Grogster
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Joined: 31/12/2012
Location: New ZealandPosts: 9307 |
| Posted: 02:48am 16 Dec 2020 |
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Linear PSU's used to be everywhere, but switchmode seems to have pretty much taken over for efficiency reasons - but not noise reasons.
I see there are now even drop-in replacement modules for the common 78xx series regulators, that use SMD technology, and Silicon Chip magazine even featured a design for a circuit like that you could use as a drop-in replacement in their August 2020 issue.
However, I find that with RF designs - especially receivers, you can't beat the good ole 78 series linear regulators. They provide a very smooth and noise free output with hardly any ripple if you use decent value capacitors. Switchmode supplies have noise and a higher ripple, and seem to play havoc with certain radio modules, so I'm still old-school and still a fan of linear supplies for this kind of application. 
As we all know, linear regulators are inefficient by today's standards though, and tend to dissipate quite a bit of heat if you suck more then about 500mA from them depending on their input-to-output voltage differential.
Nevertheless, here is a three-rail module I designed for a project - and it cured all my issues I was having with the previous switchmode supply I was using.
This one mounts on a cheap $10 55mm heatsink from Jaycar(HH8570). It can accept either an AC or a DC input, but was designed to use a 13.8v DC input. I just included the bridge to make it as flexible as possible. Maximum cumulative output current of all three rails is 1A continuous. Anything more then about 750mA continuous should have a fan fitted, and connected to the 9v rail, which will move enough air, but the fan will be almost silent. 600mA or less continuous and the heatsink is all you need, although, it will get quite warm/hot. (but still within the specs for the regulators) For 50/50 duty-cycle or less, you can suck the full 1A out of it without any need for a fan.
The design is a 'Pre-regulator' concept, consisting of a 7809, 7805 and a 3940 all in series, one feeding the next, with lots of decoupling capacitance and 100n high-frequency filtering. Pretty standard linear arrangement really, just daisy-chained to help spread the dissipation heat across all three regulators so that no one regulator gets to hot and bothered under load.
If anyone is interested in this, reply here and I can upload a constructors pack including gerbers, BOM and schematic.
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