Short Notes: Power Semiconductor Diodes & Transistors

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1 Short Notes: P o w er Semiconductor Dio des & T ransistors
1.1 In tro duction
P o w er electronics in v olv es the con trol and con v ersion of electrical p o w er using semicon-
ductor devices. P o w er semiconductor dio des and transistors are k ey comp onen ts in con-
v erters, in v erters, and rectifiers, critical for GA TE Electrical Engineering. These devices
handle high v oltages and curren ts, enabling e?icien t p o w er managemen t.
1.2 P o w er Semiconductor Dio des
• Purp ose : Used in rectification, freewheeling, and protection circuits. They con-
duct curre n t in one direction with minimal losses.
• T yp es :
– Power Dio de : High curren t and v oltage ratings, used in rectifiers.
– Schottky Dio de : Lo w forw ard v oltage drop, fast switc hing, ideal for high-
frequency applications.
– F ast R e c overy Dio de : Reduced rev erse reco v ery time, suitable for high-sp eed
switc hing.
• Characteristics :
– F orw ard V oltage Drop: V
F
˜ 0.7-1 V (p o w er dio de), 0.2-0.3 V (Sc hottky).
– Rev erse Reco v ery Time (t
rr
): Time to switc h from conducting to blo c king
state.
Q
rr
=
?
trr
0
I
rr
(t)dt
where Q
rr
is rev erse reco v ery c harge, I
rr
is rev erse reco v ery curren t.
• Applications : Dio de rectifiers, sn ubb er circuits, and freewheeling in con v erters.
1.3 P o w er T ransistors
• Purp ose : A ct as switc hes or amplifiers in p o w er electronic circuits, con trolling
high p o w er wit h lo w con trol signals.
• T yp es :
– Power BJT : Curren t-con trolled, used in lo w-to-medium p o w er applications.
– Power MOSFET : V oltage-con trolled, high switc hing sp eed, ideal for high-
frequency con v erters.
– IGBT (Insulate d Gate Bip olar T r ansistor) : Com bines BJT’s high curren t ca-
pabilit y and MOSFET’s easy gate con trol, widely used in in v erters and motor
driv es.
1
Page 2


1 Short Notes: P o w er Semiconductor Dio des & T ransistors
1.1 In tro duction
P o w er electronics in v olv es the con trol and con v ersion of electrical p o w er using semicon-
ductor devices. P o w er semiconductor dio des and transistors are k ey comp onen ts in con-
v erters, in v erters, and rectifiers, critical for GA TE Electrical Engineering. These devices
handle high v oltages and curren ts, enabling e?icien t p o w er managemen t.
1.2 P o w er Semiconductor Dio des
• Purp ose : Used in rectification, freewheeling, and protection circuits. They con-
duct curre n t in one direction with minimal losses.
• T yp es :
– Power Dio de : High curren t and v oltage ratings, used in rectifiers.
– Schottky Dio de : Lo w forw ard v oltage drop, fast switc hing, ideal for high-
frequency applications.
– F ast R e c overy Dio de : Reduced rev erse reco v ery time, suitable for high-sp eed
switc hing.
• Characteristics :
– F orw ard V oltage Drop: V
F
˜ 0.7-1 V (p o w er dio de), 0.2-0.3 V (Sc hottky).
– Rev erse Reco v ery Time (t
rr
): Time to switc h from conducting to blo c king
state.
Q
rr
=
?
trr
0
I
rr
(t)dt
where Q
rr
is rev erse reco v ery c harge, I
rr
is rev erse reco v ery curren t.
• Applications : Dio de rectifiers, sn ubb er circuits, and freewheeling in con v erters.
1.3 P o w er T ransistors
• Purp ose : A ct as switc hes or amplifiers in p o w er electronic circuits, con trolling
high p o w er wit h lo w con trol signals.
• T yp es :
– Power BJT : Curren t-con trolled, used in lo w-to-medium p o w er applications.
– Power MOSFET : V oltage-con trolled, high switc hing sp eed, ideal for high-
frequency con v erters.
– IGBT (Insulate d Gate Bip olar T r ansistor) : Com bines BJT’s high curren t ca-
pabilit y and MOSFET’s easy gate con trol, widely used in in v erters and motor
driv es.
1
1.4 P o w er BJT
• Op eration : Op erates in cut-off (OFF), saturation (ON), or activ e (amplification)
mo des.
• Curren t Relations hip :
I
C
=ßI
B
where ß is curren t gain (t ypically 10-50 for p o w er BJT s).
• V oltage Rela tionship :
V
CE
=V
CC
-I
C
R
C
in co mmon-emitter configuration.
• Characteristics : High collector curren t, but slo w er switc hing due to minorit y
carrier storage. Second breakdo wn limits safe op erating area (SO A).
1.5 P o w er MOSFET
• Op erati on : Op erates in cut-off, trio de, or saturation regions. V oltage-con trolled,
requiring minimal gate curren t.
• Drain Cur ren t in Saturation :
I
D
=
1
2
µ
n
C
ox
W
L
(V
GS
-V
th
)
2
(1+?V
DS
)
whereµ
n
is electron mobilit y ,C
ox
is o xide capacitance,W/L is c hannel asp ect ratio,
V
th
is threshold v oltage, and ? is c hannel length mo dulation para meter.
• Characteristics : High input imp edance, fast switc hing (lo w t
on
,t
off
), but limited
b y on-state r esistance (R
DS(on)
).
• Applications : SMPS, DC-DC con v erters, and high-frequency in v erters.
1.6 IGBT
• Op eration : Com bines MOSFET’s gate con trol with BJT’s lo w conduction losses.
Op erate s in ON (saturation) or OFF (cut-off ) mo des.
• V oltage Drop :
V
CE(sat)
˜ 1-2 V
lo w er than B JT but higher than MOSFET.
• Characteristics : High v oltage and curren t ratings, mo derate switc hing sp eed,
robust SO A . T ail curren t during turn-off increases switc hing losses.
• Applications : Motor driv es, UPS, and renew able energy in v erters.
1.7 Switc hing Characteristics
• T urn-On Time : Includes dela y time (t
d
) a nd rise time (t
r
).
t
on
=t
d
+t
r
2
Page 3


