Presented By:
ASHU CHAUDHARY
M.Sc. Physics (1st year)
Department of Physics,
Chaudhary Charan Singh University, Meerut
POWER SUPPLY

APPARATUS REQUIRED :
•Step down transformer
•Diodes
•Capacitor
•Coil
•Resistance box
•Milliammeter
•Voltmeter
To study the half wave rectifier,
full wave rectifier and
power supply.

POWER SUPPLY
TRANSFORMER
• Step up transformer
• Step down transformer
RECTIFIER
• Half Wave Rectifier
• Full Wave Rectifier
• Full Wave Bridge Type Rectifier
FILTER
• L-Section Filter
• 𝜋-Section Filter
• C-Section Filter
VOTAGE REGULATOR
• Zener diode

A power supply is an electronic device that supplies electric energy to
an electrical load.
• It produces a DC supply from the mains supply AC sine wave.
• It prevents any AC from appearing at the output.
• It will ensure that the output voltage is kept at a constant level.
Types of power supply :
• Regulated Power Supply
• Unregulated Power Supply
A regulated power supply basically consists of four parts:
Transformer Rectifier Filter
Voltage
Regulator
Regulated
DC Output
AC
Input

In a power supply firstly the transformer converts the input voltage to a
higher or lower AC voltage as required. Then a rectifier is used to convert
the transformer output voltage to a varying DC voltage, which in turn is
passed through a electronic filter to convert it to an unregulated DC voltage.
The filter removes most, but not all of the AC voltage variations. Hence, to
remove the remaining voltage variations a voltage regulator is used at the
end of the circuit which maintains a constant DC Voltage at the output.

A transformer is an electrical device which is used to change the AC
voltage i.e. higher voltage to lower voltage and vice versa.
A transformer which increases the a.c. voltage is known as step up
transformer.
A transformer which decreases the a.c voltage is known as step down
transformer.
PRINCIPLE: A transformer is based on the principle of mutual induction
i.e. whenever the amount of current in the first coil changes an emf is
induced in the second coil.
CONSTRUCTION: It consists of two coils wound over the same
laminated soft iron core. Primary coil has NP turns and secondary coil has
Ns turns.

WORKING: When alternating voltage VP is applied to primary. This cause
flux to change in primary. This changing flux is also linked with the secondary
coil through the core and an e.m.f. is induced in the secondary coil too.
If Φ is the flux linked with each turn of the either coil, then
Induced emf in primary, 𝑒𝑝 = −𝑁𝑝
𝑑Φ
𝑑𝑡
Induced emf in secondary, 𝑒𝑠 = −𝑁𝑠
𝑑Φ
𝑑𝑡
Dividing we get,
𝑒𝑠
𝑒𝑝
=
𝑁𝑠
𝑁𝑝
;
𝑁𝑠
𝑁𝑝
= 𝑟 (Transformation ratio)
Also the voltage VP across the primary is equal to the e.m.f. induced in the
primary and the voltage VS across the secondary is equal to the e.m.f. induced
in the secondary.
∴
𝑉𝑠
𝑉𝑝
=
𝑁𝑠
𝑁𝑝
• If Ns ˃ Np then Vs ˃ Vp (Step up transformer)
• If Ns ˂ Np then Vs ˂ Vp (Step down transformer)
(primary resistance is small,
no leakage of flux,
secondary current is small)

A rectifier is an electrical device which converts AC(which periodically
reverses direction) to pulsating DC(which flows in only one direction).
PRINCIPLE: A p-n junction diode can conduct current in only one direction
when forward biased and do not conduct current in opposite direction.
USES: In Power Supply and electronic circuits where DC supply is needed.
Rectifiers are mainly of three types:
• Half-Wave Rectifier
• Full-Wave Rectifier
• Bridge Rectifier
AC Input
(Output of
transformer)
RECTIFIER
Pulsating DC
output

It consists of an AC supply, a diode and the load resistance as shown in the
following fig.
The AC voltage across the secondary windings AB changes polarities after every
half cycle.
• When positive half cycle is applied, end A becomes positive and end B
negative. The p-n junction diode is forward biased and hence it conducts
current.
• When negative half cycle is applied, end A becomes negative and end B
positive. The p-n junction diode is reverse biased and hence does not conduct
current.
Therefore current flows through the load resistance RL only during positive half
cycle and hence current flows through load always in same direction.
A
B

