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.docx  VARIABLE POWER SUPPLY.docx (Size: 163.11 KB / Downloads: 13)


A variable power supply [7] is one where you can continuously adjust the output voltage to your requirements. The conventional controlling method of variable power supply that uses manual interference (using a rheostat) has been replaced by a servo motor which is controlled by a micro-controller [2]. This in turn reduces the pain of adjusting the rheostat manually and also increases the efficiency of the system. Varying the output of the power supply is the recommended way to test a project after having double checked parts placement against circuit drawings and the parts placement guide.


The conventional method of controlling a variable power supply [7] involves the meticulous task of adjusting a rheostat that is a knob on the instrument.
This method has a lot of limitations such as human errors while varying the potentiometer, parallax error while taking readings, it is time consuming, and requires continuous monitoring in case of line voltage fluctuations.
In order to get rid of these limitations, the demand was to design a system that is accurate as well as highly efficient which eliminates the human errors.
A peek is taken into the world of computer-aided process. The present work is an implementation of micro-controller [2] interfaced with servo motor mechanism is the heart of the system wherein the use of digital technology has improved the system's efficiency immensely that is quite widely used in industries and is now very important to industries where time is important factor as regards to testing of electrical devices. This small report on Variable power supply is made to help even a novice understand how variable voltages are generated and what impact they have on testing and functioning of the industrial motors. market availability, the cost – effectiveness and the components required were designed appropriately.


The market is the ultimate destination of any project. If it is not commercially viable, any venture is not worth its salt. Thus market knowledge effects in being the absolute pre-requisite. The project is a variable supply [7]. This is a rarity, especially required on a large scale for industrial use. Companies like Siemens use it for contact measuring. Contact measuring refers to ability of the instrument to measure the correctness of the performance of the device under test which requires a constant input voltage. The available module is bulky and too expensive to be of commercial interest. The portability pointer is also on the wrong side of consumer convenience. Our venture is an effort to untie this Gordian knot.


The price tag of the auto transformer in the market ranges from Rs. 1,800 to Rs. 2,200. This is the resultant of the increasing price of the copper wires, the other side of the coin of consumer electronics. The motor used is the servomotor. The cost for etching a sq. cm. is Rs. 10. The Cost price of the final product, considering the above, is roughly estimated to be hovering around the Rs. 4,500 mark. Though, mass production would lower the rate to a reasonable Rs. 1,500 mark. An analogy could be found in the case of mobile phones produced in China with features like touch-screen made reasonably cheap.


Different types of power supplies are already available in the market. Manual control is superceded by highly accurate voltage readings. The motor used is ac servomotor, which after a lot of comparison with its counterparts was found to be the outright winner in terms of power and efficiency. Here micro controllers like 89S51 and 89C51 are used which operate at 5 and 15 V respectively. Though micro-processors being cost efficient and easily programmable, it is an outdated technology dating from the 1940s. Uses of micro controllers [2] were preferred over micro-processors taking into consideration the demand of the future industry domain, which has already switched over to PICs. Also micro controllers have flexibility ungratified by the latter. Programming codes can be Assembly language or Embedded C, of which the latter was found to be of industrial favoring due to its supple coding patterns.
This is a venture to produce an extremely fast and an accurate power supply at an efficient, thus removing the manual tuning prevalent in the commercial power supplies available in the market.


In order to have a system that is highly efficient a design was developed wherein the micro-controller is interfaced with a servomotor with the help of a controlling logic that is in the form of a high level language programming.
The basic logic is that a user will feed the voltage required in the number-pad which could be observed in the display unit. Now the micro-controller will give the start signal and the motor will start running based on the supply given to the motor. The micro-controller will monitor the running of the motor and as soon as the motor crosses the respective voltage a stop signal is given by the micro-controller to the motor. In this way the required output voltage is obtained.
A feedback circuit is also designed in case to avoid the possibility of any error in the system.


The system is entirely micro-controller controlled and starts functioning on being given an input through the keypad. On switching on the power the user has to type in the value of voltage required. This value is stored in the micro-controller in binary format. The typed value can be seen on the LCD. Then when the input is thus typed in the START key must be pressed. This begins the operation of the system.
Then the micro-controller gives start signal. The clock to the microcontroller is provided by IC 7414 [6]. The motor starts running and accordingly increases the variac output.
The voltage obtained at the output may not be exactly equal to the desired voltage; hence a feedback path is incorporated to the errors. The feedback path consists of a rectifier circuit followed by a data converter. The rectifier rectifies the ac output.
If the stored value is found to be less than observed value, then micro-controller sends a reverse signal to the MCC. The motor begins to run in the opposite direction and the above process is repeated. If stored value is more than received value then motor continues to run in forward direction and the feedback is again provided. This process continues till the observed value is equal to the keyed in value.
Thus with the help of micro-controller a error free output voltage can be obtained effortlessly.


The design of the system is simple and easy to implement. The voltage obtained at the output is stable and accurate. The system is encased in a single compact assembly. Thus, the system is portable and occupies less space. The system needs only to be plugged in to a single phase AC supply. The various parts in the system requiring constant voltage are provided through the line voltage itself by means of rectifiers, adapters, transformers, etc. The system is easy to use and extremely user–friendly due to the well programmed keypad and display. As components used are relatively less expensive and weight is placed on comprehensive programming, the system cost as well as complexity is reduced.
Some of the drawbacks of the design are the mechanical portion of the design need not give very accurate results, the DC output is a pulsated one and the cost of the entire project is a bit on the higher side

Marked Categories : were this microcontroller at 89c51are used, mini project based on power supply with varying voltage by using a keypad, variable power supply,

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