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A stage's collector sits a few tenths of a volt above its emitter. What has happened?

  • A.The collector load resistor has gone open circuit in the stage
  • B.The emitter bypass capacitor has failed short circuit to ground
  • C.The device is saturated
  • D.The device has been driven into cut-off by loss of bias

Answer: C

The device is saturated: too much base current for the load to support, typically from a divider resistor that has changed value or a leaky coupling capacitor injecting bias. Cut-off would show the collector at the supply. An open load resistor would also read low but with no current, which a measurement across the resistor settles. Two readings rather than one distinguish every case here.

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