
WIRE -1008 496 -1008 432
WIRE -624 432 -624 464
WIRE -1008 576 -1008 608
WIRE 240 272 240 80
WIRE 144 304 160 304
WIRE 160 304 160 288
WIRE 160 288 192 288
WIRE 752 832 752 800
WIRE 752 736 752 688
WIRE 752 624 752 576
WIRE 752 368 704 368
WIRE -528 32 -528 -16
WIRE -208 368 -208 320
WIRE -1008 432 -992 432
WIRE -800 480 -800 656
WIRE -800 736 -800 784
WIRE -880 432 -912 432
WIRE -784 432 -720 432
WIRE -720 240 -720 320
WIRE -720 400 -720 432
WIRE -720 432 -624 432
WIRE -720 464 -720 432
WIRE -720 576 -720 544
WIRE -528 -80 -704 -80
WIRE 240 -32 240 -80
WIRE 240 -16 240 -32
WIRE 624 368 560 368
WIRE 480 368 240 368
WIRE 752 800 672 800
WIRE 672 800 672 672
WIRE 672 608 672 480
WIRE 672 480 752 480
WIRE 752 480 752 368
FLAG -48 256 Vcc
FLAG -704 64 0
FLAG -704 -96 Vcc
FLAG -432 528 0
FLAG -432 400 Vcc
FLAG -208 720 0
FLAG -1008 608 0
FLAG -48 464 0
FLAG 752 832 0
FLAG -528 32 0
FLAG -800 784 0
FLAG -720 576 0
FLAG -720 240 Vcc
SYMBOL pmos 192 368 M180
SYMATTR InstName M1
SYMATTR Value FDS9933A
SYMBOL res 160 288 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R1
SYMATTR Value 100
SYMBOL cap -16 128 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C1
SYMATTR Value 1n
SYMBOL res 144 64 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R3
SYMATTR Value 2.2k
SYMBOL res 224 -32 R0
SYMATTR InstName R4
SYMATTR Value 0.1
SYMATTR SpiceLine tol=1
SYMBOL voltage -704 -64 R0
WINDOW 123 0 0 Left 0
WINDOW 39 24 132 Left 0
SYMATTR SpiceLine Rser=.2
SYMATTR InstName V1
SYMATTR Value 5V
SYMBOL res -224 208 R0
SYMATTR InstName R5
SYMATTR Value 1k
SYMATTR SpiceLine tol=1
SYMBOL res -240 560 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R6
SYMATTR Value 10k
SYMATTR SpiceLine tol=1
SYMBOL res -224 592 R0
SYMATTR InstName R8
SYMATTR Value 10k
SYMBOL voltage -1008 480 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V4
SYMATTR Value 2
SYMBOL Opamps\\LT1632 -48 240 R0
SYMATTR InstName U1
SYMBOL nmos -256 368 R0
SYMATTR InstName M2
SYMATTR Value FDS6630A
SYMBOL diode 736 512 R0
SYMATTR InstName D3
SYMATTR Value MURS320
SYMBOL diode 736 624 R0
SYMATTR InstName D4
SYMATTR Value MURS320
SYMBOL diode 736 736 R0
SYMATTR InstName D5
SYMATTR Value MURS320
SYMBOL res 720 352 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R2
SYMATTR Value 0.25
SYMBOL cap -544 -80 R0
SYMATTR InstName C3
SYMATTR Value 100µ
SYMBOL cap -400 256 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C2
SYMATTR Value 1n
SYMBOL res -896 416 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R9
SYMATTR Value 100
SYMBOL Opamps\\LT1632 -432 384 R0
SYMATTR InstName U2
SYMBOL voltage -800 640 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value PULSE(0 5 0.1m 10n 10n .1m .2m 10)
SYMBOL nmos -880 480 R270
SYMATTR InstName M3
SYMATTR Value FDS6961A
SYMBOL res -736 448 R0
SYMATTR InstName R10
SYMATTR Value 10k
SYMBOL res -736 304 R0
SYMATTR InstName R11
SYMATTR Value 90k
SYMBOL ind 576 352 R90
WINDOW 0 5 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName L1
SYMATTR Value 2µH
SYMBOL cap 656 608 R0
SYMATTR InstName C4
SYMATTR Value .001µ
TEXT -288 896 Left 0 !.tran 0 2m 0 10n startup
TEXT 512 912 Left 0 ;Laser Diode ( Iop = 2 amps, Ithresh = 600mA )
TEXT 424 312 Left 0 ;Guess at cable inductance and resistance
TEXT -880 832 Left 0 ;Modulation Input
TEXT -1568 528 Left 0 ;Programming Voltage for Current Source
TEXT -1200 224 Left 0 ;Ideally would like to modulate between\ndiode
threshold current and programmed\ncurrent (ie 500mA <-> 2Amps)
TEXT -936 864 Left 0 ;At least 5khz would be nice
TEXT -856 -208 Left 0 ;For simplicity, source is fixed at 5V DC\n(easy
availability and minimized heating of output transistor)
LINE Normal 896 880 896 432
LINE Normal 608 880 896 880
LINE Normal 608 432 608 880
LINE Normal 896 432 608 432
Joshua Dickerson
ends of the spectrum. That explains it. I think i got lucky because
I choose just the right value for the sense resistors. So, what op-amp
would you recommend? Any that are relatively inexpensive and easy to
find?
Best Regards,
- Joshua.
"Michael Anton" <man...@nocompusmart.spamab.ca> wrote in message news:<h7DPb.421$fh2.255@edtnps89>...
Michael Anton
like under an ohm), having rail to rail inputs will be more critical.
Why did you choose to use two outputs in parallel, rather than
doing all of this with one transistor?
Yes, they are easy to find. Just look at say TIs site, and usually
they have a column in the parametric table listing that specifies
whether it is rail to rail, and whether it is in, out or both. You may
want to watch the offset voltage, as this will affect the actual current
that you get out for a given voltage in. Also, you may want to
make sure the part has enough output drive for the transistor. At
1.5A of output current the TIP42 transistor only has an hfe of 50, so
it will need about 60mA of base drive, which is a lot to ask of
many opamps.
Just pick a part that you can get easily, and has a supply voltage
that is within the range you want. Also, it might be best to use a
part that runs on a single supply. And, while your at it, search
for the lowest price... Bear in mind that running on a lower supply
voltage means that you need to dissipate less power in the transistor.
One of the other issues with this circuit, is that your Vref is really
referenced to the positive supply, rather than ground (since you are
measuring the current through the resistor which is referenced to
the positive supply). This will cause you problems, if the actual
reference that you apply is with respect to ground, as then the
V+ power supply stability will effect your actual output current. You
could get around this by using a shunt regulator that is referenced to
the positive supply, and then use a trimpot to adjust the voltage off
of that. Then the power supply voltage would not be an issue.
Hope this helps,
Mike Anton
Christoph Bollig
> aspect was completely neglected. We are only using the laser diode
> for obtaining fluorescence spectra of rare-earth doped crystals and
> HEMA Polymers, so a modulation is not required. I am assuming that my
> final circuit is not suitable for high speed modulation or data
> transfer. To know for sure will take further design and analysis, for
> which I may or may not have the time. Hopefully someday I can get
> around to that. ;) Thanks for your response!
Please let me know, if you ever get round to it.
Thanks,
Christoph
Joshua Dickerson
should we need to in the future. Thanks for all the advice guys!
Best Regards,
- Joshua.
"Michael Anton" <man...@nocompusmart.spamab.ca> wrote in message news:<sz_Pb.303$P51.18@clgrps12>...