Ultra High Gain, low current voltage multiplier - Cap leakage tester - Page 1
Forum section: electronics / projects

author: dazz1
author_rank: Frequent Contributor
timestamp: October 03, 2023, 08:31:56 am
content: HiI want to flog an old dead horse with a new whip. I want to design a modern version of a capacitor leakage tester/ reformer.I have surveyed the available designs and not found quite what I am looking for.I want:Arduino Nano based because it is cheap and can directly drive 5V logic (and it's cheap),16ch x 3 line LCD display interfaced to the Nano (also cheap and easy) for display outputRotary encoder/push switch for user input (simple and cheap),adjustable from 15VDC to at least 500V output voltagecurrent limited from 0mA up to 5mA outputinductors yes, transformers no.no Cockcroft–Walton voltage multipliers because the stage gain is too low (need too many stages)easy to make (no custom diy parts/coils, off-pcb-parts etc)physically small size.Input voltage supply something between 12VDC and 48VDC from a standard mains power SMPS. This will be a bench test equipment, never battery powered.My questions focus on the problem of HVDC generation. The traditional methods are still an option, but I would like to take advantage of the extensive R&D on voltage multipliers for solar to mains DC. There are a number of new candidates. My favourite candidate to date is found here:https://www.nature.com/articles/s41598-023-42638-5It offers high gain and low component stress (cheaper parts, more reliable). The major disadvantage is the complexity of driving the MOSFET gates plus an oscillator etc, offset by the use of small off-the-shelf inductors. The use of small inductors and more parts will still allow for small form factor.I have not studied the circuit in sufficient detail to figure out if/how another stage could be added to further increase the voltage gain.My question is: is there a better and modern alternative voltage multiplier??The answer does not include "fly-back", "transformer", "Cockcroft-Walton" etc. They are the old dead horses.

author: moffy
author_rank: Super Contributor
timestamp: October 03, 2023, 08:57:53 am
content: You can do it with a single boost inductor, you only want 2.5W out, at a switching frequency of say 100kHz that is 25uJ energy per cycle at 5ma.

author: Someone
author_rank: Super Contributor
timestamp: October 03, 2023, 10:39:57 am
content: Quote from: dazz1 on October 03, 2023, 08:31:56 amParts get better so traditional approaches get easier/better/cheaper.https://www.eevblog.com/forum/projects/555-timer-boost-converter-(and-buck-converter)-switching-power-regulator/

author: Marco
author_rank: Super Contributor
timestamp: October 03, 2023, 03:26:55 pm
content: Quote from: moffy on October 03, 2023, 08:57:53 amIndeed, when efficiency doesn't matter "component stress" doesn't matter and extreme duty cycles don't matter ... who cares if you're burning most of the power in the MOSFET. As long as a little gets to the capacitor, you can reach your desired output voltage.

author: JohanH
author_rank: Frequent Contributor
timestamp: October 03, 2023, 04:12:05 pm
content: I have this small boost converter (not the exact link, but seems to be the same):https://www.ebay.com/itm/224509164439It goes higher than 450V when adjusted, but the output cap is 450V, so it would have to be changed. It looks like a simple circuit, but the 8-pin chip has only some Chinese characters on it, so I don't know what it says.BTW, this converter is so cheaply built. The output diode is just glued to the heat sink/casing with legs almost touching the wall. The screw holding two HY1707 Mosfets is barely tightened and the metal clip could fall and touch other components. Requires some modifications to be safer.Edit: As said below, the chip is marked with the name of the company and it could possibly be MC34063 or similar.

author: dazz1
author_rank: Frequent Contributor
timestamp: October 03, 2023, 07:07:29 pm
content: Quote from: Marco on October 03, 2023, 03:26:55 pmIt depends.I have found that many stage Cockcroft-Walton voltage multipliers suffer too high losses (low efficiency) even when using low loss diodes. So efficiency is an important consideration if the voltage multiplication losses are high enough to make it difficult to reach the target output voltage/current.Low stress components = low spec, low cost but the ready availability of very high voltage components enable things that couldn't be done before. So low component stress is desirable, not essential.The research papers are focused on voltage step-up for the purpose of power conversion, so their design goals are not closely aligned to near zero current HV instrumentation. Some of these claim simplicity by avoiding the issue of driving ungrounded MOSFETS (needing isolated high-side drivers).The advantage of using multiple inductor circuits is that the inductors tend to be smaller, higher frequency, off the shelf, and identical, leading to the potential for smaller form factor (more components, less space).Maxing the conversion frequency reduces the size of inductors, and smaller inductors can generally operate at higher frequencies. Low value, high current inductors are already used in power supplies everywhere. A circuit with multiple inductors could be a better option that one large inductor.So a multi-inductor circuit could reduce the problem of building a circuit (easier to source, cheaper to buy components, easier to build).

