The document discusses different types of power supplies including regulated, unregulated, offline UPS, online UPS, and switch mode power supplies (SMPS). It explains that regulated power supplies use voltage regulating devices like zener diodes or transistors to maintain a constant output voltage regardless of input or load variations. Unregulated supplies do not have this regulation and output voltage fluctuates with input/load. It also compares offline and online UPS configurations and their advantages. Finally, it provides a brief overview of how SMPS work and their benefits over linear power supplies.

1. REGULATED POWER SUPPLY
Dahiya Hardik

2. Regulated d.c. power supply
• A d.c. power for electronic circuits obtained from commercial a.c.
lines by using rectifier-filter system is called a d.c. power supply.
• In many electronic applications, it is desired that d.c. voltage should
remain constant irrespective of changes in a.c. mains or load.
• Under such situations, voltage regulating devices are used with
ordinary power supply. This constitutes regulated d.c. power supply
and keeps the d.c. voltage at fairly constant value.

3. Ordinary D.C. Power Supply
An ordinary or unregulated d.c. power supply contains a rectifier
and a filter circuit as shown in Fig. The output from the rectifier is
pulsating d.c. These pulsations are due to the presence of a.c.
component in the rectifier output. The filter circuit removes the
a.c. component so that steady d.c. voltage is obtained across the

4. Ordinary D.C. Power Supply
Limitations. An ordinary d.c. power supply has the following
drawbacks :
1) The d.c. output voltage changes directly with input a.c. voltage. For
instance, a 5% increase in input a.c. voltage results in approximately
5% increase in d.c. output voltage.
2) The d.c. output voltage decreases as the load current increases.

5. Regulated Power Supply
A d.c. power supply which maintains the output voltage constant
irrespective of a.c. mains fluctuations or load variations is known as
regulated d.c. power supply

6. Regulated Power Supply

7. Regulated Power Supply
Fig. shows the complete circuit of a regulated power supply using zener
diode as a voltage regulating device. As you can see, the regulated power
supply is a combination of three circuits viz.,
(i) bridge rectifier (ii) a capacitor filter C and (iii) zener voltage regulator.
The bridge rectifier converts the transformer secondary a.c. voltage
(point P) into pulsating voltage (point Q).
The pulsating d.c. voltage is applied to the capacitor filter. This filter
reduces the pulsations in the rectifierd.c. output voltage (point R).

8. Regulated Power Supply
Finally, the zener voltage regulator performs two functions. Firstly, it
reduces the variations in the filtered output voltage.
Secondly, it keeps the output voltage (Vout) nearly constant whether
the load current changes or there is change in input a.c. voltage. Fig.
shows the waveforms at various stages of regulated power supply.
When voltage regulating device is added to this ordinary power
supply, it turns into a regulated power supply.

9. Types of Voltage Regulators
• A device which maintains the output voltage of an ordinary power
supply constant irrespective of load variations or changes in input a.c.
voltage is known as a voltage regulator. A voltage regulator generally
employs electronic devices to achieve this objective.
• There are basic two types of voltage regulators viz., (i) series voltage
regulator (ii) shunt voltage regulator.

10. Types of Voltage Regulators
(i) series voltage regulator (ii) shunt voltage regulator

11. Zener Diode as a Voltage Regulator
When the zener diode is operated in the breakdown or zener
region, the voltage across it is substantially constant for a large
change of current through it.
This characteristic permits it to be used as a voltage regulator.

12. Transistor Series Voltage Regulator
Figure shows a simple series voltage regulator using a transistor and
zener diode. The circuit is called a series voltage regulator because the
load current passes through the series transistor Q1 as shown in Fig.
The unregulated d.c. supply is fed to the input terminals and the
regulated output is obtained across the load. The zener diode provides
the reference voltage.

13. Transistor Series Voltage Regulator
Operation: The base voltage of transistor Q1 is held to a relatively
constant voltage across the Zener diode. For example, if 8V zener (i.e., VZ
= 8V) is used, the base voltage of Q1 will remain approximately 8V.
Referring to Fig., Vout = VZ − VBE
(i) If the output voltage decreases, the increased base-emitter voltage
causes transistor Q1 to conduct more, thereby raising the output voltage.
As a result, the output voltage is maintained at a constant level.
(ii) If the output voltage increases, the decreased base-emitter voltage
causes transistor Q1 to conduct less, thereby reducing the output voltage.
Consequently, the output voltage is maintained at a constant level.

14. Transistor Series Voltage Regulator
Limitations:
(i) Although the changes in zener current are much reduced, yet the
output is not absolutely constant. It is because both VBE and VZ
decrease with the increase in room temperature.
(ii) The output voltage cannot be changed easily as no such means is
provided.

15. Transistor Shunt Voltage Regulator

16. Transistor Shunt Voltage Regulator
• A shunt voltage regulator provides regulation by shunting current away
from the load to regulate the output voltage. Fig. shows the circuit of
shunt voltage regulator.
• The voltage drop across series resistance depends upon the current
supplied to the load RL. The output voltage is equal to the sum of zener
voltage (VZ) and transistor base-emitter voltage (VBE)
i.e., Vout = VZ + VBE
• If the load resistance decreases, the current through base of transistor
decreases. As a result, less collector current is shunted. Therefore, the
load current becomes larger, thereby maintaining the regulated voltage
across the load. Reverse happens should the load resistance increase.

17. Transistor Shunt Voltage Regulator
Drawbacks: A shunt voltage regulator has the following drawbacks :
(i) A large portion of the total current through RS flows through
transistor rather than to the load.
(ii) There is considerable power loss in RS.
(iii) There are problems of overvoltage protection in this circuit.
For these reasons, a series voltage regulator is preferred over the shunt
voltage regulator.

