Pumpkin Problems

[AndrewT]

Originally Posted by AndrewT

Replace the IN to OUT diode with a 30V Zener.

Originally Posted by KatieandDad

So you were talking about your Zener then, not the one in my circuit.

Yes.

[AndrewT]

Is there any possibility the Nch and Pch FETs are swapped?

[KatieandDad]

I was confused.

I knew that the 10V zener was perfectly safe.

I'm on the point of giving up with the Pumpkins anyway as I cant stop them oscillating. Just going to try the other one to see if its the same.

GRRRRRRRRRRR

[KatieandDad]

In (+) In (0V) and in (-)

Are all shorted on the board.

There is nothing else connected except for the PSU.

[KatieandDad]

Both Pumpkins are exactly the same which almost rules out component failure.

The odd thing is that the regulators are providing a clean +/- 36V into resistive loads.

As soon as a Pumpkin is connected, the 20MHz waveform appears on the supply rails, even when bypassed with 220uF + 220uF + 10uF + 120nF + 220nF.

[KatieandDad]

Funny thing is they "work", they just have this strange "whooshing" noise.

[KatieandDad]

All components are the correct value and the correct way round.

I'm at a complete loss as to why they are oscillating.

I even suspected the 'scope but another shows the same story.

[KatieandDad]

Maybe the excitement of the Pumpkin is this oscillation. Andrew T came up with a different approach saying, maybe they are supposed to oscillate.

[KatieandDad]

Funny how all the "Design Engineers" out there cannot even offer an explanation as to why the Pumpkins are oscillating.

I have a feeling that they all do this and that I am the first to notice it.

[Salas]

Originally Posted by KatieandDad

Both Pumpkins are exactly the same which almost rules out component failure.

The odd thing is that the regulators are providing a clean +/- 36V into resistive loads.

As soon as a Pumpkin is connected, the 20MHz waveform appears on the supply rails, even when bypassed with 220uF + 220uF + 10uF + 120nF + 220nF.

I would delete one by one the decoupling capacitors hanging off the supply rails on the Pumpkin starting with the 120n & 220n. Checking if the oscillation would back off or even stop. There could be a chance they twist the phase margin of the supplies.