Govt. Exams
Entrance Exams
Zener diodes operate in reverse breakdown region maintaining nearly constant voltage for voltage regulation applications.
N-channel enhancement mode MOSFETs require positive gate voltage to create inversion layer for conduction.
MOSFETs have fastest switching due to voltage-controlled operation without minority carrier storage effects.
LEDs emit light through electroluminescence when forward biased with sufficient current. The energy of emitted photons equals the bandgap energy of the semiconductor material.
In BJT, the current gain (beta or hFE) is defined as the ratio of collector current to base current: β = Ic/Ib, so Ic = Ib × β. Beta typically ranges from 50 to 500 for most transistors.
BJT operates in three distinct regions: Active region (linear amplification with both junctions forward biased), Saturation (both junctions forward biased, acts as switch ON), and Cutoff (both junctions reverse biased, acts as switch OFF).
Zener diodes have low forward resistance (like normal diodes in forward bias) but the unique property is controlled reverse breakdown at a specific voltage for regulation purposes.
Silicon PN junctions have a built-in barrier potential of approximately 0.7 V at room temperature (25°C), while germanium junctions are around 0.3 V.
A PN junction diode exhibits rectification property, allowing current to flow easily in the forward direction (low resistance) and blocking it in the reverse direction (high resistance).
