1. Introduction
Dr. Kakade K.P

2. CH.1 Introduction 1-1 Introduction
˙Power electronic circuits convert electric power from one form to
another using electronic device (switch).
˙Relatively small power loss in the device.
˙Real devices absorb some power when in the on state and when
transitions between on and off, but circuit efficiencies can still
be quite high.

3. 1-2 Converter classification
˙AC-DC converter Rectifier
˙DC-AC converter Inverter
˙DC-DC converter Chopper
˙AC-AC converter (AC Voltage Controller)

4. 1-3 Electronic switches
Diode :
Fig.1-1

5. reverse recovery time trr ＜ 1μs become important in
Rectifier Diode :
reverse recovery time trr ＜ 1μs become important in
high-frequency applications.
Scottky diodes :
metal-to-silicon barrier rather than a p-n junction. forward voltage drop ≒0.3V.; turn on and off faster than p-n junction diodes.
Thyristors:
Fig.1-2
→Three-terminal devices；switching fre. =10~20kHz；in high- power applications.

7. Transistors : Fig.1-3~1-5
are operated as switches ( in the fully on or fully off state )in power electronics circuits, not operated as an amplifier circuit. ( in the active or linear region ).
include bipolar junction transistors (BJTs), MOSFET, insulated-gate bipolar junction transistors.(IGBTs).

8. BJTs : Rating up to 1200V, 400A; operating up to approximately 10kHz.
Power BJTs generally are available in higher voltage and current rating than MOSFETs. A current-controlled device.

9. MOSFET : A voltage-controlled device; are of the enhancement type
rather than the depletion type. Drive circuit to turn a MOSFET on and off is usually simpler than that for a BJT. Rating are up to 1000Vand 50A. Switching speeds are faster than BJT and up to/beyond the 100kHz range.

10. IGBT : is an integrated connection of a MOSFET and a BJT
IGBT : is an integrated connection of a MOSFET and a BJT. The drive circuit is like that of the MOSFET, while the on-state
characteristics are like that of the BJT. Switching speeds up to
about 20kHz and have replaced BJT in many applications.

11. 1-4 Switch selection
depends not only on the required voltage and current levels but also on its switching characteristics.
GTOs provide the control of both turn-on and turn-off, SCRs of turn-on but not turn-off, and diodes of neither.
The BJT is a minority-carrier device, whereas the MOSFET is a majority-carrier device which does not have minority-carrier storage delays, giving the MOSFET an advantage in switching speeds.
BJT switching times may be a magnitude longer than for the MOSFET. Therefore the MOSFET generally has lower switching losses.

12. GTO : Can be turned off with a negative gate current，but its magnitude must be very large compared to the turn-on current.
Triac : is capable of conducting current in either direction; is equivalent to two antiparallel SCRS.
MCT: is equivalent to the GTO but without the high turn-off gate current requirement；has an SCR and two MOSETs. One MOSFET turns the SCR on，and one MOSFET turn the SCR off.