Here's where I'm at with this. Really appreciate everyone's help thus far - I'm digesting everything if not replying to every point. All suggestions welcome.
(I missed a coupla labels on the negative side, that "+8.2Vpk" note refers to maximum unsmoothed ripple, and the 1000uF/16V caps could easily be 2200uF/10V)
I switched to 12.6V to bring the current and smoothing requirements down, and the hFE of the Sziklai pairs should bring this into the realm of reality. The points made thus far about going with a single supply are well taken, but my main reason for doing this bipolar is to keep pass element dissipation to a minimum. I'm planning to use the PSU case as the heatsink FYI, and the PSU is its own box separate from the 1U rackmount unit (a 4-channel microphone preamplifier). I had to refer to the XRK SLB supply for output topology, but I'm not trying to clone it obvs. If this is starting to look better to people, I'd love to know 2024 preferred part #s for the Schottky bridge and TO-92 and TO-220 transistors, as well as any supporting elements I'm missing. Cheers!
(I missed a coupla labels on the negative side, that "+8.2Vpk" note refers to maximum unsmoothed ripple, and the 1000uF/16V caps could easily be 2200uF/10V)
I switched to 12.6V to bring the current and smoothing requirements down, and the hFE of the Sziklai pairs should bring this into the realm of reality. The points made thus far about going with a single supply are well taken, but my main reason for doing this bipolar is to keep pass element dissipation to a minimum. I'm planning to use the PSU case as the heatsink FYI, and the PSU is its own box separate from the 1U rackmount unit (a 4-channel microphone preamplifier). I had to refer to the XRK SLB supply for output topology, but I'm not trying to clone it obvs. If this is starting to look better to people, I'd love to know 2024 preferred part #s for the Schottky bridge and TO-92 and TO-220 transistors, as well as any supporting elements I'm missing. Cheers!
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Thank you, that informs my HT supply! And thanks for the detailed thoughts in your last post.
So in post #23, let’s say the series resistors are each 100R (-6dB @ 1.59Hz) and as you can see I’ve nixed the base resistance. hFE should easily exceed 2000. Draw per supply could be up to 900mA, for purposes of this calc.
.9A / 2000 = .00045A base current per side, for a .09V drop across 200R, which we round up to 0.1V.
So if bipolar losses are:
-0.8V at the bridge
-0.2V at the bases
-1.2V at the output
…and we need 12.6V out, then our smoothing had better result in at least 14.8V. The bridge should put out at least 17Vpp, so I suppose the question becomes whether 13,600uF per side will do that job (I dunno if 87% of p-p is attainable). If it does so handily, then we can figure out what modicum of attenuation is required across the bases — or to your other point, what sort of series diode we may wish to insert. Or greater resistance for that matter.
Am I closing in on reality here?
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Don't see the advantage of the bipolar circuit. Twice as many components. Just take the top part of the circuit only and connect the CT to the middle. OK so the top half will need twice as much current but the circuit still floats. If you want to do the design with a MOSFET then you would need a P enhancement for the top part.
I can dig it. Down that path: No reason to use ‘lytics within the cap mult if I can make the base a gate and do something like 10K/10uF or 47K/2.2uF. I’m not familiar with the form you mocked up in LTSpice. What about secondaries in series and heaters in series to shrink the size of the bulk cap a bit - still the same compound? That would let me use 12V relays without a second regulator. Also, not to nitpick, but it looks like you’ve got the headroom issue in that sim that we’ve been lightweight wrestling with — about 6.1V smoothed.
Another version using mosfet 😉
I am not really sure how to design the compound current amp for lowest dropout. It’s possible that 2x6800u might not cut it up front, and 3x6800u would be best at this 1.8A draw (heaters plus relays). Output cap might depend on source resistance, but I could certainly throw a 1000u/16V at it. Also maybe the drains need their own small value resistors, dunno.
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Well, shoot. I developed this within my means, picked parts for minimum dropout, and PSUD2 still tells me to sit 'n' spin -- even at the minimum draw of 1.2A. Maybe I'm doing something wrong.
If you want low dropout then take a look at this chip. https://www.microchip.com/en-us/product/mic5158
So you just want a floating supply that provides DC to your tubes. Getting 6.3V DC from 6.3V AC can be problematic as you have found.
As you can put the heaters in series just go with a 12.6V DC supply single ended but floating. So 6.3V winding in series, a full wave rectifier with 8A sckottys and something like the MIC29502 low dropout regulator or similar. Don't reinvent the wheel.
As you can put the heaters in series just go with a 12.6V DC supply single ended but floating. So 6.3V winding in series, a full wave rectifier with 8A sckottys and something like the MIC29502 low dropout regulator or similar. Don't reinvent the wheel.
Nevermind, I had my wires crossed. But I do have another noob Q:
Looks like single 8A diodes have a forward voltage of .55V ish (unless @baudouin0 is referring to a particular part I’m not seeing on Mouser), but that SBM1045VSS pictured upthread is .3V at 1.5A. So that’s -.3V from a full wave, or -.6V from a full wave bridge, yes?
Looks like single 8A diodes have a forward voltage of .55V ish (unless @baudouin0 is referring to a particular part I’m not seeing on Mouser), but that SBM1045VSS pictured upthread is .3V at 1.5A. So that’s -.3V from a full wave, or -.6V from a full wave bridge, yes?
Yep I use the SBM1045VSS. Usually the diodes with low reverse voltage have lower forward voltage drop, so 2 x vfwd for full wave as you go through 2 on full wave. Note the current through the diodes is bigger than the output current as they are only on for a bit of the time.
What do you do, just float ‘em above the board? I’m not able to picture a DO-201 heatsink.
Also! This Diodes common cathode TO-220. Pity there’s no common anode equivalent.
Also! This Diodes common cathode TO-220. Pity there’s no common anode equivalent.
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