700 Watts Class D Power Amplifier in the iPod Size
Single-ended Class A was the dominant circuit topology in the gain of the audio signal, as Lee De Forest invented the triode in 1906. This simple circuit configuration provides good linearity, but the unit still conduct current topology is very inefficient.
Class A single-ended amplifier has an efficiency of over 25% at maximum power. The most problematic feature of the Class A in efficiency was the large amount of current that maintained high idle energy consumption in the device output, even without power.
The double-ended Class B amplifier was invented to solve the deficit in power consumption at idle by introducing a concept of switching two output devices only half of the cycle to carry audio device. By eliminating the slow flow, the efficiency of class B up to 78.5% at the maximum output power and no power consumption at idle.
A class AB amplifier is usually a small stream at idle (in the order of mA) via two mechanisms. Although similar in the effectiveness of the Class B, Class AB crossover distortion eliminated by adding a shell conduction angle. Thus, the class AB was the dominant power amplifier topology.
The efficiency of linear amplification is due to its charge state and the bus voltage, determined no device parameters such as current gain hFE FT or transition frequency. The power loss is caused by the product of the voltage across the power device and the current through the device. Since the topology is in the linear region of operation, the power losses and high efficiency is usually less than 25%. Class AB audio amplifiers require large thermal management systems, such as heat and more power the speaker will be emitted.
There are dynamic modulation of the power supply designed to provide a higher efficiency than Class AB, Class H and Class G topology and reach these approaches sacrifice performance audio and rely on power-switching topologies.
Thank you to the low Qg in the MOSFET gate drive that is easy to control, the IC also deal with the noise sensitive analog section on the same chip. In addition, low Qg in the low power MOSFET gate drive, so all four phases of the pilot will fit in a small MLP package.
The example of the resulting design is 4 ” x 2.8″ board room that offers a complete design of the size of an iPod has 90% efficiency and offers performance comparable to an audio output of the class AB amplifier. The last class-D design makes for better audio quality with superior energy efficiency at lower cost to reach this topology makes even closer to the ideal amplifier.
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