Low noise TEC driver design - adjustable linear voltage regulator

[mk795]

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!

 

[Roff]

What ripple? It is a linear x3 voltage boost amplifier with current limited only by heatsinking for servo control.
The original problem was wrong gain and insufficient current.

You may be not used to my Test Engineering background where I use a sawtooth to demonstrate a transfer function. (except I did not show the XY plot.)

Peltier module with the ratings (Imax = 1.9 A, Vmax=15.4 V). The system is PID controlled

If you check my design again it has the correct gain (for V+=15) for 0 to 5V input and easily drives 50 A with the right PNP drive and PS on a lowly LM358 which is not rail to rail out. Yet this is rail to rail out.

I figured I was misinterpreting something. I was right. I shouldn't be here during happy hour.

 

[danadak]

Post # 14 phase margin may be inadequate :

Regards, Dana.

 

[Roff]

Here is a discrete op amp that is stable. I can provide LTSpice .asc and MJ15004 spice model if anyone is interested.

 

[Roff]

Post # 14 phase margin may be inadequate :

View attachment 144531


Regards, Dana.

That circuit might be stable if you used a power PNP, which will have much higher collector-base capacitance.
I haven't tried it.

 

[danadak]

That circuit might be stable if you used a power PNP, which will have much higher collector-base capacitance.
I haven't tried it.

Thnaks, it did make all the difference :

Regards, Dana.

 

[Roff]

Thnaks, it did make all the difference :

View attachment 144558


Regards, Dana.

I don't understand. You have 24v out with 5v in, but your closed loop gain is 1.2.
Also- did you see the circuit I posted, just above my last post?

 

[Tony Stewart]

Post # 14 phase margin may be inadequate :

View attachment 144531


Regards, Dana.

with > 20V on 8 Ohms those transistors will not only fry eggs too.

Asymmetrical high current DC servo's are not easy to do and demand proper design with a half bridge with voltage controlled current sources, VCCS with both current and voltage feedback. The current feedback gives some 1st effects while current feedback of voltage control any shunt capacitance makes it unstable.

Thus the Falstad proof of concept fails to simulate reality of instability without the junction capacitance and parasitic inductance expected. Complementary emitter followers can be made to be VCCS but then a small negative supply is needed. With a project that demands up to 3A * 24V = Hot huge heatsinks rated for twice the expected losses are critical for reliability to operate at only half the maximum temp rise.

Perhaps a Crown DC200 Audio power amp is what you need ( 200W DC coupled) !!

> 50W servo designs are not easy to do! In the old days we had 750 W 1Hp linear motors control the fastest 207 14" HDD for Burroughs with expensive motors and fancy servo designs in the 70's.

Time for a Design Review on the Design Specs !!