Bipolar transistors

What is the main use of a photocoupler, which combines an LED and a phototransistor in one package?

  1. ATo amplify current greatly
  2. BTo generate power from sunlight
  3. CTo transmit a signal while keeping the input and output electrically isolated
Show answer and explanation

Answer: C. To transmit a signal while keeping the input and output electrically isolated

In a photocoupler, the input electrical signal lights an LED, and a phototransistor receives that light to pass the signal to the output side. Because input and output are connected only by light, signals can be exchanged between circuits at different potentials while keeping them electrically isolated. It is used in power supplies and industrial equipment for noise immunity and safety.

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More Bipolar transistors questions

  1. What is the main reason for using a current-feedback bias circuit with an emitter resistor in a transistor amplifier?
  2. In an amplifier, what is the DC voltage and current state of the transistor with no input signal called?
  3. Which distortion tends to occur in a class B push-pull amplifier in which NPN and PNP transistors handle the positive and negative half-cycles?
  4. What is the role of a coupling capacitor placed between amplifier stages?
  5. How does the current gain hFE of a silicon bipolar transistor generally change as temperature rises?