Wavelength Electronics LDTC0520, Руководство пользователя

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LDTC0520 / LDTC1020
PAGE 19
LDTC1020-00400-A Rev B
FL OPERATION, continued
6.
DISABLING THE OUTPUT CURRENT
The output current can be enabled and disabled
using the on-board toggle switch.
A remote voltage signal can be use to control the
output status of the laser driver. Connect a zero
volt signal to the “LD SHD” (pin 3 on Connector
J2) to ENABLE output current to the laser diode.
A voltage level greater than 3 V, but less than 5V,
will DISABLE output current to the laser diode.
This input was design for TTL inputs.
Both the LD SHD voltage and the on-board
toggle switch must be enabled before the LDTC
can drive current.
NOTE:
Do not insert or remove the laser diode from the
FL500 circuit with power applied to the unit.
In Constant Current Mode, the transfer function
between the total input voltage and the laser diode
current for the LDTC0520 is
I
LD
= 250 mA / V
where
I
LD
is the current through the laser diode.
The transfer function for the LDTC1020 is
I
LD
= 500 mA / V
In Constant Power Mode, the transfer function
between the input voltage and photodiode cur-
rent is
I
PD
= 1 mA / V
7. LASER DIODE SETPOINT AND
MODULATION
The laser diode set point voltage determines the
amount of current that is delivered to the laser.
In Constant Current mode the set point voltage
is directly proportional to the laser diode current.
In Constant Power mode the set point voltage
is directly proportional to the photodiode current,
allowing for control of the optical power of the light
emitted by the laser diode.
The set point voltage can be adjusted either by
using the onboard ISET trim pot, or by applying an
external set point voltage. The voltage range of
either the external set point voltage or the voltage
created with the onboard ISET trim pot can be from
zero to 2.5 volts. A dip switch set lets you choose to
use only the on-board potentiometer or the external
voltage. Figure 10 shows how to set Switch 1
position 1 to select the voltage source.
LDREF
C
C
| CP
TREF
EXT
INT
LDREF
C
C
| CP
TREF
EXT
INT
Figure 10
Source of LD set point voltage
Use Onboard
Trimpot Only
Use External
Voltage Only