30 Watts Small Power Amplifier

Overview

The circuit was based on different types of transistors to produce a mini power amplifier that would provide an output of 30 Watts.

Terminology

• Power Amplifier – a type of amplifier built and designed for the purpose of delivering and supplying sufficient and maximum high output power to directly drive loudspeakers or loads, within a given percent of distortion
• BC550 – an NPN general purpose transistor with low current and low voltage used for low noise stages in audio frequency equipment
• MPSA56 – a PNP general purpose transistor enclosed in a TO-92 package and used for amplification and switching with features of low current with 500 mA maximum and low voltage with 80 V maximum
• BC183 – a complementary silicon planar epitaxial transistor used in AF small signal drivers and amplifiers as well as in low power universal applications due to its feature of good linearity of DC current gain
• TIP141 – a silicon epitaxial-base NPN power transistor in monolithic Darlington configuration, mounted in TO-218 package with integrated anti-parallel collector-emitter diode and used in linear and switching industrial equipment

Circuit Explanation

The components used in the circuit are widely available in the market which makes them more reasonable to utilize. In some situations, the use of small amplifier would be required but with having a good quality of operation. This circuit is already fixed in such a way that it will not require any innovation. A Darlington pair exists in the power stage as denoted by transistors Q9 and Q10, which are enclosed in a TOP3 package. The Darlington pair consists of two transistors arranged in such a way that the first transistor’s emitter feeds into the second transistor’s base. The advantages of using this pair is for amplification of weak signals and providing particularly high current gain which reflects into a high input impedance for the whole Darlington circuit when compared to a single transistor.

A suitable heatsink should be provided for the Darlington pair. Between the heatsink and the transistors is a silica and mica ointment, also known as thermal paste, for better absorption of high temperature. The bias current across the circuit is being regulated by the 250 Ohms trimmer TR1. This is done by placing the terminal to one of the resistors R20 or R21 with a multimeter while setting the scale to 200 mV. The adjustment of TR1 is started until a visual indication or result shows 12 mV. This voltage drop is in reference with the 30 mA current. The amplifier is then left to operate for about 15 minutes without the presence of an input signal. The measurement is done again and if the desired voltage is not attained, the adjustment should be repeated under 30 mA current again.

Application

The mini power amplifier having a 30 W power output can be easily used and directly connected to tape recorders, tuners, and CD players to enhance the quality of audio and video systems. It can also be used as a repeater power amplifier and for online covering broadcast. For some high-end designs, they are being utilized for satellite communications transmitters with high peak to average ratio signals.

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