Semiconductor Devices

Power diodes, Bipolar junction transistor, Field Effect transistor, MOSFET, IGBT, SCR.
SCR-VI characteristics.
Introduction to Power Converters: Diode rectifier, controlled rectifier, Inverter, DC to DC converters.

Power Electronics is related to both Power and Electronics engineering.
Power engineering focuses on efficient electrical energy generation, transmission, and utilization.
Electronics engineering focuses on distortion-less data transmission at low power levels.

Power Electronics applies electronic principles at the power level.
Uses semiconductor power switches like thyristors and MOSFETs.
Efficient, withstand high voltage and current with fewer losses.
Used for switching, inverters/converters, and power amplifiers.
Commonly made of silicon (Si), with silicon carbide (SiC) and gallium nitride (GaN) also used.

Power diodes.
BJT (Bipolar Junction Transistor).
MOSFET (Metal Oxide Semiconductor Field Effect Transistor).
IGBT (Insulated Gate Bipolar Transistor).
SCR (Silicon Controlled Rectifier).
BJTs, MOSFETs, and IGBTs are controllable switches, turned on/off by control signals.

Consist of a PN junction.
Conduct when forward biased.
Allow current in one direction (anode to cathode), acting as an electrical valve.

Made of silicon p-n junction with anode and cathode terminals.
Forward biased when the anode is positive relative to the cathode.
Conduct fully when diode voltage exceeds the cut-in voltage (0.7V for Si).
Reverse biased when the cathode is positive relative to the anode.
Small leakage current flows when reverse biased.
Leakage current increases with reverse voltage until breakdown voltage is reached.

Three-terminal semiconductor device with two p-n junctions.
Used as amplifiers or current-controlled devices in electronic circuits.
Electrons and holes act as charge carriers.
Terminals: base, emitter, and collector.
Less current flows between base and emitter; larger current between collector and emitter.
Types: NPN and PNP.
Operating Regions:
- Active: operates as an amplifier.
- Saturation: fully on, acts as a switch with collector current equal to saturation current.
- Cut-off: fully off, collector current is zero.
Applications: Amplifiers and switches in devices like mobile phones and TVs.

Applying voltage to the gate creates an electric field and a depletion region in the channel.
The depletion region reduces free charge carriers, reducing channel conductivity.
In n-type FET, negative gate voltage reduces electron flow.
In p-type FET, positive gate voltage reduces hole flow.
Varying gate voltage modulates current flow.

Electric charge flows through a semiconducting channel between source and drain.
High input impedance at low frequencies.
MOSFET is the most widely used type.

Designed for high power levels.
Voltage-controlled.
Acts as electrical switches and amplifiers, controlling current flow based on gate voltage.
Types:
- Depletion Mode: Requires Gate-Source voltage (VGS) to switch "OFF" (normally closed).
- Enhancement Mode: Requires Gate-Source voltage (VGS) to switch "ON" (normally open).
Four terminals: source (S), gate (G), drain (D), and body (B) (often body is connected to the source).
The width of a channel along which charge carriers flow (electrons or holes).

Drain and source are heavily doped N+ regions, substrate is p-type.
Current flows due to negatively charged electrons (n-channel MOSFET).
Gate electrode is insulated from the semiconductor by a silicon dioxide layer.
The input resistance of the MOSFET is extremely high way up in the Mega-ohms $( M\Omega )$
Charge carriers enter at the source and exit via the drain.

Switching and amplification in electronic circuits.
Fast switching and amplification of small signals.
Power regulation in DC motors.
Chopper circuits (high switching speed).
Microcontrollers and microprocessors (high efficiency and low power consumption).
SMPS (Switch Mode Power Supply).
H bridge circuit, buck converters and boost converters.

Full Form: BJT (Bipolar Junction Transistor), MOSFET (Metal Oxide Semiconductor Field Effect Transistor).
Definition: BJT is a three-terminal device for switching and amplification; MOSFET is a four-terminal device for switching.
Types: BJT (NPN and PNP), MOSFET (P/N-channel enhancement/depletion).
Terminals: BJT (emitter, base, collector), MOSFET (source, drain, gate, body).
Charge Carriers: BJT (electrons and holes), MOSFET (electrons or holes).
Polarity: BJT (bipolar), MOSFET (unipolar).
Controlling Quantity: BJT (current-controlled), MOSFET (voltage-controlled).
Input Impedance: BJT (low), MOSFET (high).
Temperature Coefficient: BJT (negative), MOSFET (positive).
Switching Frequency: BJT (low), MOSFET (high).
Power Consumption: BJT (more), MOSFET (less).
Losses: BJT (high switching losses, lower conduction losses), MOSFET (lower switching losses, high on-resistance and conduction losses).
Applications: BJT (low current applications, amplifiers, oscillators), MOSFET (high power applications, power supplies).

Combines MOSFET and BJT characteristics for high current and low saturation voltage.
Integrates an isolated gate using a FET for control input.
Three terminals: Emitter, Gate, Collector.
"Insulated Gate" (MOSFET input) has very high input impedance.
"Bipolar" (BJT output) has bipolar nature with current flow due to both types of charge carriers.
Consists of four alternating layers (P-N-P-N) controlled by a metal-oxide semiconductor (MOS) gate.
Allows handling of large currents and voltages using small voltage signals.
It is a voltage-controlled device.

Made of four semiconductor layers forming a PNPN structure.
Collector (C) electrode attached to P layer.
P+ substrate used with an N- layer on top forming PN junction J1.
Two P regions fabricated on top of N- layer forming PN junction J2.
N+ regions diffused over the P region.
Emitter and gate are metal electrodes; the gate is insulated using silicon dioxide.
Base P+ layer injects holes into the N- layer (injector layer).
The N- layer is the drift region, thickness proportional to voltage blocking capacity.
The P layer above is the body of IGBT.
The N- layer has a path for current flow between emitter and collector via a channel created by the voltage at the gate electrode.

Power electronics applications: inverters, converters, and power supplies.
Switching power supplies in high power applications, variable frequency drives (VFD), electric cars, trains.
Motor drive systems, uninterruptible power supplies, induction cookers.
Inverters in home appliances (air conditioners and refrigerators), industrial motors, and automotive main motor controllers.