Is A SEPIC Convertor Really All That Efficient ?

It came up recently, friend of mine has an application where it would be good. I told him it would take me a LONG time to design one from scratch. But anyway I thought of something.

Many years ago in the TV days I was working on a plasma and it had a SEPIC running one of the screen voltage. They do pull current like a CRT.

Thing is, it had a well regulated SMPS. Tye SEPICs are for going from buck to boost seamlessly, right ? But it would never have to boost. Before that SMPS comes out of regulation it would probably shut down.

So why did they use a SEPIC ? Are they THAT good ? I can understand you need something to control those voltages but to have to boost it ? I know how plasma TVs work, so maybe they wanted control over this one voltage. But to have to be able to boost it ? Why ?

 

[Bill Sloman]

On Sunday, September 22, 2019 at 12:21:23 PM UTC+10, jurb...@gmail.com wrote:

It came up recently, friend of mine has an application where it would be good. I told him it would take me a LONG time to design one from scratch. But anyway I thought of something.

Many years ago in the TV days I was working on a plasma and it had a SEPIC running one of the screen voltage. They do pull current like a CRT.

Thing is, it had a well regulated SMPS. Typically SEPICs are for going from buck to boost seamlessly, right ? But it would never have to boost. Before that SMPS comes out of regulation it would probably shut down.

So why did they use a SEPIC ? Are they THAT good ? I can understand you need something to control those voltages but to have to boost it ? I know how plasma TVs work, so maybe they wanted control over this one voltage. But to have to be able to boost it ? Why ?

Maybe having two inductors to play with meant that they could get the components into the space available.

Real designs are often constrained by non-electronic requirements - you can end up needed a really efficient converter because you can't get much cooling air past the place you have got to squeeze the converter into.

In one system I worked, the start-up had spent a bundle on a carefully styled egonomic case, which made it tricky to get rid of the waste heat from the Peltier junction we'd had to put in to get tighter temperature control at the sensing head than had been originally thought necessary.

--
Bill Sloman, Sydney

 

[Tim Williams]

No idea. Situation dependent.

Maybe you hit the nail on the head, maybe it needs a zero-energy state while
in standby? Or under startup conditions, it needs to start from zero
(whereas a boost can't avoid the first bit of inrush)?

About splitting the inductor: the physical limitations Bill mentioned, are
unlikely I would think. Not to say it can't happen, just that it likely
will take a lot of conditions to be worthwhile.

I think it would bother me more, that I'd lose the ripple-saving property.
No shared core means almost double the inductor volume, and higher ripple
needs somewhat bigger capacitors.

It's still possible you find a pair of inductors which happen to fit just
perfectly, whereas you can't find a dual that does -- that would be exactly
such a case where it might win. (The offerings for large coupled inductors,
off the shelf, is pretty pitiful.)

If custom windings are included (which they definitely would for a consumer
plasma TV), it gets a lot harder to argue that.

SEPIC is also a fertile ground to tack on additional windings, for modest
ratios (in the 1-3 range, say) and inversion (negative outputs). Though
maybe they didn't need, or take advantage of, that in your example.


Last SEPIC I designed in, was for a 12V output, while accommodating an
automotive voltage range (operational under cold cranking (6V) to load dump
(>60V)). (Operation was not required during load dump, it just turned out
that way; a feature only possible thanks to the tiny load current drawn by
the module. It actually ended up rated a whopping 200V, making a MOV
suitable to handle faster surges.)

Tim

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

<jurb6006@gmail.com> wrote in message
news:4b8bfb95-3f6e-4749-aca4-98a0424114ce@googlegroups.com...
It came up recently, friend of mine has an application where it would be
good. I told him it would take me a LONG time to design one from scratch.
But anyway I thought of something.

Many years ago in the TV days I was working on a plasma and it had a SEPIC
running one of the screen voltage. They do pull current like a CRT.

