LLC with an explicit discrete Lm

I need a number (~20) of fixed voltages in the range of 4-20V.
Isolated and non-isolated, for SIC MOSFET gate drivers, 20V for a small 
D class audio amplifier, 3.3V and 5V for logic and 10V for some 
auxiliary circuits. The input voltage is in the range of 10.8-15V,
maybe 40W in total.

Due to the number of output rails the complexity of the secondary sides 
does matter. This basically kills all the PWM forward-derived 
topologies, as they need output inductors. A flyback might be an option,
but I am considering a different aapproch: a stiff LLC "pump" propelling
several way-too-good toroidal transformers (primary Lm in the millihenry 
range), connected in parallel. This will allow me to optimize their 
properties to match the requirements of a given rail and keep the number 
of windings within the sane range. Lower inter-winding capacitace of 
unrelated secondaries would be a benefit too. I'll try to make the 
effective primary inductance match the LLC design requirements, but if
it is too high, I plan to compensate with a parallel choke. Something 
along the lines of the ideal transformer model of an LLC converter, but
this time the equivalent circuit is taken literally.

Has anybody seen anything like that before? Does it make sense?

	Best regards, Piotr

On Sun, 24 Nov 2019 18:22:03 +0100, Piotr Wyderski
<peter.pan@neverland.mil> wrote:

>I need a number (~20) of fixed voltages in the range of 4-20V.
>Isolated and non-isolated, for SIC MOSFET gate drivers, 20V for a small 
>D class audio amplifier, 3.3V and 5V for logic and 10V for some 
>auxiliary circuits. The input voltage is in the range of 10.8-15V,
>maybe 40W in total.
>
>Due to the number of output rails the complexity of the secondary sides 
>does matter. This basically kills all the PWM forward-derived 
>topologies, as they need output inductors.

A multi-output forward doesn't need inductors and has decent
cross-regulation, but you can't PWM regulate. How about a buck
switcher ahead of the forward? 

Or no regulation ahead but low-drop linear or switching regs after, as
needed. I've done that a few times.

Power supply design is often a giant puzzle.



-- 

John Larkin         Highland Technology, Inc

lunatic fringe electronics 

jlarkin@highlandsniptechnology.com wrote:

> A multi-output forward doesn't need inductors and has decent
> cross-regulation, but you can't PWM regulate. How about a buck
> switcher ahead of the forward?

This reminds me the buck-pre-regulated push-pull and indeed is a viable 
option.  An unregulated Baxandall driving the trafos through a magnetic 
amplifier is another.

> Or no regulation ahead but low-drop linear or switching regs after, as
> needed. I've done that a few times.

Too complex overall. Curently I have been considering the TV-like 
approach: make the transmitting side overly complex for the beneft of 
simplified receivers. Can have a big net gain, given the number of 
secondaries.

> Power supply design is often a giant puzzle.

Surprisingly, it is the auxiliary PSU that drives me nuts. The main 
power train turned out to be pretty straightforward, even if pretty 
advanced: a totem-pole PFC powering a high-voltage LLC converter.

	Best regards, Piotr

On Sun, 24 Nov 2019 19:34:50 +0100, Piotr Wyderski
<peter.pan@neverland.mil> wrote:

>jlarkin@highlandsniptechnology.com wrote:
>
>> A multi-output forward doesn't need inductors and has decent
>> cross-regulation, but you can't PWM regulate. How about a buck
>> switcher ahead of the forward?
>
>This reminds me the buck-pre-regulated push-pull and indeed is a viable 
>option.  An unregulated Baxandall driving the trafos through a magnetic 
>amplifier is another.
>
>> Or no regulation ahead but low-drop linear or switching regs after, as
>> needed. I've done that a few times.
>
>Too complex overall. Curently I have been considering the TV-like 
>approach: make the transmitting side overly complex for the beneft of 
>simplified receivers. Can have a big net gain, given the number of 
>secondaries.
>
>> Power supply design is often a giant puzzle.
>
>Surprisingly, it is the auxiliary PSU that drives me nuts. The main 
>power train turned out to be pretty straightforward, even if pretty 
>advanced: a totem-pole PFC powering a high-voltage LLC converter.
>
>	Best regards, Piotr

Small switchers, like TPS54302, with a cheap stock inductor, are easy.
So it can make sense to keep the power parts, especially the
transformer, simple and regulate on the secondary. Really small stuff
can use linear regs.

If your main converter has to make a lot of AC anyway, maybe you can
couple that into some small transformers to get the low power stuff. 



