Agilent Technologies 6621A, Service Manual

Page: 27 / 156

The fixed overvoltage sensing circuit will activate when it
senses a voltage that is approximately 120% of the
maximum rated output voltage for the associated output. If
the output voltage exceeds this threshold, the OV GATE
signal is generated via diode CR358 and fires the SCR. Note
that the fixed overvoltage sensing circuit will also activate
the OV DRIVE signal via diode CR359 (REMOTE OV TRIP).
The OV DRIVE signal then transmits the overvoltage
condition to the ± OV terminals via diode CR356, and
transformer T301 as previously described.
Remote Overvoltage Trip - Any output's OV can be triggered
from its ± OV terminals by connection to a remote device
(see Operating Manual) or another output's ± OV terminals.
By connecting the OV terminals of up to 8 outputs together,
an overvoltage shut down on any of the outputs will also
trigger the OV and shutdown the remaining outputs.
As shown in Figure 2-9, the trip signal enters at the ± OV
terminals and is coupled through pulse transformer T301,
diode CR360, and the overvoltage detector circuit to
generate OV GATE through CR357 and shut down the
supply.
2-17