author: Marco
author_rank: Super Contributor
timestamp: October 03, 2023, 07:36:59 pm
content: It's a one off, put a bigger heatsink on the MOSFET and use whatever inductor you need for a simple boost circuit ... who cares what value it is? Throw in a 600V SiC Schottky diode, they're cheap enough.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: October 03, 2023, 08:17:21 pm
content: Quote from: dazz1 on October 03, 2023, 07:07:29 pmThere are also other factors in play.For high power, the duty cycle / conversion ratio matters. Very narrow pulses are less likely to manage continuous conduction, and become more ringing converters.24V to 500V is 21:1 ratio, whilst doing that in two switching stages allows you to have two 4.6:1 ratios.For your very light current needs, you may be fine with a single switching element. KISS is the best here.I was researching 'smallest' high voltage power devices for another design, and here are some candidates - note the small Co and Crs value, allow for higher ringing frequencies.IGBTFGD5T120SH 1200 V, 5A 209pF 11pF 2pF 57cHGTD1N120BNS9A 5.3a 1200v 67cIKN01N60RC2ATMA1 IGBT 600V 2A 55pF 4pF 2.5pF SOT223 25cMOSFETNCE70T1K2K Wuxi 700V 4A 1.1Ω@10V,2A 41W N Channel TO-252 304pF 17pF 0.5pFFQD2N90TM 900 V, 1.7 A, 7.2 Ω, Dpak $ 0.583MS3N100HGD0 MASPOWER 1000V 3A 5.2Ω TO-252 390pF 45pF 5.5pF 37c lcscIPN95R3K7P7A SOT223 950V 3.7 ohms 2A 196pF 47pF 3pF 39c/3k mouserIPN70R2K0P7SATMA1 SOT223 700 V 2 Ohm 3A 130pF ? pF 2pF $ 0.250 /1kThe Infineon SOT223 parts may be good enough for your needs here.You would pair those withfastest, lowest capacitancediodes - possible parts might be ROHM RFU02VSM8STR 800V 200mA, or Diodes Inc US1NWF-7 1.2KV 1A

author: duak
author_rank: Super Contributor
timestamp: October 04, 2023, 05:06:05 am
content: You might consider a piezoelectric transformer. They were used for LCD backlight AC voltage sources so you might be able to score one out of a laptop if you can't get one new.https://hackaday.com/2015/12/12/piezoelectric-transformers-are-a-thing-have-you-used-one/Cheers,

author: jonpaul
author_rank: Super Contributor
timestamp: October 04, 2023, 05:15:59 am
content: What's your problem with C-W multipliers? IIn 1980s, we designed and manufactured 13 stage Crockofft-Walton multipliers at 40 kHz to obtain 12kV at 1 watt.7,000 were deployed in flying hardware.Jon

author: Marco
author_rank: Super Contributor
timestamp: October 04, 2023, 07:14:25 am
content: Standard multipliers aren't suited to variable voltage, but you can replace the source with a boost circuit.

author: jonpaul
author_rank: Super Contributor
timestamp: October 04, 2023, 02:36:15 pm
content: Hello: Au Contraire!Crockofft Walton voltage multiplesa output is PROPORTIONAL to input.Professional variable HV PS modules and lab supplies are eitherInvereter with variable DC bus >>N stage multiplierORFlyback with variable DC busHV out and rectifier,See notes/schematics ffrom Bertran, Del, HV EngineeringJon

author: David Hess
author_rank: Super Contributor
timestamp: October 04, 2023, 10:01:02 pm
content: My go-to circuit is a boost converter driving a Cockcroft–Walton multiplier. At higher voltages a flyback converter can also directly drive a Cockcroft–Walton multiplier.I would not consider anything else unless I needed the lowest noise or higher output currents.

author: daisizhou
author_rank: Super Contributor
timestamp: October 04, 2023, 10:48:15 pm
content: The text above is only the mark of the power supply manufacturer, not the chip model.This chip looks like MC34063 or similar chip

author: dazz1
author_rank: Frequent Contributor
timestamp: October 05, 2023, 08:00:47 am
content: Quote from: duak on October 04, 2023, 05:06:05 amI hadn't heard of these before so I read up on them. They look almost perfect for HV, low power instrumentation applications. I say almost because:they seem to be difficult to source and,they are best suited to HV, zero current applications.But now I know about them, I will keep them in mind for future applications.

