Voltage Multipliers (for our tube projects...)

[Ben N]

Cool project--and it doesn't even need a heat sink!

[Ripthorn]

Well, while looking at a project on "the other forum" I found this schem.  It is the switching power supply for the blackstar ht dual pedal and gets upwards of 300V to drive 12a_7's, etc.  Check it out, it looks very simple yet functional.  I haven't priced parts for it yet, however.

Edit, it's not letting me post the whole thing, the ... should be the "other" forum, add that to http://....org/members/bajaman/Baja/Blackstar/Blackstar%20HT%20power%20supply.png.

[frequencycentral]

Well, while looking at a project on "the other forum" I found this schem.  It is the switching power supply for the blackstar ht dual pedal and gets upwards of 300V to drive 12a_7's, etc.  Check it out, it looks very simple yet functional.  I haven't priced parts for it yet, however.

http://....org/members/bajaman/Baja/Blackstar/Blackstar%20HT%20power%20supply.png

I'm getting a dead link.

[Renegadrian]

yeah you have to add the domain by yourself...

[jacobyjd]

lol...

[Ice-9]

I have a blackstar pedal and have had a look at the voltage multiplier circuit and it looks to work the same way as most smps with a mosfet switching the inductor to generate the HV. I have not traced it out myself, i  would like to see this schematic but haven't a clue what " the other forum" in the link is, can anyone help , 

[Renegadrian]

free stompboxes.org without that space

[davidallancole]

I found this while looking around today.  It uses the 555 timer in a similar configuration to the Nixie tube driver.  Instead of being just a boost converter, it is a flyback boost converter.  It isn't really adjustable, but its something different to look at.

http://www.supertex.com/pdf/app_notes/AN-H36.pdf

[Ice-9]

I came across this information on flyback smps and thought i would post it in case anyone wants to know about these HV psu's
http://www.dos4ever.com/flyback/flyback.html

[Mick Bailey]

I've been using the nixie tube design for a long time and get 298v no load and 270v under load. There are two key points to remember; 1. The lower the 'on' resistance of the MOSFET, the higher the voltage. 2. Current handling and (therefore) output voltage are highly dependent upon the inductor. I wind my own on ferrite rod, which measure 150mH and take about 10 minutes to make.

The diode HAS to be a fast recovery type - a 1N4xxx will not work in this circuit. 

Also, the 2.2uF cap is better replaced by a larger value - I've always used 47uF, but it depends what you're hanging off the end.  I also use a 2.5k trimmer for VR1.

An interesting aspect of the design is that the ripple is ultrasonic, so as long as the input is well smoothed you get much reduced hum compared to conventional PSU designs. I use 12v, 4A switched-mode laptop PSUs. This circuit generates high peak loads on the supply and for best results use a minimum of 2A, 12v DC.

The shocks off this are the same as any high voltage supply - don't think that because it's fed from 12v it's any kinder - the output from this really smarts!

[frequencycentral]

I've been using the nixie tube design for a long time and get 298v no load and 270v under load. There are two key points to remember; 1. The lower the 'on' resistance of the MOSFET, the higher the voltage. 2. Current handling and (therefore) output voltage are highly dependent upon the inductor. I wind my own on ferrite rod, which measure 150mH and take about 10 minutes to make.

The diode HAS to be a fast recovery type - a 1N4xxx will not work in this circuit. 

Also, the 2.2uF cap is better replaced by a larger value - I've always used 47uF, but it depends what you're hanging off the end.  I also use a 2.5k trimmer for VR1.

An interesting aspect of the design is that the ripple is ultrasonic, so as long as the input is well smoothed you get much reduced hum compared to conventional PSU designs. I use 12v, 4A switched-mode laptop PSUs. This circuit generates high peak loads on the supply and for best results use a minimum of 2A, 12v DC.

The shocks off this are the same as any high voltage supply - don't think that because it's fed from 12v it's any kinder - the output from this really smarts!

