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HNC Electrical and Electronic Engineering
Year One - 2013/14
Module: Module Digital & Analogue Devices

Power
Supplies

Keith A
...
Hudson

2

Digital / Analogue
03 December, 2013

Contents
1

Linear Power Supply (Q1a)
...
1

Transformer
...
2

Rectifier
...
3

Smoothing
...
4

Regulator
...
5

The Power Supply
...
7

3

Switched Mode vs
...
8

4

Construction of a Linear Power Supply (Q3a)
...
1

Power Source
...
2

Transformer (TR1)
...
3

Rectifier (BR1)
...
4

Smoothing (C1)
...
5

Regulator (U1)
...
6

Load (RV1)
...
7

Complete circuit - simulation
...
8

Complete circuit - wired
...
13

6

Power Supply Analysis and Improvements (Q3c)
...
17

HNC Electrical and Electronic Engineering

Year One: 2013/14

Keith A
...
4
Figure 2: The changes in the wave form of the voltage / current
...
4
Figure 4: Bridge using separate diodes
...
5
Figure 6: Regulator TO-220 package
...
6
Figure 8: Block diagram of a switched mode power supply
...
10
Figure 10: The power supply under full load
...
11
Figure 12: Almost 5V output
...
7mA
...
7mA
...
12

Tables
Table 1: Types of transformer
...
7
Table 3: Advantages / disadvantages - Switched mode and Linear power supply
...
13
Table 5: Line Regulation
...
13
Table 7: Power loss
...
15
Table 9: Efficiency of the Rectifier (calculated at full load)
...
16
Table 11: Efficiency of the Rectifier (calculated at full load)
...
Hudson

Digital / Analogue
03 December, 2013

4

1 Linear Power Supply

(Q1a)

The purpose of a linear power supply is to provide a suitable voltage and current to a specific load
...
The available high voltage (mains), alternating current must be
converted into a low voltage, regulated, direct current
...
C
...
C
...
The values of the components
are dependent upon the input voltage, current and the requirements of the load
...


A
...
Voltage
Input

Transformer

Rectifier

Smoothing

Regulator

D
...
Voltage
Output

Figure 1: The conversion steps
...


The components required to convert A
...
mains voltage to a suitable D
...
low voltage are shown in Figure 1
...


1
...
(electrical4u
...
d
...
This causes a
magnetic flux that is concentrated by the soft iron core
...
This induces an EMF (voltage) in the
secondary winding
...
For further
explanation see Faraday’s Law of Electro-magnetic Induction
...
Hudson

Digital / Analogue
03 December, 2013

5

Table 1: Types of transformer

Number of
Primary
Windings

Number of
Secondary
Windings

Transformer
Type

N

>N

Step-up

N

N

1:1
(Isolation)

N


Step-down

Result
O/P Voltage
>
I/P Voltage
O/P Voltage
=
I/P Voltage
O/P Voltage
<
I/P Voltage

For our power supply a step-down transformer will be used to reduce the high voltage (see Figure 2
...
2), high current power
...


1
...
2 from the transformer into direct current
...
3 shows the result of full-wave rectification
...
(There may be circumstances were only negative voltages are required
...
) Half wave rectification is achieved by only allowing
positive (or negative) current to flow
...
A half-wave rectifier combined with a centre-tapped transformer, also results in a full wave rectification
...


Figure 4: Bridge using separate diodes
Figure 5: Bridge diode package

1
...
3)
...
4)
...
They are usually electrolytic type capacitors with a value over
470μF
...
Hudson

6

Digital / Analogue
03 December, 2013

1
...
To produce a constant output voltage (see Figure 2
...
The most popular form for these solid state devices is the TO-220
package (see Figure 6)
...
The ‘xx’ indicates the output voltage,
common are 5 and 12V
...
5 The Power Supply
Figure 7 shows a complete power supply circuit
...
These are not part of the power supply
...
Next are the smoothing capacitor and the regulator
...
Hudson

Digital / Analogue
03 December, 2013

7

2 Load Regulation

(Q1b)

Load regulation is a measure of how the output voltage of a power supply is affected by changes to the output
load (current)
...

