Hi,
Just some info...
Multiple users of this forum, saying that a compound transistor often oscillate...
That's not true if you use it right, directly mounted to the base resistor to the first transistor.
So do not install the resistor on the board and then go with a piece of wire to the base, Wrong!
And mount a small resistor also in the emittor wire of the first transistor, see the schematic .
Here you can see a earlier version of my design, with two compound power sections.
Extreem low noise reference section and good dynamic behavior, this schematic is not compleet! just to let you see how you aslso can do it.
DC Ri, how good are you building it? in my test setup it was smaler than 0.0001 Ohm.
Noise onder full load? about 2uV RMS 80Khz bandwith.
This schematic is tested with the ADA4077-2 and the NE5532A, but know i have better Opamps, to get the Ri @ high frequenties, of lower, better fase margin.
This is the Ri @ high frequency, "F" is the dual compound transistor, 100Khz 14m Ohm!
Dynamic behaviorJust a sample of one of the measurements, NO! the the design is not ringing, This is one of my torture test for power supply's
The dynamic load is connected via two cables of 50 cm and in the dynamic load is mounted a MKP capacitor 6,8uF.
The ringing what is visible, is caused by the residual induction of the twisted connecting cables and the 6,8uF.
It is verry hard for the power supply to get the error puls low as in this picture.
Test with 2 compound transistors, NE5532A and a 9.5-Amp load puls.
If i remove the 6,8uF capacitor then there is no ringing, just about 5 a 8mV drop and in 15uSec flat line. look at the line in the middle of the picture,
no droop 10mV/Dic is not enough to sense the Ri of this measurement.
Opamps
A OPA140/2140, TLE2071 and my compound power transistor wil give you an nice phase margin and a low Ri of your power supply.
This design is from the
Harrison Division of Hewlett Packart @ the end of 1950's... still going strong with modern components and some atention
My comments are intended only to show what is possible with an old design and new components.
Not to demonstrate a complete power supply design.
There are many ways to make a good linear power supply, this is just one of them.
Kind regarts
Blackdog