CPU fan buck converter, miniature

Winfield Hill wrote...
Winfield Hill wrote...

Winfield Hill wrote...

https://www.dropbox.com/s/wttdn9r8np3o0t6/buck_CPU-fan.JPG?dl=0

I had finished a new PCB version of my compact
250A analog pulser, with a newly-added CPU fan.
The fan was powered with an 78L12, hey, there
wasn't room for much else. But it was obvious
its 300mA would overheat the TO-92 regulator,
plus what a waste of power! I needed to fit a
buck converter. This called for a SOT-23 part;
no room for a SO-8, and SON or LFCSP packages
not allowed, too hard to solder. There are lots
of low-voltage candidates, but RIS-796A is used
up to at least 40 volts. Only one part fits the
bill: LM2842Y. And it runs at 1.25MHz, allowing
for a small inductor. The PCB circuit is only
0.4 x 0.5 inches, fits on a corner of the PCB.
(The AOZ1282CI is a close alternate 36V 450kHz.)

Here's why this is a miniature buck converter.
It's in the little green circle at the lower
right corner, of a fairly-small 3x3-inch PCB.

https://www.dropbox.com/s/iqxegp4he8d6ast/buck_in-796A.JPG?dl=0

Save yourself a copy, you might need it oneday.
I imagine it's got about 5W of capability.

Here's my smallest 100V fan supply (on the
RIS-796 non-A "digital version"). It's quite
a bit larger - high voltage dictates a larger
inductor, and an SO-8 converter package buck
converter IC. Once again, only an NSC-TI part,
the LM5163, gets the nod. Thankfully it's a
synchronous part, saving a sod-123 diode. With
0.33-ohm lo-side MOSFET, only 30mW of I2R loss,
despite a high 100V to 8 to 12V step-down ratio.

https://www.dropbox.com/s/glk4u573rnpu959/buck_CPU-fan_100V.JPG?dl=0

The 100V capability of the RIS-796 v.3 enables
pulsing 32V, 3.5A COB LEDs, which can have an
excess drop of up to 50V at 25A or higher.
Click to expand...

Oops, possible problem with the DropBox link.

https://www.dropbox.com/s/f33qz4uqrd1gv8i/buck_CPU-fan_100V.JPG?dl=0

Note the 1-ohm resistor in series with Cout.
The LM5163 needs this for a feedback signal.
Another unusual aspect, the boost cap, C13,
must not be larger than 2.2nF. But it's a
super-handy IC design, working to 100 volts.


--
Thanks,
- Win
 
On 28 Jan 2020 05:47:44 -0800, Winfield Hill <winfieldhill@yahoo.com>
wrote:

Winfield Hill wrote...

Winfield Hill wrote...

Winfield Hill wrote...

https://www.dropbox.com/s/wttdn9r8np3o0t6/buck_CPU-fan.JPG?dl=0

I had finished a new PCB version of my compact
250A analog pulser, with a newly-added CPU fan.
The fan was powered with an 78L12, hey, there
wasn't room for much else. But it was obvious
its 300mA would overheat the TO-92 regulator,
plus what a waste of power! I needed to fit a
buck converter. This called for a SOT-23 part;
no room for a SO-8, and SON or LFCSP packages
not allowed, too hard to solder. There are lots
of low-voltage candidates, but RIS-796A is used
up to at least 40 volts. Only one part fits the
bill: LM2842Y. And it runs at 1.25MHz, allowing
for a small inductor. The PCB circuit is only
0.4 x 0.5 inches, fits on a corner of the PCB.
(The AOZ1282CI is a close alternate 36V 450kHz.)

Here's why this is a miniature buck converter.
It's in the little green circle at the lower
right corner, of a fairly-small 3x3-inch PCB.

https://www.dropbox.com/s/iqxegp4he8d6ast/buck_in-796A.JPG?dl=0

Save yourself a copy, you might need it oneday.
I imagine it's got about 5W of capability.

