Frosty_47

Hello every one!

I am trying to limit the current down to anywhere between 2.5A-3A. Basically, I like to limit the current to my Pettier Cooler that I like to use to chill my over clocked CPU. I don't want to use a resistor because that would be to inefficient and a lot of heat would be generated. I would like to use LM350 regulator to limit the current. I found this in the datasheet...



Will that work for LM350 as well ? If it works, than the 0.4Ohm resistor should only dissipate around 3.6 Watts + 3.75 Watt regulator dissipation. So the total heat dissipation should be around 7.35 Watts than ?. If my calculations are accurate than this is much better than using a resistor to limit the current. Or is it ?

Thanks,


Andrew Frost

kchriste

You would waste exactly the same amount of heat. The only advantage of using a constant current source is that the current will stay steady if the input voltage varies.
If you wish to be efficient, you must use a current mode switching regulator.

__________________
--- The days of the digital watch are numbered. ---

Frosty_47

The peltier I have is 150W so at 12V input it will consume 12.5Amps. In order to limit the current to 3 Amps with a resistor, I would have to use a 3 Ohm resistor. That means the resistor would have to dissipate 9 Watts. I do want a constant current source though. I do no like to go with switching due to noise issues and inexperience. I don't like to go with a single resistor either. So will this circuit limit the current to 3A?



Thanks!

Frosty_47

On the other thought, Switching regulator will definitely be of much higher efficiency but, I never dealt with switching before so it might be little bit scary for me. Although I must admit, that if I never start, than I will never get any experience with switching regs. If I were to implement switching regulator instead, will it cause any problems with my PSU due to noise? Will I have to add noise filters?

Thank you!

Hardwire

Do you mean "Peltier"? A thermoelectric module?

Frosty_47

Yes I meant "Peltier" thermoelectric cooling pad... I apologies for my miss typing...

Frosty_47

Can someone please make a recomendation for a particular switching current regulator that I can use to limit the current to 3 A...

Thank you !

Hardwire

Is it rated for 12V? I mean, is it 150W at 12V or is it always 150W no matter what the voltage range? Probably not, but I'm not too familiar with the details of these modules. Are you having trouble because you are cooling the processor down TOO much and getting condensation or something? Is that why you want to limit the current and not cool as much?

Off the top of my head, I can't think of any better/simpler way than just using the resistor. 9W isn't too bad. Just get a 3 25W power resistor and don't worry about wasting the current. Try to mount the resistor on metal so it sinks some heat. 9W might get a little hot.

How about buying a less powerful Peltier module that will do what you want with 12V?

Hero999

This circuit will do what you want.

Origional PDF

__________________
What's so bad about Microsoft?

Get Opera it's simply a superb browser.

Frosty_47

Thank you for your suggestions!

I don't understand one part of the circuit that Hero999 provided. Where am I going to get +15V for pin 8 and -15V for pin 4 of the TL082?
Oh, and in order to limit the current to 3A, all I will have to do is change the value of R6? But to what value? Please explain.

Thank you very much!

Hero999

It doesn't need to be +15V and -15V, it could be +12V and -12V which is supplied by a typical computer power supply.

__________________
What's so bad about Microsoft?

Get Opera it's simply a superb browser.

Frosty_47

The -12V on my PSU is limitted to 0.5A, will that be sufficient ? Oh, and what value should R6 be in order to limit the current to 3A ?

Thank you Hero999!

Hero999

Off course the -12V 0.5A supply will be fine. All the current comes from the +12V rail, the -12V is only used by the op-amp which doesn't take much.

The article I posted shows you how to calculate the resistor values.

__________________
What's so bad about Microsoft?

Get Opera it's simply a superb browser.

things

peltiers aren't very efficient, so running them at under the power they require will be very unneficient. please also remember, peltiers don't generate cold, they only move heat to the other side, so basically the lower the power you give them, the lower the heat moving capacity is.

__________________
The 3 laws of science....
1. If it smells bad, It's chemistry.
2. If it's mushy, It's biology.
3. If it doesn't work, It's physics.
www.laserpointerforums.com A forum for disscusion of lasers and laser shows!
www.laserchat.org IRC chat for laser and electronic related stuff.

Frosty_47

I read the article over and over and can't seem to find (or perhaps understand) how to calculate the value of R6. Please help me out. I would greatly appreciate it.

Thanks!