Switching regulator replacement for 7805
That's a very good point... the design I'm testing the regulator in has
a fair bit of C filtering, but no series L.
On 12/04/2016 02:45 PM, Chris Albertson wrote:
Surprisingly good as a drop-in replacement.
Question: Suppose you are doing a new design and had space on the PCB for
one more small passive part. I wonder how the performance of the switcher
with an LC filter compares with the 7805. Yes, I think this is fair. It
is a trade off, It costs me one more inductor but I gain hugely reduced
power consumption and heat.
Or stated another way: You have shown the noise difference for drop in to
existing circuit. What about two roughly equivalent new design circuits?
How much to we pay in dollars and complexity to get equivalent noise?
Thanks a lot for this work. Headed over to eBay right now....
(My application uses LiPo battery and needs to have stable voltage as the
battery drains but my current solution is noisyand those 78xx chips waste
far to much power. )
On Sun, Dec 4, 2016 at 10:50 AM, John Ackermann N8UR jra@febo.com wrote:
I found a cute little switching regulator that's a drop-in replacement for
an LM7805: http://www.ebay.com/itm/261243604047
I got a couple to play with, mainly to see how bad the noise would be.
Here are spectrum analyzer and PN shots comparing a cheap surplus OCXO when
driven by a regular 7805 and by the switching replacement.
The switching frequency is supposed to be 2 MHz but you can see that it's
more like 2.4 MHz. Whether this performance is sufficient for any
application is up to you. It sure runs a lot cooler than a 7805, though!
John
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Hi
The most common thing to miss on decoupling a switcher is that both the output
and the input will generate crud that sprays all over the place. Series L on both
the input and output are a really good idea. Microhenry (as opposed to milihenry)
chokes are generally good enough. Values are dictated more by board space than
anything else. 22 uH is not a bad starting point. A SRF above 3 MHz would be a
good idea :)
Bob
On Dec 4, 2016, at 3:14 PM, John Ackermann N8UR jra@febo.com wrote:
That's a very good point... the design I'm testing the regulator in has a fair bit of C filtering, but no series L.
On 12/04/2016 02:45 PM, Chris Albertson wrote:
Surprisingly good as a drop-in replacement.
Question: Suppose you are doing a new design and had space on the PCB for
one more small passive part. I wonder how the performance of the switcher
with an LC filter compares with the 7805. Yes, I think this is fair. It
is a trade off, It costs me one more inductor but I gain hugely reduced
power consumption and heat.
Or stated another way: You have shown the noise difference for drop in to
existing circuit. What about two roughly equivalent new design circuits?
How much to we pay in dollars and complexity to get equivalent noise?
Thanks a lot for this work. Headed over to eBay right now....
(My application uses LiPo battery and needs to have stable voltage as the
battery drains but my current solution is noisyand those 78xx chips waste
far to much power. )
On Sun, Dec 4, 2016 at 10:50 AM, John Ackermann N8UR jra@febo.com wrote:
I found a cute little switching regulator that's a drop-in replacement for
an LM7805: http://www.ebay.com/itm/261243604047
I got a couple to play with, mainly to see how bad the noise would be.
Here are spectrum analyzer and PN shots comparing a cheap surplus OCXO when
driven by a regular 7805 and by the switching replacement.
The switching frequency is supposed to be 2 MHz but you can see that it's
more like 2.4 MHz. Whether this performance is sufficient for any
application is up to you. It sure runs a lot cooler than a 7805, though!
John
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At Farnell, they're listed under Power Supplies rather than Switching
Regulators (which is a subdivision of Semiconductors).
It makes sense since one is a board product and the other a chip, but when
the board product is a drop-in replacement for a TO220, less sense!
On Sun, Dec 4, 2016 at 7:44 PM, John Ackermann N8UR jra@febo.com wrote:
And Digikey does stock the Murata part, for about $4.30. Why I couldn't
find it when searching their site for switching regulators, I don't know.
John
On 12/04/2016 02:39 PM, John Ackermann N8UR wrote:
Thanks for that pointer! When I searched Digikey, I wasn't able to find
anything that was in the 3-lead TO-220 case. I will definitely check
out the Murata units, as I suspect they perform better than this one.
John
On 12/04/2016 02:01 PM, Adrian Godwin wrote:
Thanks for this. I've seen something similar from Murata :
http://uk.farnell.com/murata-power-solutions/oki-78sr-5-1-5-
w36-c/converter-dc-dc-1-o-p-7-5w-1-5a/dp/2102101
Since they're a mainstream supplier of inductors they may have managed
better performance - it would be interesting to compare.
