Model 2790 SourceMeter
®
Switch System User’s Manual 2-17
Cable discharge circuit (7751 and 7753)
Leakage capacitance exists between signal paths on the switching module and in the test
cables. This capacitance can be high enough to store a high voltage charge from the
V-source of the 7751/7753 module.
As shown in Figure 2-6, capacitance exists between the source terminals (C
SO
) and the
sense terminals (C
SE
). These capacitors can be charged by the V-source of the 7751/7753
module during the HIPOT test. This unwanted voltage charge could ignite the inflator if it
is connected to a bridgewire.
To prevent a high voltage charge from appearing across the inflator, a discharge circuit is
used. As shown in Figure 2-6, channel 20 is closed to provide discharge paths through
100kΩ resistors.
In general, the discharge circuit is controlled as follows:
• When the interlock opens, channel 20 closes to discharge the capacitors. Channel 20
remains closed as long as interlock remains open (see “Interlock” in Section 5 for
details).
• Opening channel 22 closes channel 20 for approximately 5msec to discharge the
capacitors. Opening channel 22 selects the I-source (V-source disconnects from
rest of module and DUT).
In general, with the test cables connected to the module and the input channels (i.e., 1 and
2) closed, the following sequence should be used to properly perform cable discharge:
1. Open channel 21 to disconnect the V-source and I-source from the input.
2. Open channel 22 to perform cable discharge.
NOTE If channel 22 is already open, performing the MULT:OPEN operation will not
close channel 20 to perform cable discharge. However, the OPEN:ALL opera-
tion will perform cable discharge.
When the OPEN:ALL operation is performed, the following sequence of actions
occur:
1) Opens channel 21 to disconnect all sources.
2) Opens channel 22.
3) Closes channel 20 for 5msec to perform cable discharge.
4) Opens all channels.
NOTE In Section 5, the test procedure for HIPOT uses the OPEN:ALL operation to
perform cable discharge (see steps 7 and 11 in Table 5-6).
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