Design and Construction of an Over and Under Voltage Protection Circuit Device [180-240v]

Design and Construction of an Over and Under Voltage Protection Circuit Device [180-240v]

Chapter One

Aims and Objectives of the project.

The aim of this project is to develop an over and under voltage protection circuit device to protect the connected load from damage. The fluctuation in AC mains supply is frequent in homes and industries due to voltage regulation problems. The sensitive electrical and electronic devices in these conditions can get easily damaged. It is preferable to have a device to protect the load. The objective to achieve the aim include; To develop an over and under protection circuit device using comparators for detecting the under and over voltage, to develop a program that will conveniently implement the circuit.

CHAPTER TWO

THEORETICAL BACKGROUND

POWER SUPPLY UNIT

Power supply unit is essential for the operation of electrical and electronic instruments and systems. The power supply to a system or instrument can be derived from the single AC mains. The majority of the DC supply required for electronics and control equipment is provided by means of stepping down and rectifying alternating current (220V at 50Hz). The term power supply in this context is used to refer to the complete circuitry which performs the conversion from AC to DC including the mains which will be required to provide the alternating voltage. The term also includes any further circuitry that maybe included to improve the operation of the supply such as ripple filters, voltage regulator, etc.

In the bridge rectifier circuit shown in fig 2.2, it requires four diodes; the transformer used is not center-tapped and has a maximum voltage of Vmax. The full wave rectifier is available in three distinct forms;

Four discrete diodes
One device inside a four-terminal case
As part of array of diode in an IC (integrated circuit)

DIODE BRIDGE or BRIDGE RECTIFIER

A diode bridge is a device that changes Alternating Current (AC) to Direct Current (DC). A diode bridge is an arrangement of four (or more) diodes in a bridge configuration that provides the same polarity of output for either polarity of input. When used in its most common application, for conversion of an alternating current (AC) input into a direct current (DC) output, it is known as a bridge rectifier. A bridge rectifier provides full-wave rectification from a two-wire AC input, resulting in lower cost and weight as compared to a rectifier with a 3-wire input from a transformer with a center-tapped secondary winding. The essential feature of a diode bridge is that the polarity of the output is the same regardless of the polarity at the input.

Basic operation:

According to the conventional model of current flow originally established by Benjamin Franklin and still followed by most engineers today^[11], current is assumed to flow through electrical conductors from the positive to the negative pole. In actuality, free electrons in a conductor nearly always flow from the negative to the positive pole. In the vast majority of applications, however, the actual direction of current flow is irrelevant. Therefore, in the discussion below the conventional model is retained. In figure 2.3 and 2.4, when the input connected to the left corner of the diamond is positive, and the input connected to the right corner is negative, current flows from the upper supply terminal to the right along the red (positive) path to the output, and returns to the lower supply terminal via the blue (negative) path.

CHAPTER THREE

CIRCUIT DESIGN AND ANALYSIS

DESIGN AND ANALYSIS

The complete circuit is composed of various stages which includes power supply, reference voltage source (regulator), voltage comparator for high/low voltage detection (cut offs) and relay driver stage.

POWER SUPPLY UNIT

The DC proportional to the charging input voltage is obtained from the bridge rectifier. The diode bridge rectifier is capable of handling currents up to 1 Amp. The transformer used has a rating of 220 x 24V 500mA .

DESIGN CONSIDERATION OF SHUNT FILTER CAPACITOR

The following mathematical calculations were used to find the value of the smoothening capacitor used for this project work, using the formula. ^[5

CHAPTER FOUR

OPERATIONAL ANALYSIS OF THE CIRCUIT

HOW THE CIRCUIT WORKS

This circuit protects load (such as TV set, refrigerators, HI-Fi system, etc) from over and under voltages. The transformer is a step down transformer that is used to reduce the main voltage from 220volts down to 24 volts A/C of one ampere. This (1 amp) current is sufficient to drive circuit since the voltage is a step down. AC voltage is passed through the rectifier unit, which is made up of four (4) diodes used to create the rectifier bridge for full wave rectification. The rectifier unit converts the AC voltage to a DC voltage. After rectification, the DC voltage is passed through the filter for smoothing. The filter is made up of capacitors where any residual ripples or AC leakage is removed.

