I've finally gotten the 175V supply to a place where it deserves it's own thread. I ended up designing the supply for 100 mA of current at 175V (17.5W) so that people wouldn't ever feel like they are pushing the supply towards its limit (also keeps heat down at "max" load). The max recommended load will be below the actual supply goal (probably 60 mA) so that this unit can be built inside of a case without worry of excessive heat building up inside an enclosure. The design is based around (currently) the UCC3813-2 IC but I'm providing provisions to use similar IC's with very minimal parts changes. It's designed to operate from a 9-15V DC source. Here's the schematic:
(http://imgur.com/m51vg.jpg)
Parts List (including resistor/cap packages):
R1: 15k 0805
R2, R7: 0.1 Ohm 2W 2512
R3: 200k 0805
R4: 2.9k 0805
R5: 100k 0805
R6: 100k 1206
R8: Not needed
R9: See notes below
R10: See notes below
C1, C2: 470 pF 0805
C3: 22uF 200V low ESR
C4: See notes below
C5, C6: 1000pF C0G 0805
C7: .1uF 0805
C8: 10uF Ceramic 1206
C9: .022uF 0805 200V
C10: See notes below
U1: UCC3813-2 (preferred) or UC3843
Q1: Low RdsOn N-Channel MOSFET, I like the ST Micro STP9NM50N as a candidate
D1: UF4004, 4005, 4006 or 4007
L1: 15 uH, 3A + inductor --> Bourns SDR1806-150ML looks like a good candidate and fit for the board
In and Out connector: 158-P022ESDVP-E Eagle connector or similar screw block terminal
Here's a picture of the layout as it currently is:
(http://imgur.com/h28RZ.jpg)
At 2" x 1", the board is really made to fit inside a 1590 style case without much fuss. All of the parts mount directly to the top of the board and there are (currently) two jumpers. The one on the bottom is put in place to give the IC and associated components a stronger ground plane and I'm debating on the need of it. I may take it out depending on how my first prototype build goes. The FET is a TO-220 package that will need heatsinking.
With the IC I tried to go with the more modern UCC3813 but if this isn't available, a UC3843 can be used as well. The only differences is that the UCC3813 has an internal 12V Zener diode shunt regulator that limits the top VCC (hence the 1/2 W 100 Ohm resistor in series with the input VCC to the IC) whereas the UC3843 can get up to a 30V VCC without issues (meaning short R10). Also, the UC3843 doesn't have current blanking on the current sense pin and will require the R9, C10 parts to be placed (small RC filter of 10 Ohms and 1000 pF). If using the 3813, R9 gets shorted and C10 isn't stuffed. Also I've found that with my prototype build, a snubber circuit isn't necessary. I've still placed parts (R8, C4) just in case one is needed, but if not then these parts don't need to be stuffed.
I'm hoping to have this board verified by next week and when I do, I will post a parts list that includes Mouser part #'s and total cost (should be under $15). We're also talking about stocking these boards at PAiA if there is enough interest, but if we do this then I will probably try to shrink the layout more and use a double-sided board.
Thoughts/comments/criticisms?
Great news !
is there any chance to have a board design with non surface mount components ?
60mA is large enough !
Hey Cliff, good to see this project 'lift off'. I'm going to have to get a parts order together before I try it. Interesting that you chose an SMD layout - that puts it out of reach for me (and maybe some others too) but I'll work up a perf/PCB layout for through hole components based on your layout. Is this going into your 6BM8 based build?
Nice design, Cliff.
Quite apart from that, have you considered the safety issues with even a properly-operating board like this?
Thoughts/comments/criticisms?
Looks pretty tight ! As in small footprint...
What is the ~cost of building a PS like this ?
HMmm...I'm seeing a lot of possibilities here.
THANKS!
I will have to give this one a try Cliff. very good looking layout.
Quote from: R.G. on November 08, 2009, 08:37:32 AM
Nice design, Cliff.
Quite apart from that, have you considered the safety issues with even a properly-operating board like this?
