These instruments generate current pulses whose amplitude is largely independent of the load voltage. This makes them ideal for pulsing device whose voltage may vary with time (for instance, the voltage drop of laser diodes may vary with temperature, or explosive squibs which change impedance during ignition). This voltage independence is a trade-off with speed. If faster rise times are required, consider using pulsed voltage instruments instead.
Pulsed voltage laser diode drivers require a resistance in series with the device under test (usually a diode) in order to limit the current. The output current is then defined by an equation similar to IOUT = (VPULSER – VDIODE) / (RSERIES + RDIODE). Although this introduces a small dependence on VDIODE, much faster rise times can be achieved with this approach than with true pulsed constant current instruments.