Semiconductor and Tube Components Flashcards

In a bipolar junction transistor (BJT) amplifier circuit, which operating region is characterized by the base-emitter junction being forward-biased and the base-collector junction being reverse-biased?

Answer: Active region

For a BJT to function as an amplifier, it must operate in the active region. This condition is achieved when the base-emitter junction is forward-biased, allowing current to flow into the base, and the base-collector junction is reverse-biased, allowing the collector to gather the charge carriers injected by the emitter.

What is the primary function of the control grid in a triode vacuum tube?

Answer: To regulate the flow of electrons from the cathode to the plate.

The control grid is positioned between the cathode and the plate (anode). By applying a variable voltage to the grid, the electrostatic field is altered, which in turn controls the number of electrons that can pass from the cathode to the plate. This allows the triode to amplify signals.

A technician is designing a simple voltage regulator circuit. To maintain a constant output voltage despite variations in input voltage or load current, which component should be used and how should it be connected?

Answer: A Zener diode in reverse-bias.

A Zener diode is specifically designed to operate in its reverse breakdown region, where it maintains a nearly constant voltage (the Zener voltage) across a wide range of reverse currents. When placed in reverse-bias across a load, it acts as a voltage regulator.

Which of the following describes the correct biasing for a P-N junction diode to be in a forward-biased condition, allowing significant current to flow?

Answer: The P-type material is connected to the positive terminal and the N-type material to the negative terminal of the voltage source.

To forward-bias a P-N junction diode, the positive terminal of the external voltage source must be connected to the P-type material (anode) and the negative terminal to the N-type material (cathode). This connection opposes the internal barrier potential, reduces the depletion region width, and allows majority carriers to flow across the junction.

What is a key difference between a Bipolar Junction Transistor (BJT) and a Field-Effect Transistor (FET)?

Answer: BJTs are current-controlled devices, while FETs are voltage-controlled devices.

The fundamental operational difference is that a BJT is a current-controlled device, where a small base current controls a larger collector current. In contrast, a FET is a voltage-controlled device, where the voltage applied to the gate terminal controls the current flow through the channel between the source and drain.

In a common-emitter NPN transistor circuit operating in the saturation region, what are the biasing conditions of the junctions?

Answer: Both base-emitter and base-collector junctions are forward-biased.

In the saturation region, the transistor acts like a closed switch, allowing maximum collector current to flow. This state is achieved when both the base-emitter junction and the base-collector junction are forward-biased.