Funny you mention this. When I first finished the supply, I placed my hand across the load resistor to feel if it was getting hot and got a small tingle (175V w/ 50 mA limit). After I went through and redesigned everything for 100 mA, I again placed my finger on the minimum load resistor and got the shit shocked out of me! No joke about the safety issues of a supply like this! I'll definitely attach an adequate warning label (and disclaimer) to the build-ready documents.
Also, I understand you guys not liking the SMD components. I'll try to do a second PCB version with 1/4W resistors and through-hole caps to see what I can get. Size will go up of course, but for some this isn't the issue. I have a large collection of 0805 resistors and caps and so I tend to go for those parts when I do layouts now. They do make DIP versions of the UC3843 and UCC3813 and so going through-hole isn't such a big deal.
Cost should be about $12 with Mouser although using a better quality FET will increase the cost by a few dollars.
Oh and thanks for the kind words guys! I've taken enough away from this community, it's time to give back :).
Quote from: Cliff Schecht on November 08, 2009, 01:39:06 PM
Funny you mention this. When I first finished the supply, I placed my hand across the load resistor to feel if it was getting hot and got a small tingle (175V w/ 50 mA limit). After I went through and redesigned everything for 100 mA, I again placed my finger on the minimum load resistor and got the sh*t shocked out of me! No joke about the safety issues of a supply like this! I'll definitely attach an adequate warning label (and disclaimer) to the build-ready documents.
Good idea. Just from some safety stuff I was forced through like beef through a hamburger grinder:
20ma DC through the chest is sufficient to clamp the heart down to inaction
20ma of 50-60 cycles starts ventricular fibrillation very efficiently
Skin resistance for dry skin is about 20K
Safety labs declare any accessible voltage of over 42V as hazardous on the face of it
"Accessible" means you can touch non-grounded (to a third-wire safety ground) metal
You may want to make people agree to a legal release before giving it to them. It's a PITA, but less than the PITA of even one legal action brought by the non-technical survivors of a less-than-clever builder who does something dumb. Anytime lawyers touch anything it gets complicated, expensive, and uncertain. :icon_eek:
Yeah I'm not sure about where we would stand legally if PAiA sold these boards built, as a kit or as a blank PCB. That's not my department though, so I'll see what the elders say.
It's scary how easy it can be to kill yourself with electricity. Every shock I receive is humbling for sure. I'm shooting a safety video for IEEE next week and will make sure to include some HV warnings.
One of my lab partners once told our advisor "I'm thinking about going into patent law, maybe becoming a lawyer". I'm pretty sure he got a B. :icon_lol:
Quote from: Cliff Schecht on November 08, 2009, 01:39:06 PM
Quote from: R.G. on November 08, 2009, 08:37:32 AM
Nice design, Cliff.
Quite apart from that, have you considered the safety issues with even a properly-operating board like this?
Funny you mention this. When I first finished the supply, I placed my hand across the load resistor to feel if it was getting hot and got a small tingle (175V w/ 50 mA limit). After I went through and redesigned everything for 100 mA, I again placed my finger on the minimum load resistor and got the sh*t shocked out of me! No joke about the safety issues of a supply like this! I'll definitely attach an adequate warning label (and disclaimer) to the build-ready documents.
I'm not too familiar with this chip but most the PWM chips have a connection so you can fit a switch , thus disabline the HV. One of those little tactile switches with a spring on so that when the effect pedal cover is removed a least removes the hazard of a shock when the cover is removed,, although it doesn't help while building and testing the supply.
Working with the HV supply is about as easy as making sure that the power is removed before you do any work. I also like to have a meter watching the HV output at all times so that I have visual confirmation that the PSU is off. Better safe than shocked.
Quote from: Cliff Schecht on November 08, 2009, 04:56:05 PM
Working with the HV supply is about as easy as making sure that the power is removed before you do any work. I also like to have a meter watching the HV output at all times so that I have visual confirmation that the PSU is off. Better safe than shocked.
I'm working with 1KV and/or 150A in my lab lately. Be Careful.
Quote from: Cliff Schecht on November 08, 2009, 04:56:05 PM
Working with the HV supply is about as easy as making sure that the power is removed before you do any work. I also like to have a meter watching the HV output at all times so that I have visual confirmation that the PSU is off. Better safe than shocked.
