Wavelength Electronics PLD K-CH Series, Datasheet And Operating Manual

Page: 15 / 24

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PLDXK-CH SERIES LASER DIODE DRIVER
REMOTE LIMIT STATUS LED CIRCUIT
The LD STATUS feature can be used to drive a remote
LED in your control system. The driver has a built-in 332 Ω
current limit resistor between pin J3:3 and ground. Connect
the external LED as shown in Figure 13 .
LD STATUS
+5V H1:2
H3:3
Figure 13. Remote LIM I Status LED
SET THE CURRENT LIMIT MORE ACCURATELY
The current limit circuit is designed with a small hysteresis,
which causes the limit circuit to trip at a slightly lower current
than calculated. To fine-tune the current limit, a small offset
voltage must be factored in. Use this equation to calculate
the hysteresis offset, where V
+5V
is the supply voltage:
Offset (V) = (V
+5V
– V
IMON
) / 25.9
Then add the Offset to V
LIMIT
calculated on page 13 .
CHANGE THE PHOTODIODE RANGE,
TYPE A & B LASERS
The photodiode current range and transfer function can be
adjusted by adding an external resistor. This feature is useful
when the photodiode current of your laser falls in a range
that does not allow maximum measurement sensitivity on
the PLDxK-CH driver.
Figure 14 shows the internal resistor network of the
PLDxK-CH, and the equations explain the interaction with
the external resistor. Use a ¼ W resistor for R.
H1:2
J2:1
PD Range
Switch
554 Ω
5 kΩ
PD Range = L
µ A
µ A / V
PD Range = H
2.5 V * 10
6
R || 500 Ω
Range = µ A
µ A / V
6
R || 500 Ω
10 Transfer
Function =
2.5 V * 10
6
R || 5 k Ω
Range =
6
R || 5 k Ω
10 Transfer
Function =
R || 5 k Ω
R + 5000
R * 5000
= R || 500 Ω
R + 500
R * 500
=
PD Anode
COMMON
R
Internal Electronics External Electronics
Ω Ω
Figure 14. Adjusting the PD Range,
Type A & B Lasers
CHANGE THE PHOTODIODE RANGE,
TYPE C LASERS
The photodiode range and transfer function can be adjusted
when using Type C lasers by connecting a ¼ W resistor
between the PD Cathode (pin J1:2) and PDV (pin J3:6).
The PD current range is calculated (units are amps):
Range = 2.5 V / (R || 5 kΩ)
The transfer function is calculated (units are A / V):
Transfer Function = 1 / (R || 5 kΩ)
The value of (R || 5 kΩ) is calculated as follows (units are Ω):
(R || 5 kΩ) = (R * 5000) / (R + 5000)
ADDITIONAL TECHNICAL
INFORMATION
This section includes useful technical information on these
topics:
• Remote Limit Status LED Circuit
• Set the Current Limit More Accurately
• Change the Photodiode Range, Type A & B Lasers
• Change the Photodiode Range, Type C Lasers
• Change the Analog Input Modulation Transfer
Function
• External Setpoint Circuit
• Important Information on Grounding
• Fine Tune Deep Modulation
• PLD5K-CH and PLD10K-CH Revision A
• Cable Lengths and High Current
• Add Laser Diode Protection for Long Cables
• Additional Noise Filtering
• Monitor Calibration Circuit
• Revision B Timing Characteristics
• Product Variations
• Negative Laser Power Supply Wiring
• Output On/Off and Current Limit Timing
• Parallel PLDs for Higher Current
• Power Supplies and Noise
• Safe Operating Area Calculation