Table 2: Load regulation of a 12VDC, 0-5A power supply

𝑉 𝑛𝑜𝑚𝑖𝑛𝑎𝑙_𝑙𝑜𝑎𝑑 = 12
...
00 𝑉 (Implied in the question
...
95 𝑉
𝐿𝑜𝑎𝑑 𝑅𝑒𝑔𝑢𝑙𝑎𝑡𝑖𝑜𝑛 =

(𝑉 𝑚𝑖𝑛 _𝑙𝑜𝑎𝑑 − 𝑉 𝑚𝑎𝑥 _𝑙𝑜𝑎𝑑 )
∗ 100
𝑉 𝑛𝑜𝑚𝑖𝑛𝑎𝑙_𝑙𝑜𝑎𝑑

HNC Electrical and Electronic Engineering

(12
...
95)
∗ 100
12
...
05
𝐿𝑜𝑎𝑑 𝑅𝑒𝑔𝑢𝑙𝑎𝑡𝑖𝑜𝑛 =
∗ 100
12
...
00
𝐿𝑜𝑎𝑑 𝑅𝑒𝑔𝑢𝑙𝑎𝑡𝑖𝑜𝑛 =
12
...
417 %
𝐿𝑜𝑎𝑑 𝑅𝑒𝑔𝑢𝑙𝑎𝑡𝑖𝑜𝑛 =

Year One: 2013/14

Keith A
...
Linear

(Q2)

In a linear power supply, the supply voltage is reduced by a transformer and then it is rectified
...
Figure 8 shows the
steps involved in a switched mode power supply (Wellforces Ltd, 2012)
...
M
...
The ‘Inrush current control’ protects the power supply at start up
...
C
...
C
...
The ‘Convertor’ is a
high frequency transformer
...
C
...
C
...
Feedback is another difference
between the switch mode supply and a linear one
...

Large/heavy transformer and heat sink
...


Cost

Cheap for low power output
...


Reliability

High (decreases as temperature rises)
...


Input voltage

Efficiency significantly reduced if a wide
input range is required
...
C
...
001 – 0
...

Small/light (typically 75 – 90% less than linear
equivalent)
...

Cheap for low power output
...

(Getting cheaper
...
More components but fit on a
single PCB
...
M
...

Can be reduced using filters
...

Can accept D
...
input
...
1 – 3
...
5 – 10ms)

Year One: 2013/14

Keith A
...
1 Power Source
Amplitude of 339V and a frequency of 50Hz were selected for the generator
...
e
...


4
...
This results in an approximate step-down of 12:1
...
This actually drops the input voltage down to about 20V
...
3 Rectifier (BR1)
BRIDGE
A bridge rectifier was chosen to convert the alternating current from the transformer to direct current
...


4
...
The default value of 1mF was used
...
0V (no load) down to 20
...


4
...
The minimum input voltage for this component is
19
...
0V (Farnell UK Limited, 2013)
...


4
...


HNC Electrical and Electronic Engineering

Year One: 2013/14

Keith A
...
7 Complete circuit - simulation
Figure 9 and Figure 10 show the complete power supply circuit
...
C
...
C
...
These values could then be used to calculate various
performance figures for the power supply
...
Hudson

Digital / Analogue
03 December, 2013

11

4
...
(It is show without wires for clarity
...
A number of
meters readings were taken at various points in the circuit (See Figure 12, Figure 13 and Figure 14)
...


Figure 11: Wiring the circuit on a Digiac 3000 – Power supply module

Figure 12: Almost 5V output

Figure 13: Full load - 51
...
7mA

Year One: 2013/14

Keith A
...
The output is ‘fuzzy’ due to interference from electrical devices
in the classroom
...
Hudson

13

Digital / Analogue
03 December, 2013

5 Calculations

(Q3b)

Using the values in Figure 9 and Figure 10 various performance values can be calculated for the power supply
...
00 𝑉
𝑉 𝑚𝑖𝑛 _𝑙𝑜𝑎𝑑 = 12
...
12 𝐴
𝑉 𝑚𝑎𝑥 _𝑙𝑜𝑎𝑑 = 11
...
79 𝐴
(𝑉 𝑚𝑖𝑛 _𝑙𝑜𝑎𝑑 − 𝑉 𝑚𝑎𝑥 _𝑙𝑜𝑎𝑑 )
%𝐿𝑜𝑎𝑑 𝑅𝑒𝑔𝑢𝑙𝑎𝑡𝑖𝑜𝑛 =
∗ 100
𝑉 𝑛𝑜𝑚𝑖𝑛𝑎𝑙_𝑙𝑜𝑎𝑑

(12
...
90)
∗ 100
12
...
10
𝐿𝑜𝑎𝑑 𝑅𝑒𝑔𝑢𝑙𝑎𝑡𝑖𝑜𝑛 =
∗ 100
12
...
00
𝐿𝑜𝑎𝑑 𝑅𝑒𝑔𝑢𝑙𝑎𝑡𝑖𝑜𝑛 =
12
...
833 %
𝐿𝑜𝑎𝑑 𝑅𝑒𝑔𝑢𝑙𝑎𝑡𝑖𝑜𝑛 =

