Electronics > Beginners
24VAC to DC
AVGresponding:
If you have a point to make, please do so. Try to do it without personal insults, please.
mariush:
You could combine a basic 10-20 cents LDO (to bring voltage down to 18v..24v) or a zener diode then use a switching regulator for 3.3v
ex ap63301 : https://www.digikey.com/product-detail/en/diodes-incorporated/AP63301WU-7/31-AP63301WU-7CT-ND/10492238
32v max input , 0.8v min output, 500kHz switching, synchronous (no diode needed), small inductor... 50-60 cents and SOT-23-6 package
l78l24 is 17 cents if you buy 100 of them : https://www.digikey.com/product-detail/en/stmicroelectronics/L78L24CD-TR/497-7284-1-ND/1883403
james_s:
The nature of the question suggests a novice, so I was suggesting parts available in prototype friendly through-hole packages. If I were designing something like this today I would have no trouble using a tiny surface mount part but a beginner who is still in the development phase is probably going to want something they can easily wire up on perfboard.
OP, if you can clarify whether this is a one-off hobby project, possibly mass produced, whether you intend to hack together a prototype or make a PCB that will reduce the irrelevant answers.
Either way, full wave rectifier and switching regulator is absolutely the way to go. You can very efficiently drop 30+V down to 3.3 or 5V with a simple and cheap circuit. Pretty much every commercial product does it this way, no sensible design uses a linear regulator for such a large delta.
joeyjoejoe:
I plan on making a PCB for this and using SMT when possible.
It's a one off to start but I prefer to keep the BOM low (when possible) and have the option to produce/sell on Tindie if needed. All electronics sourced from DigiKey, wago blocks might be elsewhere since it's low current.
Here's what I came up with so far with a few notes
james_s:
That looks good at a glance, although you should be able to eliminate one of the two capacitors between the rectifier and regulator. It's not hard to find low ESR electrolytics these days, or you could use something like a 1uF ceramic close to the regulator IC, refer to the datasheet to see if there are any specific requirements.
The capacitor can be calculated like this: https://electronicbase.net/smoothing-capacitor-calculator/
Admittedly I typically just choose a value based on intuition, likely ending up with a bit larger cap that is really required but that hasn't let me down yet. I'd probably slap in 330 or 470uF then scope it under load to see how much ripple there is and verify that the ripple isn't present on the output of the regulator.
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