author: dazz1
author_rank: Frequent Contributor
timestamp: October 05, 2023, 08:10:02 am
content: Quote from: jonpaul on October 04, 2023, 05:15:59 amI don't have any problem with C-W multipliers. I have successfully used them in the past. At low input voltages and high stage counts, the diode forward voltage drops combined with other stage losses cumulatively subtract from the voltage jump at each stage. Add enough stages and the output voltage drops. On an aircraft there is 115VAC/200VAC/400Hz available and that may have been stepped up for input to the C-W multiplier.

author: dazz1
author_rank: Frequent Contributor
timestamp: October 05, 2023, 08:34:48 am
content: Quote from: jonpaul on October 04, 2023, 02:36:15 pmI have successfully applied pairs of CMOS CD4049 buffers driving a C-W multiplier up to a few 10s' of volts. The push/pull drive reduces stage count. If the buffers have a 15V supply, then the push-pull configuration provides a 30V input to the C-W.Quote from: jonpaulMy leading 'conventional' option with a constant DC bus and combination of PWM and PFM to control output voltage. PWM/PFM stay entirely within the digital domain simplifying the circuit while making the software more complex. The Arduino Nan0 has ADCs but not DACs. I expect voltage regulation/noise will be "good enough".

author: dazz1
author_rank: Frequent Contributor
timestamp: October 05, 2023, 08:38:02 am
content: Quote from: PCB.Wiz on October 03, 2023, 08:17:21 pmIt is actually quite amazing that such cheap devices now available have such good specs.

author: Marco
author_rank: Super Contributor
timestamp: October 05, 2023, 09:25:45 am
content: Quote from: David Hess on October 04, 2023, 10:01:02 pmThe multiplier needs AC current, if the transformer is delivering AC current it's not strictly a flyback any more. For a variable output voltage you need a hybrid forward/flyback, but that in itself doesn't really avoid extreme duty cycles.I wonder what the problem with extreme duty cycles in this case is though, as long as it's good at 500v. A simple flyback designed for 500V will need an extreme duty cycle at 15V, but the delivered power at 15V/5ma is extremely small too ... so the efficiency no longer matters. The efficiency is good where it matters, 500v/5ma.

author: Circlotron
author_rank: Super Contributor
timestamp: October 05, 2023, 11:47:57 am
content: Quote from: JohanH on October 03, 2023, 04:12:05 pmLooks likeSkilled electronicor Jiqian electronicJiqian mean "several thousand"

author: daisizhou
author_rank: Super Contributor
timestamp: October 05, 2023, 12:05:12 pm
content: "技强电子"--Chinese means electronics company with strong technology.This is just the brand or name of this company

author: David Hess
author_rank: Super Contributor
timestamp: October 05, 2023, 03:50:17 pm
content: Quote from: Marco on October 05, 2023, 09:25:45 amIf energy is stored in the transformer and then released, isn't that flyback?QuoteFor these types of circuits it is easier to think of the inductor or transformer transferring charge and operation at low duty cycles is discontinuous.

author: Marco
author_rank: Super Contributor
timestamp: October 06, 2023, 03:05:06 pm
content: Quote from: David Hess on October 05, 2023, 03:50:17 pmIt also has flyback, but it also has forward current transformation which would normally be almost completely stopped by secondary side diode.A normal flyback converter doesn't usefully operate in forward mode, a normal forward converter doesn't usefully operate in flyback mode ... this is a hybrid. Just looking at the primary side current it's pretty clear too, you get a partial half sine (forward) which transitions into a linear ramp (flyback). The little parasitic glitch at the start of the ramp from a normal flyback converter amplified to a functional part of the circuit.

author: Terry Bites
author_rank: Super Contributor
timestamp: October 06, 2023, 05:46:13 pm
content: Reforming caps is a bad idea. Poking your eye with a sharp stick makes more sense.New caps are not expensive. And a lot cheaper than a wrecked bit of kit and a burned down shed.https://www.eevblog.com/forum/testgear/some-guy-posts-his-version-of-mr-carlsons-lv-capacitor-tester-ultra-version/

author: dazz1
author_rank: Frequent Contributor
timestamp: October 06, 2023, 10:39:43 pm
content: Quote from: Terry Bites on October 06, 2023, 05:46:13 pmRated voltage leakage testing is a good idea. If an electrolytic can be reformed, why change it?The partner test is with an ESR meter, but that is another topic.

author: dazz1
author_rank: Frequent Contributor
timestamp: October 12, 2023, 08:20:16 am
content: HiI have continued fishing around for step-up converters. There are lots of ic options but the ones I have looked at are often limited to uA current at the desired voltage (~500VDC).Modern parts able to operate at >100kHz offer the possibility of using much smaller inductor/transformers.I will continue to look as a background effort. I have a queue of other projects to finish first.