Semiconductor and Tube Components Flashcards
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Read the first 7 Semiconductor and Tube Components flashcards as text
An SCR (Silicon Controlled Rectifier) can be triggered into conduction by:
Answer: Exceeding the forward breakover voltage or applying a positive gate current pulse while the anode is forward biased
An SCR turns on either when forward anode voltage exceeds the breakover voltage or when a gate trigger pulse is applied; once latched, the gate loses control.
Once an SCR is conducting, it can be turned OFF by:
Answer: Reducing the anode-to-cathode current below the minimum holding current level
An SCR can only be turned off by commutation — reducing anode current below the holding current, which breaks the regenerative feedback sustaining conduction.
A GTO (Gate Turn-Off Thyristor) differs from a standard SCR in that a GTO:
Answer: Can be turned OFF by applying a sufficiently large negative gate current pulse in addition to being triggered on by positive gate current
The GTO is designed with fine interdigitated gate-cathode geometry that allows a large negative gate current to extract carriers and break the latch, enabling gate-controlled turn-off unlike a standard SCR.
A TRIAC can best be described as:
Answer: Two SCRs connected in anti-parallel sharing a common gate terminal, enabling bidirectional current control
The TRIAC is functionally two SCRs in anti-parallel with one gate; it can be triggered and conduct current in both directions, making it ideal for AC power control.
The 'holding current' specification of an SCR refers to:
Answer: The minimum anode-to-cathode current necessary to keep the SCR latched in conduction after the gate signal is removed
If anode current falls below the holding current, the regenerative latch action ceases and the SCR spontaneously reverts to the blocking state.
In a vertical power MOSFET, the body diode (parasitic diode) is formed between:
Answer: The P-type body region and the N-type epitaxial drain drift region
The P-body implant and the N-epitaxial drain region form an inherent P-N junction that constitutes a diode always present in the MOSFET structure, useful for freewheeling in bridge circuits.
An IGBT (Insulated Gate Bipolar Transistor) is best described as combining:
Answer: The low on-state voltage drop of a bipolar transistor with the voltage-driven, high-impedance gate of a MOSFET
An IGBT uses a MOSFET input stage for easy gate drive with low drive power and a bipolar (P-N-P) output stage for low on-state voltage drop, combining the best of both device families.