This document discusses the components and operation of a linear DC power supply. It begins by explaining the need for DC power in electronic circuits and how power supplies convert alternating current (AC) from the wall outlet to the direct current (DC) required. The main components of a power supply are then introduced as the transformer, rectifier, filter and regulator. The transformer steps down the high voltage AC, the rectifier converts it to pulsating DC, the filter smoothes the output, and the regulator maintains a constant voltage. Different types of rectifiers like half-wave, full-wave and bridge rectifiers are also defined. Finally, the document discusses filters which further smooth the DC output voltage.

1. LINEAR DC
POWER SUPPLY
1/50

2. 2/50
i. All electronic circuits need power source to
function.
ii. Power Supply Unit is a device used to
convert, regulate and transmit the required
power to the circuit to be operated.
iii. Electronic circuits made up of
semiconductors need specific value of
Direct Current (DC) voltage.
iv. Batteries are common DC voltage source
for electronic equipment especially
portables like cell phones and iPods.
v. Most non-portable equipment uses power
supplies that operate from the AC power
line but produce one or more DC outputs.
Click to “Play” the Video

3. 3/50
POWER SUPPLY CHARACTERISTICS
i. The input is 240volt 50Hz Alternative Current (AC).
ii. A power supply unit converts the AC into DC and
provides one or more DC output voltages.
iii. Some modern electronic circuits need two or more
different voltages.
iv. Commonly required DC voltages are 48, 24, 15, 12, 9, 5,
3.3, 2.5, 1.8, 1.5, 1.2 and 1 volts.
v. A good example of a modern power supply is the one
inside a PC that furnishes 12, 5, 3.3 and 1.2 volts.

4. 4/50

5. 5/50
The operation of a DC power supply circuit
The importance of DC power supply units in electronic appliances
i. Power supply provide one or more fixed voltages with sufficient current to the
operating circuit.
ii. Electronic devices such as transistor radio, television and video cd players
operate fully or partly on DC power supply in the range of 0 to 24V.
iii. The successful operation of the device depends on the proper function of the
DC power supply. The power supply tries to provide a smooth, constant DC
voltage, as required by an electronic device.
iv. Major electronic appliances have built-in electronic circuits that take power
from a wall socket and convert it to the form and voltages required by the
other internal circuits of the appliance.

6. 6/50
Block Diagram of DC Power Supply
To load
VDC
t
Regulated smooth
D.C Supply
Regulator
A.C. Mains 230V,
50Hz A.C. voltage
VAC
t
Rectifier Pulsating type
VDC
t
Filter
Unregulated
VDC
t
Voltage Divider
Transformer VAC
t
Low A.C. voltage To step down high voltage AC to
low voltage AC
To step down high voltage AC to
low voltage AC
To convert AC to DC, but the
DC output is varying
To convert AC to DC, but the
DC output is varying
To smoothen the DC from
varying greatly to a small ripple
To smoothen the DC from
varying greatly to a small ripple
To eliminate ripple by setting DC
output to a fixed voltage
To eliminate ripple by setting DC
output to a fixed voltage
To divide DC voltage which are
different needed value circuit
To divide DC voltage which are
different needed value circuit
The function for each
block DC Power Supply
Click on the
Block to
display its
function

7. 7/50
Transformer
TransformerTransformer
Symbol

8. Input: High Voltage AC
Output: Low Voltage AC
Transformer
i. A transformer is commonly used to step
down the input AC voltage to a lower
level.
ii. For example, a transformer with a turns
ratio of 10 to 1(10:1) would convert the
240 volt 50 Hz input sine wave into a 24
volt sine wave.
iii. The low voltage AC output is suitable
for lamps, heaters and special AC
motors.
iv. It is not suitable for electronic circuits
unless they include a rectifier and a
smoothing capacitor.
Symbol Transformer
8/50

9. 9/50
Transformer + Rectifier
TransformerTransformer RectifierRectifier

10. 10/50
Transformer + Rectifier
i. There are several forms of rectifiers
but all are made up of diodes.
ii. The rectifier converts the AC sine
wave into a pulsating DC wave.
Input: Low Voltage AC
Output: Varying DC
Diodes

11. Input: Low Voltage AC
Output: Varying DC
Input: Low Voltage AC
Output: Varying DC
11/50
Transformer + Rectifier
i. A single diodes rectifier
produces half-wave varying DC.
ii. Rectifier with two or four diodes
will produce full-wave varying
DC.