On Sun, Dec 4, 2016 at 6:50 PM, John Ackermann N8UR jra@febo.com
wrote:
I found a cute little switching regulator that's a drop-in
replacement for
an LM7805: http://www.ebay.com/itm/261243604047
I got a couple to play with, mainly to see how bad the noise would be.
Here are spectrum analyzer and PN shots comparing a cheap surplus
OCXO when
driven by a regular 7805 and by the switching replacement.
The switching frequency is supposed to be 2 MHz but you can see that
it's
more like 2.4 MHz. Whether this performance is sufficient for any
application is up to you. It sure runs a lot cooler than a 7805,
though!
John
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mailman/listinfo/time-nuts
and follow the instructions there.
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Hi
Given that the parts to build one are fairly easy to get and that we likely have “nutty”
EMI requirements. Maybe a small board that drops into a 78xx footprint is the
better solution.
Bob
On Dec 4, 2016, at 3:39 PM, Adrian Godwin artgodwin@gmail.com wrote:
At Farnell, they're listed under Power Supplies rather than Switching
Regulators (which is a subdivision of Semiconductors).
It makes sense since one is a board product and the other a chip, but when
the board product is a drop-in replacement for a TO220, less sense!
On Sun, Dec 4, 2016 at 7:44 PM, John Ackermann N8UR jra@febo.com wrote:
And Digikey does stock the Murata part, for about $4.30. Why I couldn't
find it when searching their site for switching regulators, I don't know.
John
On 12/04/2016 02:39 PM, John Ackermann N8UR wrote:
Thanks for that pointer! When I searched Digikey, I wasn't able to find
anything that was in the 3-lead TO-220 case. I will definitely check
out the Murata units, as I suspect they perform better than this one.
John
On 12/04/2016 02:01 PM, Adrian Godwin wrote:
Thanks for this. I've seen something similar from Murata :
http://uk.farnell.com/murata-power-solutions/oki-78sr-5-1-5-
w36-c/converter-dc-dc-1-o-p-7-5w-1-5a/dp/2102101
Since they're a mainstream supplier of inductors they may have managed
better performance - it would be interesting to compare.
On Sun, Dec 4, 2016 at 6:50 PM, John Ackermann N8UR jra@febo.com
wrote:
I found a cute little switching regulator that's a drop-in
replacement for
an LM7805: http://www.ebay.com/itm/261243604047
I got a couple to play with, mainly to see how bad the noise would be.
Here are spectrum analyzer and PN shots comparing a cheap surplus
OCXO when
driven by a regular 7805 and by the switching replacement.
The switching frequency is supposed to be 2 MHz but you can see that
it's
more like 2.4 MHz. Whether this performance is sufficient for any
application is up to you. It sure runs a lot cooler than a 7805,
though!
John
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/
mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
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and follow the instructions there.
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On Sun, 4 Dec 2016 15:45:55 -0500
Bob Camp kb8tq@n1k.org wrote:
Given that the parts to build one are fairly easy to get and that we likely have “nutty”
EMI requirements. Maybe a small board that drops into a 78xx footprint is the
better solution.
I don't fully agree. To go full "nutty" you would want to use the chips
in the QFN packages, as those have shorter leads and a large ground pad
to keep EMI down. But soldering an 0.5mm QFN by hand is impossible
(believe me, I tried) and not everyone has an oven. Also a lot of the
EMI performance depend on what output current you expect. Using a 1A
design for 10mA is a good way to get poor EMI performance as the
chip will go from PWM (aka fixed frequency) to PFM (aka fixed on time)
mode under low load to increase efficiency. The same goes for input
voltage. So we would need to do multiple designs for different
output current and input voltage ranges... which kind of defeats
the purpose of "a small board that drops into....".
What could be done, though, is a small board with all components,
but the inductor on it. So then one could select the right inductor
for the application and solder it on. Using an inductor that is easy
to solder (like e.g. WE-PD3) with a wide selection of values should
do the trick.
Attila Kinali
--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson
If you wanted to be nutty you wouldn't go PWM at all, just like
fractional-N sythns don't just mash 2 divider values. You would sigma-delta
modulate your power stage. I don't know if you can buy one COTS, but there
are plenty of papers on rolling your own.
On Sun, Dec 4, 2016 at 4:09 PM, Attila Kinali attila@kinali.ch wrote:
On Sun, 4 Dec 2016 15:45:55 -0500
Bob Camp kb8tq@n1k.org wrote:
Given that the parts to build one are fairly easy to get and that we
likely have “nutty”
EMI requirements. Maybe a small board that drops into a 78xx footprint
is the
better solution.