If you've ever done any flying, you've heard the aphorism that there are old pilots and bold pilots, but no old AND bold pilots. 8-)
Darwin may not have gotten every little detail correct, but there is certainly a filtering process that happens when doing things with some risk involved. Quite a number of the techs that I know who have worked on tube amps for years will keep a clip lead handy and clip one end to the chassis and the other end to the first filter cap + lead. Then they wait a few minutes, and they leave the clip lead there while they are working on the amp.
The very adventuresome ones will make up a clip lead with a resistor, maybe 10K to 50K at several watts to take it easier on the filter caps if they happen to be charged when the clip lead is connected, and to smoke (instead of frying the power transformer) if they forget to remove it before powering up.
It's almost like Mother Nature doesn't care how brave you are, isn't it? :icon_lol:
I put 'smoke tape' [electrical tape] around the drain resistor.
The wire gets a loop around the power switch, then clipped to the chassis.
That, and the AC input are the two big ones, I like to measure low or no voltage across the big caps for good measure.
how about a bleeding resistor ? about 47K from HT to ground for discharging the caps after power off ?
i add one in each tube gear i work on.
Every (well-designed) SMPS will have a load resistor on the output to draw a small amount of current. Switching supplies need this minimum load resistor for stability purposes. The minimum current draw is one of design parameters you must know when choosing the feedback loop components.
So I went ahead and did a through-hole version of this board. It's a bit longer at 1" x 2.55" but it should still fit nicely in a small enclosure. I had to make more room for the FET to be heatsinked properly compared to the board above where the FET can be soldered in off the board a bit and heatsinked easily. The switch to bottom-side copper was obvious for the through-hole version of this board. Standing resistors really help save on size although I'm not sure how well they'll play out with higher frequencies. Only one jumper on this board and no component value changes (aside from eliminating R7). I'll post both this layout and the SMD version in a printer-friendly version, along with a more detailed parts list, when I get the layouts etched and verified.
This isn't the final version, but a sneak preview nonetheless:
(http://imgur.com/Fk4z2.jpg)
Great stuff Cliff !
I would be nice to see how the output looks on the scope. Also to perform some A/B tests with actual equipment.
I would like also to remind you about the discussion concerning the dead batteries, compression etc. I suppose a 4k7-10k resistor after first cap (or maybe didode?) will do the job.
I also have one question. If I need 350V for a pair of 12AX7s for example I guess it's not a problem to use 2 diodes in voltage doubling configuration?
Quote from: MetalGuy on November 09, 2009, 05:11:48 PM
I would be nice to see how the output looks on the scope. Also to perform some A/B tests with actual equipment.
I would like also to remind you about the discussion concerning the dead batteries, compression etc. I suppose a 4k7-10k resistor after first cap (or maybe didode?) will do the job.
I also have one question. If I need 350V for a pair of 12AX7s for example I guess it's not a problem to use 2 diodes in voltage doubling configuration?
As far as anybody will notice, for audio use the supply will look like 175V DC with about 100 mV of P-P ripple. The frequency of the switching is so high though (100 kHz) that the noise you will see on a scope is meaningless for audio use. The only time it could POTENTIALLY cause problems is if you have something else in the system that oscillates near 100 kHz, then this noise could "beat" down into the audible range and give you some grief. Chances are that if you are working with a circuit such as this then you know of this problem already and have enough bypass capacitance around everything to prevent SMPS noise from causing system noise.
This supply is NOT meant to emulate tube rectifiers in any way. Putting a resistor in series with the voltage output, whether before or after the caps, will just drop voltage and burn up power through the resistor. Sometimes a small resistance is necessary with solid state and tube recitifiers is used to limit in-rush current before the caps but isn't needed with this supply. The time it will take for the 175V supply to recover after an output power spike is somewhere in the microseconds..
The voltage doubliing configuration can't be used with DC, at least not without some sort of square wave generator that can quickl;y flip the polarity of the voltage feeding a typical voltage multiplier circuit (diode and cap variants). These need some sort of switching waveform to work properly. This supply isn't meant for voltages that high without a bit of redesign. Adjusting R3 slightly will allow for the voltage to be tweaked, but too much may cause instability or random white puffs of smoke to appear.