12. 12/50
Transformer + Rectifier + Filter
TransformerTransformer RectifierRectifier FilterFilter

13. 13/50
Transformer + Rectifier + Filter
i. Rectifier produces a pulsating DC, unlike a constant steady value that is
produced by a battery.
Output: Smooth DCOutput: Varying DC
Pulsating (varying) DC outputPulsating (varying) DC output Steady value DC outputSteady value DC output

14. Input: Varying DC
Output: Smooth DC
14/50
Transformer + Rectifier + Filter
ii. A filter is then used to remove the pulsations and create a constant
output.
Output: Varying DC
Pulsating (varying) DC outputPulsating (varying) DC output Constant / Smooth DC outputConstant / Smooth DC output

15. 15/50
Transformer + Rectifier + Filter
iii. The most common filter is a large capacitor.
iv. The filtered DC output have small ripples. It is suitable for most electronic
circuits.
Input: Varying DC
Output: Smooth DC

16. RectifierRectifier
16/50
Transformer + Rectifier + Filter+ Regulator
TransformerTransformer FilterFilter RegulatorRegulator

17. Input: Smooth DC
Output: Regurated DC
17/50
Transformer + Rectifier + Filter+ Regulator
i. The regulator is a component that helps to maintain a fixed or
constant output voltage.
RegulatorRegulator

18. Input: Smooth DC
Output: Regurated DC
18/50
Transformer + Rectifier + Filter+ Regulator
ii. Changes in the load or the AC line voltage will cause the output
voltage to vary.
Input: Smooth DC
Output: Regurated DC

19. 19/50
Transformer + Rectifier + Filter+ Regulator
iii. Most electronic circuits cannot withstand the variations since they are
designed to work properly with a fixed voltage.
iv. The regulator fixes the output voltage to the desired level and
maintains that value despite any output or input variations.
v. The regulated DC output is very smooth with no ripples. It is suitable
for all electronic circuits.
Input: Smooth DC
Output: Regurated DC
DC output is
very smooth
with no ripple

20. 20/50
Types of Rectifier
RectifierRectifier
Half-wave
rectifier
Half-wave
rectifier
Full-wave
rectifier
Full-wave
rectifier
Bridge
rectifier
Bridge
rectifier

21. 21/50
Types of Rectifier
RectifierRectifier
Full-wave
rectifier
Full-wave
rectifier
Bridge
rectifier
Bridge
rectifier
Half-wave
rectifier
Half-wave
rectifier

22. 22/50
HALF-WAVE RECTIFIER
Positive Cycle Operation
During the POSITIVE cycle of the input signal:
i. diode is forward biased.
ii. diode act as a CLOSED switch
iii. current flows through diode
The voltage drop at RL is the same as input signal (at positive cycle magnitude)
The output voltage keeps the shape of the input voltage

23. 23/50
HALF-WAVE RECTIFIER
Negative cycle operation
During the NEGATIVE cycle of input signal:
i. the D diode is reverse biased
ii. Diode act as OPEN switch
iii. no current flow through diode
The voltage drop at RL is zero.
VL = 0 V
I= 0 A
NEGATIVE Cycle

24. 24/50
HALF-WAVE RECTIFIER
Calculation of output voltage
Output voltage for the half-wave rectifier circuit is for the positive cycle only.
Example : Vin = 20 V
Vout = Vin – 0.7V(silicon diode)
= 20V – 0.7V = 19.3V
The output signal frequency is same frequency as input.
Vout
Vin = 20 V
Vin = 20 V
Vout = 19.3 V
0.7V(silicon diode)

25. 25/50
Types of Rectifier
RectifierRectifier
Half-wave
rectifier
Half-wave
rectifier
Bridge
rectifier
Bridge
rectifier
Full-wave
rectifier
Full-wave
rectifier

26. FULL-WAVE RECTIFIER
i. A full-wave rectifier is exactly the same as the half-wave rectifier
ii. It use 2 diodes, D1 and D2
iii. It allows unidirectional current flow through the load during the entire
sinusoidal cycle (as opposed to only half the cycle in the half-wave)
Full-wave Rectifier
Output Signal
AC input Signal
26/50

