Peltier cooler circuit

Thread Starter

tim90

Joined Jan 15, 2016
20
Hi to everybody. I need to control a peltier cooler of 17 W and with 2A of current. My circuit is this one:5421.JPG

(The voltage regulator is not the lm1084 but the lt1084). It works, but now I would like to use a h bridge to exploit the peltier both for cooling and heating.The problem is that i wanted to use a chip and i don't want to design the h bridge from myself but i didn't find any chip able to provide a 2A. So first of all, what do you think about my circuit(basically i need to add the capacitors for the power supply)? second, can you suggest my some h bridge for my application? (this is the first time that i use a peltier cooler) thank you very much
 

Dodgydave

Joined Jun 22, 2012
9,209
Looks ok, 17.7W @6V is 2.95Amps across the 0.22r resistor, gives 0.649V from your Adc to the op amp, the 0.22r resistor needs to be 3 to 5 W rating.
 

wayneh

Joined Sep 9, 2010
16,398
Or conversely, you don't need a voltage regulator if you're controlling current with your MOSFET.

I'd add a high ohms pulldown resistor from the gate to ground to ensure against the current controlling op-amp failing "open". It's an optional safety factor but good form.
 

Thread Starter

tim90

Joined Jan 15, 2016
20
Yes, i can add the pull down resistor. About the voltage regulator, i thought to use it because with 12V and 2A my mosfet should have a resistance of 3.52 ohm ( 12V/2A=6ohm but we have 2.26 for the peltier and 0.22 for the bottom resistor) so 3.52 ohm times current square, are 14W. Instead in this case the mosfet must dissipate only 2W.I really don't know if my reasoning is right. Is it? But now i was thinking that i can use a resistor just before or after the peltier cooler to lower the voltage, for example a 3ohm resistor, so 3ohm times 2A, i will reduce the voltage of 6V. But in this case i should use a 12w resistor (or more resistors to split the power) and i will lose a lot of power. Is it right??
 

Brownout

Joined Jan 10, 2012
2,390
You shouldn't need to be concerned with current. If you provide the rated voltage to your device, it should draw whatever current it needs to operate.
 

Thread Starter

tim90

Joined Jan 15, 2016
20
Yes, but if i want to reduce its effect, to switch it off or decrease the cooling action, in this way i will be able modifying the dac output. It is a question. I am not sure. Repeat, for me it is the first time that I use a peltier.
 

Brownout

Joined Jan 10, 2012
2,390
In that case, your original idea should work, assuming you've already done the analysis of your constant current generator, taking into account the parameters of your FET and maximum power <SOA> of your voltage regulator. Alternatively, you might want to just control the voltage applied to the device, using an adjustable voltage regulator, which eliminates the need for regulating voltage and current. Lastly, you might consider using voltage regulation in conjunction with duty-cycle control, which would ease the need for high-power resistors and other components.
 

wayneh

Joined Sep 9, 2010
16,398
Using a resistor to drop voltage wastes no more and no less power than the voltage regulator. One is just smarter than the other. The voltage drop across the resistor varies with the current and this would fight against your current controller. Either would probably work.

You might consider controlling the voltage regulator with the DAC, and eliminating the MOSFET. I don't have a ready example but I bet it's been done.
 

Thread Starter

tim90

Joined Jan 15, 2016
20
Do you mean in this way?

Cattura.JPG

Because I think that in this way it is not possible because the Peltier has a maximum voltage for maximum temperatura equal to 7. So i will reduce strongly the maximum cooling capability and moreover i can not use the DAC of my freescale board because i think that it can not provide to 2A.
 

Thread Starter

tim90

Joined Jan 15, 2016
20
Thank you bertus, it is very intersting. I will read it after because i have some doubts about this kind of circuit but in any case i can not use this kind of circuit because i can not use pwm in general, because close to this peltier there are some electrode and the pwm can create noise
 

wayneh

Joined Sep 9, 2010
16,398
Right. Your regulator tries to keep its control pin at ~1.25V. It normally uses a resistive voltage divider to feedback the output voltage, and controls based on that feedback. You can intervene in that feedback loop with your DAC.
 
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