Low Noise Switching Regulator

K

Kunal

Guest
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?
 
Kunal wrote:
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
Click to expand...
some hefty current. How much are we talking about?
 
Kunal wrote:
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?
Click to expand...
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?

--
John Popelish
 
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.
 
Kunal wrote:
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.
Click to expand...
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.

--
John Popelish
 
In article <1105032169.247860.100360@z14g2000cwz.googlegroups.com>,
Kunal <kunalshenoy@hotmail.com> wrote:
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.
Click to expand...
How about syncing the switcher to the pixel clock in the video board so
that the noise aliases to DC?

--
--
kensmith@rahul.net forging knowledge
 
"Kunal" <kunalshenoy@hotmail.com> wrote:

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?
Click to expand...
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.

--
Reply to nico@nctdevpuntnl (punt=.)
Bedrijven en winkels vindt U op www.adresboekje.nl
 
On 6 Jan 2005 09:22:49 -0800, in sci.electronics.design "Kunal"
<kunalshenoy@hotmail.com> wrote:

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
Click to expand...
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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