Small footprint 5V voltage regulator

LMR23630 is good, but produces a very fast rising edge (650 ps) and so may need a shield. I have a board with one of those and a TPS61175 boost, plus input and output LCs, that all fit under a single

1 x 1.5 x 0.24 inch shield. Dunno how it works yet--stuffed boards will be here in a week. Sure is nice and small though.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
https://hobbs-eo.com

Some little (non-isolated) dc/dc synchronous switcher chip, an inductor, and a few passives should fit into under 1 square inch. The problem becomes how to rectify the AC. And that devolves to finding a filter capaitor. So you need about 1000 uF 50 volts worth of cap(s) on the tall side of your board, and a schottky bridge.

Sounds like you have lots of room.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Or, with a voltage-doubler rectifier, two caps and two diodes would do the DC input part; needn't be Schottky, at these voltages the diode drop is low. UVR2A331 capacitor (330 uF, 100V) is cheap, two for under a buck in 1k qty. Not sure what a Schottky bridge costs, but don't need a 1000 uF for this kind of ripple current nowadays, even with the bridge.

The problem is, the LMR23630, like most of the other switching chips I have investigated, can't handle more than 36V. Rectified 30V AC will produce a t least

42V, and with line spikes - which are exceedingly likely - the input can go well beyond that. Line transformers are huge, and after adding some large filter capacitors, none that I found would allow me to populate the board successfully. Obviously, if I can get the input voltage to something under 20VDC, I can easily find off-the-shelf buck converters for about $1 - $2. I thought of using a controlled full wave rectifier, but I wasn't able to get it, the filter caps, and the buck converter on the board together. Per haps one of you can come up with a better design for something like a parti ally or fully controlled bridge rectifier?

A flyback converter could use a small chip and an outboard mosfet. But that needs a transformer, which is harder to find than an inductor.

You could do a SEPIC with a stock dual-winding inductor.

Do you need isolation? That suggests a flyback maybe.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

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DDAR_C44377.html

Hey, it looks like that will work. Thanks! With this I can get by with on ly about 16 small components, including an inductor of less than 0.1mH, whi ch should be pretty small. Since I am still worried about transients (OK, so I am paranoid), and since the 24VAC input is optional for this device, I think I will implement it as a plug-in module. The main device has option al Ethernet / WiFi operation. If the user chooses Ethernet, they can go wi th PoE, the optional 24VAC inverter or an external 5V supply. If they choo se WiFi, then they still have the option of 24VAC or 5V external.

** Filter electros are *extremely* effective at supressing line spikes.

.... Phil

POE is 48VDC. can you re-use the POE buck module for your 24VAC input that'd save space. you'd need bigger capacitors for 24VAC operation and some way to switch between POE and AC but all else should be good.

--
  Notsodium is mined on the banks of denial.

Thanks, everyone. With your help (especially Lasse's) I was able to cobble together a design. Now it's off to the fabricator. We'll see how it works when it gets back.

If anyone is interested, the images of the board are here: