SMPS for tube HT

[ruffrecords]

It would be great if there were a standard circuit for this. The right flyback transformer seems like the key component. Then make a PCB with whatever isolated flyback regulator chip. If it were adjustable one could use the same circuit for making a wide range of voltages and power.

I agree, this would be very useful. Anyone know a tame SMPS designer?

Cheers

Ian

 

[Bo Deadly]

I agree, this would be very useful. Anyone know a tame SMPS designer?

Actually if an off-the-shelf AC/DC unit were used to provide protection and isolation, the flyback regulator circuits would be relatively simple and need only a plain inductor.

 

[ruffrecords]

Actually if an off-the-shelf AC/DC unit were used to provide protection and isolation, the flyback regulator circuits would be relatively simple and need only a plain inductor.

Yes, but it seems bit overkill to convert the mains to a lowish dc voltage at high current only to convert it again to a voltage similar to the mains at a lower current. I guess you could start with 48V which at least can be used elsewhere.

Do you have a basic schematic of the plain inductor flyback regulator??? Might be fun to try.

Cheers

Ian

Edit: Just found this:

http://www.dos4ever.com/flyback/flyback.html

Might have a play.

 

[bluebird]

Hey Ian, I actually looked into this a while back and contacted a SMPS company that made custom units.
I gave them all the voltages and currents and asked for one unit with every thing included. I think there was a total of 4 different voltages including a 200V B+.  There was some back and forth with the techs and in the end they wern't willing to put in the work for the quantity's I was talking about. I think they had certain per-designed blocks they could put together and I was asking for too much. I didn't peruse it.

You might have more luck than me,  calling up SMPS manufactures and inquiring about their ability's and required quantity's.  You could have them design you a 6/12V 3A --- 300V 200mA ----48V 50ma or whatever your needs are,  in an open frame compact unit. If the voltages are pretty standard (for tube mic pres)  like that, I'm sure people on the forum would be interested in something like that for other projects. Perhaps a group buy for higher quantity's.

Just a thought.

 

[buildafriend]

@Tubetec: you understand exactly where I am coming from. There is rectified mains in a regular SMPS. It is not much more than a 1:1 transformer to give a 340VDC output. As you say, regular SMPS only go up to 48V or so; anything above that seems to be a bit odd. Mean Well web site says they are expanding product range by 15% a year - maybe they could expand in the HT direction?

Cheers

Ian

It would be nice if there was a "cheapo" switch mode supply available that catered towards HT valve use.. I've searched for +/- 15 but never HT. I assumed it was probably available.

 

[Bo Deadly]

Do you have a basic schematic of the plain inductor flyback regulator??? Might be fun to try.

The LM2586 is a typical flyback regulator. SoundSkulptor has used it (they used MAX1771CPA to make 300V in their mp66 schematic). Figure 21 in the LM2586 datasheet is the super basic single inductor circuit. But the same chip can be used to make multiple voltages like say +-15V using a transformer with the secondary center tap grounded. You can trick these into making higher voltages. But LM2586 only has a 3A switch. So if you put in 36V and use a 1:10 step up to get into the HT range you want, the available output current is what? I don't even know. Probably not great. This sort of thing seems like a dark art to me. Someone else do it please.

 

[bluebird]

So if you put in 36V and use a 1:10 step up to get into the HT range you want, the available output current is what? I don't even know. Probably not great. This sort of thing seems like a dark art to me. Someone else do it please.

I agree, but I think the current ability is also based around the switching frequency. Have you ever seen an aviation ac transformer made for 400hz? They can deliver the same current as they're 50/60hz cousins at a quarter of the size.

 

[ruffrecords]

. But LM2586 only has a 3A switch. So if you put in 36V and use a 1:10 step up to get into the HT range you want, the available output current is what? I don't even know. Probably not great. This sort of thing seems like a dark art to me. Someone else do it please.

Power out must be less than or equal to power in. So if you step up the voltage by 10 times then the current must be stepped down by the same amount. If the switch is limited to 3A then the output is limited to 3A/step up ratio.

Cheers

Ian

 

[ruffrecords]

JUst been looking at the UC3842 and the MAX1771. Both are attractive to me because they are available in a DIP package.

The UC3842 data sheet shows a transformer based 12V supply that works directly off the mains. Presumably by changing the transformer it could be converted to an HT supply. The same data sheet show it being used a step up dc-dc converter.

The MAX1771 seems in principle to be a very similar deivice. I have certainly come across a 300V 100mA HT supply using it (see attached pic). Looks like both devices are worthy of further investigation.

Cheers

Ian

 

[Bo Deadly]

With the right magnetics things could get a lot fancier. For example, I have no idea if you can run these transformers in reverse but if you used Eaton CTX02-15242-R in reverse with something like LT1533 it could be much lower noise and use relatively low voltage parts and thus not need an external switch. Jim Williams made a vid about LT1533 for high voltage outputs:

How To Build a Low Noise Power Supply for High Voltage (i.e. 100V up to 1000V) Transducers

Only a few mA though.