-- 

John Larkin         Highland Technology, Inc

lunatic fringe electronics 

On a sunny day (Sun, 24 Nov 2019 18:22:03 +0100) it happened Piotr Wyderski
<peter.pan@neverland.mil> wrote in <qree7q$a6k$1@gioia.aioe.org>:

>I need a number (~20) of fixed voltages in the range of 4-20V.
>Isolated and non-isolated, for SIC MOSFET gate drivers, 20V for a small 
>D class audio amplifier, 3.3V and 5V for logic and 10V for some 
>auxiliary circuits. The input voltage is in the range of 10.8-15V,
>maybe 40W in total.

For the boost converter I have this:
 https://www.ebay.com/itm/18345275960
cannot make it for 2$28 free shipping, works very well here.
For the lower voltages up to 5A a switcher with LM2596 only takes a few cm^2,
cost very little, even for 20 pieces., using those in several projects.
For isolated gate drive probably with not much current wind some E I core
using good insulated wire .. use a flat cable for multi-turns, 1V/turn.



?

jlarkin@highlandsniptechnology.com wrote:

> Small switchers, like TPS54302, with a cheap stock inductor, are easy.

I like this part, but it solves only the easier part of the problem.

> If your main converter has to make a lot of AC anyway, maybe you can
> couple that into some small transformers to get the low power stuff.

The isolated auxiliaries need to be energized even when there is no AC 
power, using battery backup. So it is simpler to power the smaller 
converter from the secondary end of the main LLC.

	Best regards, Piotr

Consider planar -- the resonant thing I showed earlier has pretty good cross 
regulation.  There's about 10nH between the secondaries.

Toroids are fine too, just a pain to wind.  If you're farming them out then 
do it however you like. ;D

To get comparable leakage, you will need short winding lengths, and 
preferably use twisted pairs or even quads for each winding to keep the 
impedance low.  Also, TLT techniques don't mind what the core is, it just 
needs to up the magnetizing impedance.

Also, don't mind adding LDOs to clean up [cross]regulation, it's just one 
more part, not a huge burden.

Also also, you can save some diodes if you use CT windings, which would be a 
pain for a hand wound transformer, but is almost free in planar.  Just a 
PITA to design them...

Tim

-- 
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

"Piotr Wyderski" <peter.pan@neverland.mil> wrote in message 
news:qree7q$a6k$1@gioia.aioe.org...
>I need a number (~20) of fixed voltages in the range of 4-20V.
> Isolated and non-isolated, for SIC MOSFET gate drivers, 20V for a small D 
> class audio amplifier, 3.3V and 5V for logic and 10V for some auxiliary 
> circuits. The input voltage is in the range of 10.8-15V,
> maybe 40W in total.
>
> Due to the number of output rails the complexity of the secondary sides 
> does matter. This basically kills all the PWM forward-derived topologies, 
> as they need output inductors. A flyback might be an option,
> but I am considering a different aapproch: a stiff LLC "pump" propelling
> several way-too-good toroidal transformers (primary Lm in the millihenry 
> range), connected in parallel. This will allow me to optimize their 
> properties to match the requirements of a given rail and keep the number 
> of windings within the sane range. Lower inter-winding capacitace of 
> unrelated secondaries would be a benefit too. I'll try to make the 
> effective primary inductance match the LLC design requirements, but if
> it is too high, I plan to compensate with a parallel choke. Something 
> along the lines of the ideal transformer model of an LLC converter, but
> this time the equivalent circuit is taken literally.
>
> Has anybody seen anything like that before? Does it make sense?
>
> Best regards, Piotr 

Hi Tim

Can you post a link to the planar thingie?

Cheers

Klaus

"Klaus Kragelund" <klauskvik@hotmail.com> wrote in message 
news:00339865-04e4-43f3-a52a-9876fd343ac6@googlegroups.com...
> Hi Tim
>
> Can you post a link to the planar thingie?

https://www.seventransistorlabs.com/Images/ResonantGateDriver.jpg
https://www.seventransistorlabs.com/Images/ResonantSupplySch.png
(mind, proto testing changes not included)

Tim

-- 
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/ 

Tim Williams wrote:

> Consider planar -- the resonant thing I showed earlier has pretty good 
> cross regulation.� There's about 10nH between the secondaries.

That's really impressive, but I don't see how a planar could host that 
many windings.

> Toroids are fine too, just a pain to wind.� If you're farming them out 
> then do it however you like. ;D

Not a problem, there is a company that could wind them in quantity.
Now it is for a proto, so the winding complexity is not a big issue.

> Also, don't mind adding LDOs to clean up [cross]regulation, it's just 
> one more part, not a huge burden.

Times the number of secondaries, 15 parts then (not all voltages need to 
be regulated).

The plan for this week: grab an LM5041, extract the full glory of it in 
the cascaded configuration and see if it suits my needs. Unfortunately, 
the built-in drivers are not particularly strong, so MOSFET selection 
will be a PITA. It looks promising and I can have SR drive for free 
(well, at the cost of even more windings...).

	Best regards, Piotr