1 – 6
Overview
by resistors R269 and R255) will still allow correct modulation con-
trol with an earth-referenced modulation signal, but it now becomes
more important that the modulation source has a balanced output
impedance. If the modulation source has a 50
Ω
output impedance
(on the center conductor of the BNC), with the outer shield at earth
(low impedance), then a “common-mode” DC error, of the order of
up to 1 mA, may be induced. The user has 4 strategies to avoid this
e
ff
ect:
1. Keep the laser diode fully floating,
2. Use a floating source for the modulation input,
3. Ensure the modulation source has a low output impedance, or
4. Balance the modulation source impedance.
1.3
Features and controls
The remaining sections in this chapter explains each part of the front
and rear panel of the LDC500. Circled numbers in the left margin
refer to Figure 1.4.
1.4
Power
1.4.1
Power entry module
A rear-panel power entry module contains a standard IEC-C13 power
connector.The power cord shipped with your LDC500 mates with the
14
power entry module, and should match the standard wall sockets for
your locale. The fuse and voltage selector is also in the power entry
block, and must show the correct voltage setting for your location.
See page v for details on fuse and voltage selection.
1.4.2
Grounding terminal
A dedicated chassis ground terminal is adjacent to the power entry
module.
13
1.4.3
Turning on power
Power to the LDC500 is controlled by the front-panel keyswitch. In
order to turn on the instrument,the key must be inserted and rotated
1
clockwise to the “1” position. The key cannot be removed when in
this position.
LDC500 Series Laser Diode Controllers
