ADN8834 simulation in action with TEC and thermistor

LTspice simulation of Laser module cooling Peltier element with the help of the Analog Devices ADN8834 controller and with input given by Vishay Thermistor NTCLE203 /NTCLE213 10 Kohms

The total application simulation circuit is reprinted on figure 1

We are going to detail the different models of these circuit constituents.

1) internal structure of PELTIER

The model of this project is copied from the following reference

SPICE model of thermoelectric elements including thermal effects

February 2000Conference Record - IEEE Instrumentation and Measurement Technology Conference 2:1019 - 1023 vol.2

DOI: 10.1109/IMTC.2000.848895 SourceIEEE Xplore

Conference: Instrumentation and Measurement Technology Conference, 2000. IMTC 2000. Proceedings of the 17th IEEEVolume: 2

The supplied netlist for the Peltier has been recreated in LTspice and can be seen on figure 2. You will find in this simulation (present in the archive to download with this project) all the parameters that influence the thermal behavior of the TE element. This will allow the user to calibrate the Peltier parameters (thermal mass, heat sink capacity) by comparison with cold and hot temperature measurements.

2) The thermistor NTCLE213/203

The thermistor precise characteristics are defined in the file.

vishay_pspice_models_voltage_driven.lib

The parameter which is application dependent is the response time which is depending upon the used medium (air), and of the fact that this air is stirred or not (NTCL213 : 5 s in stirred air / 9 s in still air for example)

3) the laser source:

This is in fact a heat source directly communicated to the thermal mass of the Peltier. You will need to evaluate how many Watts are produced and adjust the current in the source V5 to be equal to this power ( equivalence W and I)

4) the total simulation with the ADN8834

Fortunately a spice model is available directly from ADI LTspice XVII and the application circuit is reprinted from the datasheet . The advantage is that we are going to be able to test the influence of any parameter of any element, all this in order to develop the intuition of the application.

In figure 4, we perform a simulation where the initial temperature is either lower or higher than the set temperature. We see that in any case, the reached temperature converge always toward the set temperature.

In figures 5/6, we sweep the feedback resistor value (Rfeedback) in order to visualize the influence on the thermal stability. The higher the value of this resistor, the lower the temperature swing is.

On figure 7 and 8, we visualize the influence of set temperature value Tset (25°C or 27°C).

You can fix this value by mean of a virtual voltage fed to the reference thermistor: the ADN8834 will maintain flawlessly the thermal mass at the targeted Tset

On figure 9, the influence of ambient temperature changing per dwells: we see that the switching frequency is inversely proportional to the ambient temperature.

On figure 10, we see what happens to the thermal loop when the thermistor response time decreases to very low values (temperature swing decreases slightly)

In figures 11/12 :the influence the heat power of the laser on the circuit behavior, together with preceding ambient temperature changes.

with power laser:above 1000s, when the heat of the laser is on, and that the ambient is too high, the Peltier is always on but cannot cool down the thermal mass to the target.

without laser power

CONCLUSION OF THIS PROJECT: such simulation is the ideal (and inexpensive) way to prepare experiments and will give numerous results to be compared later with practical results.