Programming instructions
Diodes
Multisim Component Reference Guide 3-12 ni.com
3.7 Schottky Diode
The Schottky diode is a two-terminal device with a junction that uses metal in place of the
p-
type material. The formation of a junction with a semiconductor and metal results in very little
junction capacitance.
The Schottky diode will have a
V
F
of approximately 0.3 V and a V
BR
of less than − 50 V.
These are lower than the typical
pn-junction ratings of V
F
= 0.7 V and V
BR
= −1 50 V.
With very little junction capacitance, the Schottky diode can be operated at much higher
frequencies than the typical
pn-junction diode and has a much faster switching time.
The Schottky diode is a relatively high-current device that is capable of switching rapidly
while providing forward currents of approximately 50 A. It can operate at frequencies of 20
GHz and higher in sinosoidal and low-current switching circuits.
3.8 Silicon-Controlled Rectifier
A silicon-controlled rectifier (SCR) is a unidirectional current control device like a Shockley
diode. However, the SCR has a third terminal capable of supporting a digital gate connection,
which adds another means of controlling the current flow. The SCR switches on when the
forward bias voltage exceeds the forward-breakover voltage or when a current pulse is
applied to the gate terminal.
The SCR is triggered into conduction by applying a gate-cathode voltage (
VGK), which
causes a specific level of gate current (
IG). The gate current triggers the SCR into conduction.
The device is returned to its nonconducting state by either anode current interruption or forced
commutation. When the SCR is turned off, it stays in a non-conducting state until it receives
another trigger.
ComponentRef.book Page 12 Thursday, December 7, 2006 10:12 AM