Electronic Circuits and Amplifiers
This domain covers rectifier circuits, filters, small-signal and power amplifiers, and oscillators. Questions often require distinguishing RMS, peak, and DC values, or identifying the purpose of a circuit block.
Core facts
- Half-wave rectifier uses one diode; full-wave centre-tap uses two; bridge uses four. Bridge is common because it needs no centre tap.
- A capacitor-input filter charges near peak and reduces ripple; heavier load increases ripple.
- A common-emitter small-signal amplifier inverts the signal and provides voltage gain. Power amplifiers are class A, B, or AB; class AB reduces crossover distortion.
- An oscillator needs positive feedback and loop gain of 1 with 360° phase shift (Barkhausen criterion).
Worked example
A transformer secondary is 12 V RMS and feeds a bridge rectifier with silicon diodes. Peak secondary voltage is 12 × 1.414 ≈ 17.0 V. In a bridge, two diodes conduct in series, so the no-load DC output is about 17.0 − 1.4 = 15.6 V. With a large filter capacitor and light load, the output stays near this value; with a heavy load, it falls and ripple rises. A 12 V RMS transformer therefore does not give exactly 12 V DC after rectification.
Traps
- Using RMS where peak is required, or the reverse.
- Forgetting the two-diode drop in a bridge rectifier.
- Thinking a filter capacitor removes all ripple.
- Assuming an amplifier with gain will oscillate without positive feedback.