Download Manual LED Pulser Driver

Photo Diode Constant Current Pulse Driver
Front Panel
2VIN BNC
2V amplitude input pulse from external source typically NI BNC 2110.
Input impedance 10Kohm. If a pulse amplitude in excess of 2V amplitude
is applied the diodes Q1 & Q2 will limit the programming voltage to a
maximum of approx 1.2V this will equate to 1.2A diode current which may
damage the diode so care should taken to limit the input to 2V exactly.
OUT BNC
Output to photo diode. NB screen connection of this BNC is 1 ohm above
the common (ground) of the other BNCs. This 1ohm is the current sense
resistor. DO NOT CONNECT THE OUTER CONNECTION OF THIS BNC TO
GROUND/COMMON OF THE OTHER BNCs AS EXCESSIVE CURRENTS WILL
CAUSE DAMAGE TO THE PHOTO DIODE. Please refer to circuit diagram.
MON BNC
Enables monitoring of the current through the photo diode i.e. the voltage
drop across the current sense resistor. Typically connected to an
oscilloscope.
mA x 10
Digital potentiometer used to set the photo diode current i.e. a setting of
10 equals 100mA, 01 equals 10mA etc.
As will be seen from the sample ‘scope traces the rise and fall time of the units is approx
180nS and some over shoot is present prior to the output pulse settling the overshoot is
dependent on the type of diode used and on the current through the diode. The MON
output should be used to observe the output pulse and the ‘scope end of the lead from
the MON output should be terminated in 50ohms for optimum results especially when
monitoring sub 10uS pulses. The overshoot can be reduced but the rise time will
increase as a result please see me if you wish to discuss this option.