DoorBell Mote regulator update

The last BellMote prototype ended up having 2 LDO linear regulators, 12V and 3.3V feeding from the 12v one. I was split on using LDOs going forward. The upside is they are cheap, even 2 of them are under $2. The downside is they are inefficient and run warm/hot depending on the load. I could have gone with a single 5V LM7805 which will run even warmer, the higher the gap between Vin and Vout.

Digikey-ing around, I found these two switching regulators that are drop in SIP replacements for any LM78xx series LDOs: a RECOM 0.5A output with 7-28v input range ($2.8), and a Murata 1.5A 7-36v input range ($4.25). I tried both, and below are the results:

I won’t repeat the captions here but the clear winner is the Murata (plenty stocks at Digikey) it’s quite a bargain given the advantages. I tested it on 24VAC as well and it does not heat up at all either so it will be perfect for some coming interesting projects I have in the works that will feed on 24VAC. The RECOM regulator is just $2.8, still good enough for 16VAC but I prefer the Murata for further 16-24VAC powered projects. That said, I will offer these for sale (2 of them, one RECOM, one Murata, and I will replace the LDOs with a Murata and keep the third one). I may make a kit of this, not sure yet. For now you can grab these two from the first prototype batch, they will be worth millions when LowPowerLab is like Apple and me like Steve Wozniak 30 years from now (-:

6 thoughts on “DoorBell Mote regulator update

    • The Murata regulator comes in a 3.3V 1.5A output variant as well. I verified it can take a half rectified (1 diode + 100uF 50V cap) 28VAC input without any problems. It will give you plenty of 3.3V juice without any heat.

  1. Have you done any measurements of quiescent current on those regulators? I’ve used the 36V input version of the Recom, but for battery powered applications the relatively high quiescent current can be a problem. The Murata has a lower stated no-load input current, but I know sometimes they play tricks with datasheets to get them to look better.

    • I have not but overall it’s a better step up from using LMs in any combination. It’s definitely better than the RECOM, almost double in price, but well justified. I tried rectified 28VAC (~38Vdc) and it still won’t warm up. I know it’s not an empirical statement but I am quite sure it’s more efficient than any LM combo and without spending a lot more and using more PCB space it’s a great choice IMO. And Murata is a really good brand that I trust with a lot of parts I use.

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