Upload
ferdad4real
View
261
Download
0
Embed Size (px)
DESCRIPTION
SwitchesTransistor, BJT, MOSFET, IGBT, Diodes, ThyristorsHow are switches arranged?To realize circuit requirements and to satisfy KVL and KCL of circuitsFor quadrant operations
Citation preview
Switch and Circuit Realization
• Switches– Transistor, BJT, MOSFET, IGBT, Diodes,
Thyristors
• How are switches arranged?– To realize circuit requirements and to satisfy
KVL and KCL of circuits– For quadrant operations
Realization of Switch
• Realization of switch: Depends on– Polarity of voltage that the devices must block
in the OFF state– Polarity of the current the device must
conduct during the conduction state
Realization of Switch contd..
• Refer the figure above– Switch A must block positive voltage Vg when
in OFF state
– Must conduct positive current IL in positive direction in the ON-state
• If for all operating conditions the current and blocking voltage lie in a single quadrant
Realization of Switch contd..
• The operation can be realized using a transistor and/or a diode
SPST-Single Pole, Single Throw
Passive Switches
• Single-Quadrant Switches SPST Passive and Active Switches– Passive switches have terminals 1 and 0
while active switches have additional terminal C for control action
– Passive switches operate in ON and OFF positions depending on the voltage and current waveforms [V,I]
Passive Switches : Diode
• Passive Switch- Diode
• Ideal Diode: Requires V(t), I(t) waveforms to turn ON/OFF – Diode OFF, when– Diode ON, when
0)( tV0I0I 0)( tV
Active Switches: BJT
• Active Switch- With Control C– Thyristor, BJT, MOSFET, IGBT
• BJT: Bipolar Junction Transistor
Active switches contd..
• When control terminal C causes device to be OFF and the device is capable of blocking positive voltage
• When control terminal C causes device to be in ON-state V = 0 and is capable of conducting positive current
• The reverse block characteristics of BJT and IGBT are poor or non-existent
0V
0I
0I
Active switches contd..
• MOSFET is able to conduct current in reverse direction but is rarely used– Example:
Active Switches contd..
• Switch A can be IGBT, BJT or MOSFET
• Switch B can be Diode i.e. OFF when
0BV
Current Bidirectional 2-Quadrant Switches
• DC-AC Inverters require switches to conduct both negative and positive currents but block only positive voltages
• A current Bidirectional two Quadrant SPST switch can be realized using a transistor and an anti-parallel diode
Current Bidirectional 2 Quadrant Switches contd..
• A SPDT-single pole double throw current bidirectional two quadrant switch can be derived using two SPST switches
• Two quadrant SPDT switch
• A current Bidirectional SPDT switch– Conducts both positive and negative currents– Blocks positive voltage
Current Bidirectional 2 Quadrant Switches contd..
Three phase DC-AC Inverter• Has 3 two quadrant SPDT switches one
per phase• Each switch block input voltage Vg,
conduct output currents
Battery Charger• Battery charger
• Vbus > 0, Vbatt > 0
• Q1, Q2, D1, D2 block positive voltage Vbatt
Battery Charger contd..
• Charging mode:– IL > 0, Q1 and D2 alternately conduct current
• Discharging mode:– IL < 0, Q2, D1 alternately conduct current
Voltage Bidirectional two quadrant switches contd..
• Switch must block both positive and negative voltages and conduct positive current
• Requires an SPST switch using a series connected transistor and diode
Voltage Bidirectional 2- Quadrant Switches contd..
• In OFF state, controller turns OFF the transistor. Diode blocks negative voltage and transistor blocks positive voltage
• Blocks negative voltage up to diode voltage rating
• Blocks positive voltage up to transistor voltage rating
• Example: DC-AC Buck-Boost Inverter
DC-AC Buck Boost Inverter
• Inverter mode IL > 0
• All switches conduct only positive current
• Switches must block output AC line-line voltage
Four Quadrant SPST switch
• Four quadrant switch capable of conducting currents of either polarity and blocking voltages of either polarity