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Old 30th December 2011, 10:22 AM   #21
AndrewT is offline AndrewT  Scotland
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Replace the IN to OUT diode with a 30V Zener.
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So you were talking about your Zener then, not the one in my circuit.
Yes.
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Old 30th December 2011, 10:24 AM   #22
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Is there any possibility the Nch and Pch FETs are swapped?
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Old 30th December 2011, 10:25 AM   #23
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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
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Old 30th December 2011, 10:26 AM   #24
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In (+) In (0V) and in (-)

Are all shorted on the board.

There is nothing else connected except for the PSU.
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Last edited by KatieandDad; 30th December 2011 at 10:30 AM.
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Old 30th December 2011, 11:35 AM   #25
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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.
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Old 30th December 2011, 11:36 AM   #26
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Funny thing is they "work", they just have this strange "whooshing" noise.
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Old 30th December 2011, 01:55 PM   #27
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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.
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Old 30th December 2011, 01:56 PM   #28
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Maybe the excitement of the Pumpkin is this oscillation. Andrew T came up with a different approach saying, maybe they are supposed to oscillate.
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Old 30th December 2011, 02:05 PM   #29
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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.
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Old 30th December 2011, 02:49 PM   #30
Salas is online now Salas  Greece
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Quote:
Originally Posted by KatieandDad View Post
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.
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