06-02-2013, 03:32 PM
Introduction to Power Electronics - A Tutorial
1Introduction to Power .pdf (Size: 4.23 MB / Downloads: 94)
What is Power Electronics?
Power Electronics is used to change the characteristics
(voltage and current magnitude and/or frequency) of
electrical power to suit a particular application. It is an
interdisciplinary technology.
History of Power Devices
• Power diodes (or rectifiers)
• Bipolar transistor – 1948
– Power BJT (bipolar junction transistor) - 1960
• Thyristor or SCR (Silicon controlled rectifier) -
1957
• Power MOSFETs (Metal oxide semiconductor
field effect transistor) - 1970
– IR 400V 25A power MOSFET 1978
• IGBT (insulated gate bipolar transistor) – 1990 –
a hybrid between a MOSFET and a BJT
List of typical power devices
• Two terminal devices
• PiN diodes (for voltages >300V)
• Schottky diodes (for voltages <300V, no reverse
recovery loss)
• Three terminal devices – switches
• BJT (not used much in power converters, high
voltage blocking capability)
• MOSFET (commonly used for voltage <300V, very
fast devices)
• IGBT (for voltages >300V, a hybrid of BJTs and
MOSFETs)
• Thyristors – GTO, IGCT, ETO, MCT, etc. (high
voltage applications)
Characteristics of a Power Device
1. Block arbitrarily large forward and reverse voltages
with zero current flow when off.
2. Conduct arbitrarily large currents with zero voltage
drop when on. – no conduction losses
3. Switch from off to on or vice versa instantaneously. –
no switching losses
4. Negligible power (small voltage or current) required
to trigger switch. – for controllable switches
5. Free
Desirable Characteristics of a Power
Device
1. Small leakage current in off state.
2. Small on-state voltage drop to minimize conductive
losses.
3. Short turn-on and turn-off times (high switching
frequency).
4. Large forward and reserve voltage blocking capability
minimizes need to series several devices.
5. High on-state current rating minimizes need to
parallel devices.
Component Temperature Control
1. For high reliability, the worst-case junction temperature in
semiconductor devices is typically limited to less than 125C.
2. Some Si semiconductor devices can operate at up to 200C, but
their lifetime will be low and they likely will have poor
performance characteristics. Also, manufacturers will not
guarantee parameters above the maximum temperature of
125-150C.
3. Failure rate for semiconductor devices doubles for each 10-15C
temperature rise above 50C.