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Chapter 5 Theory of Operation
Main Output Circuitry
4
5
Non-latching relays K1904 and K1905 switch a 100-MHz, 5
th
-order,
low-pass filter (L1907 through L1909 and C1923 through C1926) into the
signal path to reduce high-frequency distortion on continuous sine waves.
If the instrument is off, if the output has been disabled, or if the output
protection circuitry has been activated, the coils of both relays are
de-energized and the main output is disconnected from the rest of the
instrument.
There are two separate output protection circuits. U1905 and U1906
(configured as comparators) monitor U1904’s output voltage and current,
and assert OUT_FAULT* (low) if potentially harmful conditions exist.
When the output amplifier is switched out, dual comparator U1907
monitors the output voltage and asserts OUT_FAULT* if it exceeds
±3.5 V. Once OUT_FAULT* is asserted, the condition is latched in the
Main Gate Array, and relays K1904 and K1905 are de-energized.
User intervention is required to re-enable the output.
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