Simple 100 Watt MOSFET using Dual Pairs of IRFP240/9240

[lineup]

I want to share an amplifier I have designed using spice model.
I have not built it. But according to my tests it performs very well.

Have a look at my attachment.
There is the simplified schematic.
I will be back with more details.

Enjoy!

 

[Veysel]

5.3 ma so high for ltp stage

 

[nigelwright7557]

u1+2 will need caps of about 47pf from b to c to stay stable.

 

[lineup]

The Power Supply

For around 100 Watt output
I would recommend 2x28 VAC, 300 VA transformer.
One such transformer should feed both channels,

Rectified the transformer should give around 2x40 VDC to the amplifier.

 

[AKSA]

Good to see you Lineup, welcome back!

Your amp topology was published in 1972 with Hitachi when they released their famous lateral mosfets (2SK134, 2SKJ49 IIRC), and became pretty much the base for most PA amplifiers, and many domestic amps too. It's a good topology!

From my experience using a single zener as the bias generator and no source resistors will bring thermal runaway at the output stage. I have found with hexfets that the bias generator should be a composite of a 4.7V zener in series with a Vbe multiplier (which drops 3.5V) and the Vbe multiplier should be a BD139 thermally bonded to one of the output devices. This controls the bias very nicely, even with low source resistors.

Hugh

 

[JeffYoung]

I've been working on something pretty similar.

Main differences:

• I'm using a JFET IPS (which also means I had to cascode it).
• I'm using a Wilson current mirror (with a potentiometer for DC offset adjustment).
• I'm using a BJT bias spreader.
• I've also got a pile of 240s/9240s so I needed drivers to keep the slew rate up.

Cheers,
Jeff.

 

[lineup]

@AKSA
Thanks for some history.
I was inspired by MAPLIN MOSFET Kit.
So, I realize this is not at all something new.
The difference is only in small details.

And I am using a VBE-multiplier. One BD139 to sense the heat.
I will publish my full schematic later.

@JeffYoung
Yes, that is pretty much the same design.
But I only have one pair off IRFP240/9240.
Thanks for your schematic.

 

[lineup]

MOSFET Full Schematic

Here is the full schematic.
The THD distortion is very low.
Even at 100 Watt out.

 

[lineup]

MAPLIN Old MOSFET Amplifier

Here is the old MAPLIN amplifier that inspired me.
It uses lateral MOS in output.
Simple but good!

 

[lineup]

Some Figures

Fourier Analysis:

8 Ohm
001 Watt THD 0.0000429%
010 Watt THD 0.0000656%
100 Watt THD 0.0002089%

4 Ohm
001 Watt THD 0.0000669%
010 Watt THD 0.0000727%
100 Watt THD 0.0001274%

The maximum power is 136 Watt into 8 Ohm.
And 263 Watt into 4 Ohm.