Hi Mick

Thanks for the info. Can you tell me what specifically what you have changed in the circuit re the lower the 'on' resistance of the MOSFET to get the voltages you mentioned? A bigger than 2.2uf cap will just give a smoother voltage right? Whats the benefit of using a 2K5 trimmer instead of 1K - just easier to tweak the right voltage?

I can second your comment about respecting the HV output of this circuit, having given my thumb a little belt of 200 volts! Ouch!

[frequencycentral]

This is from my "Sub Zero" thread:

Another thing about the SMPS, I've been leaving it running for hours hooked up to the amp. I went back to it yesterday to find it humming slightly at 195 volts, I turned it down to 190 volts and the hum went away. I don't seem to be able to get it back after hours of running at slighly lower voltage, which is a good thing!

I've noted what Mick Bailey said:

This circuit generates high peak loads on the supply and for best results use a minimum of 2A, 12v DC.

I was actually running mine (plus two submini tubes) off a 12v 500ma adapter (which actually gives out around 700ma). Today I hooked the Sub Zero up to a 12 volts / 1.5 amp bench supply. I noted immediately that I was able to dial in much higher voltages - up to 230v. I'm guessing that even higher is possible by reducing the 470R resistor. So the hum I mentioned in that quote above was the SMPS loading the supply. It seems that the higher the voltage output the higher the current draw. After 5 minutes of running at 230v either the inductor or the IRF740 burned out (not sure which, though I'm guessing the inductor, as the IRF740 is rated at 400v. Maybe the inductor burned out and took the IRF740 with it, both got really hot). I replaced them both and am now running at 195v without any hum from the bench supply. It seems that I need to upgrade my inductor - any ideas?


EDIT: Do you guys think I should start a seperate nixie SMPS thread, as a few of us are working on this so we could compare notes, and I don't want to hijack this thread?

[Ripthorn]

A separate Nixie thread would probably be a good idea.  Interesting what you noted, though.  I wonder if maybe you fed too much current through your inductor.

[Mick Bailey]

The comment about the MOSFET 'on' resistance is if you decide to experiment with different types. It needs to be below 0.5 Ohm, otherwise the circuit drops off in efficiency but make sure the voltage and current rating are adequate. The IRF740 is fine, but really does need heatsinking for valve audio projects. Note that the tab is at input voltage (12v) so it needs insulating if you decide to use the case as a heatsink.

My inductors are made as follows -

You need a 1" length of 3/8" diameter ferrite rod. I cut mine off longer lengths by nicking round the rod (use a Dremel cutting disk, saw or file) and snapping it off sharply. Use a drill chuck or vice to hold the short end.

Have ready a slightly longer piece of heatshrink tubing that is an easy fit over the rod (about 1/2" inside diameter is fine).

Take a length of 24 SWG enamelled wire and after leaving about 2" as a tail place a narrow piece of masking tape to hold it in place while you wind the wire round the rod to the other end and back. Hold this end with a small piece of tape and heatshrink the lot. The idea is you get two layers of turns on the rod. Note that I'm in England and SWG is different from AWG.

This results in a reliable inductor that runs cool and has low resistance.

My ferrite comes from stocks pulled from old transistor radios over the years - it always seems to be 3/8".

The bigger trimmer was determined by experiment to arrive at a higher voltage that would still adjust down if required.

Increasing the 2.2uF cap was purely to get rid of excessive sag on power chords. I found that bass response also improved, but this is down to what you're running off the supply.

I can say that I've found this circuit to be infallible, but the inductor has to have the current handling capacity and optimum value in order to get the output current and voltage required.

When you take a look at how the circuit operates the 12v is being shorted to ground through the inductor and the series resistance of the MOSFET, so you can appreciate the need for a fairly robust inductor. The small inductors usually recommended for Nixie supplies will not work for valve projects.