The power supply can be adjusted for a bit more headroom. I wouldn't exceed 200V as a relative max (if the switch and cap can handle this) but the output current will also be derated a bit.
I finally got around to etching and building some prototype boards today. I made a few tweaks to the design and actual board, most of which was adding enough bypass capacitance to keep everything quiet and stable. I also added in a pot/trimpot that allows the output to be adjusted from 125V to 250V, although at elevated voltage levels the output current should be derated a bit. I will post a more detailed report later but as of now the supply fires up nicely and the output voltage control works as it should. At low voltage levels with too little current draw I get some oscillations but increasing the minimum load takes care of this problem. Here's a picture of the first build:
(http://imgur.com/zY6jEl.jpg)
Here's a huge image link where you can see the SMD stuff in detail: http://imgur.com/zY6jE.jpg
I'm going to build the through-hole version soon and will post both versions when I get everything revisioned and verified. Something that always nagged me with the Nixie tube supply designs is that they weren't designed for use with audio, they were meant for use with Nixie tubes. This supply is actually meant to be used in audio applications and while I haven't tested other peoples designs, I think people will dig how this supply (doesn't) sound.
Hi Cliff,
Its great to see this working. I am glad the trimpot works for adjusting the voltage. That will be handy for dialing what ever voltages a guy needs. For determining the supply current needed, would it be safe to assume (output voltage*max current)/supply voltage?
Hi Cliff,
Great job.
I can hardly wait to build this puppy.
Quote from: davidallancole on November 15, 2009, 03:01:40 AM
Hi Cliff,
Its great to see this working. I am glad the trimpot works for adjusting the voltage. That will be handy for dialing what ever voltages a guy needs. For determining the supply current needed, would it be safe to assume (output voltage*max current)/supply voltage?
For determining the input supply current it's better to take the output power, multiply this by 1.25 (this assumes about 80% efficiency plus a good amount of breathing room) and divide by the input voltage. With a 10 W load (say 175V at 57 mA) and a 12V input, you do 10W/12V = 0.8 A, so I'd go with a 1 A supply minimum. With a 12 V supply, you should never need anything over 2 A (this is about 17 W, more than the switcher can handle safely!). I'm not sure how other people rate their supplies but my experience shows that it's always a good idea to overrate the input power supplies to non-isolated power supplies for various reasons (keeps system heat and noise down).
I've been using a 12.6V, 3.5 A supply to run this thing off of. Definitely overkill, but I've just spent too much time trying to figure out why a power supply was saturating just to figure out that the input power supply was too weak for the job. :icon_confused:
Thanks Cliff.
On a side note, I understand the use of these switchers, and also desire them for my own projects, but doesn't it seem funny using a switching power supply (probably but might be linear) to reduce 120Vac to 12Vdc and then bump that back up to 175Vdc using another switching power supply? Not to ask you to do more work, but since you know more about these supplies then me, would it be possible to build a switching supply that will give the same result as what you have made, but could be powered straight from a 120Vac source?
Quote from: davidallancole on November 15, 2009, 09:34:14 AM
Thanks Cliff.
On a side note, I understand the use of these switchers, and also desire them for my own projects, but doesn't it seem funny using a switching power supply (probably but might be linear) to reduce 120Vac to 12Vdc and then bump that back up to 175Vdc using another switching power supply? Not to ask you to do more work, but since you know more about these supplies then me, would it be possible to build a switching supply that will give the same result as what you have made, but could be powered straight from a 120Vac source?
I'm sure Cliff will give some very good reasons why this is a bad idea. It's my belief that if you were to rectify the mains voltage 110VAC or 240VAC in the UK, then you will have absolutely Zero isolation from the mains so if you were also connected to any other equipment that was wired incorrectly or faulty then you will probably die.
Quote from: davidallancole on November 15, 2009, 09:34:14 AM
Thanks Cliff.
On a side note, I understand the use of these switchers, and also desire them for my own projects, but doesn't it seem funny using a switching power supply (probably but might be linear) to reduce 120Vac to 12Vdc and then bump that back up to 175Vdc using another switching power supply? Not to ask you to do more work, but since you know more about these supplies then me, would it be possible to build a switching supply that will give the same result as what you have made, but could be powered straight from a 120Vac source?
