• Some Basic concepts:

• Unilateral and bi lateral components.

• Linear and non linear components.

• Passive and Active components.

Introduction To Power Electronics

How We Can Define Power Electronics

• Power electronics is the art of converting electrical energy from one form to another in an efficient, clean and robust manner for convenient utilization.

• Power electronics combine power, electronics and control.

• Power electronics can be defined as the application of solids state electronics for control and conversion of electric power.

• *Power electronics is based on the switching of power semiconductor devices.

Difference between linear and power electronics

• In power electronics all the semiconductor devices are operated in switching mode :either fully ON or Fully OFF.

• Where as in linear electronics for example in linear amplifier, we require to operate BJT in linear active zone or working mode. When BJT is used in power electronics we use it in Saturation and cutoff mode (switching).

• Semiconductor devices used in both linear and power electronics are common except that the power devices have larger power, voltage and current handling capabilities.

Control Characteristics of Power Semiconductor Devices

• As the power devices are operated as switches by applying the control signal or triggering signal to gate(FET) or to base(BJT).

• The o/p is obtained by varying the conduction time of these switching devices.

Classification of power devices on base of controlling

• Uncontrolled turn ON and turn OFF.

• Controlled turn ON and uncontrolled turn OFF.

• Controlled turn ON and OFF.

Power Electronics Devices

• Power Diodes

• Transistors

• Thyristors

Power Diodes

• General purpose

• High Speed

• Schottky

Power Transistors

• BJT

• MOSFET

• IGBT

• SIT

THYRISTORS

• SCR

• LASCR

• SITH

• DIAC

• TRIAC

• GTO

• GATT

Types of Power electronic circuits

• Power electronics circuits can be classified into six types:

• Diode Rectifiers.• Ac to Dc Converters. (Controlled Rectifiers)• Ac to Ac Converters. (Ac Voltage Controlled)• Dc to Dc Converters. (Dc Chopper)• Dc to Ac Converters. (Inverters)• Static Switches.

Converter Topology

Characteristic and Specification of Switches

• There are many types of power switching devices which can be used in any of the above possible circuits of power electronics.

• Each power switching device have its own advantages and disadvantages.

• The selection of power switching device depends on the voltage, current and speed requirements of the circuit.

• In the ON state when the switch is ON, it must have:

1-Ability to carry a high forward current IF ,tending to infinity.

2-Low ON state forward voltage drop VON,tending to zero.

3-low ON state resistance RON,tending to zero.

4-Low RON insure low ON state power loss PON.

• In the OFF state when the switch is OFF, it must have:

1-Ability to hold high voltage VBR, tending to infinity.

2-Low OFF state leakage current IOFF, tending to zero.

3-High OFF state resistance ROFF, tending to infinity.

4-High ROFF insure low OFF state power loss POFF.

• During turn ON and OFF process, switch must be completely ON and OFF instantaneously so that it can be used in fast switching applications. Therefore delay times must be low tending to zero.

• For turn ON and OFF must require low driving voltage and current.

• Both turn ON and OFF must be controllable.• Must have high dv/dt and di/dt so that switch can

swap high to low and low to high transitions fastly.

• Delay time td:Time required for switch to come out from cutoff, it is the time required for I to reach 10% of its max value, time required for V to reach 90% of its max value.

• Rise time tr: it is the time required for I to reach 10% to 90% transition, time required for V to reach 90% to 10% transition.

• Storage time ts: it is the time required for I to drop 90% of its max value, time required for V to rise 10% of its max value.

• Fall time tf:Time required for switch to come out from sat, it is the time required for I to drop from 90% to 10% of its max value, time required for V to rise 10% to 90% of its max value.

Switching Frequency Of device

fmax=1/(td+tr+ts+tf)

Switch Specification• When use the semiconductor devices as a

switch, the following specification should be inconsideration in accordance to the application requirement. The device manufacturer provide the parametric values in datasheet.

• Voltage rating

• Current Rating

• Switching Speed

• di/dt rating

• dv/dt rating

• Switching losses

• Gate drive requirement