Re: Low noise DC/DC converter

From: Rodney Josey (rjos_at_dodo.com.au)
Date: 01/07/05 

Date: Fri, 07 Jan 2005 14:37:57 +1000

On 24 Dec 2004 04:49:36 -0800, Winfield Hill <hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote:

>Jeroen wrote...
>>
>> Referring to the post and thread from Winfield Hill regarding a low
>> noise DC/DC convertor of August 4th:
>>
>> http://groups.google.nl/groups?hl=nl&lr=&threadm=cer27s014nf%40drn.newsguy.
>> com&rnum=1&prev=/groups%3Fq%3Dlt3439%2Bwinfield%26hl%3Dnl%26lr%3D%26selm%
>> 3Dcer27s014nf%2540drn.newsguy.com%26rnum%3D1
>>
>> I'm having the same problem, so if there's a nice working circuit,
>> I'd like to see it ;)
>
> Wow, that's a long link! It's message-ID <cer27s014nf@drn.newsguy.com>
> and here's my attempt at a shorter Google link:
>
> http://groups-beta.google.com/group/sci.electronics.design/browse_thread/
> thread/bb3edbc02ec23260
>
> Click on view as tree for better navigating.
>
> My project is on hold right now, since I lack the time to work on
> this problem. An efficient simple 1MHz level-controlled sine-wave
> power oscillator could be a critical part of the solution.
>
> Here's a copy of my Aug 4, 2004 post:
>
> My dc-dc converter specs: 5Vdc in, 1/2 to 1W max capability, three
> simultaneous "unregulated" output voltages, small, very low noise,
> high switching frequency (600kHz min to 5MHz better, etc.) -- by
> "unregulated," I mean fixed input-to-output voltage ratios, 10-20%
> tolerance allowed (if necessary I can adjust transformer windings,
> and the loads will be constant).
>
> I'm looking at Linear Technology's LT3439, almost exactly what I
> need, push-pull transformer drive, etc., but yet misses by a mile.
> http://www.linear-tech.com/prod/data***.html?data***=892
>
> The LT3439 is one of LTC's line of slew-rate controlled low-noise
> switching converters, but like the others it's limited to 250 or
> 300kHz, far too low for my application, in which I need to put the
> switching noise well above my sensitive amplifier circuit's range.
>
> Does anyone know a switching IC that's similar to the LT3439 but
> runs at MHz frequencies? Maybe with sine-wave transformer drive?

Hi Winfield & Jeroen,

I know this may sound over-the-top, BUT if your circuit has the space, you might want to consider
doing away with the "noisy" DC/DC converters and use a few NICAD or NIHM rechargeable batteries as
the power sources for the relevant voltages concerned. Higher current capacity batteries would do
for the higher current areas of your circuit with the added advantage of NO NOISE or extra low noise
from the power supply sections. I would design the circuitry such that the batteries are
'recharged' ONLY when the system is not being "actively" used - thereby transferring any noise
generating components to the system's IDLE or STANDBY periods.

Hope this helps....:).

Good Luck.

Oz_Rod

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