RECTIFIER EFFICIENCY: The rectifier efficiency for the half-wave rectifier is
given by
η =
𝑃𝑑.𝑐.(𝑜𝑢𝑡𝑝𝑢𝑡 𝑝𝑜𝑤𝑒𝑟)×100
𝑃𝑎.𝑐.(𝑖𝑛𝑝𝑢𝑡 𝑝𝑜𝑤𝑒𝑟)
=
𝐼𝑑.𝑐.
2𝑅𝐿×100
𝐼𝑎.𝑐.
2(𝑅𝐿+𝑟𝑝)
(Since, Idc =
𝐼𝑂
𝜋
, Iac =
𝐼𝑂
2
)
=
40.5
1+
𝑟𝑝
𝑅𝐿
The efficiency will be maximum when rp is neglible compared to RL.
Max. rectifier efficiency= 40.6%
RIPPLE FACTOR: The ripple factor is defined as
𝑟 =
𝑟.𝑚.𝑠. 𝑣𝑎𝑙𝑢𝑒 𝑜𝑓 𝑎.𝑐. 𝑐𝑜𝑚𝑝𝑜𝑛𝑒𝑛𝑡
𝑣𝑎𝑙𝑢𝑒 𝑜𝑓 𝑑.𝑐.𝑐𝑜𝑚𝑝𝑜𝑛𝑒𝑛𝑡
=
𝐼𝑟𝑚𝑠
𝐼𝑑𝑐
2
− 1
=
𝜋2
4
− 1
=1.21
It is clear that AC component exceeds the DC component in the output of a
half wave rectifier.

It consists of an AC supply, two diodes and the load resistance as shown in the
following fig.
The AC voltage across the secondary windings AB changes polarities after
every half cycle.
• When positive half cycle is applied, end A becomes positive and B
negative. Diode D1 becomes forward biased and hence conducts while
diode D2 becomes reverse biased and hence does not conduct. Current
flows through D1 and load resistance as shown in fig.
• When negative half cycle is applied, end B becomes positive and A
negative. Diode D1 will not conduct while D2 current. Current flows through
D2 and load resistance as shown in fig.
Hence, the current flows through the load RL in same direction for both half
cycles of input a.c. voltage. Therefore, d.c. is obtained across the load RL.

RECTIFIER EFFICIENCY: The rectifier efficiency for the full-wave rectifier is given by
η =
𝑃𝑑.𝑐.(𝑜𝑢𝑡𝑝𝑢𝑡 𝑝𝑜𝑤𝑒𝑟)×100
𝑃𝑎.𝑐.(𝑖𝑛𝑝𝑢𝑡 𝑝𝑜𝑤𝑒𝑟)
=
𝐼𝑑.𝑐.
2
𝑅𝐿×100
𝐼𝑎.𝑐.
2
(𝑅𝐿+𝑟𝑝)
(Since, Idc =
2𝐼𝑂
𝜋
, Iac =
𝐼𝑂
2
)
=
81
1+
𝑟𝑝
𝑅𝐿
The efficiency will be maximum when rp is neglible compared to RL.
Max. rectifier efficiency= 81%
This is double the efficiency of a half-wave rectifier.
RIPPLE FACTOR: The ripple factor is defined as
𝑟 =
𝑟.𝑚.𝑠. 𝑣𝑎𝑙𝑢𝑒 𝑜𝑓 𝑎.𝑐. 𝑐𝑜𝑚𝑝𝑜𝑛𝑒𝑛𝑡
𝑣𝑎𝑙𝑢𝑒 𝑜𝑓 𝑑.𝑐.𝑐𝑜𝑚𝑝𝑜𝑛𝑒𝑛𝑡
=
𝐼𝑟𝑚𝑠
𝐼𝑑𝑐
2
− 1
=
𝜋2
8
− 1
=0.482
It is clear that DC component exceeds the AC component in the output of a full wave
rectifier.

It consists of four diodes D1, D2, D3 and D4 connected to form a bridge. The AC
supply to be rectified is applied to the diagonally opposite ends of the bridge.
Between other two ends, the load RL is connected.
The AC voltage across the secondary windings PQ changes polarities after every
half cycle.

• When positive half cycle is applied,
end P becomes positive and Q
negative. Diode D1 and D3 becomes
forward biased while diode D3 and D4
are reverse biased. Hence, only diode
D1 and D3 conduct. These two diodes
will be in series through the load RL as
shown in the fig.
The current flows from A to B through the
load RL as shown in fig.
• When negative half is applied, end P
becomes negative and Q positive. Diode
D2 and D4 becomes forward biased while
D1 and D3 are reverse biased. Hence,
only diode D2 and D4 conduct. These two
diodes will be in series through the load
RL as shown in the fig.
The current flows from A to B through the
load RL as shown in the fig.

RECTIFIER EFFICIENCY: The rectifier efficiency for the full-
wave bridge rectifier is 81%.
RIPPLE FACTOR: The ripple factor for a full-wave bridge
rectifier is 0.482.

