This document discusses power MOSFETs, including their characteristics and advantages over bipolar junction transistors. Some key points: 1) Power MOSFETs can operate at high voltages up to 1400V and high currents up to 500A, with switching frequencies ranging from 10-100kHz depending on the device. 2) Power MOSFETs use a metal-oxide-semiconductor field-effect transistor design that allows the gate voltage to fully control the channel conductance. 3) Their on-resistance can be made very low, allowing them to operate efficiently at high power levels before breakdown occurs. This makes them well-suited for applications requiring high power switching.

1. POWER MOSFET
CHARACTERISTICS
Julius Edgar Lilienfeld Robert W. Bower
PATENTED BY - INVENTED BY -
MOSFET
- Source Internet

2. 1440 V/400 A
10 kHz
1000 V/50 A
100 kHz
1200 V/300 A
100 kHz
1200 V/500 A
50 kHz
TRANSISTOR FAMILY

3. G
D
S
METAL-OXIDE-SEMICONDUCTOR
FIELD-EFFECT TRANSISTOR
It is combination of field-effect concept
and MOS technology.

4. HOW MOSFET DIFFER FROM BJT ?

5. WHY WE NEED POWER MOSFET ?
VDD
VGS
Large on-load
resistance
On increasing VGS
more current flows
This leads to high power dissipation
in n-channel and breakdown occurs.
In n-channel planar
MOSFET

6. POWER MOSFET(PMOSFET)
It consists of DIFFUSED METAL-OXIDE-SEMICONDUCTOR
VGS
GATESOURCE
SOURCEMETAL
SiO2
VDD
n+ n+
n+
n+
P
n- n-
n+ n+ substrate
DRAIN
P
On-resistance can be made low if short length is used for n-channel.
npn
BJT

7. PMOSFET CHARACTERISTICS
VGS
VDS
ID
R
RD
VG
VDD
Transfer characteristics
Output characteristics
Switching characteristics

8. TRANFER CHARACTERISTICS
Variation of drain current ID as a function of gate source
voltage VGS
2 4 6 8 10 12
ID(A)
VGS(V)
VGST
Threshold voltage(VGST ) -
The minimum positive voltage
between gate and source to
induce n-channel.

9. OUTPUT CHARACTERISTICS
ActiveOhmic
iD
VDS
A
B
Cut-off
When VGS<VGST
Drainsourcebreakdownvoltage
Draincurrent(A)
Drain-source voltage
 Low value of VDS curve is linear i.e. constant on-resistance
RD.
 For given VGS on increasing
VGS curve is flat i.e. drain
current is constant.
 VGS is large, MOSFET turns
on small VDSON. MOSFET
acting as closed switch &
driven into ohmic region
(Saturation region in BJT).
 When device on PMOSFET
curve traverse from cut-off
to active region then to
ohmic region & when turns
off, takes backward journey
from ohmic to cut-off
region.

10. SWITCHING CHARACTERISTICS
VG
V1
t1
t
VGS
V1
VGSP
VGST
tdn
tr
tdf tf
td
ton
ID
t
t
 Tdn is turn on delay time during
which i/p capacitance charges to
threshold voltage(VGST).
 Rise time(tr) – gate voltage rises
to VGSP(voltage sufficient to drive
the MOSFET) & drain current rises
from zero to full-on current(ID).
Total turn-on time (ton) = tdn + tr.
 tr can be reduced using low-
impedance gate –drive source.
 Turn-off process starts at time t1.
 Turn-off delay time(tdf) – i/p
capacitance discharges from
overdrive gate voltage V1 to VGSP.
 Fall time(tf) – i/p capacitance
discharges from VGSP to VGST & ID
falls to zero.
 So, when VGS ≤VGST PMOSFET is
turned-off.