Lecture 28- Power Amplifiers II - Electronics- II (EEE 232)electronics-2.weebly.com/.../13056901/lecture_28-_power_amplifiers_ii.pdf · Lecture 28 Power Amplifiers II Class A, Class
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Electronics IILecture 28
Power Amplifiers II
Class A, Class B & Class AB Amplifiers
Muhammad TilalDepartment of Electrical Engineering
CIIT Attock Campus
COMSATS Fall 2014(Rev. 3.0)
The theme of this presentation is an inspiration from the one used in S2 Department of Chalmers University of Technology, Gothenburg, Sweden.
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• Class A amplifier uses a singletransistor for both input cycles.Because of its biasingarrangements, this amplifier alwayshas the current flowing at theoutput.
• This causes the poor efficiency asthe actual power delivered to theload is quite less than the actualpower converted.
• Most the power converted iswasted as heat thereby risking thedevice burn out if proper sinking isnot provided. Additionally sinksalso increase the cost.
Robert L. Boylestad, Electronic Devices and Circuit Theory, 8th Edition, Pearson Education Inc, ISBN: 81-7808-590-9.
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• Class B amplifier works only for1800 of output cycle. The DC biasingleaves the transistor turned offwhen there is not input ac signal.
• To obtain the output for full 3600
cycle of operation, two transistorwith output at the opposite cyclesare coupled together.
• This is termed as the push-pullconfiguration. During one halfcycle, one transistor causes theoutput to be high and during otherhalf cycle, the second transistorcauses the output to go low.
• There are multiple circuits toobtain a class B power amplifieroperation.
• For a push-pull configuration, onepossible method is to split asingle input signal into twoopposite polarity signals.
• These opposite polarity signalsare fed into two similar inputcircuits (with each operating foralternate cycle) to get a full 360degrees of operation.