CHAPTER FIVE

SUMMARY, LIMITATIONS, RECOMMENDATIONS AND CONCLUSION

SUMMARY

The over and under voltage protection circuit device (180V – 240V) circuit is an electronic device that provides protective mechanism to the appliances connected to it. Appliances such as refrigerators, TV sets, Hi-Fi systems, air conditions, computers etc. can be safe guarded using this device.

The device comprises mainly two op-amps (comparators): one responsible for the upper limit (i.e. 240V) and the other responsible for the lower limit (i.e. 180V), a transistor switch which causes the relay to energize in saturation mode and to de-energize in the cutoff mode. The relay consists of two contacts; normally close and normally open contacts. The appliance (load) is connected to the ac supply through the normally closed contact (but when the relay coil is de-energised the contact opens and breaks the circuit).

LIMITATIONS

The assembly of the components would have been easier and better if printed circuit board (PCB) was used.
Getting the device to cutoff supply and to turn on at the exact voltage specified was one of the major limitations to this project work as the device normally takes +1.09V change to respond completely to voltage variation.

RECOMMENDATIONS

Due to the limitations encountered in the course of the project work, we propose the following recommendations.

The system should be designed to be sensitive to any slight change from the specified limits using microcontroller for more accuracy.
Printed circuit board is recommended for mounting circuit components, this make the device more portable and efficient.
555 timer may also be incorporated in the circuit for sharp discrimination and delay. Though this is only desirable if the speed of switching is of little importance.

CONCLUSION

The design and construction of over and under voltage protection circuit device (180V-240V) circuit was necessitated by the need to monitor voltage supply to our household appliances and consequently protect them from the dangers of being damaged due to voltage fluctuation.

Based on the theoretical analysis, design and testing work, the following conclusion can be made.

Since the switching is automatic, the device is no doubt being used as an automatic appliance protector
The construction of this project made use of components that can be found locally.
The display of the monitored voltage is indicated simply by light emitting diode (LED) which can be understood easily by all.
The assembled unit is very compact and portable, and can easily be incorporated in electronic equipment.
The cost of construction of this project was relatively low as compared to the important function it performs. It can therefore be easily commercialized.

REFERENCES

Sedra, A. S. and Smith, K. C, “Microelectronic Circuits”, 5^th edition, Oxford University Press, Inc., New York, 2004.
Bell, E.C and Whitehead, R.W, “Basic Electronic Engineering and Instrumentation for Engineers”, Prentice Hall, Indonesia, 1975.
Theraja, B. L, and Theraja, A.K, “A Textbook if Electrical Technology”, 24^th edition, S. Chand and company Ltd, Ram Nagar, New Delhi, 2000.
Donald, A. N, “microelectronics Circuit Analysis and Design” 3^rd edition, MaGraw-Hill, New York, 2007.
Frederick, F. D, and Robert F. C, “Solid State Devices and application, 3^rd edition, Prentice Hall, 1975.
Over and Under voltage switch with relay, http://www.electronicdiagrams.com/. [Accessed, may, 2011]
National semiconductors, datasheet for LM393A, IN4739A and IN4733A. www.national.com
Garba, J. L and Agbo, D. O (2005): “Design and construction of Automatic Over voltage and under voltage Cut-Out”. An exit project work submitted to the department of Electrical/Electronic Engineering, University of Agriculture, Makurdi, Benue State, Nigeria.
Bum Asugh (1992): ”An Automatic over voltage and under voltage Cut-Out”. An exit project work submitted to the department of Electrical/Electronic Engineering, University of Agriculture, Makurdi Benue State, Nigeria.

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