Questions
8–12 questions in major PSU papers
Difficulty
Medium-Hard
Importance
Core — never skip
Overview
Analog Electronics forms the bedrock of circuit design and signal processing, heavily tested in PSU exams for its direct application in power systems and instrumentation. Mastery requires understanding non-linear device characteristics, biasing techniques, and feedback theory, which are essential for predicting circuit behavior under varying loads.
Diodes and Rectifiers
Diodes act as non-linear unidirectional switches, with Zener diodes specifically used for voltage regulation in the breakdown region. Rectifiers convert AC to DC, and performance is determined by ripple factor and rectification efficiency.
- Diode Current: I = Is * (exp(V/nVt) - 1)
- Ripple factor for Half wave: 1.21
- Ripple factor for Full wave: 0.48
- Zener Power Dissipation: P = Vz * Iz
- Peak Inverse Voltage (PIV) for Bridge Rectifier: Vm
BJT and MOSFET Amplifiers
BJTs and MOSFETs are the primary active devices used for signal amplification through proper biasing and small-signal modeling. Analyzing these requires identifying the operating region—cut-off, active, or saturation—to apply the correct gain formulas.
- BJT Gain: Av = - (Rc / re)
- MOSFET Transconductance: gm = 2 * Id / (Vgs - Vth)
- Early Effect impacts output impedance
- Condition for active region: Base-Emitter forward, Base-Collector reverse biased
- Stability factor S = (1 + Beta) / (1 - Beta * d(Ib)/d(Ic))
Op-Amp Configurations
Operational Amplifiers are building blocks for analog computation, used as inverting, non-inverting, summing, or differentiator circuits. Analyzing them assumes ideal conditions: infinite input impedance and zero output impedance.
- Non-inverting gain: Av = 1 + (Rf / R1)
- Inverting gain: Av = - (Rf / R1)
- Common Mode Rejection Ratio (CMRR): Ad / Acm
- Slew Rate = d(Vout)/dt
- Virtual ground concept at inverting terminal
Oscillators and Power Amplifiers
Oscillators generate periodic waveforms through positive feedback, while power amplifiers focus on efficiency and heat management in the final stages of a system. The Barkhausen criterion is the fundamental requirement for sustained oscillations.
- Barkhausen Criterion: |A * Beta| = 1 and Angle = 0 or 360
- RC Phase shift frequency: f = 1 / (2 * pi * RC * sqrt(6))
- Class A efficiency (theoretical max): 25% (series fed)
- Class B efficiency (theoretical max): 78.5%
- Wein Bridge frequency: f = 1 / (2 * pi * RC)
Formula Sheet
Is * (exp(V/nVt) - 1)
Vout = - (Rf/R1) * Vin
Vout = (1 + Rf/R1) * Vin
f = 1 / (2 * pi * RC * sqrt(6))
A * Beta = 1
gm = 2 * sqrt(Id * K)
Efficiency = Pac / Pdc
Exam Tip
Always verify the operating region of the transistor before applying small-signal gain formulas, as the gain expression is invalid if the device is in saturation or cut-off.
Common Mistakes
- Neglecting the Early Voltage in BJT small-signal analysis leading to incorrect output resistance calculations.
- Confusing the theoretical maximum efficiency of Class A vs Class B power amplifiers.
- Applying ideal Op-Amp formulas without checking the saturation limits of the supply voltage.
More Revision Notes
Ready to test yourself?
Play topic-wise Analog Electronics questions in Aspirant Arcade — gamified MCQ practice.
Download Free