I currently have this setup and would like to add automatic control over the PWM based on a thermistor reading. Any insights?
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2\$\begingroup\$ TECs generally don't like to be switched on and off rapidly. You don't want square waves across the TEC. You should filter them with a series inductor and capacitor to GND for each lead. And then another capacitor across the leads. This will convert the PWM to a DC bias proportional to output level. \$\endgroup\$– ACDCommented Sep 4, 2014 at 17:02
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\$\begingroup\$ See also electronics.stackexchange.com/q/28634/4512 \$\endgroup\$– Olin LathropCommented Oct 4, 2014 at 17:03
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2 Answers
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Your info is basically correct.
Unlike motor, Peltier needs no flyback diode as it does not generate harmful back EMF.
Low side switching means connection is Batt_pos, load, D of MOSFET and S of MOSFET to Batt_Neg. Send signal High to G for on. Low for off.
To build from discrete MOSFET, I do not have full circuit on hands, but, you should get tons of tutorial from web.
Full H bridge in this diagram is for hot/cold control. For hot-only, your example is fine.
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Given thermal mass of typical system, simple on/off control already give you sub-degree centigrade accuracy. Since PWM comes with no extra cost in your example heat-only setup, one try either.
At 7A, better use direct and thicker wiring for the Peltier, other than the example which use breadboard to carry bulk current.
Since the post asks for open idea, how about using H bridge for heat-cold control for even better sub-degree accuracy, either if you really need that accuracy or try it as a learning experiment.
Your device needs 7A, high current H bridge is relatively expensive while single MOSFET heat-only control is less than one US dollar.
Examples in http://www.pololu.com/category/11/brushed-dc-motor-drivers
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\$\begingroup\$ I was told to do this: Use a logic level N-channel FET like the IRLZ44 or NTE2903. Just be careful that N-channel FETs can only do low side switching. For high side switching, try the P-channel FET IRF4905 and a PN2222A to turn it on. Put a flyback diode across the FET to prevent B field collapse from spiking voltage back through the FET. With a big TEC, that might be important. What do low/high side switching mean, and how does a flyback diode work? \$\endgroup\$– M.Y.Commented Aug 5, 2014 at 15:28