HP97 The journey begins

[Harald]

(05-05-2019 01:03 AM)teenix Wrote:  

(05-04-2019 09:16 AM)Harald Wrote:  Hi Tony,

That is good news indeed!
I doubt the shielded coil will improve things a lot. It Is more likely to be a layout issue. If you like you can post the schematic and layout of the power supply section, maybe we can spot a problem.

Cheers,
Harald

Attached is the relevant part of the PCB for the PSU. Under the board is just signal paths.

GND comes in from the far left of the PCB direct to the LP2950 GND pin.

The marked 5V and GND points feed each circuit chip in a serial fashion with decoupling caps placed just prior to reaching the respective chip.

The LP2950 Vin is under the PCB from the yellow tracks.


cheers

Tony

Hi Tony,

Thanks for the schematic and layout. You have kept the Cathode of D3 close to C8, that is good. But the track from U7 pin 1, which is the internal switch, to D3 is quite long. You would want to keep that as short as possible to minimize inductance in that path. You are better of moving the choke a bit further away and moveing the diode closer.
It is important to place diode and input and output capacitor close to the IC. You need to minimize path length in all the paths that carry switched currents. The inductor path is not critical.
I'll try and print the schematic and mark the relevant paths.

Regarding the voltage specs on the amplifier IC I am not sure either. I would have thought the unregulated output of the voltage doubler IC would be ok, but that is only a guess, there is just not enough information on it available.

Cheers,
Harald