There are safety issues associated with making a homemade straight-from-the-wall powered SMPS. This type of SMPS, known as an "off-line" power supply (literally meaning off the mains line) requires some very special considerations and building techniques that isolate the dangerous 120V AC from the outputs using coupled inductors (special type of transformer). These transformers, if we were to use them for our application, would have to be wound by the builder and could potentially cause all sorts of safety issues. These special transformers, along with specialized opto-couplers, are what are used to place an isolation barrier between the input wall voltage and output sections. By instead using a SAFE (hopefully UL approved) power supply to power everything, you know that you are using safe power and I'm a lot more comfortable knowing that people are playing around with truly dangerous voltages (aside from the ones that the supply makes!).
Other reasons for not going straight off the wall include the cost would go up, the overall efficiency would go down and the board size would grow. Using already filtered and cleaned up DC from a wall wart makes my job a heck of a lot easier and worries me a lot less :).
Thanks for the response Cliff. So to sum it up, it is technically possible but would open up a whole different can of worms for the average builder?
Yes because you wouldn't be able to use off the shelf inductors like this boost design does, you're instead stuck with paying out the ass for a commercial product (especially for a toroidal core transformers) or winding your own transformers. Winding your own sucks because in order to get decent efficiency, you need to interleave of the windings or you end up with a fairly inefficient core that will get hot quickly.
Also like I said, I was going for as small of a switcher as possible. Having a transformer with at least three separate windings (primary, secondary and "housekeeping" windings) doesn't allow for a very small board..
Cliff, there's something I wish to ask to you to fully understand this development: Could this smps with its 100ma power a small tube amp like a fender Champ? I know that some problem might rise with tube heaters so I thought i could use normal diode rectification and filtering for the heaters and this smps for b+. Im I right?
Disclaimer: I may be completely wrong about this! However, I believe 100mA might be enough for a Champ (It may be close though). Voltage would be a bit low (champs typically use voltages in the 300 - 260V range) but you could still have a very "champish" sound. You won't have all of the mojo of using the 5Y3 tube rectifier (doesn't make much of a difference in SE tube amps anyway) but should be passable. As for the heater filaments, just run them from the same 12V DC supply you use for the HV supply. Keep in mind that the 6V6 power tube requires a 6.3V heater voltage so you'll have to regulate it down for that tube. The 12AX7 can use the 12V supply directly. Just make sure to increase the current rating of your 12V supply to account for the current requirements of the heaters.
Yes, looking at this proyect http://www.jjs.at/electronic/class_a_subminiature.html I understood that I could power the heathers from the same line i'm feeding the smps. What I'm not sure is what could happen if I feed 6v6 with less than 300+ volts... If I'm lucky I believe it would only sound quieter.. Is this correct?
I'll post some more specific design guidelines once I can do some more extensive testing and figure out the real limits. I really designed this supply for submini tube projects that I've been working on (about 1W and below) and I doubt that it can really push the 100mA it was designed for. I did the layouts and everything to fit parts that can handle the full load power but I haven't gotten to even test this design out with a tube design yet (test week next week!). Hopefully I can find more time soon to do the testing that I need to..
With a tube like the 6V6, in order to get the distortion one wants from the tube you need to run it at higher voltages. The datasheet says 250V requires 45mA of quiescent plate current. With a preamp tube (or two), you'll be at about 13-15 watts of power draw (pentode screen currents and triode bias currents add up here too..) which is going to start heating up the power supply. Maybe it can handle this amount of power, I'm not so sure yet because I don't have a 250V cap on the output to test everything that high (mine has a 200V part on the output). Again, I will post more details as time allows.
Whatever became of this project?
I'm getting anxious to build this sucker. I'm ready for sparks and smoke!
Did you give up on it Cliff?
+1
Been watching this hopefully from the first post.
