Electronic Circuits and Diagram-Electronics Projects and Design

Historically, audio-amplifiers have been configured as class A, class B or class AB and the art of design is well known. Also well known is the poor efficiency of these amplifiers compared to that of class D amplifiers. Whereas the theo­retical best efficiency for class B amplifiers is 78.5%, the practical upper limit is more nearly 70 % when driving a purely resistive load. But when driving real speaker loads which can have power factor angles of 60° or more, efficiency can come down to 55 % or less. Class D amplifiers, however, can attain efficiencies of 90 %, and…

A class C power amplifier is biased to operate for less than 180° of the input signal cycle, as shown in circuit. The tuned circuit in the output, however, will provide a full cycle of output signal for the fundamental or resonant frequency of the tuned circuit (L and C tank circuit) of the output. The use of such amplifiers is, therefore, limited for a fixed frequency, as occurs in communication circuits, for example. < Operation of a class C circuit is not intended primarily for large signal or power amplifiers.

  In class AB power amplifiers, the biasing circuit is so adjusted that the operating point Q lies near the cut-off voltage. During a small portion of negative half cycle and for complete positive half cycle of the signal, the input circuit remains forward biased-and hence collector current flows. But during a small portion (less than half cycle) of the negative cycle”‘ the input circuit is reverse biased and, therefore, no collector current flows during this period. Class AB operation needs a push-pull connection to achieve a full output cycle.

  Harmonic distortion in power amplifiers Output signal variations of less than 360° of the signal cycle are considered to have distortion. This means that the output signal is no longer just an amplified version of the input signal but in some ways a distorted or changed from that of the_jnput. The poor quality of music coming from radio or hi-fi system with the music or voice no longer sounding like that which was originally recorded or transmitted is the result of distortion. A good amplifier should not only give an enlarged version of the input signal at the output,…

In class B operation the transistor is so biased that zero-signal collector current is zero. Hence class B operation does not need any biasing system. The operating point is set at cut-off. It remains forward biased for only half cycle of the input signal.i.e its conduction angle is 180 degree. As illustrated in figure, during the positive half cycle of the input ac signal, the circuit is forward biased and, therefore, collector current flows. On the other hand, during negative half cycle of the input ac “signal, the circuit is reverse biased and no collector current flows.   Power and…

A class A power amplifier is defined as a power amplifier in which output current flows for the full-cycle (360°) of the input signal. In other words, the transistor remains forward biased throughout the input cycle. A schematic circuit of a series fed class A large signal amplifier using resistive load Rc is shown below. The term “series fed” is derived from the fact that the load Rc is connected in series with the transistor output. The only difference between this circuit and the small-signal amplifier circuits considered previously is that the signals handled by the large-signal circuit are in…

I had earlier discussed about power amplifiers and the classification of power amplifiers. Now let us look at the different power amplifier stages and the complete block diagram.   PRACTICAL POWER AMPLIFIER STAGES Power amplifiers are meant to amplify a weak signal until sufficient power is available to operate an output device such as a loudspeaker, a solenoid or a relay. Power amplifier, to provide the desired power amplification, has generally 3 stages (voltage amplification stage, driver stage and output stage), as shown in the block diagram given below. Voltage Amplification Stage – The signal devel­oped by the input transducer…

Introduction To Power Amplifiers An amplifier system consists of signal pick-up transducer, followed by a small signal amplifier(s), a large signal amplifier and an output transducer. A transducer is used to convert one form of energy into another type. For example a microphone is used to convert acoustical energy into electrical energy. Conversely, a loudspeaker is used to convert electrical energy into acoustical energy. A motor is a transducer that is used to convert electrical energy into mechanical energy. The input transducer produces small electrical (typically voltage) signal, that needs sufficient amplification to operate some output device such as a…

Power Amplifier Circuit – 25 Watts Description Here is the diagram of a 25 Watt power amplifier circuit made of  TDA 2009 IC.TDA 2009 has two channels each rating 12.5 watts on 4 Ohm load.Here the two channels are bridged to get a single out put channel weighting 25 W. TDA 2009 IC has also built in features such as short circuit protection,thermal protection, overload protection etc using very low external components.The most interesting factor I see about this IC is that it require no dual supply. Power Amplifier Circuit Diagram and Power Supply Circuit Schematic   Notes Do not…