Jan, are there any other measuring point that I can check to encircle the reason for that curious behavoir. By the way, I have another T-Reg perfektly working in my phonostage. Works great.
Could the reason be that I put the FDP at Q 7 position only and there are only 30 mA running through?
Could the reason be that I put the FDP at Q 7 position only and there are only 30 mA running through?
No that should be OK. If the output is higher than the ref voltage, the opamp output should draw the Vgs of the FDP down, which isn't the case in this unit.
Just to exclude everything, can you verify that the opamp is installed in the correct orientation? And the FDP in Q7, should have the metal tab facing outward (which is the opposite for when it is mounted on the PCB heatsink).
Jan
I have a new set of boards coming in this week, expected to be delivered Wednesday.
In the mean time, our friend EUVL has discovered that when the regulator is switched on without load, there is a chance that the opamp non-inverting input is driven outside its limits. The way to prevent that is to replace zener diode D7 (see attached) by two reverse-parallel small signal diodes, preferable Schottky. A good part would be Mouser 511-BAT43 or 511-BAT42.
There should be no problem with the current PCB but I will adapt the next version of the board. I will also post this on the Linear audio website and note it in the BOM.
Jan
In the mean time, our friend EUVL has discovered that when the regulator is switched on without load, there is a chance that the opamp non-inverting input is driven outside its limits. The way to prevent that is to replace zener diode D7 (see attached) by two reverse-parallel small signal diodes, preferable Schottky. A good part would be Mouser 511-BAT43 or 511-BAT42.
There should be no problem with the current PCB but I will adapt the next version of the board. I will also post this on the Linear audio website and note it in the BOM.
Jan
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