Power Amplifier Design

[Kemal Tangir]

I need to design a power amplifier with a mosfet output stage. It can be 2-3 stages. I have searched and tried different circuits but couldn't get a desired result because I am required to use single +12V supply and most of the examples are with Vdd and -Vdd. I don't know how to make a power amplifier with mosfet output stage using a single power supply or to convert a power amplifier circuit to a single supply version. Thanks in advance for the help.

 

[audioguru]

Class-D switching power amplifiers are made with Mosfets at the outputs. They use pulse-width-modulation to switch the Mosfets on and off at a high frequency. The audio modulates the duty-cycle of the switched waveform.
A TDA7294 is an audio power amplifier IC with Mosfets at its output. Its minimum supply voltage is plus and minus 10V. It usually uses a plus and minus 35V supply.

Linear power amplifiers are made with bipolar transistors at the outputs for very low distortion. Mosfets produce higher distortion and other problems. The output transistors are emitter-followers and output Mosfets are source-followers.

Most power Mosfets need a gate-source (G-S) voltage of 10V to fully turn on. Some need "only" 4.5V.
For a linear amplifier circuit if you use 10V G-S Mosfets then you need a high supply voltage.
If you use 4.5V G-S Mosfets then you need a supply voltage higher than 12V.
Maybe you can make a complicated voltage doubler circuit to convert +12V into +12V and -12V.

A power amplifier using bipolar transistors at the output will have a max output swing into an 8 ohm speaker of about 9V p-p when its supply voltage is +12V. Then the max output power before clipping is 1.27W.

A power amplifier using 4.5V G-S Mosfets at the output will have an output swing into 8 ohms of 2V p-p when its supply voltage is +12V. So the output power will be only 0.063W.