LM4780: Maximum usable power output

[yusuf]

Attached is THD+N vs Output Power plot of parallel configuration from Overture™ Series guide. Does it mean parallel configuration is unusable over 100W (due to high THD).

Thanks
Yusuf

[ttan98]

the curve shows the amplifier clips above 100W(closer to 110-120W) hence the THD rises rapidly.

Note the power supply is at +/-35V, if the PS is less than +/- 35 the power output will decrease.

[SpittinLLama]

In parallel 4 ohms means each IC in a 2 chip design sees 8 ohms. At this point it is a thermal limitation. National shows what can be done with a consevative design (meaning no fan on the heat sink and sine waves all day long). So if you want to use a bigger heat sink or since music is less demanding than sine waves you can get more power. You just need to boost the supply voltage higher. I have an amp I built that runs more like 140W but it will over heat (LM3886 protection circuitry kicks in) with sine waves. I have run it for hours doing a DJ job with out any problem. The maximum supply voltage from the LM3886 datasheet is +/-42V with a signal so you can use up to this level but you will need to use a bigger heat sink, a fan or just run music to keep it cool enough. You can only get about 60 - 70W maximum per LM3886 no matter what configuration you do or load. Just the physics limitations.

-SL

[Upupa Epops]

You don't belive me, Yusuf ? In parallel mode, by +/- 35 V rails ( unregulated, 200 VA toroidal transformer ), this amp give approximately 85 W into four Ohm, 120 W into two Ohm and 120 W into eight Ohm by bridge mode...