300V power supply.

Hi all, So I'd like to make a 300 V supply. I don't really want to start from the AC line. So I've been looking for a DC-DC converter solution.

I started here, (of course)

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Figure 13 looked nice. I then priced a pico 32195 transformer. ~$100! Ouch! (maybe I can find a cheaper one.)

I then was trolling Linear Tech/ Analog Dev. What I mostly found was a line of Xenon lamp charges. LT3420 LT3468 LT3484 LT3485 LT3585 LT3750

I haven't delved into the spec sheets, but the LT3420 looks like it will work.

Any advice on any of these parts or other ideas is welcome.

Oh over the weekend I was thinking about making a C-W generator, (mostly because I always wanted to.) I was going to make my own oscillator ~10-100 kHz, boost the voltage with a transformer and send it into a CW network. Sounds fun, but a lot of work.

Oh finally I can buy DC-DC converters from pico electronics for ~$100.

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TIA George H.

Reply to
George Herold
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5 bux chip to charge a 220uF cap to 300 volts in the better part of 4 seconds at not much better than probably 70% efficiency in practice is not exactly setting my world on fire here
Reply to
bitrex

The whole circuit could be physically small so there's that, but a 220uF

300 volt photoflash cap is gigantic and will take up most of the board space anyway.

LT seems obsessed with everything-in-the-chip solutions but at boost ratios like 5-12 volts to 300-350 the on-die switch just hamstrings the thing IMO

Reply to
bitrex

These work quite well for me, u tried these?

Might want to swap out the eletros for some Nichicon or Panasonics

Reply to
bitrex

.

es/AN118fb.pdf

was a

s

This is to bias a APD, not for a photoflash. The spec sheet says it can be used as a HV supply. I've skimmed to spec sheet, but didn't really find anything telling me what to do if I just want it to hold a voltage. I posted a question to the Analog forum... at least I think I did. The lt3750 is a beefier part.

George H.

Reply to
George Herold

t from

s/AN118fb.pdf

No, I'd be afraid to put that in a product. What's the output ripple look like with ~1-2 mA of load?

George H.

Reply to
George Herold

t from

s/AN118fb.pdf

Oh I found this too... maybe more to your liking.

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GH

Reply to
George Herold

I'd be happy to take a look for you when I get a chance, in the meantime yeah you definitely don't need 40 watts. I got some "X-ray vision" pics of it that show all the part numbers and stuff, detailed enough to trace a circuit so you could probably do a "spin off" of the design if you like using significantly smaller diodes/switch/xfrmr.

It appears to use a 38438 current-mode PWM controller and a RU7088 MOSFET.

Reply to
bitrex

Pico is insane. I don't know why anybody buys their stuff.

How much current do you want? The lower section of this will do 300 volts.

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Just skip the C-W HV stuff.

You could also buy some cheap (like $4) DC/DC converter bricks and put the outputs in series. Stack them on top of whatever power rail you already have.

--
John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
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Reply to
John Larkin

Whoa, how'd you take those pictures?

Hey, lots of stuff for $7, with free shipping. Not all of the eBay sellers add the parts needed for a bipolar output. The transformer is the most valuable part.

--
 Thanks, 
    - Win
Reply to
Winfield Hill

$100 parts? You've looked at Digikey for inverter transformers right? There are off the shelf 240-to-5V flyback transformers for $5. Run that in reverse, no problemo!

How about CCFL transformers? Lots of leakage, resonant secondary, easy to get high voltages from little input.

You didn't say how much current you need, but I guess it isn't much.

LT is literally in the business of one-chip solutions. Why do you think their one-chip solutions cost so much per part? :-)

You can probably do the CCFL route with two transistors, self excited, but some protection features would be a welcome addition.

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
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Reply to
Tim Williams

Right I already copied that out and stuck it in my notebook. What's the voltage range of the LTC3803? (it says 36 to 72 on typ. circuit) What's the turns ratio on the transformer? (12-14?)

I'd be happier with some more packaged solution form LT. Flying into unknown territory is fun, but not time efficient.

This is my second choice from LT/analog.

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George H.

Reply to
George Herold

Just using the camera on my Moto e4 smartphone, with an app called "Magnifying Glass" or somesuch - blast the PCB at about 8 inches away with light from the white LED on the front, flip the palette on the image, zoom in a bit and if you hold the phone at the right angle and autofocus everything pops right out.

The capacitors are a lil dodgy but other than that it seems well-made, layout and soldering looks the business, never had a problem with one of these modules

Reply to
bitrex

There's no limit. The internal supply is 9V, from a shunt regulator inside the chip. Note that my 9 volt offpage connector is an output, not an input. I use the 9V somewhere else.

The fet has to be able to stand the flyback voltage. Best way to determine that is to Spice it. I used an FDD7N20, rated 200 volts, because we have it.

1:1. It's one of those dual-winding inductors.
--
John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
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Reply to
John Larkin

Oh, I was going to ask about that.

Right thanks. 'true confessions'; I realized driving home tonight this was a flyback... Well... everyone mentioned it enough. :^) Anyhow, I'm home now with 'my' SMPS book "Fund. of power electronics", R.W. Erickson. And reading about flybacks.. basically, you can analyze them as buck-boosts with a turns ratio.

I think I see the Fet has to take a lot of voltage stress. An external fet may be be a good idea. And there's lots of switching transients, if I care less about efficiency, can I slow down the edges with R's in the right place?

Huh, OK... I'm going back to read about buck-boost. It's all in the duty cycle then?

George H.

Reply to
George Herold

that should be possible PC powersupplies have one for stepping about 350V down to

5V at about 2-10W as do many wall-warts. these transformers can be run in reverse.

digikey has a bunch of transformwers for a few bucks each

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dunno why they call them sifnal transformers. the parameters are series and parallel incuctance, but if you havce a spice parameters for the part you want you can probably find a close match using those numbers.

Yeah, for C-W you need a symmetrical output like Baxandall, if you just want to step up you can use a flyback converter which is simpler.

Seems to spoil all the fun. I guess it depends whether you want to learn or to do.

--
     ?
Reply to
Jasen Betts

The regular Baxandall circuit always produces a sine wave with a couple of percent of harmonic content. I've got a less efficient version - 50% rather than 95% - where the harmonic content can be a couple of orders of magnitude lower.

--
Bill Sloman, Sydney
Reply to
bill.sloman

Yeah I've mostly given up the C-W dream for now. At ~300V it looks like a flyback is a cheaper/ easier option.

George h.

Reply to
George Herold

Hi Tim, No I haven't looked for inverter transformers at DK. Do you know where they would be listed? I've looked through most of these,

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and only found useful stuff in the SMPS category.

George H.

Reply to
George Herold

s/AN118fb.pdf

down to

reverse.

transformers/73

Thanks, I was looking through the DK site at transformers.... but I guess that is not what I want... well there are some here,

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ransformers/168.

I don't have any spice parameters. I think today I'll fire up LTspice and see what I can make work... I have to do some calc's first. Say could I take one with six coils, (like this one.)

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4689 Put one on the input and wire up the other five in series as output to give me a 1:5 turns ratio?

George H.

Right that's always a trade off. I got some cheap APD's from digikey in yesterday. Part of me wants to bias 'em up and see how bad the dark count rate is. Or do I delve into flyback converters? There's never enough time in a day. :^)

George H.

Reply to
George Herold

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