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TEC for laser diode

Started by mt September 28, 2013
I have a laser diode that is cooled by a fan and a heat sink. I have a small TEC lying around and I would like to integrate that to the laser diode head. How do I go about controlling the voltage supply to maintain a stable temperature. 

Thanks for you valuable input
On Saturday, 28 September 2013 15:33:32 UTC+10, mt  wrote:
> I have a laser diode that is cooled by a fan and a heat sink. I have a sm=
all TEC lying around and I would like to integrate that to the laser diode = head. How do I go about controlling the voltage supply to maintain a stable= temperature.=20 You need to think in terms of current control rather than voltage - TEC's t= ransfer watt per amp, Sadly, the watts transferred per amp varies fairly rapidly with temperature= difference you are trying to sustain across the TEC, and a proper controll= er needs to measure the temperature on both sides of the junction.=20 Sloman A.W., Buggs P., Molloy J., and Stewart D. =93A microcontroller-based= driver to stabilise the temperature of an optical stage to 1mK in the rang= e 4C to 38C, using a Peltier heat pump and a thermistor sensor=94 Measureme= nt Science and Technology, 7 1653-64 (1996) spells it all out in fair detail, including a formula for heat transfer per= amp, which none of the application notes seem to include. E-mail me - at b= ill.sloman@ieee.org - if you can't get hold a of a copy. --=20 Bill Sloman, Sydney
On 28/09/2013 1:33 PM, mt wrote:
> I have a laser diode that is cooled by a fan and a heat sink. I have a small TEC lying around and I would like to integrate that to the laser diode head. How do I go about controlling the voltage supply to maintain a stable temperature. > > Thanks for you valuable input >
You could buy one of these - they are made for the job; <http://www.teamwavelength.com/products/default.php?show=temperaturecontrollers>

"mt"  wrote in message 
news:db7cb71a-9d3f-46b9-b814-a7202deaeaa7@googlegroups.com...

I have a laser diode that is cooled by a fan and a heat sink. I have a small 
TEC lying around and I would like to integrate that to the laser diode head. 
How do I go about controlling the voltage supply to maintain a stable 
temperature.

Thanks for you valuable input

One possibility is to use one of the modules from Analog Technologies 
(http://www.analogtechnologies.com/tec-controller.html )
and buy their eval board, which makes it relatively convenient to to tune 
the PID parameters.  I've seen temperature stability of a few milli-Kelvin 
with their modules.  A potential limitation of these modules are they are 
limited to 5V supplies, which might not be compatible with the TEC you have.

