Maker Pro
Maker Pro

Any good resources for DC power supply design?

M

Mike Noone

Jan 1, 1970
0
Hi - I end up making a lot of simple power supplies for my PCBs. Most
everything has been DC to DC - lots of linear regs, a couple dc-dc
step downs, even one step up. But I normally just choose a part and go
by what its datasheet says. Are there any good resources for what
sorts of considerations should go into choosing parts to give a clean,
stable, accurate power supply for a PCB? I'm talking about low
voltage, low current stuff. Normally I have a somewhat noisy 12V
signal coming into a PCB and I'll need 3.3V or 5V at a couple hundred
ma from it - so supplies for that sort of situation are what I'm most
interested in.

Any books/websites/app notes/etc.?

Thanks!
 
D

David L. Jones

Jan 1, 1970
0
Hi - I end up making a lot of simple power supplies for my PCBs. Most
everything has been DC to DC - lots of linear regs, a couple dc-dc
step downs, even one step up. But I normally just choose a part and go
by what its datasheet says. Are there any good resources for what
sorts of considerations should go into choosing parts to give a clean,
stable, accurate power supply for a PCB? I'm talking about low
voltage, low current stuff. Normally I have a somewhat noisy 12V
signal coming into a PCB and I'll need 3.3V or 5V at a couple hundred
ma from it - so supplies for that sort of situation are what I'm most
interested in.

Any books/websites/app notes/etc.?

Thanks!

Have a look at the HP Power Supply Cookbook:
http://www.slack.com/pdf/HP-AN90B.pdf

Dave :)
 
D

David L. Jones

Jan 1, 1970
0
Hi - I end up making a lot of simple power supplies for my PCBs. Most
everything has been DC to DC - lots of linear regs, a couple dc-dc
step downs, even one step up. But I normally just choose a part and go
by what its datasheet says. Are there any good resources for what
sorts of considerations should go into choosing parts to give a clean,
stable, accurate power supply for a PCB?

If you are really after a "nice, clean and stable" supply it's hard to
beat some of the "low noise" linear regs available.
It's common to use say a normal DC-DC converter to get your base
efficiency, and follow that with a nice low noise linear reg for
powering sensitive stuff like high end ADC's. The linear reg need only
drop a volt or two, and current requirements for parts that require
low noise supplies are usually small, so the linear reg doesn't affect
your overall efficiency much.

Dave :)
 
P

PeteS

Jan 1, 1970
0
Mike said:
Hi - I end up making a lot of simple power supplies for my PCBs. Most
everything has been DC to DC - lots of linear regs, a couple dc-dc
step downs, even one step up. But I normally just choose a part and go
by what its datasheet says. Are there any good resources for what
sorts of considerations should go into choosing parts to give a clean,
stable, accurate power supply for a PCB? I'm talking about low
voltage, low current stuff. Normally I have a somewhat noisy 12V
signal coming into a PCB and I'll need 3.3V or 5V at a couple hundred
ma from it - so supplies for that sort of situation are what I'm most
interested in.

Any books/websites/app notes/etc.?

Thanks!

All the usual suspects have good app notes.

Linear tech
TI
Analog Devices
Maxim (but see the old thread about availability)
National Semi
On Semi

and more, of course.

Each manufacturer naturally targets their own devices, but as a good
general view, Linear Tech does the best (imo, ymmv) app notes on such
things.

Cheers

PeteS
 
M

Mike Noone

Jan 1, 1970
0
If you are really after a "nice, clean and stable" supply it's hard to
beat some of the "low noise" linear regs available.
It's common to use say a normal DC-DC converter to get your base
efficiency, and follow that with a nice low noise linear reg for
powering sensitive stuff like high end ADC's. The linear reg need only
drop a volt or two, and current requirements for parts that require
low noise supplies are usually small, so the linear reg doesn't affect
your overall efficiency much.

Dave :)

Hi Dave - so for example on a current project I have a 12V power
source. It's a li-poly battery - so it fluctuates around that a bit.
It has a widely varying load on it, so it will not be particuarly
clean. I need to use this to power a 16b ADC board that has many
sensitive analog sensors on it. The board needs a 5V supply. It
shouldn't draw more than 200ma peak. I think 50-100ma will be the
normal load. I also need to maintain as much efficiency as possible -
I'd really like to see 90% or better. I'd like noise on this supply to
be in the single digit micro volt range, ideally. (being that it's
powering a 16b ADC)

So are you saying that the ideal solution would be to use a DC/DC
converter to bring the voltage down to, say, 5.5V, and then use a
linear regulator to bring that down to 5V? Can DC/DC converters just
not be accurate enough?

Thanks,

-Mike
 
D

David L. Jones

Jan 1, 1970
0
Hi Dave - so for example on a current project I have a 12V power
source. It's a li-poly battery - so it fluctuates around that a bit.
It has a widely varying load on it, so it will not be particuarly
clean. I need to use this to power a 16b ADC board that has many
sensitive analog sensors on it. The board needs a 5V supply. It
shouldn't draw more than 200ma peak. I think 50-100ma will be the
normal load. I also need to maintain as much efficiency as possible -
I'd really like to see 90% or better. I'd like noise on this supply to
be in the single digit micro volt range, ideally. (being that it's
powering a 16b ADC)

So are you saying that the ideal solution would be to use a DC/DC
converter to bring the voltage down to, say, 5.5V, and then use a
linear regulator to bring that down to 5V?

