Bibliografía del curso de formación

In case you do not realise that, on a daily basis, when you activate electronic devices by switching them on, the chances are that you actually do so by switching on a Switching power Supply better known as switched-mode power supply. So, next time you turn on your computer, charge your GSM handset, turn on your low energy environment friendly electric bulb, turn on your television or even when you switch over to your inverter – you more likely than not switch on a Switching Power Supply.

These power supplies do not work on the same principle as the Linear Power Supplies because usually, Alternating Current input at mains

153 voltage, is rectified directly to obtain a Direct Current voltage without using a mains transformer,. The direct current voltage is then rapidly switched on and off by electronic switching circuitry at high high-frequency – resulting in a small, light weight, and inexpensive power supply.

Commercial switching power supplies are always regulated and when a properly insulated high-frequency transformer is used, the output will be electrically isolated from the mains voltage, which is crucial for operator safety.

Computer Switching Power Supply

One of the first wide scale commercial application of switching power supplies is the IBM computer power unit as depicted above;

It is a convenient modular device that converts the mains input AC voltage to the DC voltages needed by a personal computer and ever since the introduction of IBM PC/XT, several Personal Computer types have emerged which differ by their structure, form factors, connectors and volt/amp ratings. All invariably depend on Switching Power Supply Units for their operation.

A standard Personal Computer Power Supply Unit generates +5V, +3.3V, +12V1, +12V2, -12V and a standby 5V. Additional DC-DC converters step down 12V to the CPU core voltage and other low voltages needed for motherboard components, peripherals, floppy drive, and serial ATA connectors.

Power supplies for computers utilize switching mode technology and are ENERGY STAR compliant. This used to mean that computers consumed less than 10% of rated power in standby mode while in an active mode the efficiency of cheap models used to be 60-70%.

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4.0 CONCLUSION

In this unit we found out that electronic circuits require a wide variety of voltage levels to operate correctly and that while some functions require alternating current, most need to be supplied direct current.

It has also been made clear by this unit that DC to DC converters are used to either transform voltage levels from a given level to another, or to provide isolation.

5.0 SUMMARY

- Electrical power supplies are requires to power electrical appliances - Transformers cannot be used with direct current to increase supply voltage - Alternating current from the public mains supply is impure as it contains

electrical noise and many types of distortion

- Basic direct current power supplies produce pulsating half wave or full wave direct current

- Filter capacitors improve the waveform of basic direct current power supplies

- Voltage regulators reduce ripple and noise in the output

- Power supplies are classified into linear and switching power supplies - Switching power supplies utilise an energy storing circuit element like a

capacitor or an inductor

- Switching power supplies are more economical than linear power supplies of the same capacity

6.0 TUTOR MARKED ASSIGNMENTS

1 What is an electronic power supply?

2 Can you describe direct current power supply?

3 What role do transformers play in power supplies?

155 4 Can you sketch a centre tapped transformer with input of 220 Volts

and output of 24 Volts? And label it?

5 Sketch a basic direct current power supply and label the parts and sketch its output waveform?

6 How can you reduce the ripple in a basic direct current power supply?

7 Can you state the two broad classifications of power supplies?

8 What role do regulators play in power supplies?

9 Mention ten devices which operate from switching power supplies?

10 Discuss the principle of operation of switched mode power supplies?

11 Discuss the function of filter capacitors in power supplies?

12 What do voltage regulators do?

13 Compare and contrast the benefits of linear and switching power supplies?

7.0 REFERENCES/FURTHER READINGS A Textbook of Electrical Technology 2010

By B. L. Theraja and A. K. Theraja. Published By S. C. Chand, Semiconductor Device Fundamentals

By Robert F. Pierret Published By Prentice Hill Electrical Circuit Analysis

By C. L. Wadhwa Published By New Age International Electronic Devices and Circuit Theory 7^th Edition

By Robert E. Boylestad and Louis Nashesky Published by Prentice Hall

Network Analysis with Applications 4^th Edition By William D. Stanley Published by Prentice Hall Fundamentals of Electric Circuits 4^th Edition

By Alexander and Sadiku Published by Mc Graw Hill

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