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Registered Member #69
Joined: Thu Feb 09 2006, 07:42AM
Location:
Posts: 116
I want to build a peltier driver for closed loop temperature control of a diode laser. I want to use the first part of the circuit shown on page two of this doc (the op amp integrator) but I need to figure out how to convert that error voltage into a drive current for the Peltier. An easy matter for most of you I'm sure. Any ideas on what would be simplest? The driver stage needs to supply ~1.5A tops at 5-7V.
I'm not interested in using the MAX8521 driver just because I've never worked with SMTs before...
Registered Member #618
Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628
I would imagine you could use a gate driver chip such as a 4429,20,27, ucc those kinda drivers, but only supply it with 5-7v's and from what I've heard peltier coolers, chill soo much air that they create condensation.
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
Funny this should come up, I just wired a dev board using a very similar chip into the project we were working on--but of course I reversed the +/- so if fed 5v back into the Tset pin But it was my boss who decided that it was probably the motherboard that was broken, so he goes and plugs it into another system
In any case, the output stage you need will depend on how much temp regulation you need. Since you aren't trying to hold the wavelength to +/- 2.5 GHz (or well under a GHz in my case), and you don't have to warm the diode, you should be able to get away just using a comparator on the output of the integrator, feed him into a mid sized MOFET, and call it a day.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
Something like this
any op-amp will do that has enough output current to drive the transistors The two transistors should be able to handle the maximum TEC current, power etc. they could be simple power bjt, or darlingtons, or complimentary mosfet etc. R1 senses the TEC current, so to match the +/- 1.5 V in for +/- 1.5 A out, it should be 1 Ohm (2.25W actual, use a 5W resistor) R2 is not really required, it's to protect the TEC against over current, you could put a 2A fuse instead
Registered Member #69
Joined: Thu Feb 09 2006, 07:42AM
Location:
Posts: 116
Thanks for the suggestions guys, Sulaiman that looks very good. I was just thinking of using a FET or emitter follower but wasn't sure how to get feedback to translate the error voltage linearly into a TEC current. Very simple.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I've designed a few commercial Peltier drivers for laser temperature control, and the linear ones used basically an H-bridge version of Sulaiman's circuit. The reason for using an H-bridge was so I could drive the TEC current in either direction while running off a single +5V rail.
My old employers sell very nice and cheap laser and TEC drivers designed by me @
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
My old employers sell very nice and cheap laser and TEC drivers designed by me
You couldn't afford four more screw-pedestals to make it more stable?
Nice LD rig Eric.
If it was me I would probably go for a PWM regulator like SG3525 or TL494. This is easy, since peltier is resistive load and all you need is a mosfet to switch power into the peltier. Frequency does not need to be high either.
Then I would simply use the chip's error amplifier with NTC to do the temperature sensing job.
You can as well use error amplifier in linear mode as sulaiman suggested, but that results in lots of wasted power making it more complex than PWM. Few watts is still quite hard to get rid off in miniaturized system.
Surely this is all ghetto and if you want something calibrated or digitally adjustable better go for microcontroller or that maxim IC.
Thanks for the suggestions guys, Sulaiman that looks very good. I was just thinking of using a FET or emitter follower but wasn't sure how to get feedback to translate the error voltage linearly into a TEC current. Very simple.
Error amplifier will always ''take care'' to equalize it's inputs, so mosfets will work as well. It's just the matter of some more dissipation.
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
Peltiers does not behave completely like resistors and don't like ripple very much. So for PWM you need either very low frequency or high frequency with a filter to remove the ripple.
Registered Member #69
Joined: Thu Feb 09 2006, 07:42AM
Location:
Posts: 116
Firkragg wrote ...
Nice LD rig Eric.
If it was me I would probably go for a PWM regulator like SG3525 or TL494. This is easy, since peltier is resistive load and all you need is a mosfet to switch power into the peltier. Frequency does not need to be high either.
Then I would simply use the chip's error amplifier with NTC to do the temperature sensing job.
You can as well use error amplifier in linear mode as sulaiman suggested, but that results in lots of wasted power making it more complex than PWM. Few watts is still quite hard to get rid off in miniaturized system.
Surely this is all ghetto and if you want something calibrated or digitally adjustable better go for microcontroller or that maxim IC.
Yeah, I thought about using a PWM but I've actually never built a PWM circuit, I thought a simple linear setup would be best, it's just a couple watts of loss... I may just try it though. The more I think about it the more complicated I'm making it.
It may be ghetto but I should be able to get nearly as good results as a nice integrated PWM. I bet +/- 0.01C is doable. I'll post what I end up with in case it's of any use to anyone.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Hi guys
I don't know about ripple problems with peltiers.. never heard about it. What mechanism could cause them 'not to like ripple too much'?
From here I assumed they can be PWM'ed. Ofcourse, it is done at low frequency, in range of low hertz, just to satisfy your desired temperature resolution.
Regarding ''high frequency PWM with a filter'', such a thing is called buck converter.
Eric could even use one of those fully-integrated buck converter IC's like LM2575 and use NTC resistor feedback instead of output voltage.
But, what I actually feared is that too low DC voltage may trouble the peltier more than direct LF PWM, where it always gets it always gets it's working voltage or 0V.
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Peltier Controller
But it was my boss who decided that it was probably the motherboard that was broken, so he goes and plugs it into another system 
@ 
