[time-nuts] Switching regulator replacement for 7805
jimlux at earthlink.net
Sun Dec 4 15:08:04 EST 2016
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
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
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 <jra at febo.com> 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!
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