Yes. It might be overkill, or it might not, depending on your
application. Lots of system factors are involved, but it can't hurt to
start with a nice low noise regulated supply.
I have done this with high end 24bit sigma-delta converters using a
low noise low dropout reg like the Micrel 5255:
http://www.micrel.com/page.do?page=/product-info/products/mic5255.shtml
30uVrms noise.

In one case, I used a high efficiency custom designed 70-90VDC to 5V
DC-DC converter, and then the extra low-noise regs from the 5V rail
for the 24bit converters which didn't comsume much power on their own.
The 5V powered some higher power digitial stuff where the noise was
not critical. I still got >90% system power efficiency.

As a rule you would not power a 16bit ADC directly from a regular DC-
DC supply, you are begging for trouble.
Can DC/DC converters just not be accurate enough?

They can be, but other system factors come into play. For instance,
PCB layout can be critical. Get this wrong and it doesn't matter how
low-noise your power supply is. You can blow it all with one bad
ground track placement.

Dave :)
 
T

Terry Given

Jan 1, 1970
0
David said:
Yes. It might be overkill, or it might not, depending on your
application. Lots of system factors are involved, but it can't hurt to
start with a nice low noise regulated supply.
I have done this with high end 24bit sigma-delta converters using a
low noise low dropout reg like the Micrel 5255:
http://www.micrel.com/page.do?page=/product-info/products/mic5255.shtml
30uVrms noise.

In one case, I used a high efficiency custom designed 70-90VDC to 5V
DC-DC converter, and then the extra low-noise regs from the 5V rail
for the 24bit converters which didn't comsume much power on their own.
The 5V powered some higher power digitial stuff where the noise was
not critical. I still got >90% system power efficiency.

As a rule you would not power a 16bit ADC directly from a regular DC-
DC supply, you are begging for trouble.




They can be, but other system factors come into play. For instance,
PCB layout can be critical. Get this wrong and it doesn't matter how
low-noise your power supply is. You can blow it all with one bad
ground track placement.

alas poor femptoFarad, it buggered him, Horatio

Cheers
Terry
 
B

budgie

Jan 1, 1970
0
Hi Dave - so for example on a current project I have a 12V power
source. It's a li-poly battery - so it fluctuates around that a bit.
It has a widely varying load on it, so it will not be particuarly
clean. I need to use this to power a 16b ADC board that has many
sensitive analog sensors on it. The board needs a 5V supply. It
shouldn't draw more than 200ma peak. I think 50-100ma will be the
normal load. I also need to maintain as much efficiency as possible -
I'd really like to see 90% or better. I'd like noise on this supply to
be in the single digit micro volt range, ideally. (being that it's
powering a 16b ADC)

So are you saying that the ideal solution would be to use a DC/DC
converter to bring the voltage down to, say, 5.5V, and then use a
linear regulator to bring that down to 5V? Can DC/DC converters just
not be accurate enough?

I'm currently looking at some integrated DC-DC stepdowns for both final 5V load
and also as pre-regs to some linears.

RECOM (in deutchland) make some TO-220-pin-compatible switchers. I'm hoping to
find other sources for these, as I also have a couple of 12V->5V linear regs in
need of thermal relief.
 
Hi - I end up making a lot of simple power supplies for my PCBs. Most
everything has been DC to DC - lots of linear regs, a couple dc-dc
step downs, even one step up. But I normally just choose a part and go
by what its datasheet says. Are there any good resources for what
sorts of considerations should go into choosing parts to give a clean,
stable, accurate power supply for a PCB? I'm talking about low
voltage, low current stuff. Normally I have a somewhat noisy 12V
signal coming into a PCB and I'll need 3.3V or 5V at a couple hundred
ma from it - so supplies for that sort of situation are what I'm most
interested in.

Any books/websites/app notes/etc.?

Thanks!

Hi Mike,
check this link http://www.emittsol.com/section/market-analysis/
ma100002.html

Srinivas
EMITT Solutions
 
C

colin

Jan 1, 1970
0
Mike Noone said:
Hi - I end up making a lot of simple power supplies for my PCBs. Most
everything has been DC to DC - lots of linear regs, a couple dc-dc
step downs, even one step up. But I normally just choose a part and go
by what its datasheet says. Are there any good resources for what
sorts of considerations should go into choosing parts to give a clean,
stable, accurate power supply for a PCB? I'm talking about low
voltage, low current stuff. Normally I have a somewhat noisy 12V
signal coming into a PCB and I'll need 3.3V or 5V at a couple hundred
ma from it - so supplies for that sort of situation are what I'm most
interested in.

Any books/websites/app notes/etc.?

I always seem to be doing the same thing, my solution of choice now is to
use integral swith type lm2594, and lowest esr caps you can and get the
layout extremly tight, a second LC filter next to this helps a lot too and
another LC next to the adc or as already suggested use low drop/low noise
linear regs, but be aware linear regs arnt that good at rejecting switching
frequency noise.

For higher power/efficiency a synchronous rectifier type is good such as
dual mosfet driver type tps40054.

I always seem to need far more different voltages than I would like.

Colin =^.^=
 
Top