Power Supply Basics: Unregulated & Regulated DC

In this in-depth presentation, Dr. G.S. Virdi, Former Chief Scientist at CSIR-Central Electronics Engineering Research Institute (Pilani, India), walks you through the complete lifecycle of a power supply—from raw AC or DC input to a clean, regulated output.

What You’ll Learn:

Power Supply Architecture: Understand the end-to-end block diagram, including transformers, rectifiers, filters, and regulation stages.

Unregulated DC Supplies: Explore how transformer-rectifier-filter combinations yield basic DC rails and the limitations you need to account for.

Regulated DC Supplies: Dive into regulation techniques, with a focus on switching regulators and voltage-inverter topologies. Learn how pulse-width oscillators, diodes, and capacitors work together to deliver stable voltages.

Efficiency & Applications: Discover why switching regulators can achieve up to 90% efficiency and where to apply each type of supply in real-world electronic circuits.

Who Should Watch:
Ideal for electronics students, design engineers, and hobbyists seeking a clear, practical guide to designing reliable power supplies for any DC-powered system.

1. Unregulated and Regulated
Power Supplies

Dr. G.S. Virdi
Former Chief Scientist
CSIR-Central Electronics Engineering Research Institute -
Pilani, India

2. POWER SUPPLY SYSTEM
The power supply system has an input which is either ac or dc
and, for our discussions, a dc output. This dc output is used to
power some form of electronic circuitry.
The input could be the 240V 50Hz mains supply or a dc supply
from a car battery or even a power rail within an existing circuit.

3. POWER SUPPLY SYSTEM
 Breaking this system down , we will first look at the ac
voltage change and ac to dc conversion.
 Then, we will look at some simple dc regulation circuitry

6. Stages of Power Supply
Power supplyPower supply: a group of circuits that convert the
standard ac voltage (120 V, 60 Hz) provided by the wall
outlet to constant dc voltage
TransformerTransformer : a device that step up or step down the ac
voltage provided by the wall outlet to a desired amplitude
through the action of a magnetic field

7. Stages of Power Supply
RectifierRectifier: a diode circuits that converts the ac input
voltage to a pulsating dc voltage
The pulsating dc voltage is only suitable to be used as a
battery charger, but not good enough to be used as a dc
power supply in a radio, stereo system, computer and so
on.

8. Stages of Power Supply
There are two basic types of rectifier circuits:
Half-wave rectifier
Full-wave rectifier - Center-tapped & Bridge full-wave rectifier
In summary, a full-wave rectified signal has less ripple
than a half-wave rectified signal and is thus better to apply
to a filter.

9. Stages of Power Supply
FilterFilter: a circuit used to reduce the fluctuation in the
rectified output voltage or ripple. This provides a steadier
dc voltage.
RegulatorRegulator: a circuit used to produces a constant dc
output voltage by reducing the ripple to negligible amount.
One part of power supply.

11. Types of Regulator
Fundamental classes of voltage regulators 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.
Types of Regulator

12. Types of Regulators
Control element in series with load
between input and output.
Output sample circuit senses a
change in output voltage.
Error detector compares sample voltage with
reference voltage → causes control element to
compensate in order to maintain
constant out put voltage.
Regulated DC Power Supply Types of Regulator

13. Types of Regulators
The resistor R
1 and R
2 sense a change in the output
voltage and provide a feedback voltage.
The error detector compares the feedback voltage with a
Zener diode reference voltage.
The resulting difference voltage causes the transistor Q
1
controls the conduction to compensate the variation of
the output voltage.
The output voltage will be maintained
at a constant value of:
Zo
V
R
R
V









2
1
1
Op-Amp Series Regulator

14. Types of Regulators
The transistor Q
1 is the series control element.
• Zener diode provides the reference voltage.
Transistor Series Regulator

15. Regulated Power Supply
Transistor Series Regulator
Since Q
1
is an npn transistor, V
o
is found as:
•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 V
o causes
V
BE to decrease.
 The decrease in V
BE reduces conduction through the pass-
transistor, so load current decreases.
 This offsets the increase in load resistance, and a relatively
constant load voltage is maintained
oZBE VVV 

