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Contents:- • General description of Power Supply • Advantages/Disadvantages of SMPS • Block diagram of SMPS • Basic topologies and practical • requirements • Working of various SMPS topologies: 1. Flyback Converter 2. Push-pull Converter 3. Half bridge Converter 4. Full bridge Converter • Applications of SMPS • Conclusion
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Power Supply:-Any device that supplies electricpower to an electric load.The different types of powersupplies include:-Battery-DC power supply-AC power supply-Linear regulated power supply-Switched mode power supply-Programmable power supply-Uninterruptible power supply
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Switched Mode Power Supply: An electrical power supply that incorporates a switching regulator to convert electrical power efficiently. It transfers power from a source, to a load, while converting voltage and current characteristics. Voltage regulation is achieved by varying the ratio of on- to-off time.
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Advantages of SMPS over Linear Power Supplies: • 1. Lower weight • 2. Smaller size • 3. Higher efficiency • 4. Lower power dissipation • 5. Wide ac input voltage range • 6. Reduced costsDisadvantages of SMPS: 1. Complexity of the circuit
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Block diagram of a SMPS 1. Input rectifier stage: It is used to convert an ac input to dc. A SMPS with dc input does not require this stage. The rectifier produces unregulated dc which is then passed through the filter circuit.
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• 2. Inverter stage: – The inverter stage converts DC, whether directly from the input or from the rectifier stage described above, to AC by running it through a power oscillator, whose output transformer is very small with few windings at a frequency of tens or hundreds of kilohertz. 3. Output transformer: - If the output required is to be isolated from input, the inverted AC is used to draw the primary windings of a high frequency transformer. This converts the voltage up or down to the required output level on it’s secondary winding. 4. Output rectifier: - If the dc output is required, the ac output from the transformer is rectified. 5. Regulation: - Feedback circuit monitors the output voltage and compares it with the reference voltage.
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Factors to be considered while selecting atopology for a particular application:- • 1. Is input-to-output dielectric isolation required for the application? • 2. Are multiple outputs required? • 3. Does the prospective topology place a reasonable voltage stress across the voltage semiconductors? • 4. Does the prospective topology place a reasonable current stress across the voltage semiconductors? • 5. How much of the input voltage is placed across the primary transformer winding or inductor? • Typical maximum output power available from each topology: Converter Topology Maximum output power Flyback 200W Forward 300W Push-pull 500W Half bridge 1000W Full bridge >1000W
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Use of non-isolated topologies: • Non isolated topologies are the simplest, with the three basic types using a single inductor for energy storage. Type Power(W) Relative Energy Voltage Relation Features Cost Storage Buck 0-1000 1.0 Single 0 ≤ Out ≤ In Continuous inductor V2=D.V1 current at output Boost 0-150 1.0 Single Out ≥ In Continuous inductor V2=V1.[(1)/(1-D)] current at input Buck- 0-150 1.0 Single Out ≤ 0 No boost inductor V2= -V1[(D)/(1-D)] continuous current
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Use of various transformer isolated topologies:
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Working of various SMPS Topologies:1. Flyback converter:
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Mode 1 Operation -- Q1 ON• Current builds up in the primary winding• Secondary winding has the opposite polarity D1 OFF• C maintains the output voltage, supplies load current
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Mode 2 Operation -- Q1 turned OFF• Polarity of the windings reverses• Diode D1 conducts, charging C and providing current to the load RL• Secondary current falls to 0 before the next cycle begins
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Conclusion:• The most common SMPS topologies: flyback, push-pull, half bridge and full bridge converters have been outlined.• Each has it’s own particular operating characteristics and advantages, which makes it suitable to particular applications.• Some of the most common applications of SMPS have been discussed.References:www.wikipedia.orgwww.howstuffworks.comPhilips semiconductors manualLambda semiconductors manualMotorola semiconductors manualMicrochip manual