Thing is, it had a well regulated SMPS. Tye SEPICs are for going from buck
to boost seamlessly, right ? But it would never have to boost. Before that
SMPS comes out of regulation it would probably shut down.

So why did they use a SEPIC ? Are they THAT good ? I can understand you need
something to control those voltages but to have to boost it ? I know how
plasma TVs work, so maybe they wanted control over this one voltage. But to
have to be able to boost it ? Why ?

 

[bitrex]

On 9/22/19 11:42 AM, Tim Williams wrote:

No idea.  Situation dependent.

Maybe you hit the nail on the head, maybe it needs a zero-energy state
while in standby?  Or under startup conditions, it needs to start from
zero (whereas a boost can't avoid the first bit of inrush)?

About splitting the inductor: the physical limitations Bill mentioned,
are unlikely I would think.  Not to say it can't happen, just that it
likely will take a lot of conditions to be worthwhile.

I think it would bother me more, that I'd lose the ripple-saving
property. No shared core means almost double the inductor volume, and
higher ripple needs somewhat bigger capacitors.

It's still possible you find a pair of inductors which happen to fit
just perfectly, whereas you can't find a dual that does -- that would be
exactly such a case where it might win.  (The offerings for large
coupled inductors, off the shelf, is pretty pitiful.)

If custom windings are included (which they definitely would for a
consumer plasma TV), it gets a lot harder to argue that.

SEPIC is also a fertile ground to tack on additional windings, for
modest ratios (in the 1-3 range, say) and inversion (negative outputs).
Though maybe they didn't need, or take advantage of, that in your example.


Last SEPIC I designed in, was for a 12V output, while accommodating an
automotive voltage range (operational under cold cranking (6V) to load
dump (>60V)).  (Operation was not required during load dump, it just
turned out that way; a feature only possible thanks to the tiny load
current drawn by the module.  It actually ended up rated a whopping
200V, making a MOV suitable to handle faster surges.)

Tim

IIRC the late Vladimir Vassilevsky refereed to them as "septic converters"

 

[Lasse Langwadt Christense]

søndag den 22. september 2019 kl. 22.03.31 UTC+2 skrev bitrex:

On 9/22/19 11:42 AM, Tim Williams wrote:
No idea.  Situation dependent.

Maybe you hit the nail on the head, maybe it needs a zero-energy state
while in standby?  Or under startup conditions, it needs to start from
zero (whereas a boost can't avoid the first bit of inrush)?

About splitting the inductor: the physical limitations Bill mentioned,
are unlikely I would think.  Not to say it can't happen, just that it
likely will take a lot of conditions to be worthwhile.

I think it would bother me more, that I'd lose the ripple-saving
property. No shared core means almost double the inductor volume, and
higher ripple needs somewhat bigger capacitors.

It's still possible you find a pair of inductors which happen to fit
just perfectly, whereas you can't find a dual that does -- that would be
exactly such a case where it might win.  (The offerings for large
coupled inductors, off the shelf, is pretty pitiful.)

If custom windings are included (which they definitely would for a
consumer plasma TV), it gets a lot harder to argue that.

SEPIC is also a fertile ground to tack on additional windings, for
modest ratios (in the 1-3 range, say) and inversion (negative outputs).
Though maybe they didn't need, or take advantage of, that in your example.


Last SEPIC I designed in, was for a 12V output, while accommodating an
automotive voltage range (operational under cold cranking (6V) to load
dump (>60V)).  (Operation was not required during load dump, it just
turned out that way; a feature only possible thanks to the tiny load
current drawn by the module.  It actually ended up rated a whopping
200V, making a MOV suitable to handle faster surges.)

Tim


IIRC the late Vladimir Vassilevsky refereed to them as "septic converters"

afair it was a different goofy configuration he came up with and called and
an anti-septic converter

 

[bitrex]

On 9/22/19 7:17 PM, jlarkin@highlandsniptechnology.com wrote:

On Sun, 22 Sep 2019 16:03:23 -0400, bitrex <user@example.net> wrote:

On 9/22/19 11:42 AM, Tim Williams wrote:
No idea.  Situation dependent.

