Transcript Switching - دانشگاه تهران

‫الکترونیک صنعتی‬
‫دانشگاه تهران – بهزاد آسائی‬
‫‪1385‬‬
‫ترانزیستور‬
Bipolar Junction Transistors (BJTs)
2
‫صنعتی الکترونیک‬
BY: B. Asaei
‫ترانزیستور‬
Generic BJT Application
Clamped Inductive
Load
3
‫صنعتی الکترونیک‬
BY: B. Asaei
‫ترانزیستور‬
Bipolar Junction
Transistors (BJTs)
C
I
I
C
B
B
D
M
D1
C
  D  M+  D+  M
B
4
‫صنعتی الکترونیک‬
BY: B. Asaei
MOSFET I-V Characteristics and Circuit Symbols
i
D
[v
- V
GS
= v
GS( th)
]
DS
ohm ic
V GS5
active
V GS4
V GS3
V
GS2
V
GS1
V
5
<
GS
V
v
GS( th)
BV
DS
DSS
‫صنعتی الکترونیک‬
BY: B. Asaei
MOSFET Switching Models for Buck Converter
V
D
d
Io
D
r
DS (on )
F
R
G
C gd
+
V
G
GG
C
S
• Buck converter using power MOSFET.
• MOSFET equivalent circuit valid for
on-state (triode) region operation.
D
C
gd
I = f(V )
GS
D
G
C
gs
S
6
gs
• MOSFET equivalent circuit valid for offstate (cutoff) and active region operation.
‫صنعتی الکترونیک‬
BY: B. Asaei
Turn-on Equivalent Circuits for MOSFET Buck Converter
• Equi val ent ci r cui t
dur i ng t d(on) .
D
V
in
•
I o
F
C
R
+
V
i
GG
Equi val ent ci r cui t
dur i ng t r i .
D
G
C
• Equi val ent ci r cui t
dur i ng t f v1 .
R
G
+
V
gs
V
in
i
GG
G
C
Cg d1
+
+
7
GG
i
GG
i
gs
Vin
• Equi val ent ci r cui t
dur i ng t f v2 .
V
V
DC
C gd1
R
G
Io
F
C
I o
R
in
DC
C gd1
G
V
G
I o
DS (on )
G
C
gs
G
‫صنعتی الکترونیک‬
r
BY: B. Asaei
C gd2
MOSFET-based Buck Converter Turn-on Waveforms
• Free-wheeling diode
assumed to be ideal.
(no reverse recovery
current).
8
‫صنعتی الکترونیک‬
BY: B. Asaei
Paralleling of MOSFETs
D
• MOSFETs can be easily
paralleled because of
posit iv e t emperat ure
coefficient of r DS( on) .
Rd
Q
1
G
S
• Posit iv e t emperat ure coefficient leads t o t hermal
st abilizat ion effect .
• If r DS( on) 1 > r DS( on) 2 t hen more current and t hus
higher power dissipat ion in Q2 .
• Temperat ure of Q2 t hus increases more t han
t emperat ure of Q1 and r DS( on) v alues become
equalized.
9
‫صنعتی الکترونیک‬
BY: B. Asaei
‫ارزیابی‬
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10
As shown in Figure 1.1, a variety of circuitries in power electronics can be produced today with
MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) or IGBTs (Insulated Gate
Bipolar Transistors), which were introduced into the market one by one in the mid 80’s.
Compared to other switchable power semiconductors, such as conventional GTO-thyristors,
these types of transistors have a number of application advantages, such as active turn-off even
in case of short-circuit, operation without snubbers, simple control unit, short switching times
and, therefore, relatively low switching losses.
The production of MOSFETs and IGBTs is comparatively simple and favourable and can easily
be managed by today’s technologies in microelectronics.
It was mainly due to the rapid development of IGBTs and power MOSFETs that power
electronics continued open up new markets, and that their fields of application increased
tremendously at the same time. Bipolar high-voltage power transistors that were still very
common a few years ago, have been almost completely replaced by IGBTs.
‫صنعتی الکترونیک‬
BY: B. Asaei