16. Regulated Power Supply
Determine the output voltage for the regulator
below.
(Solution: 10.2 V)
Example

17. Regulated Power Supply
Calculate the output voltage and Zener current for
R
L=1kΩ.
(Solution: V
o=11.3 V; I
z≈36 mA)
Example

18. Regulated Power Supply
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.
Shunt Regulator Circuit

19. Regulated Power Supply
Op-Amp Shunt Regulator

20. Regulated Power Supply
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 R
1 and R
2.
A feedback voltage obtained from voltage divider R
1 and R
2
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 current through resistor R
S is thus controlled to drop a
voltage across R
S
so that the output voltage is maintained.
Op-Amp Shunt Regulator

21. Regulated Power Supply
The control element is a transistor, in parallel with the load. While,
the resistor, R
S
, is in series with the load.
The operation of the transistor shunt regulator is similarsimilar to that of
the transistor series regulator, except that regulation is achieved
by controlling the current through the parallel transistor
Transistor Shunt
Regulator

22. Regulated Power Supply
The switching regulator is a
type of regulator circuit which
its efficient transfer of power to
the load is greater than series
and shunt regulators because
the transistor is not always
conducting.
The switching regulator passes
voltage to the load in pulses,
which then filtered to provide a
smooth dc voltage.
Switching Regulator

23. Regulated Power Supply
Step-Down Configuration
With the step-down (output is less than the input)
configuration the control element Q
1 is pulsed on and
off at variable rate based on the load current.
The pulsations are filtered
out by the LC filter.
Switching Regulator

24. Regulated Power Supply
Step-up configuration
The difference is in the placement of the inductor and the
fact that Q
1
is shunt configured.
During the time when Q
1 is off
the V
L adds to V
C stepping
the voltage up by some
amount.
Switching Regulator

25. Regulated Power Supply
Voltage-inverter configuration
output voltage is of opposite
polarity of the input.
This is achieved by V
L
forward-
biasing reverse-biased diode
during the off times producing
current and charging the capacitor for voltage production
during the off times.
With switching regulators 90% efficiencies can be achieved.
Switching Regulator

26. Regulated Power Supply
Regulation circuits in integrated circuit form are widely used.
Their operation is no different but they are treated as a
single device with associated components.
These are generally three terminal devices that provide a
positive or negative output.
Some types have variable voltage outputs.
A typical 7800 series voltage regulator is used for positive
voltages.
The 7900 series are negative voltage regulators.
These voltage regulators when used with heat sinks can
safely produce current values of 1A and greater.
The capacitors act as line filtration.
IC Voltage Regulators

27. Regulated Power Supply
Several types of both linear (series and shunt) and
switching regulators are available in integrated circuit (IC)
form.
Single IC regulators contain the circuitry for:
(1)reference source
(2)comparator amplifier
(3)control device
(4)overload protection
Generally, the linear regulators are three-terminal devices
that provides either positive or negative output voltages that
can be either fixed or adjustable.
IC Voltage Regulators

28. Regulated Power Supply
The fixed voltage regulator has an unregulated dc input
voltage V
i applied to one input terminal, a regulated output
dc voltage V
o
from a second terminal, and the third terminal
connected to ground.
Fixed-Positive Voltage RegulatorFixed-Positive Voltage Regulator
The series 78XX regulators are the three-terminal devices
that provide a fixed positive output voltage.
Fixed Voltage Regulator

29. Regulated Power Supply
An unregulated input voltage
V
i is filtered by a capacitor C
1
and connected to the IC’s IN
terminal.
The IC’s OUT terminal
provides a regulated +12 V,
which is filtered by capacitor
C
2
.
The third IC terminal is
connected to ground
(GND)
Fixed Voltage Regulator

30. Regulated Power Supply
IC PartIC Part Output Voltage Output Voltage
(V)(V)
Minimum VMinimum V
ii (V) (V)

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
Positive-Voltage Regulators in the 78XX Series
Fixed Voltage Regulator