Maybe you hit the nail on the head, maybe it needs a zero-energy state
while in standby?  Or under startup conditions, it needs to start from
zero (whereas a boost can't avoid the first bit of inrush)?

About splitting the inductor: the physical limitations Bill mentioned,
are unlikely I would think.  Not to say it can't happen, just that it
likely will take a lot of conditions to be worthwhile.

I think it would bother me more, that I'd lose the ripple-saving
property. No shared core means almost double the inductor volume, and
higher ripple needs somewhat bigger capacitors.

It's still possible you find a pair of inductors which happen to fit
just perfectly, whereas you can't find a dual that does -- that would be
exactly such a case where it might win.  (The offerings for large
coupled inductors, off the shelf, is pretty pitiful.)

If custom windings are included (which they definitely would for a
consumer plasma TV), it gets a lot harder to argue that.

SEPIC is also a fertile ground to tack on additional windings, for
modest ratios (in the 1-3 range, say) and inversion (negative outputs).
Though maybe they didn't need, or take advantage of, that in your example.


Last SEPIC I designed in, was for a 12V output, while accommodating an
automotive voltage range (operational under cold cranking (6V) to load
dump (>60V)).  (Operation was not required during load dump, it just
turned out that way; a feature only possible thanks to the tiny load
current drawn by the module.  It actually ended up rated a whopping
200V, making a MOV suitable to handle faster surges.)

Tim


IIRC the late Vladimir Vassilevsky refereed to them as "septic converters"

It'a a nice topology.

https://www.dropbox.com/s/gc6g6g1cqbwnoh4/T770_Sepic_2.jpg?raw=1

That one adjusts from 0 to +75 volts. Output is essentially
constant-power limited, about 7 watts, which is ideal for my load.

anything to avoid this rube-goldberg-type kind of loop control circuit
would be nice:

<https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/196/5355.TL431.PNG>

I see lots and lots of papers analyzing it but none of them seem to come
out and say "this is just a mess" directly?

 

On Sun, 22 Sep 2019 16:03:23 -0400, bitrex <user@example.net> wrote:

On 9/22/19 11:42 AM, Tim Williams wrote:
No idea.  Situation dependent.

Maybe you hit the nail on the head, maybe it needs a zero-energy state
while in standby?  Or under startup conditions, it needs to start from
zero (whereas a boost can't avoid the first bit of inrush)?

About splitting the inductor: the physical limitations Bill mentioned,
are unlikely I would think.  Not to say it can't happen, just that it
likely will take a lot of conditions to be worthwhile.

I think it would bother me more, that I'd lose the ripple-saving
property. No shared core means almost double the inductor volume, and
higher ripple needs somewhat bigger capacitors.

It's still possible you find a pair of inductors which happen to fit
just perfectly, whereas you can't find a dual that does -- that would be
exactly such a case where it might win.  (The offerings for large
coupled inductors, off the shelf, is pretty pitiful.)

If custom windings are included (which they definitely would for a
consumer plasma TV), it gets a lot harder to argue that.

SEPIC is also a fertile ground to tack on additional windings, for
modest ratios (in the 1-3 range, say) and inversion (negative outputs).
Though maybe they didn't need, or take advantage of, that in your example.


Last SEPIC I designed in, was for a 12V output, while accommodating an
automotive voltage range (operational under cold cranking (6V) to load
dump (>60V)).  (Operation was not required during load dump, it just
turned out that way; a feature only possible thanks to the tiny load
current drawn by the module.  It actually ended up rated a whopping
200V, making a MOV suitable to handle faster surges.)

Tim


IIRC the late Vladimir Vassilevsky refereed to them as "septic converters"

It'a a nice topology.

https://www.dropbox.com/s/gc6g6g1cqbwnoh4/T770_Sepic_2.jpg?raw=1

That one adjusts from 0 to +75 volts. Output is essentially
constant-power limited, about 7 watts, which is ideal for my load.

