Programming instructions

Voltage Reference
 National Instruments Corporation 12-33 Multisim Component Reference Guide
12.3 Voltage Reference
The output voltage of the Zener reference diode is set at approximately 6.9 V and requires a
high voltage supply. The band-gap voltage reference diode has a significant advantage over
the Zener reference diode in that it is capable of a lower minimum operating current and has a
sharper knee.
The band-gap reference relies on matched transistors and is therefore easily integrated along
with biasing, buffer and amplifier circuitry to give a complete reference diode.
The LM285/LM385 series are examples of micropower two-terminal band-gap voltage
reference diodes. These devices are designed to operate over a wide current range of 10
µA to
20 mA.
The features of these devices include exceptionally low dynamic impedance, low noise, and
stable operation over time and temperature. The low operating current make these devices
suitable for micropower circuitry, such as portable instrumentation, regulators and other
analog circuitry that requires extended battery life.
Note Many types of two-terminal 1.2 V voltage reference diodes offer the same performance,
but are not all directly interchangeable. Minor differences in regulation voltage and in
allowable or required capacitive loading may affect a circuit.
12.4 Voltage Regulator
The linear IC voltage regulator is a device used to hold the output voltage from a dc power
supply relatively constant over a wide range of line and load variations. Most commonly used
IC voltage regulators are three-terminal devices.
There are four types of IC voltage regulators: fixed positive, fixed negative, adjustable, and
dual tracking. The fixed-positive and fixed-negative IC voltage regulators are designed to
provide specific output voltages. The adjustable regulator can be adjusted to provide any dc
output voltage within two specified limits. The dual-tracking regulator provides equal positive
and negative output voltages.
The regulator input-voltage polarity must match the device’s rated output polarity regardless
of the type of regulator used.
IC voltage regulators are series regulators, that is, they contain internal pass transistors and
transistor control components. The internal circuitry of an IC voltage regulator is similar to
that of the series feedback regulator.
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