Please help with simple class D project!

[xiguo]

I have to design a simple class D amplifier for a class project. It has to meet the following specs:

Max output power = 500mW
HND = 0.01%
Efficiency = 85%

We are given two stable 1.5V supplies and are allowed to use any commercially available transistors and op amps.

Right now I only have a very basic working model (attached), and of course it is not even close to meeting the specs. Right now the output only swings from around 1.5V to -1.5V, which cannot deliver 500mW of power with an 8 ohm load.

How can I improve the design so that I can meet the specs? Please, any suggestions would very greatly appreciated. Thank you very much.

[BWRX]

With +/-1.5V rails, an 8ohm load, and a half bridge output stage you can achieve a theoretical output power of about 0.282Wmax or 0.141Wrms. With the same rail voltages, an 8 ohm load, and a full bridge output stage you can achieve a theoretical output power of 1.125Wmax or 0.563Wrms.

If you can build a boost converter you could increase the rail voltage quite a bit and be capable of more output power with a half bridge output stage.

[xiguo]

Thank you for the reply.

I have tried to do a full-bridge but can't get it to work. I am having trouble finding a schematic of a simple full-bridge amplifier (I can only find block diagrams). Does anyone have a schematic of a very simple full-bridge amplifier that I might be able to use?

Thank you very much.

[BWRX]

Just double the half bridge. Instead of connecting the load to ground it gets connected to the output of the second half bridge. Don't forget that each half bridge is driven 180 degrees out of phase with respect to each other (one side is inverted).