27. FULL-WAVE RECTIFIER
Positive cycle operation
During the positive cycle:
i. the M terminal becomes positive, G becomes zero (earth) & N becomes
negative.
ii. Diode D1 is forward biased while diode D2 is reverse biased
Thus, the current will flow along M,D1,A, RL,G.
A
B
G
27/50

28. FULL-WAVE RECTIFIER
Negative cycle operation
During the NEGATIVE cycle:
i. M terminal becomes negative, G becomes zero (earth) and N becomes
positive.
ii. D2 is forward biased, while D1 is reverse biased
iii. Thus , the current will flow along N, D2, C, B, RL, G.
OUTPUT wave is always POSITIVE because the current that flows through RL
(load) is same direction for both the positive and negative cycle.
c
28/50

29. FULL-WAVE RECTIFIER
Output signal negative cycle
Output Voltage is formed at both cycle.
Frequency of output is twice of the input frequency.
Output Voltage
29/50

30. 30/50
Types of Rectifier
RectifierRectifier
Half-wave
rectifier
Half-wave
rectifier
Full-wave
rectifier
Full-wave
rectifier
Bridge
rectifier
Bridge
rectifier

31. BRIDGE RECTIFIER
Positive Cycle Operation
Bridge rectifier use four diodes, D1, D2, D3 and D4
During the POSITIVE input cycle :
i. D1 and D2 diodes are forward biased
ii. D3 and D4 are reverse biased
The current will flow along G, D, D2, C, N, M, A, D1,B, RL,G.
31/50

32. BRIDGE RECTIFIER
Negative cycle operation
During the NEGATIVE input cycle:
i. D3 and D4 diodes are forward biased
ii. D1and D2 are reverse biased.
The current will flow along G, D, D3, A, M, N, C, D4,B, RL,G.
32/50

33. BRIDGE RECTIFIER
Output voltage
33/50
Notes: PIV is Peak Inverse Voltage.

35. Comparison between two diodes rectifier and four diodes rectifier

36. FilterFilter
( Vr )p-p
Va.t.
Va.t.
V
t
V
t
Figure 5.5.2 : Pure DC voltage Figure 5.5.3:Ripple DC voltage
 The output of rectifier circuit is the pulsating DC voltage .
 The resulting pulsating dc signal smooth the output voltage, we used filter circuit
 The main function of filter is to convert pulsating DC voltage to the ripple DC
voltage or as good as pure DC voltage(Figure 1) and free from pulse which is
similar to the value obtain by battery.
 However, not all the filter can produce pure DC voltage .The output voltage from
filter normally is not really stable. This voltage is the mixture of DC voltage with
the AC voltage (ripple voltage) as shown in figure 2.

37. Types FilterTypes Filter
• The best filter circuit is the filter that can decrease as much as the value of Vr p-p
produce by ripple DC voltage .The other type of filter are
1. Capacitor filter
2. RC filter
3. LC filter
4. Π- Type Filter

38. 1.5 RC filter

39. 1.6 LC & π filter

40. 1.7 Voltage Regulator
1.7.1 The voltage regulator circuits construct by using Zener
diode

41. 1.7 Voltage Regulator
1.7.3 The voltage regulator circuits construct by using Serial transistor

42. 1.7 Voltage Regulator
1.7.3 The voltage regulator circuits construct by using Integrated
Circuits

44. 1.8 Voltage Divider
Voltage divider rule is a simple way of determining the output voltage across
one of two impedances connected in series

45. 1.91.9 The schematic diagrams of a simple power supply
unit which includes full-wave rectifier, filter and Zener
diode voltage regulator.

46. 46
1.91.9 The schematic diagrams of a simple power supply unit which
includes full-wave rectifier, filter and IC voltage regulator.

47. 47
1.91.9 The schematic diagrams of a simple power supply unit which
includes Bridge rectifier, filter and IC voltage regulator.

48. EE3110 Oscillator 48
DC Linear Power Supply
Rectifier
Circuit
Filter
Circuit
Regulator
Circuit
Voltage
Divider
Transformer
Halfwave
Rectifier
Fullwave
Rectifier
Bridge
Rectifier
Capacitor
filter
RC filter
LC filter
π filter
Zener
Diode
Serial
Transistor
Integrated
Circuit (IC)
IC
LM78XX
IC
LM79XX
AC
230V
DC