Semiconductor Devices & Circuits Flashcards
7 cards from real CET practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Semiconductor Devices & Circuits flashcards as text
What does the thermal resistance θJA represent in a transistor datasheet?
Answer: Temperature rise per watt of power dissipated from junction to ambient air
θJA (junction-to-ambient thermal resistance) quantifies how many degrees Celsius the junction temperature rises for each watt of dissipated power.
In a CMOS inverter, when the input is logic HIGH, which transistor is ON?
Answer: The NMOS transistor
A HIGH input turns on the NMOS (pulling output to GND) while turning off the PMOS, producing a LOW output.
The transition frequency fT of a BJT is the frequency at which:
Answer: The current gain β drops to unity (1)
fT (unity-gain bandwidth) is the frequency at which the common-emitter current gain magnitude falls to 1, marking the device's useful amplification limit.
Which type of semiconductor device is used as the basis of a UJT (Unijunction Transistor) relaxation oscillator?
Answer: A device with one p-n junction, one emitter, and two base contacts
A UJT has a single emitter junction on an N-type silicon bar with two ohmic base contacts (B1 and B2) used to trigger oscillations.
In power electronics, a freewheeling (flyback) diode is placed across an inductive load primarily to:
Answer: Clamp and recirculate inductor current when the switch turns off
When the switch opens, the inductor's collapsing field generates a back-EMF; the freewheeling diode provides a safe current path to prevent voltage spikes from damaging the switch.
The reverse recovery time (trr) of a diode is important in which type of application?
Answer: High-frequency switching circuits
In high-frequency switching circuits, a long trr causes the diode to conduct briefly in reverse during switch transitions, wasting power and causing noise.
What is the main advantage of a MOSFET over a BJT in high-frequency switching power supply designs?
Answer: Majority-carrier operation with no minority-carrier storage delay
MOSFETs use only majority carriers, so there is no minority-carrier storage time, enabling much faster turn-off compared to BJTs.