Here's my smallest 100V fan supply (on the
RIS-796 non-A "digital version"). It's quite
a bit larger - high voltage dictates a larger
inductor, and an SO-8 converter package buck
converter IC. Once again, only an NSC-TI part,
the LM5163, gets the nod. Thankfully it's a
synchronous part, saving a sod-123 diode. With
0.33-ohm lo-side MOSFET, only 30mW of I2R loss,
despite a high 100V to 8 to 12V step-down ratio.

https://www.dropbox.com/s/glk4u573rnpu959/buck_CPU-fan_100V.JPG?dl=0

The 100V capability of the RIS-796 v.3 enables
pulsing 32V, 3.5A COB LEDs, which can have an
excess drop of up to 50V at 25A or higher.

Oops, possible problem with the DropBox link.

https://www.dropbox.com/s/f33qz4uqrd1gv8i/buck_CPU-fan_100V.JPG?dl=0

Note the 1-ohm resistor in series with Cout.
The LM5163 needs this for a feedback signal.
Another unusual aspect, the boost cap, C13,
must not be larger than 2.2nF. But it's a
super-handy IC design, working to 100 volts.
Click to expand...

What happens if the bootstrap cap is bigger?



--

John Larkin Highland Technology, Inc

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"
 
On Tuesday, January 28, 2020 at 11:06:13 AM UTC-5, jla...@highlandsniptechnology.com wrote:
On 28 Jan 2020 05:47:44 -0800, Winfield Hill <winfieldhill@yahoo.com
wrote:

Winfield Hill wrote...

Winfield Hill wrote...

Winfield Hill wrote...

https://www.dropbox.com/s/wttdn9r8np3o0t6/buck_CPU-fan.JPG?dl=0

I had finished a new PCB version of my compact
250A analog pulser, with a newly-added CPU fan.
The fan was powered with an 78L12, hey, there
wasn't room for much else. But it was obvious
its 300mA would overheat the TO-92 regulator,
plus what a waste of power! I needed to fit a
buck converter. This called for a SOT-23 part;
no room for a SO-8, and SON or LFCSP packages
not allowed, too hard to solder. There are lots
of low-voltage candidates, but RIS-796A is used
up to at least 40 volts. Only one part fits the
bill: LM2842Y. And it runs at 1.25MHz, allowing
for a small inductor. The PCB circuit is only
0.4 x 0.5 inches, fits on a corner of the PCB.
(The AOZ1282CI is a close alternate 36V 450kHz.)

Here's why this is a miniature buck converter.
It's in the little green circle at the lower
right corner, of a fairly-small 3x3-inch PCB.

https://www.dropbox.com/s/iqxegp4he8d6ast/buck_in-796A.JPG?dl=0

Save yourself a copy, you might need it oneday.
I imagine it's got about 5W of capability.

Here's my smallest 100V fan supply (on the
RIS-796 non-A "digital version"). It's quite
a bit larger - high voltage dictates a larger
inductor, and an SO-8 converter package buck
converter IC. Once again, only an NSC-TI part,
the LM5163, gets the nod. Thankfully it's a
synchronous part, saving a sod-123 diode. With
0.33-ohm lo-side MOSFET, only 30mW of I2R loss,
despite a high 100V to 8 to 12V step-down ratio.

https://www.dropbox.com/s/glk4u573rnpu959/buck_CPU-fan_100V.JPG?dl=0

The 100V capability of the RIS-796 v.3 enables
pulsing 32V, 3.5A COB LEDs, which can have an
excess drop of up to 50V at 25A or higher.

Oops, possible problem with the DropBox link.

https://www.dropbox.com/s/f33qz4uqrd1gv8i/buck_CPU-fan_100V.JPG?dl=0

Note the 1-ohm resistor in series with Cout.
The LM5163 needs this for a feedback signal.
Another unusual aspect, the boost cap, C13,
must not be larger than 2.2nF. But it's a
super-handy IC design, working to 100 volts.