31. Regulated Power Supply
Fixed-Negative Voltage RegulatorFixed-Negative Voltage Regulator
The series 79XX regulators are the three-terminal IC
regulators that provide a fixed negative output voltage.
This series has the same features and characteristics as
the series 78XX regulators except the pin numbers are
different.
Fixed Voltage Regulator

32. Regulated Power Supply
IC PartIC Part Output Voltage Output Voltage
(V)(V)
Minimum VMinimum V
ii (V) (V)

7905 -5 -7.3
7906 -6 -8.4
7908 -8 -10.5
7909 -9 -11.5
7912 -12 -14.6
7915 -15 -17.7
7918 -18 -20.8
7924 -24 -27.1
Negative-Voltage Regulators in the 79XX Series
Fixed Voltage Regulator

33. Regulated DC Power Supply
using transistors.
A low ripple regulated DC power supply designed based
on transistors is shown here. Such transistor voltage
regulators are suitable for application where high output
current is required. Conventional integrated series
regulators like 7805 can only deliver up to 1A.
 Additional series pass transistors have to be added to the
7805 based regulator circuit for improving their current
capacity.

34. Description.
on transistors. Transistor Q1 (2N 3054) and Q2 (2N 3055) fThe
circuit shown below is a basic series voltage regulator based orm a
darlington pair. Resistor R1 provides the base current for Q1 and also
keeps the zener diode D2 in the active region. The overall working of
the circuit can be demonstrated by explaining two situations.
When the input voltage (output of the rectifier section) increases, the
output voltage of the regulator (Vout) also increases. This increase in
Vout decreases the base emitter voltage of Q2 because the zener
diode D2 is operating in the breakdown region and the voltage across
it is unchangeable. This decrease in V
BE increases the collector
emitter resistance
  of Q2 and so the output voltage (Vout) gets
reduced accordingly.
Regulated DC Power Supply
using transistors.

35. Regulated DC Power Supply
using transistors.
When the output load increases, the output voltage
(Vout) gets reduced. This decrease of output voltage
(Vout) makes V
BE
of Q2 to decrease. This reduces the
collector emitter resistance of Q2 and so the output
voltage gets increased accordingly

36. Regulated DC Power Supply using
transistors
Notes.
If 5A bridge is not available, then make one using 6A6 diodes.
Transistor Q2 requires a heat sink.
An optional 5A fuse can be added in series to the output.
Breakdown voltage of the zener diode D2 must be chosen according to the
output voltage you need
Regulated DC Power Supply using
transistors.
Regulated DC Power Supply using
transistors.

37. Comparison of power supplies

, linear (unregulated) supplies
can handle large surge current
loads. This is because linear
supplies typically contain large
output capacitors to handle those
surges well.
Voltage regulation: switchers are highly
regulated supplies. They will maintain
fixed voltage until they re ach maximum
load and then will “crowbar” to zero volts
to protect to the eoutput stages.
Linear supplies will slowly drop in output voltage while
supplying m ore and more current

38. Comparison of power supplies
Their atre the most fundamental difference between
switchers and unregulated supplies.
Even though a switcher cannot handle the higher current surges,
if it can output as much current as you would expect for a given
servo application, then they will actually help the servo accelerate
much faster because system voltage will be maintained at
maximum level.
However, if your servo application requires surge currents in
excess of 50 Amps or more, the switchers may not be cost
effective. Getting 50 amps from a Moog Animatics 20 Amp supply
is easy, Getting 50 amp from Moog Animatics switchers would
require placing multiples units in parallel, so it may not be cost
effective to do so
.

39. Comparison of power supplies

40. 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.
The three types of switching are step-up, step-down,
and inverting.

41. Summary
Switching regulators are more efficient than linear making
them ideal for low voltage high current applications.
IC regulators are available with fixed positive or negative
output voltages or variable negative or positive output
voltages.
Both linear and switching type regulators are available in IC
form.
Current capacity of a voltage regulator can be increased
with an external pass transistor.

42. Thank You
G.S.VIRDI