power_amplifiers-1p - Power Amplifiers 1 Definitions In...

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1 Power Amplifiers
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2 Definitions In small-signal amplifiers the main factors are • amplification • linearity •gain Large-signal or power amplifiers function primarily to provide sufficient power to drive the output device. These amplifier circuits will handle large voltage signals and high current levels. The main factors are •efficiency • maximum power capability • impedance matching to the output device
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3 Amplifier Types • Class A • Class B • Class AB • Class C • Class D
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4 Class A Amplifier The Q-point (bias level) must be biased towards the middle of the load line so that the AC signal can swing a full cycle. Remember that the DC load line indicates the maximum and minimum limits set by the DC power supply. The output of a Class A amplifier conducts for the full 360 ° of the cycle
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5 Class B Amplifier A Class B amplifier output only conducts for 180 ° or ½ of the input signal. The Q-point (bias level) is at 0V on the load line, so that the AC signal can only swing for ½ of a cycle.
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6 Class AB Amplifier This amplifier is in between the Class A and Class B. The Q-point (bias level) is above the Class B but below the Class A. The output conducts between 180 ° and 360 ° of the AC input signal.
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7 Class C The output of the Class C conducts for less than 180 ° of the AC cycle. The Q-point (bias level) is at cutoff, the output signal is very small.
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8 Class D The Class D output is more like a pulse. It does not resemble the AC sine wave input.
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9 Amplifier Efficiency Efficiency refers to the ratio of output to input power. The lower the amount of conduction of the amplifier the higher the efficiency.
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10 Series-Fed Class A Amplifier This is similar to the small-signal amplifier except that it will handle higher voltages. The transistor used is a high power transistor.
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11 AC Operation: Series-Fed Class A Amplifier A small input signal will cause the output voltage to swing to a maximum of V cc and a minimum of 0V. The current can also swing from 0 mA to I C (SAT) (V CC / R C )
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Input Power: Series-Fed Class A Amplifier The power into the amplifier is from the DC supply. With no input signal, the DC current drawn is the collector bias current, ICQ. Power input:
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power_amplifiers-1p - Power Amplifiers 1 Definitions In...

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