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SMPS for vacuum tube power amplifiers.(status: back at it)
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SK_Caterpilar_SK:
Okay...back at it but quite a bit dissapointed and hopeless this time. The latest circuit with the TL494 is not working the way I inteded it.. The controller spazzes out when the tubes begin pulling a whole lot of power.. It can cope with resistive loads great but cant handle dynamic loads. It simply wants to regulate the voltage too tight that it just goes nuts when the tubes want to pull more power (bass note or something). It spazzes out goes 90% duty and trips the OCP on the 13A 12V powersupply...optionally it burns a mosfet.

So its not working. I had 3 tries at this problem. LT3751 which did not work at all. Not even a single pulse from it. Custom controller which burned five mosfets before it worked at all, and the TL494, which keeps spazzing out tripping OCP and burning mosfets. My frustration has reached beyond borders. I have no idea what to do at this point.

I think this project was doomed the day I made the decision to go on. I spent too much money and time on the project that did not work so im kind of hopeless at this point.

For the ones supporting me and helping me thank you all, but this project inevitably met its end with a big failure sticker on its archive. Unless someone knows a proper SMPS design, because apparently I dont at all.
FreddieChopin:

--- Quote from: SK_Caterpilar_SK on June 08, 2019, 09:49:35 pm ---So it has been a while since I posted something and now its time for a question.

I have not had any time to make the powersupply at all. I still have the second version on paper not an actual working device but I have got some time toi sniff arround my prototype. the previous problem was that the entire PSU seems quite inefficient. The mosfet gets blistering hot and so does then switching transformer.

I have looked at the gate voltage and it seems fine to me, but the  transformer has an extreme amounth of oscillation. More specifically I was measuring ground to drain of the mosfet. That said on the high side of the G voltage it pulls short 2 ground on the drain (just saying so you dont have to figure out on your own.). Could this be causing the heating of the transformer and the mosfet? Interesting is that any capacitor in the input (bypass capacitor- electrolitic) right close to the switching transformer it gets very, very hot.

I dont really know why this is happening, so far my knowledge about SMPS are rather basic. I did design another powersuply completely, but since I did not know about this issue Im pretty sure it will happend again.

I have hope in your reply Tim :D. Would just a snubber network solve this or it is something that needs a more proper solution. I have a feeling it is going to require a proper solution.

On the oscilloscope where there is only one waveform I have measured between D and S  (G30N60-its not a mosfet-IGBT but a really expensive one that works really well, does not heat up as much as a IRFZ44. This heating issue stays a problem even for really low on resistance mosfets like for 100A above mosfets). The frequency of oscillation is 840kHz.

So how can I make it more relyable and efficient? Assuming the controller will be a TL494 in the future powersupply. Also I would not mind using a different chip if that makes it better.

--- End quote ---

Dumb question but is your probe compensated? Connect it to square wave test pins on scope and adjust until it's perfect rectangle.
SK_Caterpilar_SK:
Checked against control and other square waves on the poversupply board.(fet drive signal from TC4420). The transformácie by that time was already through hell and back but i think I saw such ugly waveform because I was running a IGBT instead of a FET. That original power supply is dead by now. (Funny it wasn't the fet nor the circuit itself that died but the voltage regulation that was horribly underdone.)
Audioguru again:
I was 19 years old in 1964 when I sold my vacuum tubes amplifier assembled kit (that needed its tubes replaced often) to an old geezer and replace it with a solid state amplifier that still works well today. I have not seen a working vacuum tube since then, but there is a store that sells a solid state amplifier with a couple of vacuum tubes glowing on top (not in the amplifier circuit) that are sold to old audiophools.
mrjoda:
Hi  SK_Caterpilar_SK,

I found this topic quite interesting. The idea of SMPS for tube (headamp) is in my head a few weeks (actually more than weeks). I started slowly, bought some books, read a lot of literature. The whole schematic is in my head... briefly...

My ideas went down, when i found that isolated RF wire for primary winding is almost impossible to buy without selling a kidney. And insulation at least 4kV primary/secondary is another chapter. Chinese supplier for whole transformer is the cheapest and most available solution...

The optocoupler feedback is quite issue. A BIG issue. Fortunately, i have access to bode100 in our company so it can by done.

Maybe this topic is starter for me for comeback from ideas to project.


And last point :
your pcb from previous page is wrong and messy. EMC hell ;)

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