Rev. 01/2021
14
Test Load
A common method to test the driver is to connect a regular silicon rectifier diode to the
driver output. Attention has to be paid to the junction capacitance of the diode. Only fast
recovery diodes (or similar) have as low a parasitic capacitance as laser diodes have. To
achieve reasonable test results, the parasitic elements of the test diode and the connection
must be very similar to a laser diode. Regular silicon rectifier diodes have a junction
capacitance of several microfarads and are not a suitable test load! The use of these diodes
will result in incorrect current measurement at the pulse edges!
Power Supply
To obtain a good pulsing performance with the driver, it requires an appropriate power
supply unit (PSU). The PSU has to supply not only the power that is delivered to the laser
diode but also the power to compensate for the losses in the driver itself. Please take into
account that the laser diode power varies strongly when the output current is modulated.
Although the driver is equipped with a large input capacitance of 12 mF to buffer these
power peaks, the power supply has to deliver the required power fast enough to avoid input
voltage drops. For excessive modulation of the output current, the PSU output impedance as
well as the line impedance between PSU and diode driver has to be as low as possible.
When the input voltage drops below 20.0 V the driver shuts down automatically. To remove
this condition the enable line has to be toggled (switched off and on again).
Cooling
The driver produces up to 220 W of losses. Thus, the baseplate has to be mounted on a heat
sink to ensure proper operation and prevent an overtemperature shutdown. If working with
high currents above 90 A, it is recommended to cool the power inductors as well. This can be
achieved easily by placing the diode driver with its heat sink in the air flow of a fan.