 

[Clifford Heath]

On 23/9/19 11:27 am, jlarkin@highlandsniptechnology.com wrote:

On Sun, 22 Sep 2019 19:38:22 -0400, bitrex <user@example.net> wrote:

On 9/22/19 7:17 PM, jlarkin@highlandsniptechnology.com wrote:
On Sun, 22 Sep 2019 16:03:23 -0400, bitrex <user@example.net> wrote:

On 9/22/19 11:42 AM, Tim Williams wrote:
No idea.  Situation dependent.

Maybe you hit the nail on the head, maybe it needs a zero-energy state
while in standby?  Or under startup conditions, it needs to start from
zero (whereas a boost can't avoid the first bit of inrush)?

About splitting the inductor: the physical limitations Bill mentioned,
are unlikely I would think.  Not to say it can't happen, just that it
likely will take a lot of conditions to be worthwhile.

I think it would bother me more, that I'd lose the ripple-saving
property. No shared core means almost double the inductor volume, and
higher ripple needs somewhat bigger capacitors.

It's still possible you find a pair of inductors which happen to fit
just perfectly, whereas you can't find a dual that does -- that would be
exactly such a case where it might win.  (The offerings for large
coupled inductors, off the shelf, is pretty pitiful.)

If custom windings are included (which they definitely would for a
consumer plasma TV), it gets a lot harder to argue that.

SEPIC is also a fertile ground to tack on additional windings, for
modest ratios (in the 1-3 range, say) and inversion (negative outputs).
Though maybe they didn't need, or take advantage of, that in your example.


Last SEPIC I designed in, was for a 12V output, while accommodating an
automotive voltage range (operational under cold cranking (6V) to load
dump (>60V)).  (Operation was not required during load dump, it just
turned out that way; a feature only possible thanks to the tiny load
current drawn by the module.  It actually ended up rated a whopping
200V, making a MOV suitable to handle faster surges.)

Tim


IIRC the late Vladimir Vassilevsky refereed to them as "septic converters"

It'a a nice topology.

https://www.dropbox.com/s/gc6g6g1cqbwnoh4/T770_Sepic_2.jpg?raw=1

That one adjusts from 0 to +75 volts. Output is essentially
constant-power limited, about 7 watts, which is ideal for my load.



anything to avoid this rube-goldberg-type kind of loop control circuit
would be nice:

https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/196/5355.TL431.PNG

I see lots and lots of papers analyzing it but none of them seem to come
out and say "this is just a mess" directly?


Mine works fine. That LTC chip is great. I have the Spice model if
anyone is interested. The slope compensation thing, controlled by R8,
really helps.

I would be happy if you shared the Spice model for the whole circuit. I
assume that LTC provides the LTSpice model for the LTC chip...

Clifford Heath.

 

On Sun, 22 Sep 2019 19:38:22 -0400, bitrex <user@example.net> wrote:

On 9/22/19 7:17 PM, jlarkin@highlandsniptechnology.com wrote:
On Sun, 22 Sep 2019 16:03:23 -0400, bitrex <user@example.net> wrote:

On 9/22/19 11:42 AM, Tim Williams wrote:
No idea.  Situation dependent.

Maybe you hit the nail on the head, maybe it needs a zero-energy state
while in standby?  Or under startup conditions, it needs to start from
zero (whereas a boost can't avoid the first bit of inrush)?

About splitting the inductor: the physical limitations Bill mentioned,
are unlikely I would think.  Not to say it can't happen, just that it
likely will take a lot of conditions to be worthwhile.

I think it would bother me more, that I'd lose the ripple-saving
property. No shared core means almost double the inductor volume, and
higher ripple needs somewhat bigger capacitors.

