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Introduction To
SCHOTTKY
Rectifier and
Application
Guidelines
Kevin Wu, AE Manager
Taiwan Semiconductor
Why SCHOTTKY?
For Silicon devices, the forward voltage
drop of the pn-junction rectifier can not be
reduced below about 0.8 volts even if the
device is not required to block higher reverse
voltage. In the case of the output rectifiers
used in power supplies for computers and
telecommunications, this voltage drop is a
large fraction of the output voltage of 5V or
less. This results in a loss in the power supply
efficiency by 20% - 30%. For Schottky bar-
rier rectifier they can exhibit a very low for-
ward voltage drop leading a smaller conduc-
tion loss than that of pn-junction rectifier, and
switching speeds approaching zero-time. This
combination hence makes Schottky barrier
rectifiers ideal for the output stages of switch-
ing power supplies.
Schottky diodes
Presently the breakdown voltage of the Sili-
con Schottky diode cannot be reliably made
larger than 200V. However, the drawback
of the Silicon Schottky rectifier can be ad-
dressed by fabricating the devices by using
other semiconductor materials, such as gal-
lium arsenide and silicon carbide.
Schottky diodes have positive and nega-
tive sides. They are shown below.
Advantage:
- Switching speed faster than a comparable
pn-junction diode
- Very low forward voltage drop (VF)
- Having much less voltage overshoot dur-
ing device turn-on than comparable pn-
junction diodes
Disadvantage:
- Limited high-temperature operation
- High leakage
- Limited breakdown voltage range for
Silicon Schottky diode
Switching Characteristics
A Schottky diode turns on and turns off
faster than a comparable pn-junction diode.
The basic reason is that Schottky diodes are
majority-carrier devices and have no stored
minority carriers that must be injected into the
device during turn-on and pulled out during
turn-off.
Trade-off
The four most important application char-
acteristics of a Schottky are:
- forward voltage drop
- reverse leakage current
