Author Topic: SMPS Project?  (Read 281 times)

HamSandwich

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SMPS Project?
« on: January 10, 2018, 07:36:02 PM »
Hola,

Are there any SMPS projects out there? I see there's a few posts here and there about them, but no 'here is the schematic, layout, parts lists' etc. I don't expect to find them on a pedal building site, although Grind Custom used to have one I think, but that seems gone. An available PCB isn't critical, but from what I understand, a good layout can make a huge difference in one of these things.

Ideally it could produce 250-300VDC, and maybe enough current to power 3ish 12A#7 tubes? I'm not looking for one to fit in any particular project, but a basic SMPS circuit that could be used in a number of different ideas.

Thanks for your help!

somnif

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Re: SMPS Project?
« Reply #1 on: January 10, 2018, 07:57:51 PM »
The problem with DIY power supply projects is they tend to be on the dangerous side. Working with mains voltages and current means anyone providing projects to people of unknown skill levels needs to consider "am I liable for what happens to the half brain dead ape like creatures who managed to poke a soldering iron into this thing?"

And really at the end of the day, most DIY projects would end up within ~20% of the price of a commercial option, so there isn't a fantastic motivation on that side as well.

They do exist, but you have to dig a bit, and be very VERY careful with them.

tcpoint

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Re: SMPS Project?
« Reply #2 on: January 10, 2018, 07:59:14 PM »
There's some pretty cool modules from China and they're pretty cheap.  I bought one and it's on my todo list.I

HamSandwich

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Re: SMPS Project?
« Reply #3 on: January 10, 2018, 08:22:24 PM »
The problem with DIY power supply projects is they tend to be on the dangerous side. Working with mains voltages and current means anyone providing projects to people of unknown skill levels needs to consider "am I liable for what happens to the half brain dead ape like creatures who managed to poke a soldering iron into this thing?"

And really at the end of the day, most DIY projects would end up within ~20% of the price of a commercial option, so there isn't a fantastic motivation on that side as well.

They do exist, but you have to dig a bit, and be very VERY careful with them.
I hear ya man.

Thatís part of the reason Iím going with SMPS. Wall power and itís scary amps are relegated to 12V or whatever wallwart instead of brought into the confines of a box that connects to me.

I know you have to be safe with an SMPS, just as much wall power and traditional poser transformer. I have built a few amps and am somewhat comfortable with it, but not AS comfortable as an SMPS. Now I sound like Iím convincing myself, donít I?  ;D

Iíll keep on digging, thanks!

There's some pretty cool modules from China and they're pretty cheap.  I bought one and it's on my todo list.I

Thanks! I saw those! I am dubious of that kind of stuff mostly from a lack of experience with them. For some reason I trust my hands and eyes more than a chinese fab, which is probably not logical. Ah well.

gtr2

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Re: SMPS Project?
« Reply #4 on: January 11, 2018, 07:18:32 AM »
There are some good online tools available for switch mode power supplies calculations.  Texas Instruments has one and maybe a few other manufacturers.
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thomasha

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Re: SMPS Project?
« Reply #5 on: January 11, 2018, 04:05:08 PM »
I built a lot of the 12v to 250v SMPS types.
But they don't have that much current available, or get too hot.
For low wattage, like 250v at 20mA, it's OK though. I think maybe a small 12au7 PP would work to.
The kind of inductor is very important, otherwise you end up with a whistle. It must be shielded and also have a small ESR. Same for the caps and the Mosfet. The mosfet can get really hot too, sometimes a heatsink is required so the voltage won't drop after some time. I like to use this schematic>
http://www.desmith.net/NMdS/Electronics/NixiePSU.html

But there are cheaper chips that do the same.

Now something complicated would be one SMPS for the whole amp.

I saw some projects where they used a small flyback transformer to produce the high voltage and the filament supply at the same time, but then it gets big and complicated.
To wind this kind of transformer without the proper equipment is already a nightmare.
In this case it's easier to buy a chinese one on aliexpress.


HamSandwich

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Re: SMPS Project?
« Reply #6 on: January 12, 2018, 11:26:09 AM »
There are some good online tools available for switch mode power supplies calculations.  Texas Instruments has one and maybe a few other manufacturers.

Thank you, I'll have a look!

I built a lot of the 12v to 250v SMPS types.
But they don't have that much current available, or get too hot.
For low wattage, like 250v at 20mA, it's OK though. I think maybe a small 12au7 PP would work to.
The kind of inductor is very important, otherwise you end up with a whistle. It must be shielded and also have a small ESR. Same for the caps and the Mosfet. The mosfet can get really hot too, sometimes a heatsink is required so the voltage won't drop after some time. I like to use this schematic>
http://www.desmith.net/NMdS/Electronics/NixiePSU.html

But there are cheaper chips that do the same.

Now something complicated would be one SMPS for the whole amp.

I saw some projects where they used a small flyback transformer to produce the high voltage and the filament supply at the same time, but then it gets big and complicated.
To wind this kind of transformer without the proper equipment is already a nightmare.
In this case it's easier to buy a chinese one on aliexpress.



Good info here, thanks!


I've also found some 'NIXIE' supplies on ebay, but some of the inductors look like they may be the danger you mentioned. I'll do some more digging.

Cheers guys!

gtr2

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Re: SMPS Project?
« Reply #7 on: January 13, 2018, 11:14:56 AM »
Some of the nixie power supply circuits on the net have some bad resonance as mentioned.  Proceed with caution, even though it's still low current, for instance 20mA at 170-220VDC, it can still kill you in the right circumstance.

You can also get some ringing from MLCCs.

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HamSandwich

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Re: SMPS Project?
« Reply #8 on: January 13, 2018, 03:37:07 PM »
Thanks, Josh! Warnings heeded.

The more I dig the more doing a 12VAC 24W wallwart into the secondaries of a 12V 25W transformer with the primary at 240V seems like an easier, or at least more understandable, and perhaps stable(?) way of doing it. Price and size being the only apparent detractors. Now itís time to learn about fuses  :'(

tcpoint

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Re: SMPS Project?
« Reply #9 on: January 13, 2018, 11:43:12 PM »
Or you can use some space charge tubes (low voltage tubes made for automobile radios).  They were pretty cheap, last I looked.  Or the Korg nutube is a low voltage - power efficient tube.  It's manufactured by a fluorescent bulb maker in Japan.  They are pretty pricey at $50 a dual triode.  You can also use a 12.6vac and use a voltage multiplier to get medium voltages  (you can do a search on a cavalli SOHA headphone amplifier or a CTH headphone amplifier for some examples.

WormBoy

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Re: SMPS Project?
« Reply #10 on: January 16, 2018, 04:52:31 AM »
Tube Town in Germany has a kit for a module that turns 12V into max. 220V @15mA: https://www.tube-town.net/ttstore/Kits/Power-Supply/TT-VPump-Voltage-Converter::6163.html. I built one of these, and it works, but I still need to build a pre-amp with it, so it is not tested by me in practice yet (not sure if that would be a real recommendation anyway  ;D).

HamSandwich

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Re: SMPS Project?
« Reply #11 on: January 18, 2018, 12:45:08 AM »
Thanks guys! Iíve ended up just going with a reverse transformer and wallwart. Plenty of amps, cheap and less likely to have noise issues! Thanks for all the responses.