Voltage regulation circuits like the zener diode and three-terminal regulators can maintain a constant output voltage despite fluctuations in load conditions or input voltage. A zener diode operates in reverse bias to regulate voltage at a specific breakdown voltage. A three-terminal voltage regulator integrated circuit provides precise voltage control with only a few external components and has built-in protections like overcurrent prevention. The adjustable three-terminal regulator uses a resistor network and reference voltage to set the output voltage.

1. Voltage Regulation:
is the measure of a circuit’s ability to
maintain a constant output voltage
for changes in load condition or input
voltage

2. Zener diode
A zener is a specially doped p-n
junction diode that is designed to Characteristic Curve
operate in reverse bias without
IF
damage.
Zener Diode Symbol
A K
V
VR Z
0.1 IZ max VF
Practical Working
Range 0.1 to 0.8 I Z IZ
MAX is known as the
Zener region. Vz
0.8 IZ max
remains almost
IR
constant.

3. Zener Diode Shunt Regulator

4. As the resistor is in series with the zener diode, the voltage drop across
the resistor and the voltage drop across the zener equal the supply
voltage. Voltage across the resistor is 6V the zener is 12V.
Vs = VRload. + Vz
The series resistor and the zener diode essentially form a series circuit,
therefore the voltage across the series resistor plus the zener voltage will equal
the supply voltage.
Component functions
Rs Limits the zener current to a safe value.
Vz maintains a constant voltage across the load unit by controlling the
current through the series resistor.

5. Three Terminal Regulators.
• Three terminal regulators are integrated circuits (IC’ s)
that have been designed to input a varying low voltage
D.C. and provide a low voltage fixed output D.C. voltage.
They also have many built in features that make them
easy to use and very versatile.
•
They require very few additional components.
•
• They have protection against short circuit currents.
•
• They have automatic thermal shutdown (they reduce the
output when they reach a predetermined temperature)
•
They have very constant output voltage.
•
They have very small ripple output.

6. 3 terminal voltage regulator
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7. Regulator
• Voltage Regulator is a compact device that can
provide precise voltage control The 3 Terminal
integrated Circuit with the addition of only a
few external components.
• The 3-T regulator also has built-in over-
current, short-circuit and over-temperature
protection
• The 3-T regulator has high ripple rejection and
good transient response.
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8. The terminal regulators come in a range of fixed
voltages or can be adjustable to almost any desired
voltage by the addition of a simple zener diode or
resistor network
• A complete power supply using a fixed voltage
three-terminal regulator is shown below.

9. Terminal Identification

10. In the above circuit the voltage between the output terminal and the adjustable
terminal is set internally in the regulator at 1.25V. This voltage is connected
across the 220Ω resistor which will cause a current of 5.7mA to flow through it.
This current will also flow through the 1kΩ resistor causing a 5.7 V drop across it.
(Ohm’s law, V=I x R, 0.057 x 1000 = 5.7 V).
Therefore, the output voltage can now be determined by adding VR1 plus VR2
V output = VR1 + VR2 = 1.25 V + 5.7 V = 6.92 volts.