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Learning Contents
Lesson 13. Voltage Regulator 1. Voltage regulator
II
2. Zener Diode Regulator
3. Linear Regulator
4. Switching Regulator
5. IC Voltage Regulator
Learning Goals
1. Understand structure and operation of Zener diode and linear regulator
2. Understand structure of switching regulator and IC voltage regulator
1. Voltage regulator 2. Zener diode regulator
• Diode regulators: can use a series of diode or Zener diode.
• Fundamental classes are linear regulators and switching
regulators.
• Two basic types of linear regulator are the series
regulator and the shunt regulator.
• The series regulator is connected in series with the
load and the shunt regulator is connected in parallel
with the load.
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2. Zener diode regulator 2. Zener diode regulator
• Zener diode • Reversed bias characteristics of Zener diode
Forward bias: like regular diode
Reversed bias:
• Operated at “break-down” region, (PIV or VZ)
• VZ = const
Usage: always at reserved bias to be “reference
voltage”
Very large range of VZ ~ 1,8V ÷ 200V
2. Zener diode regulator 2. Zener diode regulator
• Equivalent model
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2. Zener diode regulator 3. Linear regulator
• For low current power supplies - a simple voltage Series Regulator Circuit
• Control element in series with load between input and
regulator can be made with a resistor and a zener
output.
diode connected in reverse.
• Output sample circuit senses a change in output voltage.
• Zener diodes are rated by their breakdown voltage
• Error detector compares sample voltage with reference
Vz and maximum power Pz (typically 400mW or
voltage → causes control element to compensate in order
1.3W). to maintain a constant output voltage.
3. Linear regulator 3. Linear regulator
Advantages: Disadvantages:
• Simple • Low efficiency
• Low output ripple voltage • Large space requirement if heatsink is needed
• Excellent line and load regulation • Can not increase voltage above the input
• Fast response time to load or line changes
• Low electromagnetic interference (less noise)
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3. Linear regulator 3. Linear regulator
Op-Amp Series Regulator
Op-Amp Series Regulator
• The resistor R1 and R2 sense a change in the output voltage
and provide a feedback voltage.
Control
Element • The error detector compares the feedback voltage with a
Zener diode reference voltage.
• The resulting difference voltage causes the transistor Q1
VREF controls the conduction to compensate the variation of the
output voltage.
Sample
Error Detector Circuit • The output voltage will be maintained at a constant value of:
R
Vo 1 1 VZ
R2
3. Linear regulator 3. Linear regulator
Transistor series regulator Transistor Series Regulator
• Since Q1 is a npn transistor, Vo is found as:
VBE VZ Vo
• The response of the pass-transistor to a change in load
resistance as follows:
• If load resistance increases, load voltage also increases.
• Since the Zener voltage is constant, the increase in Vo
causes VBE to decrease.
• The decrease in VBE reduces conduction through the
pass- transistor, so load current decreases.
• The transistor Q1 is the series control element. • This offsets the increase in load resistance, and a
• Zener diode provides the reference voltage. relatively constant load voltage is maintained.
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3. Linear regulator 3. Linear regulator
Shunt Regulator Circuit
Op-Amp Shunt Regulator
• The unregulated input voltage provides current to the load.
• Some of the current is pulled away by the control element.
• If the load voltage tries to change due to a change in the load
resistance, the sampling circuit provides a feedback signal to a
comparator.
• The resulting difference voltage then provides a control signal to
vary the amount of the current shunted away from the load to
maintain the regulated output voltage across the load.
3. Linear regulator 3. Linear regulator
Op-Amp Shunt Regulator Transistor Shunt Regulator
• When the output voltage tries to decrease due to a change in
input voltage or load current caused by a change in load
resistance, the decrease is sensed by R1 and R2
• A feedback voltage obtained from voltage divider R1 and R2
is applied to the op-amp’s non-inverting input and compared
to the Zener voltage to control the drive current to the
transistor. • The control element is a transistor, in parallel with the load.
• The current through resistor RS is thus controlled to drop a While, the resistor, RS, is in series with the load.
voltage across RS so that the output voltage is maintained. • The operation of the transistor shunt regulator is similar to that
of the transistor series regulator, except that regulation is
achieved by controlling the current through the parallel
transistor.
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3. Linear regulator 3. Linear regulator
Transistor Shunt Regulator Transistor Shunt Regulator
• Resistor RS drops the unregulated voltage depends on current • The output voltage to the load is:
supplied to load RL.
Vo VL VZ VBE
• Voltage across the load is set by zener diode and transistor base- • voltage across the load is set by the Zener diode voltage and the
emitter voltage. transistor base-emitter voltage.