[Ice-9]

Thanks Mick,

some great info there on the inductor. Im about to start ordering some components for the psu to have a go building one. One question i have on winding your own inductors is how do you measure the uH value.  (not sure if my DVM does H, i will have to have a look)

[frequencycentral]

Well I don't really fancy rolling my own inductor, so I'm on the search for a suitable replacement. The one I used was this one:

Rapid part number: 88-1630  MIN RADIAL INDUCTOR 100UH RC, 11mm x 6.5mm (Low current) £0.47

http://www.rapidonline.com/productinfo.aspx?&tier1=Electronic+Components&tier2=Inductors+And+Chokes&tier3=Leaded+Inductors&tier4=Low+current+radial+lead+inductors&moduleno=64730&catref=88-1630&kw=88-1630

I have found that it's suitable for voltages up to ~190v, and I would estimate that at those voltages it draws ~400ma. The data shet say it handles up to 1.5 amp, so I don't know why mine burnt out.....?

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I've been looking at this One:

Rapid part number: 88-1003  HIGH CURRENT BOBBIN INDUCT 5.4A 100UH RC

It's way more expensive at £2.64, and physically larger at 14mm x 26.4mm, but would be unlikely to go into meltdown as it handles up to 5.4 amps.

http://www.rapidonline.com/productinfo.aspx?tier1=Electronic+Components&tier2=Inductors+And+Chokes&tier3=Leaded+Inductors&tier4=High+current+inductors&moduleno=72640

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Just looking at gut shots of the Nano head and the JJS Class A, they both seem to use something like this:

Rapid part number:   88-2883  77A SUPPRESSION COIL 100UH RC (11mm x 26mm) £0.52

http://www.rapidonline.com/Electronic-Components/Inductors-And-Chokes/Leaded-Inductors/High-current-leaded-suppression-chokes/79278/kw/

.....which is actually a choke. Hmm so what's the diff between a choke and an inductor?

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I'm pretty happy withe the SMPS I have right now using the first inductor I linked to, as the maximum voltage output (and it's current draw) suit the tubes I'm planning to use it with. But I reckon it would be cool to make a super small SMPS powered amp with a full size dual triode (12AU7 say) and a full size pentode (EL84?) running at ~250 volts, so it would be nic to develop this nixie SMPS to do the job.

[Ripthorn]

A choke is just another kind of inductor.  A choke is usually a term for an inductor that filters out something you don't want, like RF noise.

[Ice-9]

These are the inductors ive ordered from rs they work out at about £0.95 each,  i will be experimenting as soon as all the bits turn up.

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=3963493

[Mick Bailey]

Thanks Mick,

some great info there on the inductor. Im about to start ordering some components for the psu to have a go building one. One question i have on winding your own inductors is how do you measure the uH value.  (not sure if my DVM does H, i will have to have a look)

I originally used a very simple circuit with a scope http://images.google.co.uk/imgres?imgurl=http://www.edn-europe.com/cmsimages/0507/64f1.jpg&imgrefurl=http://www.edn-europe.com/cheapandeasyinductancetesterusesfewcomponents%2Barticle%2B1480%2BEurope.html&usg=__tXlNxZ34KPTWnRgqtnlE8IRViX0=&h=444&w=588&sz=38&hl=en&start=16&um=1&tbnid=37t2pg7dckHUgM:&tbnh=102&tbnw=135&prev=/images%3Fq%3Dsimple%2Binductor%2Bmeasurement%26hl%3Den%26safe%3Doff%26sa%3DN%26um%3D1

This is very accurate, reliable and easy to build. I then bought an LCR meter from Hong Kong - about £7 plus postage. I like the meter, but I like the scope method even better as it is more accurate and has a greater range.

Sorry, I just noticed in my earlier post I said 150mH, Should be 150uH

[Mick Bailey]

Rick

Re: Rapid part number:   88-2883  77A SUPPRESSION COIL 100UH RC (11mm x 26mm) £0.52

This would be my choice - I've got some of these in 150uH but have not tried them yet. Current handling and DC resistance seem good and I chose these as the best commercial match to my own DIY inductors. The circuit is sensitive to inductance dependent upon load and it's worth getting a few values due to the low cost/high postage ratio and playing about with them.

BTW, I've found that 100uH causes heavy current draw without increasing the output voltage and causes excessive load on the MOSFET.  Very high open circuit voltages can be achieved by increasing the inductance even more, but the impedance then increases and therefore the on-load voltage reduces. I've built a lot of these circuits and now always use 150uH