Transcript Speckle Reduction in Ultrasound Image by Adaptive Filter

Power Semiconductor Devices
Xi Liu
Biomedical Engineering
ECE423
Introduction
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What are Power Semiconductor Devices (PSD)?
They are devices used as switches or rectifiers
in power electronic circuits
What is the difference of PSD and low-power
semiconductor device?
 Large voltage in the off state
 High current capability in the on state
Classification
Fig. 1. The power semiconductor devices family
Important Parameters
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Breakdown voltage.
On-resistance.
Trade-off between breakdown voltage and onresistance.
Rise and fall times for switching between on
and off states.
Safe-operating area.
Power MOSFET: Structure
Power MOSFET has much higher current handling
capability in ampere range and drain to source blocking
voltage(50-100V) than other MOSFETs.
Fig.2.Repetitive pattern of the cells
structure in power MOSFET
Power MOSFET: R-V Characteristics
An important parameter of a power MOSFET is on resistance:
Ron  RS  RCH  RD , where RCH 
L
W nCox (VGS  VT )
Fig. 3. Typical RDS versus ID characteristics of a MOSFET.
Thyristor: Structure
 Thyristor is a general class of a four-layer pnpn
semiconducting device.
Fig.4 (a) The basic four-layer pnpn structure.
(b) Two two-transistor equivalent circuit.
Thyristor: I-V Characteristics
Three States:
 Reverse Blocking
 Forward Blocking
 Forward Conducting
Fig.5 The current-voltage
characteristics of the pnpn device.
Applications
Power semiconductor devices have widespread
applications:
 Automotive
Alternator, Regulator, Ignition, stereo tape
 Entertainment
Power supplies, stereo, radio and television
 Appliance
Drill motors, Blenders, Mixers, Air conditioners
and Heaters
Application: Automotive
Table. 1. Power Devices in automotive systems.
Future Developments
For future power conversion applications, new
semiconductor devices are needed to be developed.
1.Structure Improvement
Insulated Gate Bipolar Transistor (IGBT), static induction
transistor (SIT) and MOS-controlled thyristor (MCT) .
Future Developments
2. Material Improvement
Silicon carbide (SiC), with a higher field characteristic,
is a promising candidate for high power, high
temperature and high frequency applications.
 High electric breakdown property
 High carrier drift velocity
 High thermal conductivity
 The native oxide of SiC is SiO2
Conclusion
The development of power semiconductor
devices is very essential for modern electronics.
The power devices based on new structures and
materials are promising and commercially
realistic for future electronic developments.
Thanks!