Class A Power Amplifier with 40W Output

Figure 1 

The circuit was designed to produce an audio power amplifier that operates in the range of Class A type while providing a power output of 40 Watts.

• Class A – refers to an output stage where the bias current is greater than the maximum output current thus, all output transistors are always conducting current due to its linearity and low distortion
• MPSL01 – an NPN amplifier designed for high voltage, general purpose amplifiers and gas discharge display driving, enclosed in a TO-92 package
• PMD16K100 – a 3-terminal monolithic epitaxial base structures NPN Darlington power transistor with built-in base to emitter shunt resistors and CVD glass passivated to increase reliability and provide reduced high-temperature reverse leakage current while the other features include low thermal resistance for more useable power and lower operating temperatures, hermetically sealed, and guaranteed for operating junction temperature range of 0º – 200ºC
• 2N6284 – a complementary silicon epitaxial-base NPN power transistor in monolithic Darlington configuration mounted in Jedec TO-3 metal case intended for general purpose amplifier and low frequency linear and switching industrial applications since it has integrated anti-parallel collector-emitter diode

In normal operation of the circuit, the final stage of the power amplifier is producing 40 W for every 8 Ohms of load. A very high current is allowed to flow since the power transistors are always in the ON state. Because of this, the consumption of power is also very which would always result to a very high temperature being emitted. On the other hand, this is very ideal for the transistors to work well because of much better characteristics of audio that they can achieve due to low distortion.

The final amplifier can be designed in a simple manner but would require an experience in this field of assembly. The circuit is utilizing Darlington transistors as the main component of the circuit design. It is placed at the output stage to provide a much higher current gain because the current amplified by the first transistor is further amplified by the second transistor. The two transistors are connected in such a way that the emitter of the first transistor is connected to the base of the second one. They come in transistor-like integrated circuit packages and produced an American company known as Lambda. The Darlington transistors can also be replaced with components that would provide the same desired output.

The whole circuit should be enclosed in a casing that is wide enough to provide sufficient space including a large heatsink and a strong power supply. The use of Class A approach is for more linear and less complex design of the circuit.

The design of the 40W power amplifier is typically applied for FM broadcast including broadband VHF or RF range. In other applications, this power amplifier increases the power of loudspeakers with high resistance and low voltage. Similarly, it can be used for high-end stereo TVs, compact stereo, surround sound amplifiers, component stereo, and self-powered speakers.

Source:users.otenet.gr/~athsam/power_amplifier_40w_class_a.htm