Dc-Dc converter 0.8v->12 volt

[schrodingerscat]

Im hoping to string together a self powered fan for a processor (just an project, not very practical, i know). I am hoping to do this by placing a TEG module between the heatsink and processor. Unfortunately, under tests, this doesnt generate much more than 0.8 volts or so.


So, im hoping to make a dc step-up circuit. Does anybody know of a circuit that will work at such a low voltage?

Thanks!

 

[John Sorensen]

0.8 volts

At how many mA? You don't just need voltage, you need power. I doubt you'll find a switcher that operates that low anyway, but you can check Linear Technologies and Analog Devices sites.

j.

 

[Nigel Goodwin]

This is yet another variation on the perpetual motion theme :lol:

 

[Monkeyman87]

Not neccesarily. I'm not sure what a TEG module is but if one of the peltier effect sandwich thingies were sandwiched between the processor(very hot) and the fan(cool) It would produce power. Actually an interesting idea since it would be self adjusting. If the processor were cold then the fan would not work (no temp difference) but if the processor were hot there would be a high temp difference and the peltier effect thing would start producing the power to drive the fan. Sorry this is sort of topic since he asked about the step up circuit :lol:

 

[John Sorensen]

It would be perpetual motion if the fan was being used to heat the processor, but as it is the processor is making waste heat from a separate source.

I know that LT or AD make single cell step ups, but whether they work down to 0.8V... I dunno. Plus, how much power can a peltier put out? Me thinks not enough to power a fan.

j.

 

[Optikon]

It would be perpetual motion if the fan was being used to heat the processor, but as it is the processor is making waste heat from a separate source.

I know that LT or AD make single cell step ups, but whether they work down to 0.8V... I dunno. Plus, how much power can a peltier put out? Me thinks not enough to power a fan.

j.

I agree, the author needs to make sure enough power is available to run the fan of his choice. Also assume whatever converter you use to get there is somewhere in the neighborhood of 70-90% efficient. Switcher of course. I have already done a 1V boost converter (85% eff.) So, 0.8V isnt that much of a stretch. Dunno bout the lin tech, ADI guys.. But I recall some controllers down to 1V input.. anyhow, it can be done provided you can get enough power out of peltier device.

 

[Monkeyman87]

I've seen fans for personal cooling that used a peltier to provide power from an alcohol lamp. If your running a Pentium 4 you have plenty of heat and therefore plenty of power to run a small fan I think peltier devices are somewhat efficient.

 

[Oznog]

There are 3 problems:
1. A Peltier does not generate much current.
2. No logic of any kind works from 0.8V. It will have to be stepped up to even power the power converter itself. As such, there is a bootstrapping problem. In theory, you might use a battery backup to create 3V or whatever the power converter needs to start.
3. The Peltier generates power based on temp differential. This is contrary to the needs of the processor, which requires a low temp differential. I.E. the Peltier will generate x mW when the heatsink is at 120F and the processor is at 200F, it acts as a restriction to the heat flow. The processor is much better off being hooked straight to the heatsink, then it'd be at 120F.

 

[schrodingerscat]

Cheers for the replies!
Sorry for the lack of details, but the TEG can generate 0.21 watt at a load of 100ohms and a temp difference of 27 degrees C. (57 hot side, 30 cold side).
Ye are right, unfortunately this wasn’t as much power as I was expecting. But its just an idea im trying to play around with. Its not ment to be perpetual motion theme (??), im just hoping to convert any waste heat into usable, albeit small, power. I have heard since that Thermoelectrics are only a few % efficient in generation mode.
As monkeyman said, I was hoping it would be self controlled.

Cheers for the post oznog, it was very helpful. I was thinking that since it’s a semiconductor device, the thermal conductivity of it would be good enough not to cause too much of a temperature difference, but a high enough voltage to be usable. As far as I can tell, the current output is proportional to heat flux through the device, so hopefully power output should be high-ish even if the voltage is low.

Does anybody know if the load is high on the TEG that the heat flux through the TEG will be reduced? And optikon, how did you build your 1v boost circuit?

 

[Optikon]

Cheers for the replies!
Sorry for the lack of details, but the TEG can generate 0.21 watt at a load of 100ohms and a temp difference of 27 degrees C. (57 hot side, 30 cold side).
Ye are right, unfortunately this wasn’t as much power as I was expecting. But its just an idea im trying to play around with. Its not ment to be perpetual motion theme (??), im just hoping to convert any waste heat into usable, albeit small, power. I have heard since that Thermoelectrics are only a few % efficient in generation mode.
As monkeyman said, I was hoping it would be self controlled.

Cheers for the post oznog, it was very helpful. I was thinking that since it’s a semiconductor device, the thermal conductivity of it would be good enough not to cause too much of a temperature difference, but a high enough voltage to be usable. As far as I can tell, the current output is proportional to heat flux through the device, so hopefully power output should be high-ish even if the voltage is low.

Does anybody know if the load is high on the TEG that the heat flux through the TEG will be reduced? And optikon, how did you build your 1v boost circuit?

Switched capacitor multiplier on front end to take the small volts and get it up to a level so that I could use a more standard boost converter topology. Design was around 1 Watt capable which, I think is in your ballpark here.

 

[justDIY]

Texas Inst has a boost converter that provides 3.3 to 5v from as little as 0.9v ... TPS61020 i believe.

https://focus.ti.com/docs/prod/folders/print/tps61020.html