What happens if the bootstrap cap is bigger?
Click to expand...
The fan speeds up, flies off the board, and heads for parts unknown. :)
GH
--

John Larkin Highland Technology, Inc

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"
Click to expand...
 
jlarkin@highlandsniptechnology.com wrote...
Winfield Hill wrote:

Another unusual aspect, the boost cap, C13,
must not be larger than 2.2nF. But it's a
super-handy IC design, working to 100 volts.

What happens if the bootstrap cap is bigger?
Click to expand...

The chip has an onboard 5V supply that run
s fromthe up to 100V input. That supply has n
o bypass capacitor, but runs everything on
the buck converter, incuiding both MOSFETs.
They point out youmusty avoid overburdening
that supply, anf the boost cap is too bi
gthe chip , canbe damaged. Frankly, I'm glad
they avoided both bypass cap and catch diode.


--
Thanks,
- Win
 
tirsdag den 28. januar 2020 kl. 14.48.03 UTC+1 skrev Winfield Hill:
Winfield Hill wrote...

Winfield Hill wrote...

Winfield Hill wrote...

https://www.dropbox.com/s/wttdn9r8np3o0t6/buck_CPU-fan.JPG?dl=0

I had finished a new PCB version of my compact
250A analog pulser, with a newly-added CPU fan.
The fan was powered with an 78L12, hey, there
wasn't room for much else. But it was obvious
its 300mA would overheat the TO-92 regulator,
plus what a waste of power! I needed to fit a
buck converter. This called for a SOT-23 part;
no room for a SO-8, and SON or LFCSP packages
not allowed, too hard to solder. There are lots
of low-voltage candidates, but RIS-796A is used
up to at least 40 volts. Only one part fits the
bill: LM2842Y. And it runs at 1.25MHz, allowing
for a small inductor. The PCB circuit is only
0.4 x 0.5 inches, fits on a corner of the PCB.
(The AOZ1282CI is a close alternate 36V 450kHz.)

Here's why this is a miniature buck converter.
It's in the little green circle at the lower
right corner, of a fairly-small 3x3-inch PCB.

https://www.dropbox.com/s/iqxegp4he8d6ast/buck_in-796A.JPG?dl=0

Save yourself a copy, you might need it oneday.
I imagine it's got about 5W of capability.

Here's my smallest 100V fan supply (on the
RIS-796 non-A "digital version"). It's quite
a bit larger - high voltage dictates a larger
inductor, and an SO-8 converter package buck
converter IC. Once again, only an NSC-TI part,
the LM5163, gets the nod. Thankfully it's a
synchronous part, saving a sod-123 diode. With
0.33-ohm lo-side MOSFET, only 30mW of I2R loss,
despite a high 100V to 8 to 12V step-down ratio.

https://www.dropbox.com/s/glk4u573rnpu959/buck_CPU-fan_100V.JPG?dl=0

The 100V capability of the RIS-796 v.3 enables
pulsing 32V, 3.5A COB LEDs, which can have an
excess drop of up to 50V at 25A or higher.

Oops, possible problem with the DropBox link.

https://www.dropbox.com/s/f33qz4uqrd1gv8i/buck_CPU-fan_100V.JPG?dl=0

Note the 1-ohm resistor in series with Cout.
The LM5163 needs this for a feedback signal.
Click to expand...

how well does that work on a board full of bypass caps ?
 
On Tue, 28 Jan 2020 11:09:23 -0800 (PST), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

tirsdag den 28. januar 2020 kl. 19.56.23 UTC+1 skrev John Larkin:
On Tue, 28 Jan 2020 10:40:55 -0800 (PST), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

tirsdag den 28. januar 2020 kl. 14.48.03 UTC+1 skrev Winfield Hill:
Winfield Hill wrote...

Winfield Hill wrote...