A filter circuit is a device which removes the AC component of rectifier
output but allows the DC component to reach the load.
• A filter circuit should be installed between the rectifier and the load as
shown in fig.
The filters can be classified in 2 parts:
• Active filter
• Passive filter

FILTERS
Active Filters
High Pass Filter
Low Pass Filter
Band Pass Filter
Band Stop Filter
All Pass Filter
PassiveFilters
Capacitor Filter
Choke Input Filter
𝜋-Filter
ACTIVE FILTER:
An active filter is a type
of electronic filter that
uses active components
such as an amplifier.

PASSIVE FILTER:
A passive filter is built with passive components such as capacitors,
inductors and resistors.
Different types of filters are as follows:
CAPACITOR FILTER:
It consists of a capacitor C placed across the rectifier output in parallel
with load RL. The pulsating direct voltage of the rectifier is applied
across the capacitor. As the rectifier voltage increases , it changes the
capacitor and also supplies current to the load. At the end of quarter
cycle, the capacitor is charged to the peak value Vm of the rectifier
voltage.
A
B
C
D
E
F

Now the rectifier voltage starts to decrease. As this occurs ,the
capacitor discharges through the load and voltage across it.
The voltage across load will decrease only slightly because
immediately the next voltage peak comes and charges the
capacitor. This process is repeated again and again and the
output voltage waveform becomes ABCDEF. This may be seen
that very little ripple is left in the output.
The capacitor filter circuit is extremely popular because of its
low cost, small size and little weight.

It consists of a choke input filter L Connected in a series with a rectifier
output and a filter capacitor C across the load. Only a single filter
section is shown in fig.
1
2
3

• The pulsating output of the rectifier is applied across terminals 1 and
2 of the filter circuit. As discussed before, the pulsating output of the
rectifier contains a.c. and d.c. components. The choke offers high
opposition to the passage of a.c. components but negligible
opposition to the d.c. components. The result is that most of the a.c.
component appears across the choke while whole of d.c. component
passes through the choke on its way to load. This result in the
reduced pulsations at the terminal
• At terminal 3, the rectifier output contains d.c. components and the
remaining part of a.c. components which has manages to pass
through the choke. Now, the low reactance of filter capacitor by-
passes the a.c. component but prevent the d.c. component to flow
through it. Therefore, only d.c. component reaches the load. In this
way, the filter circuit has filtered out the a.c. component from the
rectifier output, allowing d.c. components to reach the load.

•It consists of a filter capacitor C1 connected across the rectifier
output, a choke L in series and another filter capacitor C2
connected across the load.
• The pulsating output from the rectifier is applied across the
input terminals 1 and 2 of the filter. The filtering action of the
three components C1 , L and C2 of this filter is describe below-
1
2

• The filter capacitor C1 offers low reactance to a.c. components of
rectifier output while it offers infinite reactance to the d.c.
components. Therefore, capacitor C1 bypasses an appreciable
amount of d.c. component while d.c. component continues its
journey to the choke L.
• The choke L offers high reactance to the a.c. component but it offers
almost zero reactance to the d.c. component. Therefore, it allows
the d.c. components to flow through it, while the unbypassed a.c.
component is blocked.
• The filter capacitor C bypasses the a.c. component while the choke
has failed to block. Therefore, only d.c. component appears across
the load and that is what we desire.

Zener diode
A properly doped crystal diode which has a sharp breakdown voltage is
known as a zener diode.
The following points may be noted about the zener diode:
• A zener diode is like an ordinary diode except that it is properly doped so
as to have a sharp breakdown voltage.
• A zener diode is always reverse connected i.e. it is always reverse
biased.
• A zener diode has sharp breakdown voltage called zener voltage.
• When forward biased, its characteristics are just those of ordinary diode.
• It may be seen that it is just like an ordinary diode except that the bar is
turned into z-shape.

• Zener diode has two states:
i) On state
ii) Off state
• Zener diode as voltage stabliser:
A zener diode is used as a voltage regulator to provide a constant
voltage from a source whose voltage may vary over sufficient range. The zener
diode of zener voltage Vz is reverse connected across the load RL across which
constant output is desired. The series resistance R absorbs the output voltage
fluctuations so as to maintain constants voltage across the load.
On state
Off state

• Suppose the input voltage increases. Since the zener is in breakdown
region, the zener diode is equivalent to a battery. It is clear that output
voltage remains constant. The axcess voltage is dropped across the
series resistance R. This will cause an increase in the value of total
current. The zener will conduct the increase of current while the load
current remains constant. Hence the output voltage remains constant
irrespective of the changes in the input voltage.