1 Short Notes: P o w er Semiconductor Dio des & T ransistors
1.1 In tro duction
P o w er electronics in v olv es the con trol and con v ersion of electrical p o w er using semicon-
ductor devices. P o w er semiconductor dio des and transistors are k ey comp onen ts in con-
v erters, in v erters, and rectifiers, critical for GA TE Electrical Engineering. These devices
handle high v oltages and curren ts, enabling e?icien t p o w er managemen t.
1.2 P o w er Semiconductor Dio des
• Purp ose : Used in rectification, freewheeling, and protection circuits. They con-
duct curre n t in one direction with minimal losses.
• T yp es :
– Power Dio de : High curren t and v oltage ratings, used in rectifiers.
– Schottky Dio de : Lo w forw ard v oltage drop, fast switc hing, ideal for high-
frequency applications.
– F ast R e c overy Dio de : Reduced rev erse reco v ery time, suitable for high-sp eed
switc hing.
• Characteristics :
– F orw ard V oltage Drop: V
F
˜ 0.7-1 V (p o w er dio de), 0.2-0.3 V (Sc hottky).
– Rev erse Reco v ery Time (t
rr
): Time to switc h from conducting to blo c king
state.
Q
rr
=
?
trr
0
I
rr
(t)dt
where Q
rr
is rev erse reco v ery c harge, I
rr
is rev erse reco v ery curren t.
• Applications : Dio de rectifiers, sn ubb er circuits, and freewheeling in con v erters.
1.3 P o w er T ransistors
• Purp ose : A ct as switc hes or amplifiers in p o w er electronic circuits, con trolling
high p o w er wit h lo w con trol signals.
• T yp es :
– Power BJT : Curren t-con trolled, used in lo w-to-medium p o w er applications.
– Power MOSFET : V oltage-con trolled, high switc hing sp eed, ideal for high-
frequency con v erters.
– IGBT (Insulate d Gate Bip olar T r ansistor) : Com bines BJT’s high curren t ca-
pabilit y and MOSFET’s easy gate con trol, widely used in in v erters and motor
driv es.
1
1.4 P o w er BJT
• Op eration : Op erates in cut-off (OFF), saturation (ON), or activ e (amplification)
mo des.
• Curren t Relations hip :
I
C
=ßI
B
where ß is curren t gain (t ypically 10-50 for p o w er BJT s).
• V oltage Rela tionship :
V
CE
=V
CC
-I
C
R
C
in co mmon-emitter configuration.
• Characteristics : High collector curren t, but slo w er switc hing due to minorit y
carrier storage. Second breakdo wn limits safe op erating area (SO A).
1.5 P o w er MOSFET
• Op erati on : Op erates in cut-off, trio de, or saturation regions. V oltage-con trolled,
requiring minimal gate curren t.
• Drain Cur ren t in Saturation :
I
D
=
1
2
µ
n
C
ox
W
L
(V
GS
-V
th
)
2
(1+?V
DS
)
whereµ
n
is electron mobilit y ,C
ox
is o xide capacitance,W/L is c hannel asp ect ratio,
V
th
is threshold v oltage, and ? is c hannel length mo dulation para meter.
• Characteristics : High input imp edance, fast switc hing (lo w t
on
,t
off
), but limited
b y on-state r esistance (R
DS(on)
).
• Applications : SMPS, DC-DC con v erters, and high-frequency in v erters.
1.6 IGBT
• Op eration : Com bines MOSFET’s gate con trol with BJT’s lo w conduction losses.
Op erate s in ON (saturation) or OFF (cut-off ) mo des.
• V oltage Drop :
V
CE(sat)
˜ 1-2 V
lo w er than B JT but higher than MOSFET.
• Characteristics : High v oltage and curren t ratings, mo derate switc hing sp eed,
robust SO A . T ail curren t during turn-off increases switc hing losses.
• Applications : Motor driv es, UPS, and renew able energy in v erters.
1.7 Switc hing Characteristics
• T urn-On Time : Includes dela y time (t
d
) a nd rise time (t
r
).
t
on
=t
d
+t
r
2
• T urn-Off Time : Includes storage time (t
s
) and fall time (t
f
).
t
off
=t
s
+t
f
• P o w er Loss : Switc hing and conduction losses:
P
switc h
=f·(E
on
+E
off
), P
cond
=I
2
R
DS(on)
(MOSFET) or I
C
V
CE(sat)
(IGBT/BJT)
where f is switc hing frequency , E
on
,E
off
are switc hing energies.
1.8 Key Notes for GA TE
• Understand dio de rev erse reco v ery and its impac t on switc hing losses.
• Compare BJT, MOSFET, and IGBT for switc hing sp eed, losses, and applications.
• Practice n umericals on switc hing times, p o w er losses, and safe op erating area.
• F o cus on IGBT c haracteristics, as they are pr ev alen t in mo dern p o w er electronics.
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