How best to drop ~180V?

Get a life you granny f****ng h*mo. You need to head in to oxford street to see your mates and escape that landlord for a while.

" Michael Asshole Terrell"

( snip more psycho abuse)

** This Terrell asshole is a criminal psychopath.

An autistic cretin & a paranoid aggressive.

Paranoid schizophrenics are incurable.

...... Phil

"The Real Andy"

** This seemingly anonymous CUNT is "Andrew Pearson" of Brisbane, Queensland.

He used to spend his life sucking c**ks at "Jupiters Technology".

A despicable bunch of slimy, criminal cunts in the so called "gaming industry" .

Andrew is far, far worse than any of them.

The criminal cunts booted the autistic Pearson out, over three years back.

Cos he was a useless, brain dead pile of shit.

Now the vile, autistic, psychopath, waste of space, is a full time drug addict.

Go get f***ed - Andy.

....... Phil

Yawn...

Thanks very much for your help. I have Art of Electronics, and am reading it now.

That's good. :-)

Tell us more about your application. What are your goals?

--
 Thanks,
    - Win

Although I'm offended by Phil's tone, which isn't conversational, and is certainly impolite, I'll address his remarks. First, we still don't know Ross Tucker (NS7F) rjtucke's actual application, although he's come back with a short response. Let's assume it's a tube amplifier of some sort, audio or RF. We also don't know if his 520V is regulated or not, but if it was we'd assume he'd seek a way to simply change its regulation voltage.

One might assert that actual supply voltages aren't very important for tube amplifiers, but unregulated power supplies suffer from ac-line variations, voltage droop under load, and ripple losses. Arguably the voltage range resulting from the sum of these effects compromises the best-possible performance of a tube amplifier, and indeed one often finds a regulator employed in tube circuits.

Furthermore, if one takes an already-wide unregulated voltage range and applies it to a lower voltage, such as 350 vs 520 volts, using a fixed voltage drop such as with zeners, the variation compared to the new lower voltage is nearly 50% higher. If one didn't have a regulated supply before, he'd certainly want one now! That's my story, and I'm sticking to it. :-)

Phil suggested six 5-watt 28V zener diodes in series to drop 170V. The 5-watt dissipation rating comes from assuming the junction is operated at 200C (which is too high, BTW) and the zener leads are maintained at 75C or lower. But the latter would be very difficult to do with six closely-spaced diodes dissipating 14 watts, so even though each zener is dissipating only 2.3W, it's likely the zener junction temp will still approach 200C. So Ross would have to add 9 volts for 5% zener tolerance to his already-wide voltage spread, plus up to 32 volts for the zener tempco, according to the 1n5352 datasheet. That's another 41V or 12%. It doesn't look good to me.

As a last comment, one should consider what will happen to these series zeners under the condition of a short-circuit fault. Ask, how much current will the 520V supply deliver into a 170V load?

While I'm not enthusiastic about fixed-voltage-dropping schemes, if I were still to choose this, I'd make an active zener using a power transistor and resistor to dissipate the heat, and thereby avoid dissipation in the voltage-reference components, e.g.,

. 20-watt adjustable-voltage active zener . . n-channel MOSFET . 520V in 1.5k, 100W IRF620, 10W sink Vin-170V . ----+-------/\\/\\--------- d s --/\\/\\-+---- 100mA max . | g 10 | . | | 1n4744A | . | +----|

Correction, fixing the 22k and 1.5k resistor locations:

. 20-watt adjustable-voltage active zener . . n-channel MOSFET . 520V in 1.5k, 100W IRF620, 10W sink Vin-170V . ----+-------/\\/\\--------- d s --/\\/\\-+---- 100mA max . | g 10 | . | | | . | +----|

"Winfield Hill"

** ROTFL.

So this posturing Win character ACTUALLY expects folk he has regularly publicly slandered to be polite to him ?

What an ass.

** So stop right there. ** Far too much assuming.

** It is the simplest solution with a useful degree of voltage regulation and far less dissipation that a resistive divider.

Here is what I actually posted - since Win is just about to misrepresent it .

----------------------------------------------------------------------

" ** 6 x 5 watt zeners in series - 28 volts each. Mounted apart on a tag strip for heatsinking and ventilation. "

----------------------------------------------------------------------

** Told ya !!!

** Not when mounted the way I said to.

** Once devices are fitted - there is no voltage tolerance issue.

The tempco of a 28 volt, 5W zener is +23mV/C - so each rises by only 2.5 volts in my example.

Once the zener's operating temp stabilises - there is no tempco issue.

The OP can adjust the zener string to get an exact voltage outcome.

Win has assumed the OP has a production line to deal with.

Occam is having kittens.

** A 160mA , M205 fuse will solve that nicely.

........ Phil

In article , Winfield Hill wrote: [huge snip]

Hello Win. Let's wallow in some nostalgia.

Use a big old triode as a cathode follower, with the grid driven by a single HV transistor (or even another valve or MOSFET?) doing the 350V regulation.

/ | | | 520V---+---| | | | | | | | A G C | | +-------+-----+-->350V / | | | \\ +----/\\/\\/----+ | / | | | | | \\ | / | / | \\ | \\ | / c\\| | +| | |-----+-----+ ===C | e/| _|_ | | | | /_\\ | | | | | | | +-------+-------+ \\ | \\_|_ / | Zener/_\\ 100+V? \\ | | | | 0V------------+-------------+-----+--0V

It costs a heater transformer, but avoids the heastsink and semiconductor protection problems.

--
Tony Williams.

Ah yes, and a single mpsA42 transistor serves fine, thanks to your use of a high-voltage zener, and a diode to handle startup and short-circuit protection for the transistor.

In a regulator circuit like this tubes have the attractive property of not requiring a pullup resistor to Vin, which is big nuisance issue when using n-channel power MOSFETs. One could use a depletion-mode MOSFET, but there are very few to choose from that can handle much current or power.

--
 Thanks,
    - Win