Give up? No! I used this power supply in my little amp in the November Submission thread. As of now I just need to do one more build to verify that the design works as it should at higher voltages. I had some lockup problems with the supply when I ran it at higher voltages, essentially being when I plugged in the power the SMPS didn't boot up properly and the FET gets really hot (enough to permanently attach a nut to the drain tab!). I think this is because I used an older variant of the controller IC that I usually use and I'm thining that my build with all of the correct parts will work properly. The newer generation of the UC3842 controllers have built in soft-starts to prevent the lockup problems that I'm having. I'll put this on my to-do list but I've got another big amp on the bench that I need to finish before I get back to my miniature designs.
Great stuff Cliff! I do have a question or two about the components used building this supply or similar.
How important is component selection with regard to the resistors and caps. The internet has me confused with one builder using x type of cap and another using z type.
Are Tantalum caps and metal film resistors a necessity or is it just a builders preference? I believe this has been covered in other topics but not specific to SPMS (I did a search here).
anyway, thanks for the great design and if this is a silly concern please chalk it up to another newb.
Bob
There are certain places where you want to use the correct type of part. These parts are usually low value, high accuracy and high precision although there are other places (like the RC timing circuit) where you again don't want to use cheap resistors and caps. The caps are really critical on the output however, they need to be the special low esr types specifically designed for power supplies. A common trick for supplies like this is to put lower voltage caps in series to keep cost and size down while getting the voltage and esr ratings you need. And in certain parts of the circuit you want to use NP0/C0G ceramic caps. None of these parts are extraordinarily expensive, aside from the MOSFET switch, and the SMPS controller can be ordered for free from TI's website (up to 5 free samples per part).
Thanks Cliff!
> If I need 350V ... not a problem to use 2 diodes in voltage doubling configuration?
Won't work. The raw output is NOT symmetrical AC like you get from a wall-transformer. Your other diode has nothing to catch.
How does it work? Get a loooong fishing pole. Clamp the handle to the dock. Pull the rod down 12 inches. Let go. The tip will fly up above level. If you do it right, it can fly-up more than 12 inches, maybe more than 120 inches. This switcher does the same: the transistor flicks the coil with 12V and it flies-up to some higher voltage, which we catch with a diode. For maximum efficiency with real-world parts, you usually only ask for 1:10 fly-up: 120V. Asking for more makes your losses much higher. However the "better way" is more and more-tricky parts. Cliff has accepted "modest" efficiency to get simplicity and 1:15 to 1:20 fly-up.
It's as good as a 1-coil 12V converter gets.
Before you think of it: no, you can't "stack" two of these modules to get 350V, because the output is not isolated. Ah, it would work with TWO 12VDC isolated bricks into two modules, but be careful which brick you get your heater from.
And 12AX7 will usually run very fine with 175V, as long as you don't expect to drive 400V power tubes.
> doesn't it seem funny using a switching power supply ...to reduce 120Vac to 12Vdc and then bump that back up to 175Vdc
You forgot "isolate the audio circuit from wall wiring".
You can turn wall 120VAC into 160VDC VERY simply with a rectifier and cap. However if you touch the audio circuit (guitar jack) and PA mike or concrete or radiator, you may die.
You ALWAYS want a transformer to isolate you from the wall-power.
Classically we wind a big chunk of iron working at 50/60Hz, paying full attention to insulation and spark-over.
If we had 100KHz wall-outlets, the transformer could be far smaller/lighter. But it still needs to be wound with full isolation and insulation. Only that gets tougher in small size.
The problem is very solvable. The 12VDC wall-bricks, also PC power supplies, use a 100KHz transformer for isolation as well as voltage conversion. I've looked at designing my own, and decided the design and the for-sure SAFETY issues were not worth risking my life. There's guys who do this for a living, and other guys who get paid to check their work. I can buy a fully-approved brick for under a buck a Watt. Even with the second voltage conversion, and the general silliness of double-conversion, it still is the best way for normal people to do it.
> Could this smps with its 100ma power a small tube amp like a fender Champ?
"Like" a Champ, sure. But not with 6V6 or EL84 which need over 250V to make full power. Use the AC/DC Radio tubes: 25L6, 50C5, etc. These are built with fat cathodes and will make a whole Watt with 110V on the plate. A few are rated over 150V and as much as 10Wpdiss. Two 25L6 or two 6Y6... heck, one 6Y6 at 200V 75mA 2.6K load will pump 6 Watts which is Champ turf.
