Electronic Fundamentals
What you must understand
Know the physics and behaviour of semiconductor devices: diodes (including Zener and light-emitting), bipolar transistors as switches and amplifiers, and field-effect transistors in principle. Understand rectification (half-wave, full-wave, bridge), smoothing and voltage regulation, and the purpose of filters. Study operational amplifiers at a functional level: inverting, non-inverting, comparator and the idea of feedback. Understand logic families and the difference between analogue and digital signals, plus the function of common sensors and transducers (thermocouples, RTDs, strain gauges, LVDTs, tachogenerators) and their signal conditioning. Recognise the role of printed circuit boards, connectors, shielding and bonding in electromagnetic compatibility.
Traps in questions
- Diode direction: conduction is anode-to-cathode when forward biased above the junction threshold (about 0.6–0.7 V for silicon).
- Zener use: operated in reverse breakdown to regulate voltage - not as a rectifier.
- Transistor terminals: base, collector, emitter for bipolar; a small base current controls a larger collector current.
- Op-amp ideal assumptions: infinite input impedance, zero output impedance, very high open-loop gain.
- Sensor output type: know which devices give a voltage, a resistance change, or a current, because that determines the conditioning circuit.
Worked example
A bridge rectifier fed with AC produces full-wave rectification; the output ripple frequency is twice the input frequency. A 400 Hz supply therefore gives 800 Hz ripple, which is easier to smooth with a smaller capacitor than a 50 Hz supply.
Rule of thumb
When a question describes a device changing resistance with temperature or strain, suspect an RTD or strain gauge and think of a bridge circuit as the readout.