TEC laser diode driver circuit

The ultra-simple laser diode and TEC driver is shown in the figure below. It uses a portable radio case to provide variable current to a low-power laser diode, and the laser tube is cooled by a TEC (Thermal Energy Converter).

The laser diode driver is a current adjustable regulator using a current limiting resistor. Additional filtering and reverse polarity protection ensure that there is no inrush current or transient when the power is turned on. The driver MOSFET is cooled by a TEC only and the operating point is set by a potentiometer. As there is only one MOSFET as an active device, precise temperature control is not possible, but it is enough to keep the diode cool. It is used to provide power for a crystal laser (Crstallaser) driving a 35mW red laser diode. LD1, TH1 and TEC1 are connected to the laser head using a 10-lead cable connector. LED2 provides a rough indication of the voltage across the TEC as current flows through it.

Note that the voltage at the TEC is the same as the laser diode voltage based on the relationship between the LD power and the desired TEC power. It is also derived from a fixed 12VDC input.

For low-power crystal lasers, the TEC is almost redundant because the maximum current of the laser diode is less than 100mA.

In fact, acceptable cooling can be achieved without using any active devices, simply by placing the laser diode in series with the TEC. Even better is the use of MOSFETs.

It is recommended to use a regulated 12VDC power supply. It would be ideal if 7812 is used to provide a 15V~20VDC power supply.

Any common type of adjustable regulator can be used. The LT1084lC is the simplest, but the LM317 is also good. As with the MOSFET, the BU271A is highly recommended.

Caution: This is a more or less constant current driver without optical feedback. Therefore, laser diodes with a narrow operating current range are not suitable for this circuit.