LM 323 3-Amp, 5-Volt
Positive Voltage Regulator
Linear Regulators- Standard/NPN
Positive Voltage - Fixed
This project involves the analysis and simulation of a 3-
Amp, 5-Volt Positive Voltage Regulator designed and built by
National Semiconductor. A basic overview of linear voltage
regulators will be addressed. The claims of the manufacturer
will be tested to determine the simulated parameters for input
voltage range, load impedance, and maximum drive current.
Today, nearly all electronic circuits need some supply
voltage. This regulated voltage must be clean, steady,
and known. A linear voltage regulator creates this
known voltage by means of transistor operating in their
forward active regions and zener diode operating in
their breakdown regions. The LM323 is a linear voltage
regulator. A simulation of this circuit will be made to
determine it’s effectiveness.
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LM 323 3-Amp, 5-Volt Positive Voltage Regulator
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What is a VOLTAGE REGULATOR?
A VOLTAGE REGULATOR provides an output voltage
Under changing conditions such as:
1. Load Impedances and Load Currents
2. Unregulated or Fluctuating DC Input Voltage
Note: LINEAR VOLTAGE REGULATORS can be either
fixed or adjustable, depending on what the user demands.
The LM 323 is a Fixed Linear Voltage Regulator. This
means the regulated output of this circuit is designed to
be fixed at 5V.
What are VOLTAGE REGULATORS used for?
Almost any electronic circuit needs a VOLTAGE REGULATOR.
4. Almost all electronic circuits.
What kind of VOLTAGE REGULATORS are there?
There are basically 2 main types:
1. Linear Regulators- Standard (internal feedback), Low-Dropout
(external feedback), and Quasi Low-Dropout, etc.
These types of circuits use the transistors operating in their linear
active regions and zener diodes operating in their breakdown
regions to create regulated voltages.
2. Switching Regulators- Buck, Buck-Boost, Boost, Flyback,
These types of regulators require switching circuits to either step
up or step down the voltage.
The LM 323 is a Standard Linear Voltage Regulator.
How does a basic STANDARD LINEAR
For a Linear Voltage Regulator to output a regulated
1. An unregulated DC voltage source is connected
to a voltage controlled current source.
2. The current from this source is passed through
some load impedance (RLOAD).
3. A voltage (VOUT) is created across RLOAD.
4. A feedback SENSOR that is connected to
VOUT and the voltage controlled current source
5. The SENSOR compares VOUT with some
reference voltage (VREF).
6. If VOUT is equal to VREF, the SENSOR does
7. If VOUT is different from VREF, the SENSOR
inputs a voltage to the voltage controlled current
8. The current source changes its output current to
RLOAD until VOUT = VREF.
Note: VOUT not VREF acts as a regulated output
National claims the LM 323 Linear Voltage
1. Take an unregulated DC input voltage
between 7V and 20V and output a
5V (+/- 1%) regulated constant voltage.
2. It is also claimed to have a maximum output
current of 3A.
I will test these claims in simulation:
1. Perform a DC sweep of the input voltage
from 0V to 30V while monitoring the output
voltage with nominal loads.
2. Change the load impedance to determine
maximum output current.
Input Voltage Load Impedance Output Voltage Output Current
7-14V 1M ohms 4.94V 4.94uA
7-14V 1k ohms 4.94V 4.94mA
7-14V 3 ohms 4.94V 1.7A
7-14V 2.5 ohms 4.5V 1.84A
7-14V 1 ohm 1.8V 1.8A
Note that outside the input voltage range 7-14V the circuit does not
act as a voltage regulator.
The simulated linear voltage regulator works
very well given the following conditions:
1. Unregulated DC input voltage between 7V
2. With a load impedance greater than 2.5
Reasons that the simulation does not agree with
the claimed specs of National:
1. The intrinsic values of the transistors were not
given in the LM 323 handout. This means the
values of Beta and various impedances for the
transistors are different than in the simulation.
This will lead to different data measurements.
According to National, the Advantages and
Disadvantages of the LM 323 are:
1. Easy to use.
2. Internal overcurrent and thermal
3. No circuit adjustments are needed.
4. Low cost.
1. Output voltage cannot be adjusted
2. It is available at only certain voltages.
3. It is difficult to increase its current