18. Voltage Stabilizer
A Voltage Stabilizer is an electrical device which is used to provide a
constant voltage output to a load at its output terminals irrespective of
any change/ fluctuation in the input i.e. incoming supply.
The basic purpose of a Voltage Stabilizer is to protect the electrical/
electronic gadgets (for example – Air conditioning Unit, Refrigerator, TV,
etc.) from the probable damage due to Voltage Surge/ fluctuations,
Over Voltage and Under Voltage conditions.

19. How a Voltage Stabilizer Works?
The basic work of a Voltage Stabilizer is to carry out two necessary functions
i.e. Buck and Boost function. Buck and Boost function is nothing but the
regulation of a constant voltage from over voltage and under voltage
circumstances.

20. Advantages of Voltage Stabilizers
Advantages:
Negligible output waveform distortion
Not Frequency dependent
Will attenuate voltage spikes if required

21. Uninterruptible Power Supply (UPS)
An Uninterruptible Power Supply (UPS) is defined as a piece of
electrical equipment which can be used as an immediate power source
to the connected load when there is any failure in the main input
power source.
When there is any failure in main power source, the UPS will supply the
power for a short time. This is the prime role of UPS. In addition to
that, it can also able to correct some general power problems related
to utility services in varying degrees. The problems that can be
corrected are voltage spike (Sustained over voltage), Noise, Quick
reduction in input voltage, Harmonic distortion and the instability of
frequency in mains.

22. Off-line UPS

23. Off-line UPS
• In this type of UPS, the system always remains on battery, whether
mains ac is present or not. When mains ac is present, it provides power
to DC supply of inverter section as well as charges the battery
simultaneously.
• When mains ac is not present, it will run the connected load till the
battery has a recommended dischargeable level. In online UPS, the
batteries are always connected to the inverter, so that no power
transfer switches are necessary.
• When power loss occurs, the rectifier simply drops out of the circuit
and the batteries keep the power steady and unchanged.

24. Off-line UPS
Advantages of Offline UPS:
• Offline UPS has high efficiencies, since charger is not continuously on.
• The power handling capacity of charger is reduced.
• Offline UPS are not very costly.
• Internal control is simpler in offline Uninterruptible Power Supply.

25. Off-line UPS
Disadvantage of Offline UPS:
• Since offline UPS provides mains supply when it is present, the output
contains voltage spikes, brownouts, blackouts.
• There is finite transfer time from mains to inverter when mains supply
fails.
• Output of offline Uninterruptible Power Supply is not perfectly
reliable.
Applications of Offline UPS:
• Computers, printers, scanners etc use offline UPS.
• Emergency power supplies, EPABX.

26. Online UPS

27. Online UPS
• The offline/standby UPS (SPS) offers only the most basic features,
providing surge protection and battery backup.
• When mains supply is not available ,then inverter is turned on.
• Inverter takes power from the battery .the load is connected to
inverter output through UPS static switch. The power flow diagram is
shown.
• The mains statics switch is always on and keeps load connected to the
mains. The mains static switch turned off when mains is not available.
• When the charger feeds power only to the battery .hence handling
capacity is reduced.

28. Online UPS
Advantages of Online UPS:
• It provides isolation between main supply and load.
• Since inverter is always ON, the quality of load voltage is free from
distortion
• All the disturbances of supply such as blackout, brownouts, spikes etc
are absent in the output.
• Voltage regulation is better
• Transfer time is practically zero since inverter is always ON.

29. Online UPS
Disadvantages of Online UPS:
• Overall efficiency of UPS is reduced since inverter is always ON.
• The wattage of the rectifier is increased since it has to supply power
to inverter as well as charge battery
• Online UPS is costlier than other Uninterruptible Power Supply
Systems.
• Applications of Online UPS:
• Induction motor drives and similar other motor control applications.
• Intensive care units, medical equipments.

30. SMPS (Switch Mode Power Supply)
An electrical power supply that incorporates a switching regulator to
convert electrical power efficiently.
It transfers power from a source, to a load, while converting voltage
and current characteristics.
Voltage regulation is achieved by varying the ratio of onto-off time.

31. SMPS (Switch Mode Power Supply)

32. SMPS (Switch Mode Power Supply)
1. Input rectifier stage:
It is used to convert an ac input to dc. A SMPS with dc input does not
require this stage. The rectifier produces unregulated dc which is then
passed through the filter circuit.
2. Inverter stage:
The inverter stage converts DC, whether directly from the input or from
the rectifier stage described above, to AC by running it through a
power oscillator, whose output transformer is very small with few
windings at a frequency of tens or hundreds of kilohertz.

33. SMPS (Switch Mode Power Supply)
3. Output transformer:
If the output required is to be isolated from input, the inverted AC is
used to draw the primary windings of a high frequency transformer.
This converts the voltage up or down to the required output level on
it’s secondary winding.
4. Output rectifier:
If the dc output is required, the ac output from the transformer is
rectified.
5. Regulation:
Feedback circuit monitors the output voltage and compares it with the
reference voltage.

34. SMPS (Switch Mode Power Supply)
Advantages of SMPS:
1. Lower weight
2. Smaller size
3. Higher efficiency
4. Lower power dissipation
5. Wide ac input voltage range
6. Reduced costs

35. SMPS (Switch Mode Power Supply)
Disadvantages of SMPS:
1. Complexity of the circuit
Applications of SMPS:
1. Machine tool industries
2. Security Systems • (Closed circuit cameras)
3. Support supplies with PLC’s
4. Personal Computers
5. Mobile Phone chargers