TLK33 Peltier cells controller

by Andrea Cattaneo
TLK33 the Peltier cell controller

There are many ways to cool or heat surfaces, among them the use of Peltier cells, layers of different semiconductors that allow you to absorb heat on one side and release it on the other.

The fields of application are many: from storage and transport of biological samples, to cooling of optical sensors, in lasers, in small portable car refrigerators, in mini cold water dispensers, in temperature control of electrical panels and so on.

The advantages are:

  • Small footprint
  • Control through electronic and non-mechanical components (e.g. compressors) therefore no maintenance and no noise
  • Vibration resistance
  • Absence of chemical elements (e.g. gas) that make the solution non-polluting during the disposal

However, control of Peltier cells often requires complex, specially designed control circuits.

The TLK33 regulator is specifically designed to directly control Peltier cells with currents up to 7A.

The peculiarity of TLK33 is to automatically invert the current sent to the cells, exchanging, when necessary, the cold side and the hot one therefore being able to perform an accurate hot / cold control.



How Peltier cells work

By passing a direct current through the contact surface of two different conductors, it is demonstrated that on one side heat is absorbed (cold side) and on the other side heat is generated (hot side). This is called the Peltier effect.

Positive o negative Peltier coefficient

For a given material, the direction of the current defines which side will be cold and hot.

Different materials have Peltier coefficients (coefficients used for calculating the amount of heat generated / absorbed by each joint).
Interesting is the fact that some materials have positive coefficient and others negative, that is, they generate an inversion of the cold side with respect to the hot side.

The Peltier effect is more evident in semiconductors, those doped P have a positive coefficient, those doped N have a negative coefficient.

P type and N type Peltier cells

Structure of a Peltier cell

To perform heat transfer, each junction absorbs few mV but several Amperes of current.
The solution adopted in the most common applications is to connect N-type and P-type semiconductors in series, through a copper strip.

By applying positive voltage to cell N and negative voltage to cell P, the upper side cools and the lower side heats up, reversing the voltage also changes the direction of heat transfer.

A normal Peltier cell contains a few hundred junctions connected in series, in this way higher working voltages are obtained (e.g. 12, 24 V DC), maintaining the same current.

 Peltier cell structure

Typical Installation

Peltier cells are used to control the temperature in several applications, most of which are for cooling.
To subtract heat, the cold side is firmly adhered to the body to be cooled.
The heat subtracted from the cold side is then transferred to the hot side, together with the operating heat of the cell itself.
On this side, the heat must therefore be dispersed into the external environment through special heat sinks.
This solution, due to its reduced dimensions, is used where it is necessary quickly cool small material quantities.

TLK33 , the Peltier cells controller

A special PID regulator (TLK33) has been developed by Ascon Tecnologic, specifically to control Peltier cells.

This compact regulator, only 33x75 mm, is able not only to modulate but, above all, to invert the supply voltage of the Peltier cells, without the need for additional circuitry.

In this way the TLK33 allows you to control both the power and the thermal flow direction(heating or cooling) accurately keeping the right temperature at thermal condition changes.

The complete system

A complete solution includes: a sensor, a PID controller (TLK33) and a Peltier cell.
The TLK33 can be connected with the most common sensors thanks to the universal input (RTD, T / C, mA and so on) and can perform a PID control with automatic action reversal(cold <-> hot).
Its command output can directly supply a current up to 7 Ampere.
In addition, TLK33 can be supplied with two auxiliary alarm outputs and two digital inputs.

TLK33 the ideal instrument for accurate control of Peltier cells, in any sector.

For more details, visit the TLK33 dedicate page