It's still possible you find a pair of inductors which happen to fit
just perfectly, whereas you can't find a dual that does -- that would be
exactly such a case where it might win.  (The offerings for large
coupled inductors, off the shelf, is pretty pitiful.)

If custom windings are included (which they definitely would for a
consumer plasma TV), it gets a lot harder to argue that.

SEPIC is also a fertile ground to tack on additional windings, for
modest ratios (in the 1-3 range, say) and inversion (negative outputs).
Though maybe they didn't need, or take advantage of, that in your example.


Last SEPIC I designed in, was for a 12V output, while accommodating an
automotive voltage range (operational under cold cranking (6V) to load
dump (>60V)).  (Operation was not required during load dump, it just
turned out that way; a feature only possible thanks to the tiny load
current drawn by the module.  It actually ended up rated a whopping
200V, making a MOV suitable to handle faster surges.)

Tim


IIRC the late Vladimir Vassilevsky refereed to them as "septic converters"

It'a a nice topology.

https://www.dropbox.com/s/gc6g6g1cqbwnoh4/T770_Sepic_2.jpg?raw=1

That one adjusts from 0 to +75 volts. Output is essentially
constant-power limited, about 7 watts, which is ideal for my load.



anything to avoid this rube-goldberg-type kind of loop control circuit
would be nice:

https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/196/5355.TL431.PNG

I see lots and lots of papers analyzing it but none of them seem to come
out and say "this is just a mess" directly?

Mine works fine. That LTC chip is great. I have the Spice model if
anyone is interested. The slope compensation thing, controlled by R8,
really helps.

 

On Mon, 23 Sep 2019 11:31:24 +1000, Clifford Heath
<no.spam@please.net> wrote:

On 23/9/19 11:27 am, jlarkin@highlandsniptechnology.com wrote:
On Sun, 22 Sep 2019 19:38:22 -0400, bitrex <user@example.net> wrote:

On 9/22/19 7:17 PM, jlarkin@highlandsniptechnology.com wrote:
On Sun, 22 Sep 2019 16:03:23 -0400, bitrex <user@example.net> wrote:

On 9/22/19 11:42 AM, Tim Williams wrote:
No idea.  Situation dependent.

Maybe you hit the nail on the head, maybe it needs a zero-energy state
while in standby?  Or under startup conditions, it needs to start from
zero (whereas a boost can't avoid the first bit of inrush)?

About splitting the inductor: the physical limitations Bill mentioned,
are unlikely I would think.  Not to say it can't happen, just that it
likely will take a lot of conditions to be worthwhile.

I think it would bother me more, that I'd lose the ripple-saving
property. No shared core means almost double the inductor volume, and
higher ripple needs somewhat bigger capacitors.

It's still possible you find a pair of inductors which happen to fit
just perfectly, whereas you can't find a dual that does -- that would be
exactly such a case where it might win.  (The offerings for large
coupled inductors, off the shelf, is pretty pitiful.)

If custom windings are included (which they definitely would for a
consumer plasma TV), it gets a lot harder to argue that.

SEPIC is also a fertile ground to tack on additional windings, for
modest ratios (in the 1-3 range, say) and inversion (negative outputs).
Though maybe they didn't need, or take advantage of, that in your example.


Last SEPIC I designed in, was for a 12V output, while accommodating an
automotive voltage range (operational under cold cranking (6V) to load
dump (>60V)).  (Operation was not required during load dump, it just
turned out that way; a feature only possible thanks to the tiny load
current drawn by the module.  It actually ended up rated a whopping
200V, making a MOV suitable to handle faster surges.)

Tim


IIRC the late Vladimir Vassilevsky refereed to them as "septic converters"

It'a a nice topology.

https://www.dropbox.com/s/gc6g6g1cqbwnoh4/T770_Sepic_2.jpg?raw=1

That one adjusts from 0 to +75 volts. Output is essentially
constant-power limited, about 7 watts, which is ideal for my load.



anything to avoid this rube-goldberg-type kind of loop control circuit
would be nice:

https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/196/5355.TL431.PNG

I see lots and lots of papers analyzing it but none of them seem to come
out and say "this is just a mess" directly?


