Re: Groundplane in poweramplifier PCB design

In article <b9u1g.17910$6e2.1665@xxxxxxxxxxxxxxxxxx>,
Ban <bansuri@xxxxxxxxxxxx> wrote:
[...]
D1 will be 2V +/-10%, because the LED is operated at 1/10 its rated current

Its more because it is a green LED than the low current. I got the wrong
number when I said 3V.

and the current through Q3 will be between 2 and 2.6mA. You are right it is
stable. But I was talking about Q4, which has a beta of 100. Without
adjustment and temperature compensation it will take from 0.9 to 1.7mA when
idle.

I disagree with this. The input stage current and offset voltage will be
what moves. If Q4's collector current changes, the circuit will servo it
back.

I call that at least 1% THD. Don't forget, the input pair is the
reference and when the current ratio is 1:2, distortion will blossom, no
matter how high the gain will be.

I don't see how you got the 1%. Could you expand on it?

I don't see it as likely that the voltage on C3 can ever reverse. How
did you conclude that?

Well normally the bias current would be 1.3mA/Beta = 5uA and the voltage on
the cap -120mV, but when the O/P goes to +40Vp 20Hz, the current of 1.3mArms
*25ms / 100uF will let it have +200mV.

The supply is only 35V. I don't see the output swinging more than 33V or
so.


!
!/
-----+---+-------!
! ! !\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.

It won't help at all, 5A is the max current for 100W load. 40V steady are
200W.

Huh????

--
--
kensmith@xxxxxxxxx forging knowledge

.

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