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Series MOSFET regulator better with just voltage ref on gate or with error amp?
Series MOSFET regulator better with just voltage ref on gate or with error amp?
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Old 15th January 2007, 02:15 PM   #11
SY is offline SY  United States
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Series MOSFET regulator better with just voltage ref on gate or with error amp?
Jack, my info came from the Errol Dietz EDN paper reprinted in Pease's "Troubleshooting." He shows the effect of bypassing the reference resistor and the output on noise and source impedance.
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Old 15th January 2007, 04:35 PM   #12
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Series MOSFET regulator better with just voltage ref on gate or with error amp?
i think you have to take a look at the charts in 2/95 Audio Amateur -- at any rate, here are some bandwidth limited results integrated over 10 seconds -- using a 5223A storage scope and a 5a22n differential amplifier -- it's a much lower noise setup than my TDS3012B -- (edit) I also use the Jim Williams "cookie tin" isolation method and zero out the charge on the preamp before each measurement:

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BASELINE:

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Old 15th January 2007, 07:56 PM   #13
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Series MOSFET regulator better with just voltage ref on gate or with error amp?
From my experience: simple source follower is enough for grids of output toobs and pre powering.
I used an one transistor error amp in the power supply with positive feedback by current that applies voltage to tubes when they are hot and start consuming current.
I can repost the schematic if you want.
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Old 15th January 2007, 08:44 PM   #14
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Series MOSFET regulator better with just voltage ref on gate or with error amp?
Jack, I don't mean to be greedy but... could you do this with both an output and reference bypass? And a little higher current- 5mA is less than the chip needs to regulate properly, or at least is on the hairy edge.

I'll try to scan some of Dietz's results.
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Old 16th January 2007, 01:59 AM   #15
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Series MOSFET regulator better with just voltage ref on gate or with error amp?
Jack, I am totally wrong here. On reviewing the Dietz paper, he shows noise voltage versus frequency, which is in the microvolt range. But without knowing his measurement bandwidth, it's likely that the rms value is pretty high as you're seeing.

The interesting thing about his results is that the value of the output bypass controls that noise spectrum because of the interaction with the source resistance and inductance of the 317.
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Old 16th January 2007, 10:59 PM   #16
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Hi, Wavebourn.

I am encouraged by your comments, as well those from SY.
Quote:
I can repost the schematic if you want.
Yes, that would be interesting, thanks.

Hi, SY,

Could an LM317 be used effectively as a current source, to develop a fixed voltage across a resistor to apply to the gate of a MOSFET series regulator, do you think? It would avoid having a string of high-voltage zeners, which I don't like the idea of, or a string of VR tubes, which would be unwieldy and take up space.
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Old 17th January 2007, 12:56 AM   #17
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Series MOSFET regulator better with just voltage ref on gate or with error amp?
Quote:
Originally posted by ray_moth
Hi, Wavebourn.


Yes, that would be interesting, thanks.

Here you go:

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Old 17th January 2007, 01:48 AM   #18
Wavebourn is offline Wavebourn  United States
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Series MOSFET regulator better with just voltage ref on gate or with error amp?
A first, it starts softly, raising a voltage up slowly, waiting for tubes to warm up and to start consuming a current. As the result of a current, due to a positive feedback it more quickly increases output voltage up to a regulated value, after that a positive feedback stops working, but a negative feedback starts to dominate, stabilizing output voltage on a given level, and decreasing a ripple level, without a costly and heavy chokes, without vacuum tubes to regulate output voltage.

Please be advised that no one polarity of a rectifier and filter cap must be grounded!
Also, it produces a negative bias voltage that may be used for good, otherwise leave it as is (it is a positive feedback loop for soft starting).

Vout=12V*(R5/(R6+R7)) so you may vary output voltage.
Minimum input voltage should be no less than 5V + ripple + Vout + 12V.

However, you may use it for another voltages. For example, 36V zener may be used for a bias stabilizer (it is a shunt regulator that takes the current from the entire amp), and resistors in feedback recalculated for 350V output (however, make sure that selected transistors and electrolytics can work on such voltages), to power 6L6 amp. 400V rectified in such case would be enough.
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Old 17th January 2007, 02:08 AM   #19
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Series MOSFET regulator better with just voltage ref on gate or with error amp?
Now how do I fit this into my tube amp ?
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Old 17th January 2007, 08:48 AM   #20
ray_moth is offline ray_moth  Indonesia
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Hi Wavebourn,

Thanks for putting up the schematic and the explanation. I must be a bit slow, I can't see a positive FB loop nor what would cause a soft start nor how it senses the amp starting to draw current. Could you please give me a clue?
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