G-class with LM3886

[Elias]

Hello!

Have you seen any G-class amplifiers realised using LM3886 amplifier chip? I'm building an active loudspeaker system with surrounds so I need efficient amplifiers to be able to cope with the heat from 12 channels. The one G-class amplifier I know is done with TDA7294 http://www.st.com/stonline/books/pdf/docs/1057.pdf but somehow I feel that LM3886 might perform equally well or even better since LM3886 seems to have better distortion graphs, open loop gain and PSRR.

Please share your wisdom

-Elias

[AGGEMAM]

Uhm, the TDA7294 aren't very efficient. Only around 50% which is the same as the LM3886.

[Dxvideo]

What's the "Class G" ?

[djk]

http://www.diyvideo.com/forums/showt...threadid=28875

[tlmadsen]

HI

Class-G is aoutput stage "topology" where you have two or more sets of different PSU voltage, like +/- 20 V and +/- 55 V. Each voltage have its own "set" of output transistors.
This configuration take full advantage of the big creast-faktor in music (i.e. large difference in the avage power level used and the peak power levels. This is typically in the 10-30 dB range !!).
For most of the time the class-G amplifier will only be running on the lower voltage. When a peak comes along the higher voltage and output transistors will then "kick-in" when the peak are higher than the lower voltage can handle.
The difficult part of a class-G amplifier is to make the "transistion" between the two "sets" of voltage and output transistors, but is is possible.
By having two sets of PSU-voltage where you are runing on the lower most of the time your amplifier becomes much more efficient and you can use something like half or less size heatsink (realitively speaking).

You most likely use a class-G amplifier everyday since some af the drivers/amplifiers used for ADSL tranmision are class-G amplifiers.


I read somewhere that class-G amplifiers are also used for high power sonars for subs. Make some kind of sense.

I think it would be extremely difficult to make the LM3886 into any kind of class-G amplifier, since it is already "born" class-AB.
Maybe you could make a "semi" class-G amplifer using a power op-amp like the LM3886. This would had to "sense" the level of input signal and then in some way (MOSFET !) switch between two or more sets of PSU-voltage.

Let us all know if you succed

Thomas

[Dxvideo]

Hmmm So if I'm not wrong, in the TDA7294's datasheet, "the high efficiency application" is a good example for class-g! Is it?