Basic of Diode Rectifiers

Basic of Diode Rectifiers

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  Basic of Rectifiers RajeshB. Lohani Dept. of E & TC Goa College of Engineering 1 References Electronic Device Theory Robert Boylestead and Nashelsky Electronic Devices and Circuits by Allan Mottershead Integrated Electronics by Millman Halkias Weber State University. EMT212/4 – Analogue Electronic II Courtesy : Google images The presentation focus on the basics of rectifier.
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  Learning Objectives 2 i) Understandthe basic operation of rectifier circuits. ii) Analyze the different types of rectifiers.
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   A rectifieris a circuit which converts the Alternating Current (AC) input power into a Direct Current (DC) output power.  Diode and SCR are primarily used in rectifier circuits.
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  Difference between ACand DC signals. AC (Alternating current) DC (Direct Current) AC signal Flows one way, then the other way, continually reversing direction. Direct Current signal always flows in the same direction, but it may increase and decrease. Continually changing between positive (+) and negative (-). A DC signal is always positive (or always negative), but it may increase and decrease. Rate of changing direction is called the frequency of the AC and it is measured in hertz (Hz). Frequency is zero. Average value of signal is zero. It will always have average value.
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  step #1: increase/ decrease rms magnitude of AC wave using transformer step #2: convert full-wave AC to half-wave DC (still time-varying and periodic) step #3: employ low-pass filter to reduce ripple component by > 90% step #4: employ voltage regulator to eliminate ripple step #5: supply dc load .
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  The Half-Wave Rectifier Half-wave rectifier – has one diode and utilizes only alternate half-cycles of the input signal.  Constant voltage drop model is employed.  What if for Small inputs?  Regardless of the model employed, one should note that the rectifier will not operate properly when input voltage is small (< 1V)  Those cases require a precision rectifier (diode with op amps). PIV = Vm Ripple frequency = 50 Hz
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  Full-Wave Rectifier Center-tapping ofthe transformer PIV = 2Vm Ripple frequency = 100 Hz 6-0-6 means RMS value 6-0-6
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  Full-Wave Rectifier When instantaneoussource voltage is positive, D1 conducts while D2 blocks… when instantaneous source voltage is negative, D2 conducts while D1 blocks
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   An alternativeimplementation of the full-wave rectifier is bridge rectifier  Does not require center-tapped transformer  Four diodes instead of two Bridge Rectifier PIV = Vm Ripple frequency = 100 Hz
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  The Rectifier witha Filter Capacitor  Filters are required to remove the ripple components so as to get regulated dc output voltage free from unwanted ac components. Why is this example unrealistic?  Because for any practical application, the converter would supply a load (which in turn provides a path for capacitor discharging) The PIV for the above capacitor filter is 2Vm.  Mainly passive components like Capacitors, Inductors and their combination are used in filter circuits.
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  The Rectifier witha Filter Capacitor with load
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  Relationship between Peak-to-peak andrms value.
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  Disadvantages of HalfWave Rectifier •Ripple production is more •Harmonics are generated •Utilization of transformer is very low •Efficiency of rectification is low Advantages of Half Wave Rectifier •Affordable •Simple connections •Easy to use as the connections are simple •Number of components used are less Applications of Half Wave Rectifier •Power rectification •Signal demodulation: for demodulating the AM signals. •Signal peak detector: for detecting the peak of the incoming waveform. Rectifier Efficiency Rectifier efficiency is the ratio of output DC power to the input AC power. For a half wave rectifier, rectifier efficiency is 40.6%. Half-waveRectifier: Takeaways
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  Disadvantages of FullWave Rectifier Expensive and complicated circuit. Advantages of Full Wave Rectifier The rectifier efficiency of a full wave rectifier is high (81.2%.) The power loss is very low Number of ripples generated are less Applications of Full Wave Rectifier 1. For supplying polarized voltage in welding and for this bridge rectifiers are used. 2. For detecting amplitude of modulated radio signals. Full-waveRectifier: Takeaways
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  16 Learning Outcomes  Theviewer will be able to classify the different types of rectifiers.  Assemble and test the rectifier circuits.  Select rectifier circuit as per applications. Constructive criticisms are welcome for further improvement. You can reach me at: [email protected] This presentation has been peer-reviewed by Dr. Samarth Borkar. Thanks to Mr. Pushpshil Satardekar for support.
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  Dedicated to myloving parents Late. Janaki B. Lohani and Mr. Basant B. Lohani (Retd. Principal) 17
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  Thank You foryour time.