200W class A psu considerations with IRF240

[DUG]

I have a question regarding the definition of CLASS A.

Let's for the moment assume a complimentary/symmetry output stage with active devices in both the top and bottom positions.

Let's assume +/- 16V rails and an 8R load. Let's also assume the device can go to rail just to make it easier.

If my Iq is set to 0.1A and in a positive swing the peak current in the + side goes to 2A and the negative side is minimal. (lets say 0.001A)

That would be class AB.

If I set the Iq to 2.5A and had the same output swing and the bottom device maintained the 2.5A so the top device would have to supply 4.5A (2A o/p + 2.5A Iq from the bottom device)

That would be class A because the bottom device was still in a conduction mode.

What about in between.

I set my Iq to 1A and design the circuitry to maintain that as a minimum.

The positive swing goes to 16V @ 2A output.

The upper device supplies 3A and the lower device still supplies 1A.

This should also be class A...The inactive device (lower) is still maintaining conduction and has not "shut off".

This definition seems to be in accordance with this thread:

What is the definition of Class A?

So if you have designed the output stage not to go below a certain current (never shut "off") then you have class A.

Even on a 400W with only 0.5A Iq.

This should make your class A power supply calculations easier.

Thoughts anyone?

[djk]

400W out of four Hexfets?

Have you calculated the junction temperature?

How will it look with a 55°C ambient temperature?