> some problem might rise with tube heaters
Since Cliff's plan starts from isolated 12VDC, as armstrom says, you just find 12V-heater tubes. Uh, that's actually a problem: the AC/DC radios ran five tubes in series from 110VAC. In series they all got the same current so the heater voltage was adjusted for the size of the cathode: 35V on the rectifier, 50V on the power tube, 12V on each small tube. And any of these tubes pulls more current and less voltage than Cliff's supply could deliver, even if you were desperate enough to double-convert for a job as simple as heating.
There were a few 6.3V versions, notably 6Y6. But Cliff's supply won't get to 175V at good current with a 6V supply. And the 6Y6's heater current is SO high (1.2A!) that it would be mighty wasteful to drop 12V to 6V. (And a resistor is all you need/want.)
There is 12FX5 (look for 60FX5 data). Typical performance is 110V, 47mA, 3K, 1.3 Watts out. At 150V 36mA (plate) 3.2K load it can make 2W. So two 12FX5 in 1.6K load fed 155V 92mA could be a whopping 4 Watts, "like" a 5W-6W Champ. The pair plus your 12A?7 can be heated from the raw isolated 12VDC, 0.35A needed.
But why? The cost of a good 12VDC couple-Amp brick plus Cliff's module is not much less than a Champ PT. It may be a pound lighter, but you still need an OT and a speaker: it won't be iPod light. The 12FX5 is stunningly cheap, but you'll want to re-diddle stage gains to account for the lower B+ voltage (and the 'FX5's high sensitivity). Quicker and as-cheap to go buy a Valve Jr and cut the nastiness out.
Be realistic. Build the small-tube end of a Champ or Dyna or other small tube circuit. Then a 12VDC brick and an internal voltage-booster makes sense. When you need big tubes and big audio transformers, KISS, use a 60Hz HV PT.
Can I power my 3 pieces 6DJ8 Tubes amp ? running 260Volt ?
this tiny SMPS can handle 200mA ?
can not wait the finish board
Cal
Sorry this has been on the back burner for so long guys, I've been incredibly busy with school/work plus getting my internship at TI setup and other various crap. I'm going to do another version of this board soon and hopefully it will be the last revision. I think I will increase the size of the board just a bit so that I can switch to through-hole components, SMD boards are a nightmare with no solder masks!
BUMP
Has the sun set on this project?
Here is the 320VDC/20mA SMPS which is sufficient for driving 3 x 12AX7's(assuming that maximum current consumption per triode is 3mA, so, 3mA x 6 triodes = 18mA, but normally triodes consume about less than a 1mA). MOSFET has to be heatsinked (cause it will dissipate about 7W of power, and according to datasheet, temp. will rise aboit 60-80C degree for every 1W).
(http://img13.imageshack.us/img13/2816/hybridsmps.th.jpg) (http://img13.imageshack.us/i/hybridsmps.jpg/)
One more thing, I didnt found anything about error amp compensator(i.e. pin 1.), so I just copied it from Cliff's SMPS, maybe he can tell us how we can determine it?
Here are design notes that I found on various app notes:
Vin = 12V
Vout = 320 V
fmin = 100 kHz
Iout = 20 mA
ton/toff = (Vout + VFD1 + VFD2) / (Vin - VsatQ1 - VsatQ2) = 30.89
ton(max) + toff = 1 / fmin = 1 / 100kHz = 0.00001
toff = (ton(max) + toff) / ((ton/toff) + 1) = 0.000000313S
ton = (ton(max) + toff) - toff = 0.000009687S
CT = 4.0 x 10-5 x ton(max) = 0.0000000003 / 387.4pF / 470pF
RT = 1.72/(CT x Fmin) = 1.72 / (470pF x 100kHz) = 36595R / 33K
Ipk(switch) = 2 Iout x ((ton/toff)+1) = 1.2756A
Lmin = ((Vin(min) - VsatQ1 - Vsatq2) / Ipk(switch)) x ton = 0.0000789 = 78.9uH / 125uH
I'pk(switch) = ((Vin(min) - VsatQ1 - Vsatq2) / Lmin) x ton = 0.805A
Rsc = 0.33 / I'pk(switch) = 0.33 / 1.0075 = 0.327 / 0.409R / 0.39R
Vripple(p-p) = ( Vout / Vref) x 1.5x10-3 = (320 / 2.5) x 1.5x10-3 = 0.192V
Co(min) = ( Iout / Vripple(p-p) ) x ton = (20mA/0.192) x 0.000009687 = 0.000001009 / 1uF I'm going to put 4.7uF.
