24-01-2013, 10:36 AM
STUDY OF CHARACTERISTICS OF SCR, MOSFET AND IGBT
[attachment=48244]
AIM: To study various characteristics of SCR, MOSFET and IGBT.
APPARATUS:
S.No EQUIPMENT Qty
1. SCR,MOSFET AND IGBT KIT
2. PATCH CARDS 1 set
THEORY:
Silicon Controlled Rectifier: Silicon Controlled Rectifier is a four-layer three junction p-n-p-n
switching device. It has three terminals, Anode, cathode and gate. In normal operation of
thyristor anode held with high positive potential with respect to cathode and gate has a small
positive with respect to cathode.
When Anode is made positive with respect to cathode and switch is open in the gate circuit
,then p-n junction j1 and j3 are forward biased ,where as j2 becomes wider and j1 thinner at j1
and j3. There is no base current in transistor t2 and hence that of t1.under such conditions the
SCR is in a state of blocking forward direction. If now gate is made positive w.r.t. cathode or
switch is closed , a small gate current will flow through junction j2 as a result anode starts flows
if anode current is greater than latching current of SCR.SCR is forward conduction state or
simply SCR is closed state.
MOSFET: A Power MOSFET has three terminal called drain, source and gate. MOSFET is a
voltage controlled device. As its operation depends upon the flow of majority carriers only.
MOSFET is uni polar device. The control signal or gate current less than a BJT. This is because
of fact that gate circuit impedance in MOSFET is very high of the order of 109 ohm. This larger
impedance permits the MOSFET gate be driven directly from microelectronic circuits. Power
MOSFET’s are now finding increasing applications in low-power high frequency converters.
IGBT: IGBT is a new development in the area of Power MOSFET Technology. This device
combines into it’s the advantages of both MOSFET and BJT. So an IGBT has high input
impedance like a MOSFET and low-on-state power loss in a BJT.IGBT is also known as metal
oxide insulated gate transistor (MOSIGT). Conductively –modulated field effect transistor
PROCEDURE:
SCR CHARACTERISTICS:
A) Forward V-I Characteristics:
1. The connections are made as shown in the circuit diagram.
2. Switch on the power supply .Apply constant VAK voltage say 10V varying VAA
3. Gradually increase the gate current till the SCR becomes on i.e. VAK and IA
4. Now VAK is increased gradually and IA noted for two to three readings,
5. Steps 3 to 4 are repeated for another values of VAK say 30V.
6. Tabulate the readings in the tabule.
7. Plot a graph of VAK versus IA for different(two) values of IG
B) Reverse V-I Characteristics :
1. Now reverse the polarities of the anode voltage source.
2. Open the switch in the gate circuit.
3. Note down the readings of anode voltage and current by increasing the value of
voltage source in the anode circuit.
C) Gate Characteristics:
1. Now open the switch in the anode circuit.
2. Set the gate circuit voltage source and anode circuit voltage source as per the given
value.
3. Note down the readings of gate voltage and gate current by reducing the value of gate
side rheostat.
[attachment=48244]
AIM: To study various characteristics of SCR, MOSFET and IGBT.
APPARATUS:
S.No EQUIPMENT Qty
1. SCR,MOSFET AND IGBT KIT
2. PATCH CARDS 1 set
THEORY:
Silicon Controlled Rectifier: Silicon Controlled Rectifier is a four-layer three junction p-n-p-n
switching device. It has three terminals, Anode, cathode and gate. In normal operation of
thyristor anode held with high positive potential with respect to cathode and gate has a small
positive with respect to cathode.
When Anode is made positive with respect to cathode and switch is open in the gate circuit
,then p-n junction j1 and j3 are forward biased ,where as j2 becomes wider and j1 thinner at j1
and j3. There is no base current in transistor t2 and hence that of t1.under such conditions the
SCR is in a state of blocking forward direction. If now gate is made positive w.r.t. cathode or
switch is closed , a small gate current will flow through junction j2 as a result anode starts flows
if anode current is greater than latching current of SCR.SCR is forward conduction state or
simply SCR is closed state.
MOSFET: A Power MOSFET has three terminal called drain, source and gate. MOSFET is a
voltage controlled device. As its operation depends upon the flow of majority carriers only.
MOSFET is uni polar device. The control signal or gate current less than a BJT. This is because
of fact that gate circuit impedance in MOSFET is very high of the order of 109 ohm. This larger
impedance permits the MOSFET gate be driven directly from microelectronic circuits. Power
MOSFET’s are now finding increasing applications in low-power high frequency converters.
IGBT: IGBT is a new development in the area of Power MOSFET Technology. This device
combines into it’s the advantages of both MOSFET and BJT. So an IGBT has high input
impedance like a MOSFET and low-on-state power loss in a BJT.IGBT is also known as metal
oxide insulated gate transistor (MOSIGT). Conductively –modulated field effect transistor
PROCEDURE:
SCR CHARACTERISTICS:
A) Forward V-I Characteristics:
1. The connections are made as shown in the circuit diagram.
2. Switch on the power supply .Apply constant VAK voltage say 10V varying VAA
3. Gradually increase the gate current till the SCR becomes on i.e. VAK and IA
4. Now VAK is increased gradually and IA noted for two to three readings,
5. Steps 3 to 4 are repeated for another values of VAK say 30V.
6. Tabulate the readings in the tabule.
7. Plot a graph of VAK versus IA for different(two) values of IG
B) Reverse V-I Characteristics :
1. Now reverse the polarities of the anode voltage source.
2. Open the switch in the gate circuit.
3. Note down the readings of anode voltage and current by increasing the value of
voltage source in the anode circuit.
C) Gate Characteristics:
1. Now open the switch in the anode circuit.
2. Set the gate circuit voltage source and anode circuit voltage source as per the given
value.
3. Note down the readings of gate voltage and gate current by reducing the value of gate
side rheostat.