300vdc power supply design?

[ShaunAndFRED]

Hi Dave and EEVBloggers!

I loved the entire series on designing the lab bench supply, and I was wondering if you might feel so inspired to start again... but with a 300 vdc bench supply? Not to say do the entire design start to finish again, but I thought it would be cool to talk about the different challenges and design elements of higher voltage supplies. I guess I felt inspired by the Xantrex teardown. Maybe that's just me though. Anyway, love the blog! Keep it up!

[Rerouter]

its really a specilised bit of kit, however if you want something like it, my first though would be use an isolation transformer with a few turns short on the output, rectified mains is about 335V DC, from there you can get away with linear stage probably loosing 10V for a nice stable output, as for linear voltage regulation for very high voltages, you can get away with a 5V op amp suprisingly, you have an npn on your op amps output, that is used to pull down a main pass element pnp's base, and turn it irrespective of the voltage its regualting, the transistors just have to be able to cope with the voltage (quite a few capable)

if you want fancy like the torn down one, its pretty much buy or buggered, as a whole lot of time and thought went into that thing,

[Psi]

If you want variable output up to 300V you can make it a little easier and safer by first designing and building a low voltage variable AC power supply, (say 40V or example).

When you have it all working add a stepup transformer plus bridge rectifier and you have variable high voltage DC.
You can even add optoisolated feedback so it regulates from the high voltage output.

At least when doing it that way most of the design and testing is at safe voltages.
However it is a little more complex as your going
AC mains into step down transformer and bridge -> DC 40v -> regulated voltage (0-28AC) --> stepup transformer (28-212v) -> bridge rectifier -> DC 0-300v

[nitro2k01]

DC 40v -> regulated voltage (0-28AC)

Wait what, DC->AC? That doesn't sound like quite the easy beginnner's project...

[Bored@Work]

This is one of those projects were if you need to ask how to do it you probably shouldn't do it.

[N2IXK]

This is one of those projects that can be a pain with solid state, but is trivial using those funny glass FETs with the built-in pilot light. Such power supplies were a fixture on test benches during the tube era, so a look at a typical schematic should give you some ideas.

The Heathkit PS-4 provided 0-400V @ 150 mA, using a pair of common, still-in-production 6L6 tubes as pass elements:

http://www.nostalgickitscentral.com/heath/schematics/heathkit_schema_ps4.pdf

[Psi]

DC 40v -> regulated voltage (0-28AC)

Wait what, DC->AC? That doesn't sound like quite the easy beginnner's project...

Sure it is, 555 timer or other 50hz pulse/sine generator into a 5A opamp.  Done.
or an H bridge if you want a more DIY approach.


Ever try working on a 230VAC to 0-300VDC variable voltage power supply? its anything but easy due to the safety aspects compared to a low voltage power supply.

[Zero999]

AC mains into step down transformer and bridge -> DC 40v -> regulated voltage (0-28AC) --> stepup transformer (28-212v) -> bridge rectifier -> DC 0-300v

Seems a bit complex.

Convert the mains voltage to DC first but it would be far easier to use a fly-back regulator to get a regulated 300VDC supply. A standard off the shelf 48VDC SMPS could be used for the first bit and there are plenty of standard ICs which can be used to make a 48V to 300V converter.