Peltier Controller Schematic

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Can anyone point me to a schematic for a Peltier constant temperature
controller?

Thanks for any leads

Re: Peltier Controller Schematic


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Sloman A.W., Buggs P., Molloy J., and Stewart D. 93%A microcontroller-
based driver to stabilise the temperature of an optical stage to 1mK
in the range 4C to 38C, using a Peltier heat pump and a thermistor
sensor94% Measurement Science and Technology, 7 1653-64 (1996)

It's fairly detailed. E-mail me for a reprint - snipped-for-privacy@ieee.org
is a real address.

Analog Devices sell the ADN8831 integrated circuit controller for this
job

http://www.analog.com/static/imported-files/data_sheets/ADN8831.pdf

http://www.analog.com/static/imported-files/tech_articles/37488110918229TEC=
_Application_Brief2.pdf

and the data sheet includes a circuit diagram. It won't do as well as
my circuit, but it is a lot simpler.

The Linear Technology LTC1923 is comparable, and the data sheet is
more informative

http://cds.linear.com/docs/Datasheet/1923f.pdf

When I last looked, neither of them included my formula for
calculating the heat transferred by the Peltier junction (in watts per
amp)as a function of the temperature difference across the junction
and the thermal resistances in the path.

I've recently sneaked that into the Review of Scientific Instruments

Sloman A.W. 93%Comment on 91%Implementing of a precision fast
thermoelectric cooler controller using a personal computer parallel
port connection and ADV8830 controller92%[Rev.Sci. Instrum. 74, 3862
(2003)]94% Review of Scientific Instruments, 75 788-9 (2004)

so that Americans - who tend not to have access the the British
journal "Measurement Science and Technology" - can take advantage of
it.

--
Bill Sloman, Nijmegen

http://cds.linear.com/docs/Application%20Note/an89.pdf


Re: Peltier Controller Schematic


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http://www.analog.com/static/imported-files/tech_articles/37488110918229TEC_Application_Brief2.pdf
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Would you shoot me a reprint of each, Bill?

There's also some stuff on how to model TECs based on datasheet
parameters in my (free) thermal control chapter,

ftp://ftp.wiley.com/public/sci_tech_med/electro-optical/thermal.pdf .

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal
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Re: Peltier Controller Schematic


<snip>
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Whoops, that's the first edition version.  The second edition one (not
as polished as the rest, have to give it a going-over sometime) is at

http://electrooptical.net/www/beos2e/thermal2.pdf .

Cheers

Phil Hobbs



--
Dr Philip C D Hobbs
Principal
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Re: Peltier Controller Schematic


On Sep 15, 1:04C2%A0pm, Phil Hobbs
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It's got a drop-off in section 20.6.2.  Thermistors aren't carbon
resistors, though NTC thermistors do have points in common with carbon
resistors, like forming super-heated channels when over-loaded.

http://www.epcos.com/web/generator/Web/Sections/ProductCatalog/Sensors/Temp =
eratureMeasurement/PDF/PDF__General__technical__information,property3D%Data=
__en.pdf;/PDF_General_technical_information.pdf

mentions that the good NTC thermistors in which we are interested are
made by sintering a mixture of metal oxides at 1000 to 1400E2%81B0%C. The
Yellow Springs Instruments application notes were a bit more specific,
but the thermistor business was sold to Measurement Specialties and
the link below no lnger works.

http://www.meas-spec.com/downloads/Long_Term_Thermistor_Stability.pdf

--
Bill Sloman, Nijmegen


Re: Peltier Controller Schematic


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http://www.epcos.com/web/generator/Web/Sections/ProductCatalog/Sensors/TemperatureMeasurement/PDF/PDF__General__technical__information,property=Data__en.pdf ;/PDF_General_technical_information.pdf
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NTCs vary a lot, especially in their (unspecified) 1/f behaviour.  The
glass bead ones are often carbon, iirc, but I'll certainly chase down
the links and fix as necessary.  Thanks for the input!

That 1/f stuff is one reason why I really like thin-film platinum RTDs,
even though their sensitivity is 10x lower at room temperature.

===========
RTD Advantages:

Low 1/f noise

Good thermal coupling (it's a lot easier to get good thermal coupling to
a flat piece of alumina than to a glass bead)

Pretty linear, easily linearized in SW or with a small negative
conductance in parallel

dR/dT reasonably comparable to linearized thermistors

===========

Figure 20.


