Could always do something kind and use an i2c isolator across the barrier and digipot on the secondary divider if anyone is expected to adjust the HV while the thing is running.
Maxim makes cheap ones if one is ok with using Maxim
Do you remember the late Vladimir Vassilevsky's "antiseptic conveter"?
It was sort of like a SEPIC/flyback that used an off the shelf transformer with large leakage inductance and recaptured the leakage energy into the secondary.
But as I recall there was a cap across primary to secondary so not strictly isolated for AC.
The idea that you ought to use flyback in a scheme for getting 20W at up to 1000V strikes me as wrong.
The problem with flyback is that you have to dump your quantum of energy in to the inductance at low voltage, then wait for the inductance to ring up t o the desired output voltage - using up some of the energy in charging the coil's interwinding capacitance - after which you have to wait a bit longer for what's left of that energy to get dump into the high-voltage reservoir capacitor.
Whenever I've tried to do it, I've ended up with bulky inductors which I've had to gap before they can store enough energy.
Forward converters - which do include centre-tapped inverter transformer sy stems (as in the Royer and Baxandall inverters) - don't have to store anyt hing like as much energy.
The catch is that you need a fairly high turns ratio to get the voltage ste p-up (but pi/2 less with the Baxandall inverter) which means a custom wound transformer, and the high turns ratio always means a relatively high induc tance secondary and a relatively low self-resonant frequency (even if you c an break up the secondary into stacked banks, which can dramatically reduce the inter-winding capacitance).
On the other hand you end up with a tolerably compact transformer and somet hing like 95% efficiency, which Jim Williams wrote a lot of application not es to gloat about (Linear Technology application notes AN45, AN49, AN51, AN
55, AN61, and AN65).
And you don't have to wrestle with the complexities of an integrated circui t switching regulator chip - none of them ever do exactly what you want the m to.
Making the output voltage variable takes an effort - I like the idea of pul se-width modulating the drive into the inductor in a Baxandall class-D osci llator, but I've never made it work with a real circuit, though it simulate s fine.
tangentially related but this is an idea I had (probably not novel) for a medium-power high voltage series battery balancing charger based on an isolated/bidirectional Cuk converter:
The bulk charge supply charges the series stack, when a sense amp detects detects one of the batteries in the stack is above the others the appropriate Cuk converter secondary on the transformer is cut in and pushes energy from that one back into the bulk charge supply cap through the primary.
Well, they're wired in series, but they act in, well, a balanced manner, so as far as the transformer is concerned, they act in parallel. If that's what you mean then yes. :)
The foil primary helps enforce flux balance, so yes the two halves will have good cross-regulation, if you were to wire it as a bipolar source instead.
I can't figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So, i am high-jacking this for a quick question:
I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7
formatting link
I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)?
Only problem with that is that the base drive current of the power transistor may be greater than the 431 can handle. May need to use a darlington on the output, which would also improve the gain around the 431. Or, perhass replace the transistor with a power mosfet.
Depending on required precision, you could do that with a single zener, resistor and power transistor. Drop the 431 altogether...
For 12V, you'd need to recalculate your voltage divider, regardless of the regulation method intended.
A 60W shunt regulator? Don't forget a collector resistor to soak up some of that power loss. Silicon resistors, loosely applied, are expensive and prone to failure.
The only apps in your reference that used pnp power devices were for a crowbar circuit and for a switching converter; chaotic after an extra inversion.
On a sunny day (Wed, 9 Sep 2020 05:21:42 -0700 (PDT)) it happened Edward Lee wrote in :
Other suggestions are good. But in these days of green looking politicians I think the question: 'Cannot you use a 12V switcher controlled supply for efficiency" is justified. After all California is already warming up to the extreme. So maybe it would help the world if you told us what you are trying to load' so much. Of course if it is US DOD top secret but then I won't help anyways. Not with this precedent.
You could fry the TL431 at 5 amps out, from too much PNP base current. A p-channel mosfet would help there, instead of the PNP.
But the answer could be 5K either way.
--
John Larkin Highland Technology, Inc trk
The cork popped merrily, and Lord Peter rose to his feet.
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
It's for overcharging protection of the batteries. Once triggered, divider ratio will get lower, until the load shift to another one in the serial chain.
Actually, with the PNP, it doesn't need a b-e resistor. Once, about 60 years ago, people used leaky germanium transistors, so using b-e resistors became folklore.
--
John Larkin Highland Technology, Inc trk
The cork popped merrily, and Lord Peter rose to his feet.
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
Or consider a collector resistor. That's easier to think about.
--
John Larkin Highland Technology, Inc trk
The cork popped merrily, and Lord Peter rose to his feet.
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
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