On 12/4/16 11:45 AM, 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?
What we just did was use a discrete Linear Tech DC/DC, with carefully
chosen output voltage, followed by a LDO with very, very good PSRR at
high frequencies.
You could probably do the same with the modular parts- saves you
designing the DC/DC - the Cui parts (and I'm sure the others) can adjust
the output voltage with a single resistor and they have very wide input
voltage range, although I don't know if they can do buck/boost, or just
buck.
For our application we had an existing DC/DC design, so in theory, we
saved time by reusing it - whether or not that's really true, I'm not
sure, different voltages, different load currents, etc. It might have
been easier/cheaper/faster to use a modular DC/DC - assuming it doesn't
have some sort of latchup or other single event effects.
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 <[email protected]> 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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