(I especially like learning from other people who have actually done the
thing under discussion--it saves my having to crawl out of the potholes
myself.)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
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Re: Peltier Controller Schematic


On Wed, 15 Sep 2010 12:06:13 -0400, Phil Hobbs

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http://www.epcos.com/web/generator/Web/Sections/ProductCatalog/Sensors/TemperatureMeasurement/PDF/PDF__General__technical__information,property=Data__en.pdf ;/PDF_General_technical_information.pdf
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Much more stable at relatively high temperatures, IME.

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Re: Peltier Controller Schematic




 Hi Spehro,
Please send me a private email, I tried to send one
to you. I wonder if I'm not smart enough to decode
your munged email address, anyway it didn't go through.
                    Thanks, MikeK



Re: Peltier Controller Schematic



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Done.


Re: Peltier Controller Schematic


On Sep 16, 2:06C2%A0am, Phil Hobbs
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Back in 1978, I made the argument that the higher thermal dissipation
of platinum thin-film RTDs meant taht they were better suited to micro-
kelvin tmperature control and measurement, if you could cope with the
heat being dissipated.

Sloman, A.W. "On microdegree thermostats", Journal of Physics E:
Scientific Instruments, 11, 967-968 (1978).

It follows from Larsen's formula for the Johnson-noise limit on RTD's
as temperature sensors.

--
Bill Sloman, Nijmegen

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AFAIK the important point to bear in mind is that the Peltier device
acts like constant-heat pump, driven by junction current, in parallel
with a resistor that shows I^2-R losses.  So the overall heat pump
action will be nonlinear (because of the I^2 factor), and it's really a
good idea to not try to PWM the thing (because of the I^2 factor).

--

Tim Wescott
Wescott Design Services
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Re: Peltier Controller Schematic


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However, with a sizeable Peltier, one should PWM the driver and then
lowpass accordingly so that the Peltier sees DC. Or almost DC.

--
Regards, Joerg

http://www.analogconsultants.com /

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That exactly what I did. Unfiltered pulse width modulation has been
known to melt the solder inside the Peltier cooler, but if you can
keep the ripple down to less than - say - 10% of the peak current, the
extra resistive losses aren't dramatic. Radio-frequency interference
from the leads to the Peltier cooler can be a problem a ripple current
levels that won't generate significant extra heating and it can pay to
filter this current to reduce the ripple content to much lower levels.

--
Bill Sloman, Nijmegen

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Yup, RF-wise I filtered the dickens out of it. Ferrite bead, cap,
another ferrite bead ...

--
Regards, Joerg

http://www.analogconsultants.com /

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Re: Peltier Controller Schematic


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I should have been more clear on that -- yes.  But it's _not_ like a
motor driver where even if you PWM slowly enough that the motor doesn't
filter it out you're still (usually) not losing massive amounts to I^2-R
losses.

So -- generate the current however you want, but make it reasonably
smooth going into the Peltier.

--

Tim Wescott
Wescott Design Services
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Re: Peltier Controller Schematic


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yep, the integrated ones I've seen is basically two buck converters
driving each
end so it can both heat and cool

-Lasse

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http://www.analog.com/static/imported-files/tech_articles/37488110918229TEC_Application_Brief2.pdf

Looks like they are finally ditching this chip but if you need a one-off
prototype it'll work:

http://www.analog.com/static/imported-files/data_sheets/ADN8830.pdf

Maybe I am, to a small extent, guilty regarding its demise because I
bought the demo kit and then decided I didn't like it that much, and
rolled my own.

--
Regards, Joerg

http://www.analogconsultants.com /

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Re: Peltier Controller Schematic


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They are now pushing the ADN8831. I've not been interested enough to
work out how it differs from the ADN8830.

--
Bill Sloman, Nijmegen


Re: Peltier Controller Schematic


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I think that's the datasheet where I found some inconsistency in a
formula or two and I let them know. Basically those chips are ok but I
found it can also be done for much less money. I mean, over $7 is a
hefty price. Even if you need a few dozen jelly-bean parts you can beat
that. Or use a low-cost uC. I can't imagine the ADN8831 selling like
hotcakes.

--
Regards, Joerg

http://www.analogconsultants.com /

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Re: Peltier Controller Schematic


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I never understood the need for a specialized Peltier cooler IC, unless
it's because they do something fancy to compensate for the nonlinearity.

Unless your problem demands hugely tight regulation you can just design
a loop with enough margin to handle the nonlinearity, and if it _does_
need the tight regulation then you either handle it with a few discretes
or with a micro.

So why a special chip?

--

Tim Wescott
Wescott Design Services
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