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Low Noise Switching Regulator

K

Kunal

Jan 1, 1970
0
I need +11V from a +15V supply using a switching regulator since I dont
have space for heat sinks for linear ones. The main concern is that I
am using it for a video board and low noise is very important.
I have looked at the Linear's LT3439, but they require an external
transformer which is 2cm on the side (too big) and lots of other
external components.
http://www.linear-tech.com/pc/productDetail.do?navId=H0,C1,C1003,C1042,C1034,P2228
Any suggestions of low noise step down switching voltage regulators
with low/small external parts?
 
R

Rob Gaddi

Jan 1, 1970
0
Kunal said:
I need +11V from a +15V supply using a switching regulator since I dont
have space for heat sinks for linear ones. The main concern is that I
am using it for a video board and low noise is very important.
I have looked at the Linear's LT3439, but they require an external
transformer which is 2cm on the side (too big) and lots of other
external components.
http://www.linear-tech.com/pc/productDetail.do?navId=H0,C1,C1003,C1042,C1034,P2228
Any suggestions of low noise step down switching voltage regulators
with low/small external parts?
You say you don't have room for heat sinks, implying that you're moving
some hefty current. How much are we talking about?
 
J

John Popelish

Jan 1, 1970
0
Kunal said:
I need +11V from a +15V supply using a switching regulator since I dont
have space for heat sinks for linear ones. The main concern is that I
am using it for a video board and low noise is very important.
I have looked at the Linear's LT3439, but they require an external
transformer which is 2cm on the side (too big) and lots of other
external components.
http://www.linear-tech.com/pc/productDetail.do?navId=H0,C1,C1003,C1042,C1034,P2228
Any suggestions of low noise step down switching voltage regulators
with low/small external parts?

Any switcher that produces very little noise is going to include "lots
of other
external components" since these will be needed to filter out the
noise that is inherent in the operation of a switcher. A simple buck
regulator will probably need at least two inductors and several
capacitors in addition to the switching components and control logic.

What output current do you need?
Is cost a serious limitation?
 
K

Kunal

Jan 1, 1970
0
I should have put in the Current required(sorry). I need >1.5A.
Cost is not a limitation. I dont mind spending more on the regulator
now rather than have my video all messed up later on.

The way I understand it is that the 'low noise' regulators are low
noise because they smooth out the corners of the switching waveform and
hence reduce harmonic energy and is not due to external component
filtering. I have seen other low noise regulators on the linear site
with low external component count.

Thanks.
 
J

John Popelish

Jan 1, 1970
0
Kunal said:
I should have put in the Current required(sorry). I need >1.5A.
Cost is not a limitation. I dont mind spending more on the regulator
now rather than have my video all messed up later on.

The way I understand it is that the 'low noise' regulators are low
noise because they smooth out the corners of the switching waveform and
hence reduce harmonic energy and is not due to external component
filtering. I have seen other low noise regulators on the linear site
with low external component count.

Thanks.

Rounding the corners of the switching waveform reduces the highest
harmonics that tend to radiate from any antenna. But it also
decreases the efficiency, making it more likely that you will need
heat sinks. But no amount of rounding gets rid of the interrupted
current going into the buck regulator which conducts noise back out
into the 15 volt supply and ground busses. I prefer to contain the
radiated noise of fast switching, high efficiency designs with good
layout and grounding techniques and shielding. Then I address the
conducted noise with low pass filtering components on both sides of
the regulator.

If you pick a candidate design, we can discuss how to apply those
noise containment techniques on that example.
 
K

Ken Smith

Jan 1, 1970
0
I need +11V from a +15V supply using a switching regulator since I dont
have space for heat sinks for linear ones. The main concern is that I
am using it for a video board and low noise is very important.
I have looked at the Linear's LT3439, but they require an external
transformer which is 2cm on the side (too big) and lots of other
external components.

How about syncing the switcher to the pixel clock in the video board so
that the noise aliases to DC?
 
M

Mac

Jan 1, 1970
0
I should have put in the Current required(sorry). I need >1.5A.
Cost is not a limitation. I dont mind spending more on the regulator
now rather than have my video all messed up later on.

The way I understand it is that the 'low noise' regulators are low
noise because they smooth out the corners of the switching waveform and
hence reduce harmonic energy and is not due to external component
filtering. I have seen other low noise regulators on the linear site
with low external component count.

Thanks.

Maybe you could use the switcher to get down to 12.5 Volts and use an LDO
or an LDO + NPN power transitor for the last 1.5 V?

Is there any airflow?

Also, don't forget that switchers also put noise on the power input
voltage rail. So you will need to filter it, too. This increases the
board space of a switcher to the point where it may not save space over a
linear regulator, even for your 6+ Watt drop. Especially if there is
guaranteed airflow.

--Mac
 
N

Nico Coesel

Jan 1, 1970
0
Kunal said:
I need +11V from a +15V supply using a switching regulator since I dont
have space for heat sinks for linear ones. The main concern is that I
am using it for a video board and low noise is very important.
I have looked at the Linear's LT3439, but they require an external
transformer which is 2cm on the side (too big) and lots of other
external components.
http://www.linear-tech.com/pc/productDetail.do?navId=H0,C1,C1003,C1042,C1034,P2228
Any suggestions of low noise step down switching voltage regulators
with low/small external parts?

I would try to go for a linear regulator. A switcher at 80% efficiency
will dissipate 3.3W. A linear regulator will dissipate 6W. If you use
3 diodes to drop 1.8V (2.7W), you'll need to dissipate 3.3W in a
linear regulator.
 
M

martin griffith

Jan 1, 1970
0
I need +11V from a +15V supply using a switching regulator since I dont
have space for heat sinks for linear ones. The main concern is that I
am using it for a video board and low noise is very important.
I have looked at the Linear's LT3439, but they require an external
transformer which is 2cm on the side (too big) and lots of other
external components.
http://www.linear-tech.com/pc/productDetail.do?navId=H0,C1,C1003,C1042,C1034,P2228
Any suggestions of low noise step down switching voltage regulators
with low/small external parts?
I'm talking to a UK transformer company at the moment, for the LT3439
since the coiltronics supplier in the UK have a MOQ of 300, and are
not at all helpful.

I've been trying to catch up on transformer design (groan)and have
come across Planar E cores from Ferroxcube, who now own the Philips
breed. These cores sit in a cut out in the PCB.

www.ferroxcube.com
and
http://www.ferroxcube.com/prod/assets/planar_er.htm
This may save you some height.


martin

Serious error.
All shortcuts have disappeared.
Screen. Mind. Both are blank.
 
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