The big TEC driver thread!

[dnar]

From what I understand the LD-Inhibit and the ilda interlock are 2 totaly different features. LD-Inhibit preventing the diode from lasing outside of a safe temp. level. Mostly implemented on boards with both LD-Driver and TEC-Controller on one board. More or less keeping the modulation input of the LD-Driver low while aktiv.
In this case I would suggest having a modulation in/out pin on the TEC-PCB which would either switch the out pin low or the in pin thru to the out pin via a relais contact thus making it suitable for any kind of LD-Driver with a modulation input.

Ok cool. For me, with P3's it makes sense to tie this in to the interlock rather than modulation. Makes wiring a lot less complex also, especially if like me you run differential modulation signals.

If your thinking of squishing an LD modulation signal, a bipolar open-collector may not be sufficient. Perhaps a MOSFET as Dave suggested, though I would be conscious of any drain-source capacitance loading.

[Solarfire]

If your thinking of squishing an LD modulation signal, a bipolar open-collector may not be sufficient. Perhaps a MOSFET as Dave suggested, though I would be conscious of any drain-source capacitance loading.

No. I'm using a relay here(Omron G5V-1 PCB signal relay), don't want to f**k with the modulation signal in any way. Plus it keeps it wide open for most typs of modulation.

[Solarfire]

Revised schematic..

[dar303]

Wow, it's great to see this much action in "my" old thread!
Are you doing a SMD version also or just god ol' through hole?

[dnar]

Revised schematic..

Looking good!

If you want to reduce part count, R16 is not necessary as the MCU outputs sink when low.

R12 appears pretty low considering the other LED's with 1k5 on 5V.

The Omron relay consumes 30mA and the relay is wired to be activated in normal use (as I would prefer). Why not change to the G1V-1 12 to lighten the regulator load? if you do this, route the GND NET at T1's emitter directly to X3-2.

Can you tweak the NTC amplifier to provide exactly 50ADC/C?

If you want another challenge, use the spare op-amp to provide a 100mV/C test output.

Looking good mate.

[Solarfire]

Are you doing a SMD version also or just god ol' through hole?

After we get the prototyp up and running and as I get time I'll probably do an SMD version also.

[dnar]

Solarfire, not wanting to throw a spanner in the works, why don't we drop the op-amp and simply use a Maxim/Dallas 1 wire temp sensor with 12 bit resolution (0.0625 deg precision)?

I have a few DS18B20 that just arrived, I'll build code for the tiny14 and see if we have enough code space if you like.

These are easier to mount than a thermistor also, having a TO-92 package with a flat edge.

[Solarfire]

Solarfire, not wanting to throw a spanner in the works, why don't we drop the op-amp and simply use a Maxim/Dallas 1 wire temp sensor with 12 bit resolution (0.0625 deg precision)?

I have a few DS18B20 that just arrived, I'll build code for the tiny14 and see if we have enough code space if you like.

These are easier to mount than a thermistor also, having a TO-92 package with a flat edge.

I just pulled the datasheet on that one and I'm always open for discussion, but did you notice the conversion time @ 12 bits of max 750ms even the 9 bits @ 93.75ms compared to an NTC is just way to slow.

[Solarfire]

General thoughts to TEC-cooling/heating of laser diodes..


When TEC cooling laser diodes a quick reacting chain of control (heat emission> sensing> counteracting) is essential for high efficiency temperature regulation. As I’ve read in most cases here on the forum people tend to place the TEC between the diode mount and the base plate. From a physics point of view, a very ineffective setup.


Bearing in mind that heat rises and cold falls: With the mentioned setup, TEC between the diode mount and the base plate, the TEC Is physically working against the laws of nature by trying to cool upward and dissipate heat downward. The Heat dissipated form the TEC into the base plate starts to rise up around the mount affecting the ambient temperature and the cooling of the mount in a negative sense. The cooling effect of the TEC has to penetrate approximately 10mm of brass (or others), against the natural direction of cold, before it ever arrives at the thermally neglected diode. The area above the diode probably never getting cool due to the rising heat dissipated from the diode into the mount. It shouldn’t be hard to see that a lot of unnecessary energy is being used here and the reaction time of heat emission> sensing> counteracting is going to be very slow no matter where you place the NTC.


I have done a lot of testing in the past 3-4 months in this area and came to the following conclusions.


1.) If going with TEC cooling, keep the thermal conductivity of the diode mount at a maximum (#1 Copper, #2 Aluminum) while keeping the mass between diode and TEC small.


2.) Maintain minimal and equal mass between NTC -> diode and NTC-> TEC (0.5-1mm).

3.) Use the natural flow of heat/cold to increase efficiency and minimize unnecessary heat dissipation. Place the TEC on top of the diode mount (cooling side down, heating side up) and use the laser case/lid as a heat sink. I’ve constructed my lasers so that the case/lid is a heat sink (doesn’t even need ventilation!).

4.) If possible turn the diode so that the die carrier is towards the top of the mount (heat dissipates away from the die instead of around it).

5.) Don’t dissipate heat or cold into optic carrying base plates.

My 2 cents worth..



Not shown: Thermal pad between TEC and heat sink. TEC attached to mount with thermal epoxy.

[mophead]

3.) Use the natural flow of heat/cold to increase efficiency and minimize unnecessary heat dissipation. Place the TEC on top of the diode mount (cooling side down, heating side up)

I'm no where remotely close to being an engineer, but that sounds completely logical to me unless there is a reason it has normally done the other way.