Mine works fine. That LTC chip is great. I have the Spice model if
anyone is interested. The slope compensation thing, controlled by R8,
really helps.


I would be happy if you shared the Spice model for the whole circuit. I
assume that LTC provides the LTSpice model for the LTC chip...

Clifford Heath.

This is about it:


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SYMATTR Description Diode
SYMATTR Type diode
SYMBOL res 496 240 R90
WINDOW 0 68 52 VBottom 2
WINDOW 3 75 53 VTop 2
SYMATTR InstName R7
SYMATTR Value 5K
SYMBOL cap 48 48 R90
WINDOW 0 60 70 VBottom 2
WINDOW 3 69 74 VTop 2
SYMATTR InstName C11
SYMATTR Value 1ľ
SYMBOL voltage 2032 400 R0
WINDOW 0 63 -39 Top 2
WINDOW 3 63 24 Bottom 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName Vset
SYMATTR Value 2.5
SYMBOL schottky 1136 -96 R270
WINDOW 0 45 32 VTop 2
WINDOW 3 -14 38 VBottom 2
SYMATTR InstName D1
SYMATTR Value BAT46WJ
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL cap 768 -64 R0
WINDOW 0 45 16 Left 2
WINDOW 3 45 50 Left 2
SYMATTR InstName C5
SYMATTR Value 1ľ
SYMBOL res 1248 272 R0
WINDOW 0 77 37 Left 2
WINDOW 3 61 73 Left 2
SYMATTR InstName R4
SYMATTR Value 5.23K
SYMBOL res 1424 0 R0
WINDOW 0 -69 46 Left 2
WINDOW 3 -62 79 Left 2
SYMATTR InstName Resr
SYMATTR Value 0.2
SYMBOL cap 1552 -32 R0
WINDOW 0 55 17 Left 2
WINDOW 3 55 52 Left 2
SYMATTR InstName C6
SYMATTR Value 3ľ
SYMBOL Opamps\\UniversalOpamp2 1632 336 R180
WINDOW 0 -94 95 Left 2
SYMATTR InstName U2
SYMBOL res 1920 48 R0
WINDOW 0 62 37 Left 2
WINDOW 3 62 70 Left 2
SYMATTR InstName R6
SYMATTR Value 2K
SYMBOL res 1760 -96 R270
WINDOW 0 -39 54 VTop 2
WINDOW 3 -44 51 VBottom 2
SYMATTR InstName Rout
SYMATTR Value 1m
SYMBOL cap 1840 0 R90
WINDOW 0 70 30 VBottom 2
WINDOW 3 82 31 VTop 2
SYMATTR InstName C3
SYMATTR Value 1
SYMBOL voltage 2176 -32 R0
WINDOW 123 -220 84 Left 2
WINDOW 0 -114 70 Left 2
WINDOW 3 -98 106 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName Vout
SYMATTR Value 90
SYMBOL schottky 2016 -96 R270
WINDOW 0 -40 40 VTop 2
WINDOW 3 -49 41 VBottom 2
SYMATTR InstName D3
SYMATTR Value BAT46WJ
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL bv 2352 -32 R0
WINDOW 0 60 69 Left 2
WINDOW 3 19 114 Left 2
SYMATTR InstName B1
SYMATTR Value V=V(HV)*I(Rout)
SYMBOL res 1600 448 R90
WINDOW 0 -13 56 VBottom 2
WINDOW 3 44 48 VTop 2
SYMATTR InstName R11
SYMATTR Value 499K
SYMBOL res 1920 336 R90
WINDOW 0 -61 60 VBottom 2
WINDOW 3 -49 57 VTop 2
SYMATTR InstName R13
SYMATTR Value 499K
SYMBOL voltage 1792 400 R0
WINDOW 123 -220 84 Left 2
WINDOW 0 49 44 Left 2
WINDOW 3 49 79 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V5
SYMATTR Value 2.5
SYMBOL res 1120 272 R0
WINDOW 0 -73 36 Left 2
WINDOW 3 -73 75 Left 2
SYMATTR InstName R9
SYMATTR Value 1K
SYMBOL cap 544 48 R90
WINDOW 0 -49 28 VBottom 2
WINDOW 3 -38 26 VTop 2
SYMATTR InstName C7
SYMATTR Value 200p
SYMBOL res 400 -80 R0
WINDOW 0 -64 46 Left 2
WINDOW 3 -57 85 Left 2
SYMATTR InstName R10
SYMATTR Value 1K
TEXT 728 -136 Bottom 2 !K1 L1 L2 1
TEXT 2264 424 Left 2 !.tran 50m startup
TEXT 688 -192 Left 2 ;DRQ127
TEXT 328 424 Left 2 ;0.8V
TEXT 2256 296 Left 2 ;T770 VH SUPPLY\nJ LARKIN July 23, 2019
TEXT 712 232 Left 2 ;ZVN4424
TEXT 1960 192 Left 2 ;CURRENT LIMIT TEST
TEXT 2088 488 Left 2 ;0 to +5V for\n0 to +75 out
TEXT 712 376 Left 2 ;5.6 W output limit
TEXT 1672 280 Left 2 ;OPA171
TEXT 2264 384 Left 2 !.options reltol = 0.01

