+AD4- Hi
+AD4-
+AD4- I would very much like to have some ideas, schematics, tips on how to
+AD4- design
+AD4- a lab power supply for experimenting with tube designs. The
+AD4- specifications
+AD4- could be like 0-500V 0-100mA... (?)
+AD4-
+AD4-
+AD4-
+AD4- I would like to build a good regulated power supply. Could i just design
+AD4- it
+AD4- like a normal low voltage PSU? like a opamp, voltagedivider, a BU508 as
+AD4- seriesregulator, and a couple of high voltage caps.??
+AD4-
+AD4-
+AD4-
+AD4- Please mail me any kind of schematics and give me some help and hints
+AD4- about
+AD4- this project...
+AD4-
+AD4-
+AD4-
+AD4- Peter
+AD4-
+AD4-
+AD4-
+AD4- Hi
+AD4-
+AD4- I would very much like to have some ideas, schematics, tips on how to
+AD4- design
+AD4- a lab power supply for experimenting with tube designs. The
+AD4- specifications
+AD4- could be like 0-500V 0-100mA... (?)
+AD4-
+AD4-
+AD4-
+AD4- I would like to build a good regulated power supply. Could i just design
+AD4- it
+AD4- like a normal low voltage PSU? like a opamp, voltagedivider, a BU508 as
+AD4- seriesregulator, and a couple of high voltage caps.??
+AD4-
+AD4-
+AD4-
+AD4- Please mail me any kind of schematics and give me some help and hints
+AD4- about
+AD4- this project...
+AD4-
+AD4-
+AD4-
+AD4- Peter
+AD4-
+AD4-
+AD4-
The LR8 is an elegant part, even though it can't handle 500V as the O.P. requested. But it's low cost and is readily available from Mouser in several package types.
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The simple regulator circuit in the second link may be suitable for retrofitting an old tube set, etc., where the wiring is well-controlled and the likelihood of a mishap such as a short is small, but without any current limiting, it's not suited for use as a lab-bench power supply, in my opinion. The circuit in Terry's link uses a 500V Vactrol to provide current limiting, which is an improvement (they're rather hard to get), but it lacks a foldback current-limit capability.
Both designs specify a TIP50 BJT-type pass transistor. Although these are rated at 500V, they are SOA-disabled like all BJTs, as I detailed before, and will be quickly destroyed if they dissipate much power at full voltage, such as happens under a short circuit. If you look at old commercial high-voltage linear power-supply designs using BJTs, you will see they stack them in series cascode as a solution to the severe SOA problem. Hence, neither design is well suited as it stands for use as a lab bench supply.
One small additional comment. Supertex LR8's are floating regulators powered from the Vin-Vout difference. This type of regulator always requires a brute-force compensation capacitor on its output. The LR8 datasheet specifies 1uF minimum, which both circuits fail to include. The 20uF capacitor after the emitter-follower has some effect, but if the TIP50's beta is 100, it looks like only 0.2uF to the regulator IC, and isn't a good substitute. After adding a capacitor, one should also add some TIP50 base resistance.
What about using the HV regulator shown on page 369 in the 2nd edition of AOE as a strating point? Maybe add a 2nd pass transistor with drain resistors and use mosfets in a TO247 pkg.
Fairchild's 240W FQA10N80C mosfet is one candidate, from Mouser at $3.82 each,
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With a large heat sink a single one of these FETs might be able to handle the pass-transistor task all by itself, especially if foldback current limiting is employed, say below 250V or so.
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