Latest project 300WRMS vertical mosfet amp with speaker protection circuit.

Latest project 300WRMS vertical mosfet amp with speaker protection circuit.

Basic dual LTP front end.
Second LTP has current mirror and Vbe multiplier into 4 vertical mosfets.

Speaker protection is done by a PIC micro controlling a relay while monitoring amp output volts.
If PIC sees DC for 500Ms it turns off relay.
There is also a 3 second delay on relay switching on to stop power up thumps.

[IMGDEAD]http://www.ckpr.talktalk.net/300WRMS.JPG[/IMGDEAD]
 
Latest project 300WRMS vertical mosfet amp with speaker protection circuit.

Basic dual LTP front end.
Second LTP has current mirror and Vbe multiplier into 4 vertical mosfets.

Speaker protection is done by a PIC micro controlling a relay while monitoring amp output volts.
If PIC sees DC for 500Ms it turns off relay.
There is also a 3 second delay on relay switching on to stop power up thumps.

[IMGDEAD]http://www.ckpr.talktalk.net/300WRMS.JPG[/IMGDEAD]

Hi Nigel,

Looks cool, however ... did you try to run it at 300W RMS continuously?
I mean - that would be cool if those 4 guys on a heatsink can handle it, but ... 300W is A LOT of heat dissipation. I would say, it sounds like a bit too much for 2 pairs of IRFP240/9240 devices (correct me if I'm wrong).

Cjeers,
Valery
 
It does need quite a big heat sink for full power continuously.

If I remember correctly you assume that 2/3 of power supply voltage is average.
This gives 33 volts times 8 amps which is about 250 watts or 125 watts per mosfet.
However mosfets are only on for 1/2 of time as music is AC.
This gives 63 watts dissipation in each mosfet.

Correct me if I missed something or got it wrong.

Bias current is around 10ma per mosfet so doesnt add much to heat.

I tested it today and it gives -3db at 50KHz so it is adequate frequency response.

[IMGDEAD]http://www.ckpr.talktalk.net/600.bmp[/IMGDEAD]
 
Last edited:
Is that your PCB design?
Nice :)

Assuming 70% efficiency in a Class AB (little idle dissipation) you have about 30% dissipation, so 300*0.3=90W total, and that at about 40% sinewave power on the rated load; at full power you actually dissipate less and even less if clipping.

FWIW I have used 4 x IRFP250/240 for ages (and earlier used 4 x 2N3773) in my [email protected] ohms Bass amplifiers with no problems at all.

Hetasink is not a finned one but the amplifier back panel, fan cooled.
 
Hi Guys

Nigel, your schematics are incredibly difficult to read. It would be easier if they had a white background. Negative space sucks the light out of the room...

Four devices is fine if the 300W is transient. You will be deaf by the weekend if you have it cranked all the time. Not a great prospect if you like building things you can play music through.

Have fun
 
Hi Guys

Nigel, your schematics are incredibly difficult to read. It would be easier if they had a white background. Negative space sucks the light out of the room...

Four devices is fine if the 300W is transient. You will be deaf by the weekend if you have it cranked all the time. Not a great prospect if you like building things you can play music through.

Have fun

The schematics are reduced before putting them online as I have limited web space.
They look fine in the CAD software.

I prefer black background as white gives me migraines and eye strain.