TDK-Lambda LC1202, Instruction Manual

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83494001 Rev H Page 18 of 27
When choosing Rs, ensure it can withstand the full output voltage across it as well as
the power dissipation caused by discharging Co (460pF) and Cc (20pF/ft) each cycle as
well as conducting the normal output current. Its power dissipation can be calculated
as,
5.3 PARALLELING UNITS
The LC1202 power supply is designed for simple parallel operation. Any model (L, S,
OEM) can be paralleled with any other model. The input power and HV output should be
connected directly together. The REMOTE connectors on the rear panel can also be
connected directly together using a "daisy chain" ribbon cable from the system control-
ler. Each of the power supplies operate at the same time with the total charge rate equal
to the sum of each.
When operating an LC1202L as a master with either one or more LC1202S's as slaves,
connect the SLAVE connector on the LC1202L to the REMOTE connector on each of
the LC1202S's. This allows control of the entire system from the LC1202L front panel
when in local mode, or the LC1202L REMOTE connector when in remote mode. The
status of each individual LC1202L and LC1202S is displayed on its front panel.
Sometimes when operating several units in parallel, the high total power generates
noise which interferes with the power supply control. This is usually due to the many in-
terconnecting control cables acting as an antenna picking up noise. The problem usually
appears as one or more of the power supplies shuts down when the output voltage in-
creases beyond a certain level. Dressing the control cables as short as possible and
close to ground or using shielded cables should help. In severe cases, it is necessary to
wrap the cables several times through large ferrite cores at the rear panel of each unit.
5.4 MEASURING HIGH VOLTAGES
A sample of the output voltage is available in the REMOTE connector. If it desired to
measure the HV output externally, care must be taken to understand the accuracy of the
measurement.
When making a DC measurement, such as when the power supply is holding voltage on
a capacitor, any HV probe and DMM combination can be used. The Fluke 80k - 40
probe with any 10MW input resistance DMM is adequate up to 40kV. Building a simple
resistor divider using appropriate HV resistors is also very straightforward. Keep in mind
that all HV resistors, including the one in the Fluke probe, exhibit a negative voltage co-
efficient, changing by up to 4% from zero to max voltage. Derating the resistors and cal-
ibrating at the operating point solves this problem.
Making a pulsed measurement with an oscilloscope requires a compensated HV probe
having a wide bandwidth. Simply connecting a DC probe, through the proper resistance,
into a scope yields a slow response adequate for only low rep rate systems. As with DC
probes, the pulsed probe resistor voltage coefficient is a problem. In addition, damage
to the resistors can occur during pulsing due to high electric field gradients. Also, stray
capacitance to nearby objects can significantly alter the pulse response. The Tektronix
P6015 is a high-performance, shielded probe and a good choice up to 40kV.
Measurements accurate to better than 0.1% can be achieved using a bias technique.
For example, if a 40V signal (40kV divided by 1000) is to be measured accurately, the
minus input of the DMM would be biased up 40V. The original signal, with respect to
ground, is fed to the plus input of the DMM. The bias can be measured accurately for
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R E P R A T E
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