Winfield Hill wrote...

https://www.dropbox.com/s/wttdn9r8np3o0t6/buck_CPU-fan.JPG?dl=0

I had finished a new PCB version of my compact
250A analog pulser, with a newly-added CPU fan.
The fan was powered with an 78L12, hey, there
wasn't room for much else. But it was obvious
its 300mA would overheat the TO-92 regulator,
plus what a waste of power! I needed to fit a
buck converter. This called for a SOT-23 part;
no room for a SO-8, and SON or LFCSP packages
not allowed, too hard to solder. There are lots
of low-voltage candidates, but RIS-796A is used
up to at least 40 volts. Only one part fits the
bill: LM2842Y. And it runs at 1.25MHz, allowing
for a small inductor. The PCB circuit is only
0.4 x 0.5 inches, fits on a corner of the PCB.
(The AOZ1282CI is a close alternate 36V 450kHz.)

Here's why this is a miniature buck converter.
It's in the little green circle at the lower
right corner, of a fairly-small 3x3-inch PCB.

https://www.dropbox.com/s/iqxegp4he8d6ast/buck_in-796A.JPG?dl=0

Save yourself a copy, you might need it oneday.
I imagine it's got about 5W of capability.

Here's my smallest 100V fan supply (on the
RIS-796 non-A "digital version"). It's quite
a bit larger - high voltage dictates a larger
inductor, and an SO-8 converter package buck
converter IC. Once again, only an NSC-TI part,
the LM5163, gets the nod. Thankfully it's a
synchronous part, saving a sod-123 diode. With
0.33-ohm lo-side MOSFET, only 30mW of I2R loss,
despite a high 100V to 8 to 12V step-down ratio.

https://www.dropbox.com/s/glk4u573rnpu959/buck_CPU-fan_100V.JPG?dl=0

The 100V capability of the RIS-796 v.3 enables
pulsing 32V, 3.5A COB LEDs, which can have an
excess drop of up to 50V at 25A or higher.

Oops, possible problem with the DropBox link.

https://www.dropbox.com/s/f33qz4uqrd1gv8i/buck_CPU-fan_100V.JPG?dl=0

Note the 1-ohm resistor in series with Cout.
The LM5163 needs this for a feedback signal.

how well does that work on a board full of bypass caps ?

Usually a big, moderate-ESR cap (like a tantalum) adds a lot of
damping to a power pour which has a bunch of low-ESR ceramics lurking
on other sheets of the schematic. In Win's case, the only load is the
fan.

sure but the datasheet has formulas for calculating the required ESR
and explains that the resulting ripple is required for operation
Click to expand...

Datasheets don't usually, or ever, address the multiple-capacitor
case, like one big aluminum or tantalum in parallel with a bunch of
ceramics.

Ripple is required? We don't want ripple!

Some regulators are stable for any amount of low-ESR caps. That's
rare. Many older data sheets don't even discuss the issue.

I invented the C3 trick here, to stabilize an LM317 with a big
zero-ESR output cap.

https://www.dropbox.com/s/7i5km22be5m0z9g/LT317_1.asc?dl=0

I'm not sure how that works, but it works.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
tirsdag den 28. januar 2020 kl. 19.56.23 UTC+1 skrev John Larkin:
On Tue, 28 Jan 2020 10:40:55 -0800 (PST), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

tirsdag den 28. januar 2020 kl. 14.48.03 UTC+1 skrev Winfield Hill:
Winfield Hill wrote...

Winfield Hill wrote...

Winfield Hill wrote...

https://www.dropbox.com/s/wttdn9r8np3o0t6/buck_CPU-fan.JPG?dl=0

I had finished a new PCB version of my compact
250A analog pulser, with a newly-added CPU fan.
The fan was powered with an 78L12, hey, there
wasn't room for much else. But it was obvious
its 300mA would overheat the TO-92 regulator,
plus what a waste of power! I needed to fit a
buck converter. This called for a SOT-23 part;
no room for a SO-8, and SON or LFCSP packages
not allowed, too hard to solder. There are lots
of low-voltage candidates, but RIS-796A is used
up to at least 40 volts. Only one part fits the
bill: LM2842Y. And it runs at 1.25MHz, allowing
for a small inductor. The PCB circuit is only
0.4 x 0.5 inches, fits on a corner of the PCB.
(The AOZ1282CI is a close alternate 36V 450kHz.)