 

[Jan Panteltje]

On a sunny day (Sun, 22 Sep 2019 13:18:01 -0700 (PDT)) it happened Lasse
Langwadt Christensen <langwadt@fonz.dk> wrote in
<ef7c380f-1564-4e15-bf64-345c83f2b8b7@googlegroups.com>:

afair
it was a different goofy configuration he came up with and called and
an anti-septic converter

So I got bored reading the news and looked up this group.
No matter what anybody says about SEPIC, I build this long ago as my lab power supply:
http://panteltje.com/panteltje/pic/pwr_pic/
12V in 0-24V out or something, powered by some LED strip supply wallwart
On 24/7 and no problems.
I use some current transformers in the design and basically most parts are from the junkbox and the ringcores from old PC supplies,
Programmed a PIC micro to drive it and measure voltage and current, do some basic math.
Nothing wrong with SEPIC.
I have this paper: slyt309.pdf from TI:
'Designing DC/DC converters based on SEPIC topology'
google finds it.

 

[Winfield Hill]

Jan Panteltje wrote...

No matter what anybody says about SEPIC,
I build this long ago as my lab power supply:
http://panteltje.com/panteltje/pic/pwr_pic/
12V in 0-24V out or something, powered by
some LED strip supply wallwart

Oh, great, another unreadable drawing.


--
Thanks,
- Win

 

[Tim Williams]

"bitrex" <user@example.net> wrote in message
newsBThF.266376$243.221111@fx36.iad...

anything to avoid this rube-goldberg-type kind of loop control circuit
would be nice:

https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/196/5355.TL431.PNG

I see lots and lots of papers analyzing it but none of them seem to come
out and say "this is just a mess" directly?

Are you sure you aren't doing plain old flyback instead? SEPIC is common
ground. (Well, there's an isolated version as well, but with the coupling
caps, it's not very useful.)

Anyway, you might not need the _Z components (that's if Vout > TL431_Vmax),
R_LED or Rbias, C1, or C3.

TSM101 and friends may be of interest. (These controllers are oddball and
hard to search for, unfortunately; you may find them under opamps, power
management, reference, or special...) You still need all the resistors,
because, what, would you expect a chip that coincidentally has precisely
what voltage ratio, output current and compensation time constant(s) you
need? So yeah, that's fine. Or perhaps you don't need such tight
regulation and a zener is fine.

Tim

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