Programming instructions

Power
Multisim Component Reference Guide 12-34 ni.com
12.4.1 Input/Output Voltage Differential Rating
The input/output voltage differential rating shows the maximum difference between V
in
and
V
out
that can occur without damaging an IC voltage regulator.
The differential voltage rating can be used to determine the maximum allowable value of V
in
as follows:
where:
V
in(max)
= the maximum allowable unrectified dc input voltage
V
out(adj)
= the adjusted output voltage of the regulator
V
d
= the input/output voltage differential rating of the regulator
12.5 Voltage Suppressor
The voltage suppressor diode is a Zener diode that is capable of handling high surges. It is
used as a filtering device to protect voltage-sensitive electronic devices from high energy
voltage transients.
The voltage suppressor diode is connected across the AC power input line to a DC power
supply. It contains two zener diodes that are connected back-to-back, making the voltage
suppressor diode bi-directional. This characteristic enables it to operate in either direction to
monitor under-voltage dips and over-voltage spikes of the AC input. It protects the power
supply from surges by shorting out any voltages greater than the V
z
(Zener voltage) ratings of
the diodes.
The voltage suppressor diode must also have extremely high power dissipation ratings
because most AC power line surges contain a relatively high amount of power, in the
hundreds of watts or higher. It must also be able to turn on rapidly to prevent damage to the
power supply.
In DC applications, a single unidirectional voltage suppressor can be used instead of a bi-
directional voltage suppressor. It is connected in shunt with the DC input and reverse biased
(cathode to positive DC).
V
in max
()
V
out adj
()
V
d
+=
ComponentRef.book Page 34 Thursday, December 7, 2006 10:12 AM