Here's why this is a miniature buck converter.
It's in the little green circle at the lower
right corner, of a fairly-small 3x3-inch PCB.

https://www.dropbox.com/s/iqxegp4he8d6ast/buck_in-796A.JPG?dl=0

Save yourself a copy, you might need it oneday.
I imagine it's got about 5W of capability.

Here's my smallest 100V fan supply (on the
RIS-796 non-A "digital version"). It's quite
a bit larger - high voltage dictates a larger
inductor, and an SO-8 converter package buck
converter IC. Once again, only an NSC-TI part,
the LM5163, gets the nod. Thankfully it's a
synchronous part, saving a sod-123 diode. With
0.33-ohm lo-side MOSFET, only 30mW of I2R loss,
despite a high 100V to 8 to 12V step-down ratio.

https://www.dropbox.com/s/glk4u573rnpu959/buck_CPU-fan_100V.JPG?dl=0

The 100V capability of the RIS-796 v.3 enables
pulsing 32V, 3.5A COB LEDs, which can have an
excess drop of up to 50V at 25A or higher.

Oops, possible problem with the DropBox link.

https://www.dropbox.com/s/f33qz4uqrd1gv8i/buck_CPU-fan_100V.JPG?dl=0

Note the 1-ohm resistor in series with Cout.
The LM5163 needs this for a feedback signal.

how well does that work on a board full of bypass caps ?

Usually a big, moderate-ESR cap (like a tantalum) adds a lot of
damping to a power pour which has a bunch of low-ESR ceramics lurking
on other sheets of the schematic. In Win's case, the only load is the
fan.
Click to expand...

sure but the datasheet has formulas for calculating the required ESR
and explains that the resulting ripple is required for operation
 
On Tue, 28 Jan 2020 10:40:55 -0800 (PST), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

tirsdag den 28. januar 2020 kl. 14.48.03 UTC+1 skrev Winfield Hill:
Winfield Hill wrote...

Winfield Hill wrote...

Winfield Hill wrote...

https://www.dropbox.com/s/wttdn9r8np3o0t6/buck_CPU-fan.JPG?dl=0

I had finished a new PCB version of my compact
250A analog pulser, with a newly-added CPU fan.
The fan was powered with an 78L12, hey, there
wasn't room for much else. But it was obvious
its 300mA would overheat the TO-92 regulator,
plus what a waste of power! I needed to fit a
buck converter. This called for a SOT-23 part;
no room for a SO-8, and SON or LFCSP packages
not allowed, too hard to solder. There are lots
of low-voltage candidates, but RIS-796A is used
up to at least 40 volts. Only one part fits the
bill: LM2842Y. And it runs at 1.25MHz, allowing
for a small inductor. The PCB circuit is only
0.4 x 0.5 inches, fits on a corner of the PCB.
(The AOZ1282CI is a close alternate 36V 450kHz.)

Here's why this is a miniature buck converter.
It's in the little green circle at the lower
right corner, of a fairly-small 3x3-inch PCB.

https://www.dropbox.com/s/iqxegp4he8d6ast/buck_in-796A.JPG?dl=0

Save yourself a copy, you might need it oneday.
I imagine it's got about 5W of capability.

Here's my smallest 100V fan supply (on the
RIS-796 non-A "digital version"). It's quite
a bit larger - high voltage dictates a larger
inductor, and an SO-8 converter package buck
converter IC. Once again, only an NSC-TI part,
the LM5163, gets the nod. Thankfully it's a
synchronous part, saving a sod-123 diode. With
0.33-ohm lo-side MOSFET, only 30mW of I2R loss,
despite a high 100V to 8 to 12V step-down ratio.

https://www.dropbox.com/s/glk4u573rnpu959/buck_CPU-fan_100V.JPG?dl=0

The 100V capability of the RIS-796 v.3 enables
pulsing 32V, 3.5A COB LEDs, which can have an
excess drop of up to 50V at 25A or higher.