Table 5: Line Regulation

The following are input voltages:
𝑉 𝑚𝑖𝑛 = 220 𝑉 (𝐴𝑚𝑝𝑙𝑖𝑡𝑢𝑑𝑒 = 310 𝑉)
𝑉 𝑚𝑎𝑥 = 250 𝑉 (𝐴𝑚𝑝𝑙𝑖𝑡𝑢𝑑𝑒 = 352 𝑉)
Δ𝑉𝑖𝑛 = 𝑉 𝑚𝑎𝑥 − 𝑉 𝑚𝑖𝑛
Δ𝑉𝑖𝑛 = 250 − 220
Δ𝑉𝑖𝑛 = 30 𝑉

%𝐿𝑖𝑛𝑒 𝑅𝑒𝑔𝑢𝑙𝑎𝑡𝑖𝑜𝑛 =

Δ𝑉 𝑜𝑢𝑡
∗ 100
Δ𝑉𝑖𝑛

0
∗ 100
30
𝐿𝑖𝑛𝑒 𝑅𝑒𝑔𝑢𝑙𝑎𝑡𝑖𝑜𝑛 = 0
...
e
...
0 𝑉
𝑉 𝑚𝑎𝑥 = 12
...
0 − 12
...
The
above tests were carried out under nominal load
...

Table 6: %Efficiency of the power supply (calculated at full load)

𝐴𝐶 𝐼𝑛𝑝𝑢𝑡 𝑃𝑜𝑤𝑒𝑟 = 𝑉𝐼𝑁 ∗ 𝐼 𝐼𝑁
𝐴𝐶 𝐼𝑛𝑝𝑢𝑡 𝑃𝑜𝑤𝑒𝑟 = 239 ∗ 0
...
85 𝑊
𝐷𝐶 𝑂𝑢𝑡𝑝𝑢𝑡 𝑃𝑜𝑤𝑒𝑟 = 𝑉 𝑂𝑈𝑇 ∗ 𝐼 𝑂𝑈𝑇
𝐷𝐶 𝑂𝑢𝑡𝑝𝑢𝑡 𝑃𝑜𝑤𝑒𝑟 = 11
...
79
𝐷𝐶 𝑂𝑢𝑡𝑝𝑢𝑡 𝑃𝑜𝑤𝑒𝑟 = 9
...
401
%𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 =
∗ 100
35
...
22% (2𝑑𝑝)
%𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 =

As Table 6 show, this linear power supply is not efficient
...
Hudson

14

Digital / Analogue
03 December, 2013

Table 7: Power loss

𝑃𝑜𝑤𝑒𝑟 𝐼𝑛 = 𝐼𝑛𝑝𝑢𝑡 𝑣𝑜𝑙𝑡𝑎𝑔𝑒 ∗ 𝐼𝑛𝑝𝑢𝑡 𝑐𝑢𝑟𝑟𝑒𝑛𝑡
𝑃𝑖𝑛 = 239 ∗ 0
...
85 𝑊
𝑃𝑜𝑤𝑒𝑟 𝑂𝑢𝑡 = 𝑂𝑢𝑡𝑝𝑢𝑡 𝑣𝑜𝑙𝑡𝑎𝑔𝑒 ∗ 𝑂𝑢𝑡𝑝𝑢𝑡 𝑐𝑢𝑟𝑟𝑒𝑛𝑡
𝑃 𝑜𝑢𝑡 = 11
...
79 = 9
...
85 – 9
...
45 𝑊 (2𝑑𝑝)

Table 7 shows that 35
...
4 W leaves as electrical power
...
45W leaves the power supply as other forms of energy
...
A small amount will be lost through the transformer, some down to internal resistance of
the windings, some due flux leakage and some as sound
...
Hudson

15

Digital / Analogue
03 December, 2013

6 Power Supply Analysis and Improvements

(Q3c)

By comparing the power going into individual components against the power out we will identify the inefficient
component
...
9 ∗ 1
...
422 𝑊

𝐴𝐶 𝑂𝑢𝑡𝑝𝑢𝑡 𝑃𝑜𝑤𝑒𝑟
∗ 100
𝐴𝐶 𝐼𝑛𝑝𝑢𝑡 𝑃𝑜𝑤𝑒𝑟
35
...
85
%𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 = 98
...

