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Starter Kit Instruction Manual Description 22
Duty cycle calculation
UPI can be used to calculate the duty factor as
follows:
df =
2UPI−ν
Plow
ν
Phigh
−ν
Plow
with v
Plow
and v
Phigh
as above.
To get the real duty cycle, df must be corrected
as follows:
dc = f
LDD
df = f
LDD
2UPI−ν
Plow
ν
Phigh
−ν
Plow
to compensate for systematic errors in the LDD100.
Actual value is f
LDD
= 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 corre c t 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 paragr aph. Actual values are Rds=10 kΩ
and Rc=10MΩ.
The corrected values fo r the peak laser cathode
and transistor drain voltage are then given as fol-
lows:
ULL
peak
= pULL + Uds
UD
peak
= pUD + 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:
I
peak
=
ULL
peak
−UD
peak
Rs
where Rs is the series resistor , actual value Rs
=0.85Ω.