Oops, possible problem with the DropBox link.

https://www.dropbox.com/s/f33qz4uqrd1gv8i/buck_CPU-fan_100V.JPG?dl=0

Note the 1-ohm resistor in series with Cout.
The LM5163 needs this for a feedback signal.

how well does that work on a board full of bypass caps ?
Click to expand...

Usually a big, moderate-ESR cap (like a tantalum) adds a lot of
damping to a power pour which has a bunch of low-ESR ceramics lurking
on other sheets of the schematic. In Win's case, the only load is the
fan.

I Spice these sorts of things when I can, or sometimes breadboard to
check stability.

Sometimes a big super-low-ESR cap, like a 56uF polymer or a 1500uF
aluminum, is brute-force stable too. On a regulator (or on an opamp
output) to ground.

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
On 2020-01-28 13:56, John Larkin wrote:

Note the 1-ohm resistor in series with Cout.
The LM5163 needs this for a feedback signal.

how well does that work on a board full of bypass caps ?

Usually a big, moderate-ESR cap (like a tantalum) adds a lot of
damping to a power pour which has a bunch of low-ESR ceramics lurking
on other sheets of the schematic. In Win's case, the only load is the
fan.
Click to expand...

Yup. It's a super low-Z lead/lag network.

I Spice these sorts of things when I can, or sometimes breadboard to
check stability.

Sometimes a big super-low-ESR cap, like a 56uF polymer or a 1500uF
aluminum, is brute-force stable too. On a regulator (or on an opamp
output) to ground.
Click to expand...

Until it dries out a bit. ;)

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
On Tue, 28 Jan 2020 14:59:04 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-01-28 13:56, John Larkin wrote:

Note the 1-ohm resistor in series with Cout.
The LM5163 needs this for a feedback signal.

how well does that work on a board full of bypass caps ?

Usually a big, moderate-ESR cap (like a tantalum) adds a lot of
damping to a power pour which has a bunch of low-ESR ceramics lurking
on other sheets of the schematic. In Win's case, the only load is the
fan.

Yup. It's a super low-Z lead/lag network.


I Spice these sorts of things when I can, or sometimes breadboard to
check stability.

Sometimes a big super-low-ESR cap, like a 56uF polymer or a 1500uF
aluminum, is brute-force stable too. On a regulator (or on an opamp
output) to ground.

Until it dries out a bit. ;)
Click to expand...

Most survive the 1-year warranty period. Actually, most survive a lot
longer.

I really like aluminum polymers, or at least some of them.

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
Winfield Hill <winfieldhill@yahoo.com> writes:

bill: LM2842Y. And it runs at 1.25MHz, allowing
....
Here's why this is a miniature buck converter.
It's in the little green circle at the lower
right corner, of a fairly-small 3x3-inch PCB.

https://www.dropbox.com/s/iqxegp4he8d6ast/buck_in-796A.JPG?dl=0

Save yourself a copy, you might need it oneday.
I imagine it's got about 5W of capability.
Click to expand...

Thanks for sharing - looks like a great part for an update project for
automotive sensor that needs to go from 12 to 24V world.

--
mikko
 
Lasse Langwadt Christensen wrote...
Winfield Hill wrote

Note the 1-ohm resistor in series with Cout.
The LM5163 needs this for a feedback signal.

how well does that work on a board full of bypass caps ?
Click to expand...

Note the high value, 1 ohm, to generate appropriate
voltage ripple at the feedback node. That's way higher
than a typical esr, and could be spoiled by lots of
bypass caps. The LM5163 datasheet, page 11, is worth
reading. They allow direct Cout to ground, if instead
you use a three-part network to generate a triangular
ramp that's in-phase with the inductor current. Note,
this isn't an "esr" situation, but for my application,
it's OK. A Cff cap across Rf can reduce output ripple.


--
Thanks,
- Win
 
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