5 Theory of Operation
150 Keysight 34970A/34972A Service Guide
To set a relay (close a channel) in the row column driver circuitry, the appropriate
row driver PNP transistor is turned on connecting the +5R supply to the positive
side of several relay coils and ZGND is applied to the negative side of the desired
relay coil through a column driver NPN transistor. To reset a relay, ZGND is
applied through an NPN row driver transistor and +5R through a PNP column
driver.
Tree latching relays are driven by complimentary transistor pairs that steer the
current through the relay coil.
The +5R supply is only enabled while the relay changes state. The table below
shows the times required for the relays to change state.
Switch Module Open Close
34901A 6 ms 6 ms
34902A 0.40 ms 1.25 ms
34903A 6 ms 6 ms
34904A 6 ms 6 ms
34905A/06A 10 ms 15 ms
34908A 6 ms 6 ms
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