Power supplies are electrical devices which supply Electrical power to Loads. The Basic function of a power supply is to convert Electricity from a source into voltage, current, and frequency to power the load. Hence, they are also referred to as Electric Power Converters. In order to understand different types of power supply, knowledge of their design is essential. Power supply, in general has four different parts. A Transformer which converts high voltage Alternative Current to low voltage Direct Current. Next comes the Rectifier which is used to convert low voltage Alternative Current to Direct Current. The next is a Filter, this is used because the direct current produced by the rectifier has ripples, hence a filter is used to reduce the ripples. The final part is the regulator which sets the Direct Current voltage to constant value by remove the ripples completely. Mainly there are 2 types of Power Supplies. They are LINEAR MODE POWER Supply and SWITCHED MODE POWER SUPPLY. The construction and working of both the supplies is dealt in detail. Linear Mode Power SupplyAs shown in Figure 1, a Linear mode power supply is more or less resembles a Bridge wave rectifier whose output is connected to a Filter capacitor. The Filter is connected to Regulator circuit. The Regulator is in turn connected with a filter and finally DC output obtained. AC mains $ is connected to Transformer where it gets steeped down or stepped up based on the requirement. The stepped Voltage is fed into the Bridge wave rectifier where AC is converted into DC #. The output of the rectifier is dc but contains very high ripples. This output is fed into a filter capacitor of required capacitance, where the ripples get almost nullified ? . This output is fed into a Regulator Circuit which provides a constant DC output %. If required another capacitor can be considered for reducing ripple. Switched Mode Power SupplyAs shown in Figure 2, a Switched mode power supply is more or less resembles a Linear Mode power supply in its basic principle of operation but consists of protection circuits, Pulse width modulator as extra components which makes the circuit highly efficient than LMPS. Here, Voltage from Mains are supplied into Mains Filter, where different noise and distortion frequencies get filtered. The Filtered voltage is then passed through Rectifier, to get converted into a DC from AC.Figure 1: Linear Mode Power Supply and its result$#?% 8Figure 2: Switched Mode Power Supply The output rectification and filter are isolated from the High Frequency switching section by a high frequency transformer, and voltage control feedback is through isolator. The control circuit is an IC containing the high frequency oscillator, pulse width modulation, voltage and current control and output shut down sections. This rectified voltage goes into power switches, if switched is on, it becomes a closed circuit and SMPS starts working. Based on this, we can state that SMPS does not function continuously like a LMPS. It switches on and off based on the requirement and hence is not heated up.Having the knowledge of both the types of Power supply, I would like to compare them based on a particular Application. I would choose Computer. The type of power supply used determines the life time of a computer (or any device). Use of a poor supply can reduce the life time, on the other hand, a high-quality Power supply can help to reduce the noise or heat generated within a computer system.In past decade, all of the personalized, desktop computers had been supplied with Linear mode power supplies. As the requirements of PC increased, its usage was also intensive. Most of the industries, institutions, it sectors started using Computers to make work easy. But the problem raised here. Due to the continuous use of computers, used to get heated up continuously. Sometimes, under worst cases, the computer used to shut down automatically and it used to start working unless the LMPS was back to stable state. This made LMPS an unfit device for Computer application. Later on, as technology developed, SMPS came into existence. The most inspired feature of SMPS is that it does not function continuously as said earlier. It works in equal interval of time. Moreover, the presence of comparator circuit used to monitor the input given to CPU.The following table gives a complete distinguish between SMPS and LMPS.Table 1: Comparison between LMPS and SMPSSl noLinear Mode Power SupplySwitched Mode Power Supply1Simplicity in design, low costComplex design, high cost2Dynamic load response time is lessDynamic load response time is high,3Has only one outputhas multiple output4Less efficiency at about 30% to 60% onlyHigher efficiency when compared to LMPS at about 80% 95Heat sink is required for transistors for heat dissipationHeat generated is very less. Hence a low-cost Heat sink is preferred6Headroom losses (for every watt delivered to the load more than one watt is lost) are present.Headroom losses are nullified7Not preferred to use in personal computersPreferred to use in personal computers8Can be used only as step-down regulatorCan be used both as step-up and step-down regulator9Uses rectifier, filter, and transformerFor step-down voltage use of transformer not required10POWER FACTOR IS 0.6 – 0.7Power factor is0.6-0.7 without PFC, 0.95 with PFC11Load Regulation-0.005% to 0.2% and line regulation-0.005%-0.05%Load Regulation-0.05% to 0.5% and line regulation-0.05%-0.2%Power supplies convert voltages from mains to lower levels in the desktop computer. During this conversion, some power is lost as heat and noise. But Efficiency, the main feature of computers is determined by how much power is utilized from the given input. In this case only SMPS survives. Moreover, SMPS keeps on sampling the output to compare with input, this characteristic provides us a better stability at the output. Hence, I would go with the statement”SMPS has better power efficiency than Linear Power Supply” But, we cannot conclude that LMPS is outdated. Many applications, such as low noise amplifiers, signal processing, data acquisition – including sensors, multiplexers, A/D converters, automatic test equipment, laboratory test equipment, control circuits even now prefer LMPS over SMPS for performance.

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