Table 9: Efficiency of the Rectifier (calculated at full load)

𝑅𝑒𝑐𝑡𝑖𝑓𝑖𝑒𝑟 𝐼𝑛𝑝𝑢𝑡 𝑃𝑜𝑤𝑒𝑟 = 𝑉𝐼𝑁 ∗ 𝐼 𝐼𝑁
𝑅𝑒𝑐𝑡𝑖𝑓𝑖𝑒𝑟 𝐼𝑛𝑝𝑢𝑡 𝑃𝑜𝑤𝑒𝑟 = 25
...
8
𝑅𝑒𝑐𝑡𝑖𝑓𝑖𝑒𝑟 𝐼𝑛𝑝𝑢𝑡 𝑃𝑜𝑤𝑒𝑟 = 20
...
9 ∗ 0
...
401 𝑊

𝑅𝑒𝑐𝑡𝑖𝑓𝑖𝑒𝑟 𝑂𝑢𝑡𝑝𝑢𝑡 𝑃𝑜𝑤𝑒𝑟
∗ 100
𝑅𝑒𝑐𝑡𝑖𝑓𝑖𝑒𝑟 𝐼𝑛𝑝𝑢𝑡 𝑃𝑜𝑤𝑒𝑟
9
...
72
%𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 = 45
...
Here is where most of the power is
‘lost’
...
9V to 12V without altering the current significantly
...

By reducing the output value of the transformer we can reduce the voltage supplied to the regulator, and hence
reduce the amount of energy converted to heat
...

Linear regulators will only produce the rated output voltage if the input voltage is at least a specific number of volts
above the rated output voltage
...

𝐷𝑟𝑜𝑝𝑜𝑢𝑡 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 (𝑉 𝑑𝑜 ) = 𝑀𝑖𝑛𝑖𝑚𝑢𝑚 𝐼𝑛𝑝𝑢𝑡 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 − 𝑅𝑎𝑡𝑒𝑑 𝑂𝑢𝑡𝑝𝑢𝑡 𝑉𝑜𝑙𝑡𝑎𝑔𝑒
The 7812 Regulator in the power supply has a Dropout Voltage, 𝑉 𝑑𝑜 = 2𝑉, although the minimum supply voltage is
specified as 14
...


HNC Electrical and Electronic Engineering

Year One: 2013/14

Keith A
...
5V
...
1
22
...
4
20
...
2
18
...
0
17
...
1
15
...
1
14
...
5V which equals the
minimum input voltage for the Regulator
...
7 ∗ 0
...
025 𝑊
𝑅𝑒𝑐𝑡𝑖𝑓𝑖𝑒𝑟 𝑂𝑢𝑡𝑝𝑢𝑡 𝑃𝑜𝑤𝑒𝑟 = 𝑉 𝑂𝑈𝑇 ∗ 𝐼 𝑂𝑈𝑇
𝑅𝑒𝑐𝑡𝑖𝑓𝑖𝑒𝑟 𝑂𝑢𝑡𝑝𝑢𝑡 𝑃𝑜𝑤𝑒𝑟 = 11
...
74
𝑅𝑒𝑐𝑡𝑖𝑓𝑖𝑒𝑟 𝑂𝑢𝑡𝑝𝑢𝑡 𝑃𝑜𝑤𝑒𝑟 = 8
...
806
%𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 =
∗ 100
11
...
87% (2𝑑𝑝)
%𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 =

Table 11 shows a massive increase in efficiency, up from about 45% to almost 80%
...
79A down to 0
...
This equates to an output power of 8
...
5W)
...
The value of the smoothing
capacitor may be the cause
...
33μF capacitor
on the input side of the regulator and a 0
...

A heat sink on the regulator would also be an improvement to the power supply
...


HNC Electrical and Electronic Engineering

Year One: 2013/14

Keith A
...
All About Circuits : Free Electric Circuits Textbooks
...
allaboutcircuits
...

electrical4u
...
d
...
[Online]
Available at: http://www
...
com/what-is-transformer-definition-working-principle-of-transformer/
[Accessed 24 11 2013]
...
L7812CP - STMICROELECTRONICS - IC, V REG +12V, 7812, TO-220FP | Farnell UK - Op
...
farnell
...

LJ Create, 2013
...
[Online]
Available at: http://www
...
com/products/product
...

Marian, P
...
Step Down Transformer
...
electroschematics
...

Wellforces Ltd, 2012
...
[Online]
Available at: http://nz
...
com/resources/introduction-linear-switching-power-supplydifferences/197/#
...

Wikipedia, 2013
...
[Online]
Available at: http://en
...
org/wiki/Diode_bridge
[Accessed 25 11 2013]
...
Load regulation - Wikipedia, the free encyclopedia
...
wikipedia
...


HNC Electrical and Electronic Engineering

Year One: 2013/14



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Title: DC Theory
Description: Engineering Science - Assignment 1 Thevenin’s and Norton’s Equivalent circuits. Principles / operation of DC Motors and Generators. Grade received: DISTINCTION Tutor: Susan Armstrong Institute: Middlesbrough College Programme: Higher National Certificate (HNC) in Electrical and Electronic Engineering

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