Digital Current/Voltage Control

Hi Kas, I just took a Peltier and slowly increased the voltage across the junction. As I raised the voltage the current followed in a fairly linear fashion. Of course as the voltage and current got higher the temperature gradient from one side to the other increased. The answer to your first question is that the voltage will dictate the current. Depending on the precision that you need you can choose the appropriate temp sensors and link them to the microcontroller and then use the PWM output of the microcontroller to drive a FET or similar device that in turn supplies power to the TEC. My Peltier which is only about 2 square inches takes 2 amps at 6 volts so you will want to size and heat sink the driver FET to handle the amount of power you will be switching. You will also have to heat sink the backside of the Peltier if you want to make the most efficient use of it.

John

Hello John,

If I may ask why do you suggest using a PWM to drive the FET and inturn the TEC as opposed to using some form of regulating transistor that you could increase the gate voltage to increase the power to the TEC, I'm guessing that would be current control which is not what you really want ? Asking more to learn and better understand your thinking here.

Thanks

Kas

Hi Kas, Shabaz has done a good job of covering the bases. Also PWM is built into the Arduino and I suspect the other boards as well so it is an easy choice. Using it to control your FET will put the power accross the peltier and minimize the power loss accross the FET. The PWM makes the FET act like a switch that is being turned on and off to provide an average amount of power to the load. You vary the power by leaving the switch on for longer or shorter periods of time. The other option is as you mentioned to use the FET or Transistor as a variable resistor. The problem with this is you will then have a much greater IR drop accross the FET which will produce heat the will have to be sunk and disposed of. If you use a logic level FET you could drive it directly off the Microcontroller which would also simplify the circuitry. There will be several variables in how you approach the design depending on how closely you want to regulate the temperature of the metal. Sounds like a fun project.

John

I want to learn about all the 3 possible types of switching. Is there any tutorial or any notes to understand the 3 different types (pwm, variable resistor,logic level) and compare them.

Hi Srinnivasan,

Your question takes us to the foundations of electronics. Switching is basically just turning electricity on and off. This is used of course in logic as the "on" state is usually interpreted as a ONE or logic "True" and the off state is interpreted as a ZERO or a logic "False". For Pulse Width Modulation we are delivering power to a load by turning the power on and off. If the power is turned on half the time and off half the time we effectively are delivering only 1/2 of the total power to the load. The linear method of controlling power to a load does not involve switching but rather using resistance to steal some of the potential power from the load. This stolen power, in the form of heat, however has to be removed and dissipated. If you are interested in learning more and doing some research on these and other electronic subjects here is a blog that I wrote a while back and several others from the forum have contributed to that gives some suggestions on where to start.

https://www.element14.com/community/people/jw0752/blog/2015/11/04/i-want-to-do-electronics-where-do-i-start

Of course you can always Google the specific subjects and explore what pops up. If you have some specific questions you have the discussion/ question posting on the e14 forum where someone usually will answer you if they understand your question. It is best to always take the time to do a good job framing your question and providing adequate background information.

John

Hi Srinnivasan,

Your question takes us to the foundations of electronics. Switching is basically just turning electricity on and off. This is used of course in logic as the "on" state is usually interpreted as a ONE or logic "True" and the off state is interpreted as a ZERO or a logic "False". For Pulse Width Modulation we are delivering power to a load by turning the power on and off. If the power is turned on half the time and off half the time we effectively are delivering only 1/2 of the total power to the load. The linear method of controlling power to a load does not involve switching but rather using resistance to steal some of the potential power from the load. This stolen power, in the form of heat, however has to be removed and dissipated. If you are interested in learning more and doing some research on these and other electronic subjects here is a blog that I wrote a while back and several others from the forum have contributed to that gives some suggestions on where to start.

https://www.element14.com/community/people/jw0752/blog/2015/11/04/i-want-to-do-electronics-where-do-i-start

Of course you can always Google the specific subjects and explore what pops up. If you have some specific questions you have the discussion/ question posting on the e14 forum where someone usually will answer you if they understand your question. It is best to always take the time to do a good job framing your question and providing adequate background information.

John