R2(fb) = R1 x ((Vout/Vref) - 1)) = 1.8k x ((320/2.5) - 1)) = 228K / 220K.
Ugh, this project needs to get finished.. It's been on the backburner for too long and I now have the time to actually work on it. The design I first posted (and the boards) have some design issues that I need to resolve though (one of them is very fundamental too :icon_confused:). I will post more later in the week. I may end up having boards for this made as etching your own double sided boards for SMD's is quite a pain.
Mensur: With the compensation, it really depends on the topology. Does your circuit ever go continuous or over 50% duty cycles?
hey guys, I am currently building an amp using a 6k6gt powertube at 200 volts with a 12at7 preamp all powered by a "flyback" smps purchased off evilbay for the low low price of 13 bucks. It seems to work ok an my firefly type projects but this one doesnt seem to want to work right and i am wondering if its a lack of current? I dont understand how to read the charts on duncan amp pages and my measuring devices are primitive at best. Can anyone tell me how many milli amps a 6k6gt will draw at 200v on the plate and screen ( or whatever the other thing is that wants voltage) I know the heater wants .4 amps and I am getting that directly from the 9 volt ps dropped through a 7805...I know its a bit shy for the heater but its the option I had...
I am getting an awsome sound at about 2 watts or so I would guess ( from the amount of dirty looks I get from my family....) the only thing is a persistant high end noise the appears on the lower notes and hangs on for a sec after they stop being played...
I would love to get this thing working and debugged as I could actualt gig in my blues band with it and it fits in a 6x3x2 enclosure and sounds great with an 8 inch jensen. Do you think I need a new power supply? here is what i am currently using http://cgi.ebay.com/Nixie-power-supply-1363-/140426808956?pt=LH_DefaultDomain_0 any help would be sweet!
You could be running into a whole slew of problems. If you are worried about the current, remove the HV connection and place a current probe in series with the HV before it hits any tubes (you measure current in series). Or you could place a 1 Ohm resistor in series with the B+ and measure the voltage drop (in parallel), the voltage drop will be exactly equal to the current if the resistor is at 1 Ohm.
It sounds like you are running into the same stability issues I had with my first few SMPS designs. It's important to know what the switcher is comfortable driving, it could be having issues with the big inductive load that makes up your output transformer/speaker combo. Unfortunately, you need more than some basic tools to do any decisive debugging. A scope to look at the switching waveforms as the noise happens would help out immensely. The problem could be that lower frequency notes take more energy to amplify and are pulling too much current. Another thought is that the power supply probably needs more filtering before it hits the transformer/plate resistors, and maybe an adjustment of the feedback network as well if possible. You could add more capacitance to the feedback to really cut down the feedback loop frequency response which helps to kill any instabilities at the expense of dynamic response (how fast the switcher can react to changes in current/voltage needs).
Post some pictures of the build and perhaps take some basic measurements (power tube current, all your B+ voltages, schematic, etc.). The more you give us, the easier and quicker we can help you.
@ Cliff, Thanks for the rapid response. I will get some pictures up asap. Should be good for a laugh if anything ( i am a total hack bro...). I n the meantime since i dont have any of the right tools I am thinking of putting in a couple of resistors at the plate and screen. Maybe like 100k at the plate and 150k at the screen? ( yes i am totaly guessing ) this should limit the amount of voltage going to the power tube thus going a little easier on the supply making it more stable? Any thoughts on the values or am i just barking up the wrong tree?
With 100K resistors tot the plat and 2mA of current, all the voltage will fall over the resistor leaving none left for the actual tube itself.
You could bias the power tube a lititle colder using a bigger cathode resistor (to pin 8 of the 6V6).
Where did the trim pot get connected? It looks like after D1 and C3, before c9? Just an attenuator?