FAQ


Can I use a PLCS-21 pulse generator for a driver with an analog signal input such as a LDP-VRM 01-12 CA?

The PLCS-21 is a digital pulse generator and only generates a 5 V high signal apart from its 0 V low state. Thus, it is not suitable for drivers with an analog signal input as only these two values are possible and also its precision is limited as only these two states need to be differentiated. For drivers which require an analog input signal PicoLAS offers the PLCS-40. The PLCS-40 is an arbitrary pulse generator (pulsed-AWG) with an internal memory which can store up to 32 freely programmable curve shapes with a maximum duration of 320 ns.

Why is does the current deviate from my set current after a calibration with a PLCS-21 and a compatible LDP-V driver?

The calibration process is carried out by ramping up the high voltage (HV) from the user definied minimum value to the maximum value. This is done by sending out a pulse with 50 ns pulse duration and varying the HV voltage between each pulse. At each data point the corresponding current value is measured and stored in the database.
Thus, it is very important how the rise time of the current signal is. If the rise time exceeds the pulse duration at a given current, the full current is not achieved anymore. This can lead to deviations between the set current and the real current if either the 50 ns measurement pulse or the later used pulse duration is below the rise time threshold. This usually happens if the impedance of the laser diode and its connections is too high. For more information please refer to the application notes “LD Connections” and “Impedance of Laser Diodes”.

Why does my LDP-C/CW 18/40/50-05 driver does not reach the full current of my external applied setpoint?

This driver series features a potentiometer which can be used to limit the maximum current in order to protect the laser diode. Please refer to the photo below for the position of potentiometer (red circle). The current limit can be increased by turning the potentiometer clockwise and decreased by turning it counterclockwise. Please read the manual for further details.

Another possibility is that the connection between the driver and the laser diode is not suitable. With long or to thin cables as a significant voltage loss occurs. Please keep in mind that the supply voltage should always be 1 V above the load which includes the cable connection. The supply voltage must be within the specifications of the driver and you can find further information in the manual.

My PicoLAS short pulse driver (e.g. from the LDP-V series) does not generate any output when I send a trigger signal. What should I check?

Please follow the “How get started guide” in the manual. If not stated differently, please always start with a short instead of a laser diode as load.

The trigger input requires a 5 V signal and is terminated with 50 Ohm. Depending on the trigger/function generator it may be possible that a specific setting or an adjustment of the voltage is needed to achieve the required 5 V. In some cases the trigger/function generator adds additional 50 Ohm, so that the received voltage at the driver is effectively halved and doesn’t trigger. An easy way to test if the correct voltage is applied is to connect the trigger/function generator to an oscilloscope with 50 Ohm input termination. If the signal displayed on the oscilloscope ranges from 0 to 5 V, it is correct and has the correct scaling. Please keep in mind that a signal with a 5 V range symmetrical around 0 V is not suitable.