Electronic Devices and Applications (Power, Control, Consumer Electronics)
What this domain tests
This domain applies semiconductor devices to power conversion and control: SCRs, TRIACs, DIACs, power MOSFETs, IGBTs, rectifiers, choppers, inverters, SMPS, UPS, and consumer appliance circuits. Expect device-selection and waveform-average questions.
Core concepts
- An SCR latches on when gate current is applied and anode is positive; it turns off when anode current falls below holding current. It conducts one direction only.
- A TRIAC conducts in both directions and suits AC phase control, such as lamp dimmers and fan regulators. A DIAC is a bidirectional trigger device often used with a TRIAC.
- Power MOSFETs switch fast and suit high-frequency, lower-voltage applications. IGBTs combine MOS input with bipolar output and suit higher-voltage switching.
- A freewheeling diode protects switches from inductive kickback. A chopper converts fixed DC to variable DC; an inverter converts DC to AC; a rectifier converts AC to DC.
- SMPS switches at high frequency for efficiency and small magnetics. UPS systems provide backup power; online UPS isolates the load continuously.
Worked example
A half-wave rectifier is fed from 230 V RMS, 50 Hz, with an ideal diode. Peak voltage Vm = 230 × √2 ≈ 325 V. Average DC output Vdc = Vm/π ≈ 103.5 V. The ripple frequency is 50 Hz, the same as the supply.
Traps
SCR latching is not the same as triggering: the gate loses control after latch-on. A TRIAC is not a DC switch. Do not use average and RMS values interchangeably in power calculations. Inductive loads need freewheeling paths.
Key points
- SCR: unidirectional, gate-triggered latching.
- TRIAC: bidirectional AC control.
- DIAC: bidirectional trigger.
- Chopper: DC-to-DC; inverter: DC-to-AC.
- Half-wave Vdc = Vm/π.