• If RL decrease, a reduced drive current to base of Q1 shunting
• If the load resistance decreases, the load current will be larger at a
less collector current.
value of:
• Load current, IL is larger, maintaining the regulated voltage across VL
load. IL
RL
• The increase in load current causes the collector current shunted by
the transistor is to be less:
IC I S I L
• The current through RS:
Vi VL
IS
RS
3. Linear regulator 4. Switching Regulator
Transistor Shunt Regulator: Example • The switching regulator is a type of regulator circuit which its
efficient transfer of power to the load is greater than series and
• Determine the regulated voltage, VL and circuit currents.
shunt regulators because the transistor is not always
(Solution: VL=8.9 V; IL=89 mA; IS=109 mA; IC=20 mA) conducting.
• The switching regulator passes voltage to the load in pulses,
which then filtered to provide a smooth dc voltage.
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4. Switching Regulator 5. IC Voltage Regulators
• The switching regulator is more efficient than the linear series • Regulation circuits in integrated circuit form are widely used.
or shunt type. • Their operation is no different but they are treated as a single
• This type regulator is ideal for high current applications since
device with associated components.
less power is dissipated.
• These are generally three terminal devices that provide a
• Voltage regulation in a switching regulator is achieved by the
positive or negative output.
ON and OFF action limiting the amount of current flow based on
the varying line and load conditions. • Some types have variable voltage outputs.
• With switching regulators 90% efficiencies can be achieved. • A typical 7800 series voltage regulator is used for positive
voltages.
• The 7900 series are negative voltage regulators.
• These voltage regulators when used with heatsinks can
safely produce current values of 1A and greater.
• The capacitors act as line filtration.
5. IC Voltage Regulators 5. IC Voltage Regulators
• Several types of both linear (series and shunt) and switching Fixed Voltage Regulator
regulators are available in integrated circuit (IC) form. • The fixed voltage regulator has an unregulated dc input
voltage Vi applied to one input terminal, a regulated output dc
• Single IC regulators contain the circuitry for:
voltage Vo from a second terminal, and the third terminal
(1) reference source
connected to ground.
(2) comparator amplifier
• Fixed-Positive Voltage Regulator
(3) control device • The series 78XX regulators are the three-terminal devices
(4) overload protection that provide a fixed positive output voltage.
• Generally, the linear regulators are three-terminal devices
that provides either positive or negative output voltages that
can be either fixed or adjustable.
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5. IC Voltage Regulators 5. IC Voltage Regulators
Fixed Voltage Regulator Fixed Voltage Regulator
• An unregulated input voltage Vi is filtered by a capacitor C1
and connected to the IC’s IN terminal. Positive-Voltage Regulators in the 78XX Series
• The IC’s OUT terminal provides a regulated +12 V, which is
filtered by capacitor C2. IC Part Output Voltage (V) Minimum Vi (V)
• The third IC terminal is connected to ground (GND). 7805 +5 +7.3
7806 +6 +8.3
7808 +8 +10.5
7810 +10 +12.5
7812 +12 +14.5
7815 +15 +17.7
7818 +18 +21.0
7824 +24 +27.1
5. IC Voltage Regulators 5. IC Voltage Regulators
Fixed Voltage Regulator Fixed Voltage Regulator
• Fixed-Negative Voltage Regulator
The series 79XX regulators are the three-terminal IC Negative-Voltage Regulators in the 79XX Series
regulators that provide a fixed negative output voltage. IC Part Output Voltage (V) Minimum Vi (V)
This series has the same features and characteristics as 7905 -5 -7.3
the series 78XX regulators except the pin numbers are 7906 -6 -8.4
different. 7908 -8 -10.5
7909 -9 -11.5
7912 -12 -14.6
7915 -15 -17.7
7918 -18 -20.8
7924 -24 -27.1
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5. IC Voltage Regulators Quiz 1.
Fixed Voltage Regulator
• Adjustable-Voltage Regulator
Voltage regulators are also available in circuit
configurations that allow to set the output voltage to a
desired regulated value.
Quiz
The LM317 is an example of an adjustable-voltage 1 Quiz Type OX Example Select
Number
regulator, can be operated over the range of voltage from
1.2 to 37 V. Question Determine the output voltage for the regulator
A. 10.2 V
B. 10.5 V
Example
C. 12.2 V
D. 12.5 V
Answer A
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Quiz 2. Summary
• Voltage regulators keep a constant dc output despite input voltage or load changes.
• The two basic categories of voltage regulators are linear and switching.
• The two types of linear voltage regulators are series and shunt.
Quiz • The three types of switching are step-up, step-down, and inverting.
1 Quiz Type OX Example Select
Number
• Switching regulators are more efficient than linear making them ideal for low voltage high
Question Calculate the output voltage and Zener current for RL=1kΩ current applications.
A. Vo=12 V; Iz≈36 mA • IC regulators are available with fixed positive or negative output voltages or variable negative
Example
B. Vo=11.3 V; Iz≈36 mA or positive output voltages.
C. Vo=11.3 V; Iz≈30 mA
D. Vo=12 V; Iz≈30 mA • Both linear and switching type regulators are available in IC form.
Answer B
• Current capacity of a voltage regulator can be increased with an external pass transistor.
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