I don't fully agree. To go full "nutty" you would want to use the chips
in the QFN packages, as those have shorter leads and a large ground pad
to keep EMI down. But soldering an 0.5mm QFN by hand is impossible
(believe me, I tried) and not everyone has an oven. Also a lot of the
EMI performance depend on what output current you expect. Using a 1A
design for 10mA is a good way to get poor EMI performance as the
chip will go from PWM (aka fixed frequency) to PFM (aka fixed on time)
mode under low load to increase efficiency. The same goes for input
voltage. So we would need to do multiple designs for different
output current and input voltage ranges... which kind of defeats
the purpose of "a small board that drops into....".
What could be done, though, is a small board with all components,
but the inductor on it. So then one could select the right inductor
for the application and solder it on. Using an inductor that is easy
to solder (like e.g. WE-PD3) with a wide selection of values should
do the trick.
Attila Kinali
--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson
time-nuts mailing list -- time-nuts@febo.com
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mailman/listinfo/time-nuts
and follow the instructions there.
On 12/4/16 12:14 PM, John Ackermann N8UR wrote:
That's a very good point... the design I'm testing the regulator in has
a fair bit of C filtering, but no series L.
I little series L and another C (so you have a pi low pass) can make a
huge difference. If the load current is reasonably constant, then the
drop across the series R of the L will be constant, so you can bump the
dc/dc output to compensate. It's pretty easy to get 60dB of rejection
from a C-L-C pi, and for 2MHz, the parts are physically small.
On 12/4/16 1:09 PM, Attila Kinali wrote:
On Sun, 4 Dec 2016 15:45:55 -0500
Bob Camp kb8tq@n1k.org wrote:
Given that the parts to build one are fairly easy to get and that we likely have “nutty”
EMI requirements. Maybe a small board that drops into a 78xx footprint is the
better solution.
I don't fully agree. To go full "nutty" you would want to use the chips
i
or buy a few of each of the commercial modules and test them. They are
an all-in-one solution with all the usual features about overtemp,
overcurrent, etc.
What you'd need to do is characterize their noise properties over load
(something not in the datasheet), and then you could design a LC filter
to knock down the rest. Or do the LDO regulator thing.. it's not
entirely clear that a dc/dc followed by a suitable LDO might not come
out ahead of a dc/dc followed by a filter.
Even for time-nuts, I suspect we're not looking to eke out the last
percent of efficiency from 96% to 97%, or handle wildly varying loads,
etc. Nor are we usually looking for absolute minimum parts cost.
On 12/04/2016 04:34 PM, jimlux wrote:
Even for time-nuts, I suspect we're not looking to eke out the last
percent of efficiency from 96% to 97%, or handle wildly varying loads,
etc. Nor are we usually looking for absolute minimum parts cost.
The little OCXO I used for testing goes from about 850ma cold to 200ma
hot (at 5V) and I noticed a very different appearance of the spectrum as
the current dropped -- at high current, the switching spurs were quite
narrow, but as the current dropped (and particularly below some
threshold I don't remember) the spurs widened out quite a bit.
Hi
I doubt that there is a significant demand for 10 ma output switchers. The
benefit of going from 12V to 2V as a switcher compared to linear is mighty
small. As a guess, I’d say that anything much under a watt is not worth doing
in this arena. That gets you up to at least 100 ma at the normal conversion
ranges. I would also suggest that the regulator you are replacing is only a
1A part. That places an upper limit on what makes sense.
If you really want the SMT parts, get an oven. A converted toaster oven is
a dirt cheap way to do it.
Bob
On Dec 4, 2016, at 4:09 PM, Attila Kinali attila@kinali.ch wrote:
On Sun, 4 Dec 2016 15:45:55 -0500
Bob Camp kb8tq@n1k.org wrote:
Given that the parts to build one are fairly easy to get and that we likely have “nutty”
EMI requirements. Maybe a small board that drops into a 78xx footprint is the
better solution.
I don't fully agree. To go full "nutty" you would want to use the chips
in the QFN packages, as those have shorter leads and a large ground pad
to keep EMI down. But soldering an 0.5mm QFN by hand is impossible
(believe me, I tried) and not everyone has an oven. Also a lot of the
EMI performance depend on what output current you expect. Using a 1A
design for 10mA is a good way to get poor EMI performance as the
chip will go from PWM (aka fixed frequency) to PFM (aka fixed on time)
mode under low load to increase efficiency. The same goes for input
voltage. So we would need to do multiple designs for different
output current and input voltage ranges... which kind of defeats
the purpose of "a small board that drops into....".
What could be done, though, is a small board with all components,
but the inductor on it. So then one could select the right inductor
for the application and solder it on. Using an inductor that is easy
to solder (like e.g. WE-PD3) with a wide selection of values should
do the trick.
Attila Kinali
--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson
time-nuts mailing list -- time-nuts@febo.com
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