[time-nuts] Switching regulator replacement for 7805
lajeunesse at mail.com
Mon Dec 5 11:09:12 EST 2016
Not impressed with the PCB layout, could have been much better. Input cap is too far from regulator, connected to ground via longish (inductive) skinny trace. Input might benefit from simple PI filter to reduce input ripple current. Output caps should each have their own via, maybe even two each. Sense resistors should be near regulator chip, they aren't, so a longish high impedance path exists for noise susceptibility.
> Sent: Sunday, December 04, 2016 at 1:50 PM
> From: "John Ackermann N8UR" <jra at febo.com>
> To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
> Subject: [time-nuts] Switching regulator replacement for 7805
> 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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