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TL431 + common base amplifier stability?
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001:

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--- Quote from: 001 on October 14, 2019, 04:17:51 pm ---
Can You say, what is the best way to replace VR tube with TL431?

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What voltage regulator do you need to replace?

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Classic
5651 http://www.r-type.org/pdfs/5651.pdf
0A2 http://www.mif.pg.gda.pl/homepages/frank/sheets/035/0/0A2.pdf
Yansi:
I have always used small-medium signal fast NPNs from TV video amplifiers for the cascode.

Such as BF259, SF359, or 2SD1264 may work sufficiently.  Do not use large power BJTs, such as BU508, they are slow as ... just too slow.
floobydust:
Similar approach with 280V 0.1A and TL431, no zener. Schematic is from http://www.next-tube.com
pdf has explanations and measurements of the specs 0.35% line, 0.5% load regulation, max 420VDC input.
T3sl4co1l:

--- Quote from: schmitt trigger on October 14, 2019, 02:15:44 pm ---I have no doubt that you have built stable high voltage references. From other threads of yours, you appear to have significant knowledge with HV circuits (with HV simplistically defined as anything larger than 30 volts).

But as I mentioned earlier, I was unsuccessful in my previous attempt..... So the trick mentioned above is something that I might try in the future.
If the need arises.

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Try putting a resistor in series with the emitter, and a small R+C across the TL431 (R6, R7, C2 in flooby's attachment above).

Note that this configuration is only rated up to the 100mA the TL431 can draw, and down to the 1mA it's specified to regulate tightly to; this is much wider than a VR tube so it's plenty fine for that application.

The cascode base voltage needs to be set to limit TL431 dissipation; at say 50mA it should dissipate less than 625mW, but preferably a lot less, like 300 or 150mW.  That's 3-6V.  We can allow more cascode voltage if a resistor is used, sized to reach this point anyway; so, if it drops 6V at 50mA, it's a 120 ohm resistor, and the cascode can be 12V.  (The cascode can also be set by a zener diode instead of a resistor divider, which is convenient if you want to make a variable regulator.)

The transistor needs to be rated for power dissipation and SOA, which should be fine for most options.  BJTs: prefer audio/ linear / driver / power output types, with wide SOA.  150V at 30mA is 5W, so a well heatsinked TO-126 will do, MJE340 for example.  MOSFETs: check that it has a wide SOA.

Prefer smaller devices (lower capacitance), which will have less impact on performance and less need for compensation.  Check compensation with a source or load step test.

If the cascode divider has a low impedance (zener or cap-bypassed), consider a ferrite bead or series resistor to the base/gate terminal, to prevent oscillation.

Tim
001:

--- Quote from: Yansi on October 14, 2019, 07:40:42 pm ---
Such as BF259, SF359, or 2SD1264 may work sufficiently.  Do not use large power BJTs, such as BU508, they are slow as ... just too slow.

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Thank You!

That is "slow"? Is 4MHz not enough for this circuit?  :-//

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