Popular 3.3V regulators for 3xNiMH? - Page 1
Forum section: electronics / beginners

author: cdevidal
author_rank: Regular Contributor
timestamp: April 25, 2022, 01:45:11 am
content: What are some popular regulators for 3.3V and 3xNiMH AAA for an ESP32? Peak current is 300mA, typical 100mA, with lots of deep sleep, and it can go as low as 3.0V officially. (Unofficially it has been known to be stable at lower.) And the discharge curve is about 80% DoD at 1.2V. I need it for a product that has to pass FCC EMI lab testing so I’m thinking an LDO such as the below, but maybe there’s a more common/better one. I am sensitive to cost, availability, and as mentioned EMI. This one is 105mV at 300mA which is pretty darned good.https://www.diodes.com/assets/Datasheets/AP7366.pdf

author: bdunham7
author_rank: Super Contributor
timestamp: April 25, 2022, 02:17:07 am
content: Multiple posts on similar topics--even different angles on the same idea--are unhelpful discouraged and unnecessary here due to the way the forum is organized.I think the LDO is a reasonable choice given the general parameters you've given. You'd need a lot more specific detail to be sure. The one thing I'd question is the cells and that discharge curve. Although I think you'll be OK given your device cutoff of <3V, is that discharge curve showing you 80% DOD @ 1.2V for those specific AAA cells at 300mA? That seems pretty optimistic and they won't get better with age. Do you have exact models of cell in mind?

author: cdevidal
author_rank: Regular Contributor
timestamp: April 25, 2022, 02:32:58 am
content: Apologies for what seems like multiple posts on the same topic but had I asked this different question in that other thread I didn’t think it would have been seen. Otherwise I would have asked there. I don’t like double posts, either.Anyway, no I don’t have a specific cell in mind. I had found a generic discharge curve with Google images. The user would install either alkaline or rechargeable and I wanted to be prepared for the lowest expected voltage.So back to the question, are there popular regulators for these cell types?

author: bdunham7
author_rank: Super Contributor
timestamp: April 25, 2022, 02:42:40 am
content: Quote from: cdevidal on April 25, 2022, 02:32:58 amOK, so in this case I think you'd be set down to 1.05V/cell or so, which seems reasonable enough. And if you aren't the one selecting the cells, that's probably the best you can do short of some final product testing.QuoteNo idea on popularity, but these days I think the trend is to use what is in stock at your supplier. And from the looks of it, the AP7366 3.3V is pretty scarce. The ideal part is the one you can actually buy...Edit: this might work and it is in stock at Mouser. It will save you some space too....https://www.mouser.com/datasheet/2/308/1/NCP167_D-2316956.pdf

author: cdevidal
author_rank: Regular Contributor
timestamp: April 25, 2022, 02:47:59 am
content: Every discharge curve I could find on Google images shows 1.2V is about 80% DoD at that current. That’s acceptable. It wouldn’t be 300mA the entire time; only on a few hundred milliseconds of transmit. Typically 100mA when running then ~100uA deep sleep for likely several hours.

author: cdevidal
author_rank: Regular Contributor
timestamp: April 25, 2022, 02:53:29 am
content: Hmm good availability is why I chose this one. I found Digi had more than enough in stock. Going to buy probably a reel of 3,000 and they have over 7,000. But perhaps they’ll sell out before I can test them….Anyway that’s what motivated the question. If there are more common/plentiful ones I want to look at those instead.

author: bdunham7
author_rank: Super Contributor
timestamp: April 25, 2022, 03:01:27 am
content: I think your battery situation is fine, but if you ever want better info than Google, user HKJ has a websitehttps://lygte-info.dk/with a whole slew of detailed testing.Are you sure on the stock at Digi-Key? I only see the 3.9V variant in any quantity....perhaps I missed it?https://www.digikey.com/en/products/filter/pmic-voltage-regulators-linear/699?s=N4IgTCBcDaIIYAcDsBmAbGkBdAvkA

author: eugene
author_rank: Frequent Contributor
timestamp: April 25, 2022, 02:32:50 pm
content: These days I worry more about availability than popularity. Fortunately, LDO's are commodity items, meaning that there are often multiple suitable choices with the same footprint. I haven't done the legwork so you'll need to check for yourself, but the one you've chosen might fall into that category; SOT-25/SOT23-5 is a popular package for LDO's,Even if a fixed regulator would suffice, I would plan on having the flexibility to use adjustable versions. That means leaving space for a couple of resistors around the adj pin which is normally unconnected in the fixed versions. All of this improves the odds that you'll be able to keep you circuit going even if specific components become impossible to obtain.