Introduction

Power electronics is the branch of electronics that uses solid-state semiconductor devices to control and convert electrical power from one form to another. Ordinary electronics handles small signals that carry information; power electronics instead handles the flow of energy itself, switching hundreds of volts and tens of amperes efficiently and with almost no loss inside the device.

The whole subject rests on a single idea: if we can control how current flows through a power semiconductor device, we can control the power delivered to any system built around it. Because these devices switch cleanly between a blocking (OFF) state and a conducting (ON) state, they behave as fast, silent, wear-free electronic switches.

Four kinds of power conversion cover almost every practical need:

• AC to DC — rectifier: converts an alternating supply into direct current.
• AC to AC — voltage controller: delivers an AC output of adjustable magnitude at the same supply frequency.
• DC to DC — chopper: converts a fixed DC level into a variable DC level.
• DC to AC — inverter: produces AC of the desired voltage and frequency from a DC source.

Converters like these are everywhere in daily life — heat controls, light dimmers, motor-speed drives, battery chargers, uninterruptible power supplies (UPS) and switched-mode power supplies (SMPS).

This chapter of Karnataka 2nd PUC Electronics (subject code 40) is built in two parts. The first part studies the power semiconductor devices themselves — the power diode, the power bipolar junction transistor (BJT), the silicon controlled rectifier (SCR), the TRIAC, the power MOSFET and the insulated gate bipolar transistor (IGBT) — covering their construction, biasing and V–I characteristics. The second part, Applications of Power Electronics, shows how these devices are wired into the four converters above, along with the gate-drive, isolation and protection circuits that a II PUC board exam expects you to explain and to draw.