Or maybe LT1683 which uses external switches and thus you could do the high voltage hack using the "simple" circuit and yet benefit from the slew limiting and low noise-ness of the LT parts.

 

[ruffrecords]

Jim Williams seems like a really nice guy. I like the way he said you can call him up on the phone and ask him any question you like. I might take him up on that.

Cheers

Ian

Edit: LT1683 looks interesting for tube  mic pre applications.

 

[Dylan W]

Jim Williams seems like a really nice guy. I like the way he said you can call him up on the phone and ask him any question you like. I might take him up on that.

Cheers

Ian

Edit: LT1683 looks interesting for tube  mic pre applications.

Unfortunately, he's no longer with us.

https://en.wikipedia.org/wiki/Jim_Williams_(analog_designer)

 

[trobbins]

I used to design smps, and imho the best path forward for diy or even small commercial runs is to settle on a quality 12VDC mains supply that has current limit and good regulation, meets all the standard safety compliances, and has a datasheet that shows the manufacturer has designed for a long service life and wide ac voltage range, and has the mains protective earth connected to one side of the 12VDC output.

You are then guaranteed of low noise, regulated heater supply, and the removal of AC mains hum from the equipment chassis.  There is also a growing arsenal of cheap 12V to HV smps - I've looked at a few and with only minor changes they are excellent - providing isolated output so you can connect the HV to the node you want to,  and with a well laid out pcb, and oodles of power even up to a pretty powerful valve amplifier level.

The latest I looked at was:
http://www.diyaudio.com/forums/power-supplies/313234-150w-12vdc-isolated-25khz-step-smps.html

 

[ruffrecords]

I used to design smps, and imho the best path forward for diy or even small commercial runs is to settle on a quality 12VDC mains supply that has current limit and good regulation, meets all the standard safety compliances, and has a datasheet that shows the manufacturer has designed for a long service life and wide ac voltage range, and has the mains protective earth connected to one side of the 12VDC output.

You are then guaranteed of low noise, regulated heater supply, and the removal of AC mains hum from the equipment chassis. 

Which is precisely the route I am talking for future heater supplies. The one exception is I cannot have one side of the 12V ouput connected to mains protective earth because the heaters in my designs need to be elevated.

There is also a growing arsenal of cheap 12V to HV smps - I've looked at a few and with only minor changes they are excellent - providing isolated output so you can connect the HV to the node you want to,  and with a well laid out pcb, and oodles of power even up to a pretty powerful valve amplifier level.

The latest I looked at was:
http://www.diyaudio.com/forums/power-supplies/313234-150w-12vdc-isolated-25khz-step-smps.html

Thanks for the link. Another interesting regulator chip to add to the list. The only thing that puzzles me is the unit operates at only 37KHz but the chip is capable of operating up to 400KHz. I think for audio work it would be preferable to work at 100KHz and above?

Cheers

Ian

 

[ruffrecords]

Unfortunately, he's no longer with us.

https://en.wikipedia.org/wiki/Jim_Williams_(analog_designer)

Blimey! He was only two years older than me. Such a shame, I would have loved to get to know him. RIP.

Cheers

Ian

 

[trobbins]

Ian, yes the need to elevate some (all?) of the heaters wrt 0V is a pain for heater-cathode voltage ratings.  If it is only some, then perhaps one option would be to use two smps modules, one for HT, and try and find another with 12V to 12V isolated output.

My view would be for the mains 12VDC supply to be a plug-pack module (rather than an open-frame module where the mains has to enter the equipment) - but that dictates PE connecting to 12VDC terminal.  The open-frame 12VDC output module option would allow the 12VDC to be elevated, and PE to connect to the output of a smps HT supply (that also provides the elevated voltage).

 

[Matador]

I found this article excellent:

http://www.desmith.net/NMdS/Electronics/NixiePSU.html

 

[Tubetec]

I had spotted a similar Nixe ht psu recently and meant to drop a reference to it here , that looks really neat that one ,no special parts required . Those chunky IRF series fets can often be found in redundant PC power supplies too,as well as high voltage bridge rectifiers and large high voltage electrolytic caps.Handy for keeping the costs down for project work and of course saving mother earth some of her precious resources.

 

[ruffrecords]

Ian, yes the need to elevate some (all?) of the heaters wrt 0V is a pain for heater-cathode voltage ratings.  If it is only some, then perhaps one option would be to use two smps modules, one for HT, and try and find another with 12V to 12V isolated output.

In practice all the heaters are elevated so there is only one heater supply.

My view would be for the mains 12VDC supply to be a plug-pack module (rather than an open-frame module where the mains has to enter the equipment) - but that dictates PE connecting to 12VDC terminal.  The open-frame 12VDC output module option would allow the 12VDC to be elevated, and PE to connect to the output of a smps HT supply (that also provides the elevated voltage).

You lost me with some of the terminology there. What is PE?

Cheers

Ian

 

[ruffrecords]

I just found a company called Current Logic that makes a 12V tp 300VDC conveter. They will do custom voltages. I have asked them to quite for a 340VDC output at 250mA.

http://www.current-logic.com/shop/index.php?main_page=product_info&cPath=4&products_id=280

Cheers

Ian