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Old 27th August 2005, 06:47 PM   #1
Danko is offline Danko  Hungary
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Question TL431: Can it regulate 300V DC?

Hi!


How much voltage can I regulate with TL431? Can I make 300V (or even higher!) with this IC? You know, the TL431+optocoupler style feedback.

It come to my mind, "what if I make a tube amplifier with switched mode powersupply for the plate-supply?" :-)


You may think, that I'm a "little bit" pervert .....:-D
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Old 27th August 2005, 07:56 PM   #2
Eva is offline Eva  Spain
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TL431 is rated at 37V so using it with higher voltages requires additional components in order to ensure that this value is not exceeded.

For example, you may use an auxiliary 12V winding to power the optocoupler and a clamping diode to protect the adjust terminal. A high voltage cascode transistor like MPSA44 would also be a solution.

Note that in order to get the 2.5V reference from 300V, a precision resistor in the lower leg of the voltage divider is required.

Anyway, I think that for such high voltages the discrete approach is preferable.
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Old 27th August 2005, 08:05 PM   #3
Danko is offline Danko  Hungary
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Eva, what do you mean under "discrete aproach"? A reference-voltage on the secondary-side, and a voltage divider, wich divides the output voltage, a comparator, and an outocoupler?
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Old 27th August 2005, 09:01 PM   #4
Danko is offline Danko  Hungary
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It looks useful, for me! :-)

Click the image to open in full size.
The picture is from tubecad.com


Thanks, Eva!
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Old 28th August 2005, 01:07 PM   #5
Eva is offline Eva  Spain
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I would use somethinkg like that:

Click the image to open in full size.
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Old 28th August 2005, 01:32 PM   #6
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Danko,
I tried the solid state one with IRF HV fets but I found the thing very sensitive to oscilation.
And the quality of the feedback resistors is also very crucial. With some there is ringing, others not.

I settled with a tube based diagram. The zeners are there for the overload protection of the 431.
As long as this is running before the PS comes up then the startup is very smooth. I use an indirect heated diode and an input inductance. (Otherwise it will want to sustain the HV due to the feedback capacitor.
It works very fine.

The HV can be set with just so much current that the HV net residue completely disappers.
I don't use a smothing capacitor over the whole unit.

This comes after a output resistor. Something like 10 mF should do.
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File Type: jpg 431 300v stabilizer.jpg (11.3 KB, 566 views)
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Old 3rd September 2005, 01:41 PM   #7
Danko is offline Danko  Hungary
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What about this? -> http://sziget.mine.nu/~danko/aramkor/Screenshot-211.png

The TL431 has to regulate onyl 50V. If i'm correct
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Old 23rd September 2005, 02:18 PM   #8
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Quote:
Originally posted by Eva
I would use somethinkg like that:


EVA -- the feedback/ref pin on the TL431 is the error opamp "V+in" -- see the Texas Instruments drawing.

You can use the TL431 for a HV supply -- consider it driving an inverting amplifier which drives a current source (i.e. a high voltage MOSFET amplifier). It's a bit more difficult to compensate since you don't have access to the error amplifier "V-in". This was the basis of an article i wrote on a microcontrolled high voltage power supply (with attribution to the folks who first brought it to mind -- Horowitz and Hill).

If you are going to the effort of building a HV regulated supply I would use a better opamp and better reference than the TL431, however.
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Old 23rd September 2005, 02:49 PM   #9
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I have a MR psu by Raleigh Audio that uses the TL431 with a 6N1P. I think there is an example on tubecad.com

In the MR case it is a shuntreg after a CCS. Works like a charm.

Regards,
Bas
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Old 23rd September 2005, 03:57 PM   #10
Eva is offline Eva  Spain
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Quote:
Originally posted by jackinnj



EVA -- the feedback/ref pin on the TL431 is the error opamp "V+in" -- see the Texas Instruments drawing.


The op-amp in that TI drawing is driving a NPN output transistor that reverses the polarity of the input signal, so actually the input pins work as if they were reversed. Note that my simplified schematic doesn't include that output transistor, so it still reflects the actual polarity with which TL431 responds.
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