Re: Groundplane in poweramplifier PCB design

On Wednesday 19 April 2006 05:00, Ken Smith wrote:
I'd worry a lot more about a reactive load.

What about a reactive load? Isn't any speaker a reactive load?

Try this idea .. Simplified circuit Ascii ART:

!
!/
-----+---+-------!
! ! !\e Q5+Q7
Q9 \! !
! !-------+
! e/! NPN !
! ! Q98 [R13]
! ! !
! ! +------------ load
! ! !
! ! [R14]
! e\! PNP !
! !-------+
! /! !
! ! Q99 !/e
---+---+-------! Q6+Q8
!\
!

Assume that Q5+Q7 are passing enough in R13 to make 2 diode drops of
current. Both Q98 and Q99 will be biased on. Q99 will be super-saturated
so its base current rating has to be enough.

Now the remaining problem is that Q4 is not current limited. It needs a
resistor in its emitter and R6 needs to be a larger value + a diode. You
can make it so that the collector current of Q4 is nearly a constant times
the collector current of Q1.

The whole R9,R10 + C5 network could be replaced by another constant
current circuit using D1 voltage.



As you can read in my reply to Ban's message, the absence of a current limiter
is intentional. I also don't plan to include one. In all the time I have used
the amp, and all the others that where built, it has not been necessary.

.