Bret Cannon 

On Saturday, September 28, 2013 9:20:34 AM UTC-4, Bill Sloman wrote:
> On Saturday, 28 September 2013 15:33:32 UTC+10, mt wrote: >=20 > > I have a laser diode that is cooled by a fan and a heat sink. I have a =
small TEC lying around and I would like to integrate that to the laser diod= e head. How do I go about controlling the voltage supply to maintain a stab= le temperature.=20
> =20 > You need to think in terms of current control rather than voltage - TEC's=
transfer watt per amp,
>=20 >=20 >=20 > Sadly, the watts transferred per amp varies fairly rapidly with temperatu=
re difference you are trying to sustain across the TEC, and a proper contro= ller needs to measure the temperature on both sides of the junction.=20
> =20 > Sloman A.W., Buggs P., Molloy J., and Stewart D. =93A microcontroller-bas=
ed driver to stabilise the temperature of an optical stage to 1mK in the ra= nge 4C to 38C, using a Peltier heat pump and a thermistor sensor=94 Measure= ment Science and Technology, 7 1653-64 (1996)
>=20 >=20 >=20 > spells it all out in fair detail, including a formula for heat transfer p=
er amp, which none of the application notes seem to include. E-mail me - at= bill.sloman@ieee.org - if you can't get hold a of a copy. Well as Bill says current control is a bit better. But if you are wrapping= a control loop around it (PI) then you can do it with just voltage too.=20 =20 The most important thing (IMHO) for a TEC is sizing the heat sink. If it's= free air cooled then you need a pretty big heat sink compared to the size= of the TEC. It's just a matter of energy conservation, all the heat that = flows through the TEC has to also leave the heatsink. =20 George H.
>=20 >=20 >=20 > --=20 >=20 > Bill Sloman, Sydney
On Saturday, September 28, 2013 9:23:39 AM UTC-4, Glenn B wrote:
> On 28/09/2013 1:33 PM, mt wrote: > > > I have a laser diode that is cooled by a fan and a heat sink. I have a small TEC lying around and I would like to integrate that to the laser diode head. How do I go about controlling the voltage supply to maintain a stable temperature. > > > > Thanks for you valuable input > > > > You could buy one of these - they are made for the job; > > <http://www.teamwavelength.com/products/default.php?show=temperaturecontrollers>
Hmm I bought one of their TEC controllers years ago. I had to hack it to get a longer integration time... and then just ended up making my own. The longer integration time gets to the debate of where to put the temperature sensor. Near the TEC, or near the laser diode. I opted for near the diode, and so a longer time constant. But others think otherwise, and I very well could be wrong. George H.
On 10/01/2013 11:04 AM, George Herold wrote:
> On Saturday, September 28, 2013 9:23:39 AM UTC-4, Glenn B wrote: >> On 28/09/2013 1:33 PM, mt wrote: >> >>> I have a laser diode that is cooled by a fan and a heat sink. I have a small TEC lying around and I would like to integrate that to the laser diode head. How do I go about controlling the voltage supply to maintain a stable temperature. >>> >>> Thanks for you valuable input >>> >> >> You could buy one of these - they are made for the job; >> >> <http://www.teamwavelength.com/products/default.php?show=temperaturecontrollers> > > Hmm I bought one of their TEC controllers years ago. I had to hack it to get a longer integration time... and then just ended up making my own. > The longer integration time gets to the debate of where to put the temperature sensor. Near the TEC, or near the laser diode. I opted for near the diode, and so a longer time constant. But others think otherwise, and I very well could be wrong. > > George H. >
There's no reason to have just one sensor. You can wrap the actuator in a local first-order loop with some fairly crude but fast sensor right at the actuator, and use that as an improved actuator in an integrating loop with a sensor where you actually want to control the temperature. That gives you high accuracy plus decent rejection of thermal forcing. 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 net http://electrooptical.net
On Tuesday, October 1, 2013 11:19:24 AM UTC-4, Phil Hobbs wrote:
> On 10/01/2013 11:04 AM, George Herold wrote: > > > On Saturday, September 28, 2013 9:23:39 AM UTC-4, Glenn B wrote: > > >> On 28/09/2013 1:33 PM, mt wrote:
<snip>
> > Hmm I bought one of their TEC controllers years ago. I had to hack it to get a longer integration time... and then just ended up making my own. > > > The longer integration time gets to the debate of where to put the temperature sensor. Near the TEC, or near the laser diode. I opted for near the diode, and so a longer time constant. But others think otherwise, and I very well could be wrong. > > > > > > George H. > > > > > There's no reason to have just one sensor. You can wrap the actuator in > a local first-order loop with some fairly crude but fast sensor right at > the actuator, and use that as an improved actuator in an integrating > loop with a sensor where you actually want to control the temperature. > > That gives you high accuracy plus decent rejection of thermal forcing. >
OK, having your cake and eating it too. Hmm, so you roll off the fast loop output at some frequency where the slow loop takes over, (high pass filter on the fast one) and then sum them. The details of that hand-off are -interesting-. Is a single pole roll off the way to go? (Drawing some PI bode plots I seem to be confusing myself. Do you roll the slow loop with a single pole low pass too?) ^ LOG(gain) | |\ \ | \ \ | \ \ <--fast loop | \ \ | \ \ | \ \ | \<--slow | | |---------------------->LOG(freq) ^gain | |\ | \ | \ /\ | \ / \ | \ \ | \ \ | | ^-----rolled off here. | |---------------------->freq But how does one pick the frequency? George H.
> 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 net > > http://electrooptical.net
On 10/01/2013 12:37 PM, George Herold wrote:
> On Tuesday, October 1, 2013 11:19:24 AM UTC-4, Phil Hobbs wrote: >> On 10/01/2013 11:04 AM, George Herold wrote: >> >>> On Saturday, September 28, 2013 9:23:39 AM UTC-4, Glenn B wrote: >> >>>> On 28/09/2013 1:33 PM, mt wrote: > <snip> > >>> Hmm I bought one of their TEC controllers years ago. I had to hack it to get a longer integration time... and then just ended up making my own. >> >>> The longer integration time gets to the debate of where to put the temperature sensor. Near the TEC, or near the laser diode. I opted for near the diode, and so a longer time constant. But others think otherwise, and I very well could be wrong. >> >>> >> >>> George H. >> >>> >> >> There's no reason to have just one sensor. You can wrap the actuator in >> a local first-order loop with some fairly crude but fast sensor right at >> the actuator, and use that as an improved actuator in an integrating >> loop with a sensor where you actually want to control the temperature. >> >> That gives you high accuracy plus decent rejection of thermal forcing. >> > OK, having your cake and eating it too. > Hmm, so you roll off the fast loop output at some frequency where the slow loop takes over, (high pass filter on the fast one) and then sum them. > The details of that hand-off are -interesting-. > Is a single pole roll off the way to go? > (Drawing some PI bode plots I seem to be confusing myself. Do you roll the slow loop with a single pole low pass too?) > > > > ^ LOG(gain) > | > |\ \ > | \ \ > | \ \ <--fast loop > | \ \ > | \ \ > | \ \ > | \<--slow > | > | > |---------------------->LOG(freq) > > > ^gain > | > |\ > | \ > | \ /\ > | \ / \ > | \ \ > | \ \ > | > | ^-----rolled off here. > | > |---------------------->freq > > But how does one pick the frequency? >
It's usually pretty simple IME--you make the inner loop as fast as you can with decent stability, and then do the same with the inner one. Normally there's enough bandwidth difference that any small phase whoopdedoos in the closed-loop response of the inner loop don't affect the outer loop much. 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 net http://electrooptical.net
On Tue, 01 Oct 2013 07:56:45 -0700, George Herold wrote:

> On Saturday, September 28, 2013 9:20:34 AM UTC-4, Bill Sloman wrote: >> On Saturday, 28 September 2013 15:33:32 UTC+10, mt wrote: >> >> > I have a laser diode that is cooled by a fan and a heat sink. I have >> > a small TEC lying around and I would like to integrate that to the >> > laser diode head. How do I go about controlling the voltage supply to >> > maintain a stable temperature. >> >> You need to think in terms of current control rather than voltage - >> TEC's transfer watt per amp, >> >> >> >> Sadly, the watts transferred per amp varies fairly rapidly with >> temperature difference you are trying to sustain across the TEC, and a >> proper controller needs to measure the temperature on both sides of the >> junction. >> >> Sloman A.W., Buggs P., Molloy J., and Stewart D. &ldquo;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 sensor&rdquo; Measurement Science and Technology, 7 1653-64 (1996) >> >> >> >> spells it all out in fair detail, including a formula for heat transfer >> per amp, which none of the application notes seem to include. E-mail me >> - at bill.sloman@ieee.org - if you can't get hold a of a copy. > > Well as Bill says current control is a bit better. But if you are > wrapping a control loop around it (PI) then you can do it with just > voltage too. > > > The most important thing (IMHO) for a TEC is sizing the heat sink. If > it's free air cooled then you need a pretty big heat sink compared to > the size of the TEC. It's just a matter of energy conservation, all the > heat that flows through the TEC has to also leave the heatsink.
Don't you mean the heat that flows through as well as the heat produced by? I thought that TEC's generated heat on their own, which accounted both for much of the nonlinearity and for their renowned inefficiencies. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com