Starter Kit Instruction Manual Description 22
Duty cycle calculation
UPI can be used to calculate the duty factor as
follows:
df =2UPI−νPlow
νPhigh−νP low
with vPlow and vPhigh as ab ove.
To get the real duty cycle, df must be corrected
as follows:
dc =fLDDdf =fLDD
2UPI −νP low
νPhigh−νP low
to compensate for systematic errors in the LDD100.
Actual value is fLDD = 1.1
4.6.4 Laser peak current
The laser peak current can be calculated by the
measurement of the current through the series re-
sistor Rs. This is provided by the values ULL and
UD, which are rectifier outputs. To correct for the
duty cycle, the rectifier values have to be taken into
account with the following formula for a correction
factor:
p= 1 + Rds
Rcdc
where Rds and Rc are resistors in the rectifier
circuit, dc is the duty cycle calculated as in the
preceding paragraph. Actual values are Rds=10kΩ
and Rc=10MΩ.
The corrected values for the peak laser cathode
and transistor drain voltage are then given as fol-
lows:
ULLpeak =pU LL +Uds
UDpeak =pU D +Uds
where Uds is the voltage drop across the recti-
fier diode, actual value Uds=0.25V.
Finally, the laser peak current is then given by:
Ipeak =ULLpeak−UDpeak
Rs
where Rs is the series resistor, actual value Rs
=0.85Ω.