Definition of a TEC Controller:
The term TEC controller is an abbreviation for "thermoelectric temperature controller", often referred to as a peltier controller. The function of a TEC controller is to provide precise, active temperature control of a thermoelectric module, also known as a peltier element. The peltier element is often referred to as a thermoelectric cooler. The primary function of the peltier cooler is to transfer heat away from a laser diode. A thermoelectric temperature controller is essentially a constant current source that operates by utilizing an electronic feedback loop which is controlled by feedback from a temperature sensor. They are usually based on an H-bridge circuit design. The H-bridge enables heating and cooling of the peltier element. Low power controllers often use a a linear power supply. High power controllers will often utilize a PWM type power supply.
Temperature Measurement Design Principle:
A TEC controller typically has a bipolar current output which is sinking and sourcing current to the peltier module. The actual temperature of the device being tested or the sample being tested is measured by a temperature sensor. The temperature sensor is often a 10 kOhm thermistor in laser applications. Other common sensors include AD590 and PT100 style integrated circuit sensors. The IC type sensors are commonly used in applications which require control of a an object temperature over a wide temperature range. The measured temperature from the sensor is compared to a pre-set temperature which has been stored in the TEC controller. An an error signal is produced which is proportional to the difference between the stored value and the measured value. The controller then produces an output current based on the error signal. This current output is connected to the peltier / thermoelectric module. This set ~ measure ~ set is a basic control loop. This is often referrred to as the auto tune loop. The complexity of the actual control loop utilized varies from a simple analog proportional loop found in most detector cooler controllers to fully digital PID (proportional-integral-differential) controllers used in precision laser diode control applications.
TEC Controller Basic Design Principles:
As discussed above, a desired set point temperature is established for the peltier controller's control loop to monitor and adjust its output (dc current) proportional to the error between the set-point and actual measured temperature. The control loop continually monitors the actual temperature and adjusts the error signal (DC current) until the set-point temperature is realized. It continues to monitor and adjust the current being sourced to the peltier element to keep the temperture within a defined range, such as +/- 1 degree Celcius. To learn more about TEC controllers, peltier coolers and temperature sensors and how they provide the three basic building blocks to control the temperature of a semiconductor laser, visit TEC Controller Basics »