Linear voltage regulator as TEC driver

Thread Starter

mk795

Joined Feb 5, 2024
3
Hi all,

I currently have a project where I want to heat a EMI sensitive device (DUT) with a peltier module. I started with an Arduino, a MOSFET driver module (IRF520N), a lab power supply, a temperature sensor attached to the hot side of the peltier-element (TEC) and a Peltier module with the ratings (Imax = 1.9 A, Vmax=15.4 V). The system is PID controlled. During heating, the DUT was not probperly working anymore. I observed voltage peaks in the voltage after the MOSFET driver that are synchronized with the negative edge (switch off) of the PWM signal. Those are likely the interferences disturbing the DUT too much.
So what I require is a low ripple (unfortunatly, I am not able to specify a specific ripple value) smooth DC voltage driving the TEC. I thought about a linear voltage regulator circuit. In addition, I need to be able to adjust the voltage in a range of 0 to 15 V (at the best with the Arduino). So, I came up with the circuit attached. I plan to convert the PWM signal with a DAC to a signal adjustable from 0 to 5 V. Then I want to amplify this signal and make it the input of my voltage regulator circuit. Unfortunatly, I am not able to deliver the 15 V. I thought the buffer might help, but I would need a resistance in series with the buffer output of at least 300 Ohm (acc. to the simulation) to get a 15 V buffer output. But still, when connecting to the non-inverting input of the third op amp, it is not working.

I am (clearly) not an expert in electronics and I would be very happy about any tipps and tricks, to make my project work. Thank you!
 

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MisterBill2

Joined Jan 23, 2018
18,491
It sems that what you really require is much better electrical isolation between the device being tested and the peltier cooler/heater. THAT should provide the disruptive influence without any circuit changes.
 

Thread Starter

mk795

Joined Feb 5, 2024
3
It sems that what you really require is much better electrical isolation between the device being tested and the peltier cooler/heater. THAT should provide the disruptive influence without any circuit changes.
The DUT is a simple micro-coil being a position sensor for an electromagnetic positioning system. The coil is not electrically connected to the peltier-device. The interference happens also, if the coil is not physically touching the peltier device, but only being in close proximity to the TEC. I lowered the PWM frequency to 1 Hz (minimum freq for Arduino Uno PWM) and can see that it reduced disturbance, but it is not as I want it. The tracking system still looses the positions roughly every 1 sec for some millisecs.
 

MisterBill2

Joined Jan 23, 2018
18,491
The DUT is a simple micro-coil being a position sensor for an electromagnetic positioning system. The coil is not electrically connected to the peltier-device. The interference happens also, if the coil is not physically touching the peltier device, but only being in close proximity to the TEC. I lowered the PWM frequency to 1 Hz (minimum freq for Arduino Uno PWM) and can see that it reduced disturbance, but it is not as I want it. The tracking system still looses the positions roughly every 1 sec for some millisecs.
OK, I understand the situation. Sometimes a linear system is the only way to go. Evidently the peltier cooling scheme is not possible to isolate adequately because of the proximity to the items being tested. It may be that using a temperature control scheme that set the DUT temperature by means of a temperature controller air stream would be a better alternative. But that is before knowing the required thermal capacity, heating and cooling.
 

Casperson

Joined Aug 11, 2021
3
Unfortunatly, I am not able to deliver the 15 V. I thought the buffer might help, but I would need a resistance in series with the buffer output of at least 300 Ohm (acc. to the simulation) to get a 15 V buffer output. But still, when connecting to the non-inverting input of the third op amp, it is not working.
The buffer is not needed. Connect the collector of your voltage regulator to 15 V and not to the output of the op amp.
 

Hymie

Joined Mar 30, 2018
1,284
The output of an AD820 op-amp is limited to around 15mA (which is typical for most op-amps), so there is no chance that the op-amp(s) can deliver the required current into an 8 ohm load.
IC U4 needs to be capable of delivering the full load current to the collector of the regulator/transistor.

You need to investigate circuits where the output current from an op-amp is increased by the use of a transistor(s).
 

Thread Starter

mk795

Joined Feb 5, 2024
3
The output of an AD820 op-amp is limited to around 15mA (which is typical for most op-amps), so there is no chance that the op-amp(s) can deliver the required current into an 8 ohm load.
IC U4 needs to be capable of delivering the full load current to the collector of the regulator/transistor.

You need to investigate circuits where the output current from an op-amp is increased by the use of a transistor(s).
Thank you! You're right... I was only focusing on the voltage, but not really concerning about the current which needs to be delivered to the load. A further challenge is the resistance of the TEC is increasing with warming it up. Unfortunately, I did not find a curve for that so I took the maximum rating for my simulation (R_TEC = U_max/ I_max = 15.4 V / 1.9 A). For TECs from other manufacturers I found values betwenn 1 Ohm and 2.5 Ohm.
Well... I will continue my research for a suitable driver circuit.
 
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