Power Output

The power output stage design has been crucial in design of the amplifier. It has played a key role in determining the voltage supply specs, the speaker, the power MOSFETs, and the rated power desired at the load. Before beginning the design, the team needed a clear understanding of the differences between rated and continuous power, also coined peak and average power respectively.

Peak v. Average Power

The key difference between average power and peak power lies in the relation in delivered power over time. Average, or continuous, power refers to the true power delivered to a load over a specific period of time, often determined for testing. Peak, or instantaneous, power refers to the maximum power that an amplifier is capable of outputting in short bursts, but not sustain. The calculations are as followed and were used in determining important specifications such as supply voltage.

As seen above, the average power will be about half that of the peak power seen at the load.

Power Calculations

When determining our amplifier’s power, we had to consider the continuous power going to be delivered to our 4 Ohm load. Originally, the team wanted to achieve 20W of continuous power at the load. However, upon design, it was important to consider the headroom of our amplifier. Headroom is defined as difference in power between the amplifier’s maximum capable power output and the average amount of power necessary to play at the desired listening level.

In order to design with proper headroom in mind, the power calculations began by setting the average power to 50W. Using the power equations specified above, the RMS and peak voltages were found. Another parameter that was set was the amplifier efficiency. This value was arbitrarily chosen to be 90% knowing that the efficiency would range between 80%-95%.

By setting the efficiency, the total power dissipation could be approximated at the output, which came out to about 1.1W. The peak voltage, needed to provide 50W at the output, is approximately 20V. Although the power loss is significantly smaller than other classes of amplifiers, it still has to be accounted for. The voltage supply has been chosen to be 24V to account for this. This is one parameter needed for choosing the power supply.

Next, using the peak voltage, the rated power has been calculated to be 100W. Similarly, the peak current has been calculated to be 5A. The importance of these values is in choosing the power supply. The MOSFETs will be pulling a peak burst of 5A, the output is rated at 100W, and 24V peak is needed to drive the MOSFETs. Thus, an external power supply was chosen to accommodate these specifications. For more details please refer to the Voltage Regulation section.

Lastly, since the rated power of our amplifier is 100W and continuous power is 50W, the headroom between these values is only 3dB. In order to increase headroom for the sake of sound quality and too avoid clipping at the output, the team decided to design with at least 10dB of headroom. Thus, the continuous power outputting to the channel will be 10W for 10dB of headroom.

Power MOSFETs

The power MOSFETs were chosen from their rated power dissipation, max

Application with the Gate Driver