Wednesday, September 14, 2011


Transistor amplifiers process the signals important. Many of them are driven so hard by large collector current input signal is either switched off or in saturation region for much of the input cycle. Thus, these amplifiers are generally classified by their mode of action. This classification is based on the amount of bias transistor and the amplitude of the input signal. It takes into account the part of the cycle, the transistor conduct. They are classified as

1. Class A amplifier.
In this case, the transistor is biased so that the flow of output current for the entire cycle of the input signal. Therefore, the operating point is chosen so that the transistor operates only in the linear region of its load line. As an amplifier can amplify the input signal of low amplitude. Since the transistor operating in the linear part of the load line, the output is exactly the same input. Thus, Class A amplifiers are characterized by a high fidelity output. These amplifiers are used when no distortion is the main objective. The operation is limited to a small central region of the load line for these amplifiers can be used to amplify may be used to amplify low amplitude signals. Also AC power transistor output is small. The global maximum efficiency, with a resistive load is 25%. The maximum possible performance of the sensor with a resistive load is 50%. If the power transformer is used, and the efficiency is 50%.

2. Class B Amplifier 
In this case, the bias transistor and amplitude are such that the output current flows only in the positive half cycle of the input signal. Zero signal collector current is zero and the weighting system is required for class B amplifiers Operating point is selected as a collector voltage cut-off. Given that the complete absence of negative side-cycle distortion of the output signal is high. Zero input signal is the best prerequisite for a Class B amplifiers because the zero IC. Transistor dissipates more power increases the signal strength. Compared to the average class of power amplifiers is less, the power loss is smaller. Thus, the overall efficiency has increased. The theoretical efficiency of the operation of class B is about 78.5%, compared with only 50% of the class action.

Class C Amplifiers
In this case, the bias transistor and the signal amplitude such that the flow of output current for substantially less than half of cycle-cycle entry. In such an amplifier is the foundation provided some negative stereotypes, so that the IC does not flow only when the positive half cycle of the signal begins. The effectiveness of the circuit is high (about 85-90%). Due to the high distortion, these amps are not used for audio-frequency. They are employed by radio frequency output power as high harmonic distortion can be removed by simple circuits.

4. Class AB Amplifiers. 
The characteristics of such an amplifier located between those of class A and B power amplifiers in class. The output current flows for more than half but less than the entire cycle.

Head Sinks 
Since the power transistors to handle large flows, they become very hot during operation and the heat generated is dissipated to the environment so that the temperature does not exceed the permitted limits. The transistor is usually connected to the metal plate (usually aluminum) to transfer heat to an aluminum plate. This is called a flat aluminum heatsink.

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