LM1117 3.3V - Don't Even Look at it the wrong way! - Page 1
Forum section: electronics / projects

author: kolbep
author_rank: Frequent Contributor
timestamp: April 12, 2017, 11:44:54 am
content: So, here is my latestTake some protoboard, stick a Wemos D1 Mini and DHT11 Sensor on it.To power it I have a 7AH, 12V alarm battery, feeding a LM1117 3V Regulator Module (a Little 3 pin board with the caps and regulator on it - From Aliexpress).Also, before the Regulator, I have a Potential divider tapping off to the A0 pin, so that I can get the battery voltage.Power it on. LM1117 Regulator goes bang in a cloud of smoke, and sends the 12v directly to the Wemos. That is dead as well.So I remove the Wemos, and Replace the LM1117 Module. Good, I am getting 3.3v to the 3.3v Wemos pin, and just under 3v to the A0 pin.Reinstall the Wemos, and it works fine, for a day or 2, Until this morning at 00:50:13, when the Battery voltage falls down to about 1.7v , and the wemos shuts down.Ok, Time to charge the battery. So I hook up one of these small Car/Motorbike battery chargers. The one that will only start charging the battery if it detects a certain voltage. Well the battery was too flat to get the charger to recognize to start charging. So I hook another Alarm battery in Parallel with the 1st one. The Charger is happy, and starts charging at just above 13v. 2 seconds later, the LM1117 regulator pops and smokes again.Change the regulator again, and it pops again.So, here is my guess what is happening:1. Maybe the Aliexpress ones are fake and faulty.2. Maybe the charger is putting out another higher voltage (even through DC shows 13.Something, and AC Shows nothing). Maybe the charger does some very short high voltage pulses that destroys the regulator (have not tried to scope it yet).I don't Know.Thought I would throw it out there, before I chuck in another LM1117.

author: DrGeoff
author_rank: Frequent Contributor
timestamp: April 12, 2017, 12:02:33 pm
content: Probably fakes, or a poor design module.I use LM1117 3V3 devices quite a bit and never had any problem, certainly nothing catastrophic as they can usually protect themselves.If you are going to pop another one in, fit a series low value resistor and hit it with the battery supply. If it smokes the resistor then something is latching up inside the regulator.

author: danadak
author_rank: Super Contributor
timestamp: April 12, 2017, 12:45:07 pm
content: Battery charger, depending on design, may have ripple that exceeds LM1117ratings. Scope will help here.Regards, Dana.

author: MagicSmoker
author_rank: Super Contributor
timestamp: April 12, 2017, 12:58:23 pm
content: Max input voltage for the LM1117-3.3V regulator is 15V, and during charging the terminal voltage for a lead-acid battery can reach 15.5V (for equalization), so that could kill it. Though the chances are very high that it was a fake, anyway, if purchased from Alibaba/Aliexpress. So that could be your problem, too.

author: CJay
author_rank: Super Contributor
timestamp: April 12, 2017, 01:00:36 pm
content: Someone here pointed out there are LM1117 'clones' out there that have a much lower than expected max voltage rating (10V I thnk)I'd be looking for a named brand and not just assuming they're all the same or swapping to another regulator type.

author: danmcb
author_rank: Regular Contributor
timestamp: April 12, 2017, 01:32:06 pm
content: It's a linear regulator. What package? TO92? check how much current you were drawing. Say that was 50mA (for example). If i/p voltage hit 13V, that package was trying to burn off ~10V x 0.05 = 0.5W. That can even be a lot even for T03 if there is no heatsink - some of these things have 80, 90 deg/W thermal resistance without it, or even more. Then you can get some thermal instability (runaway) - things fry fast. You always have to take care about power/temperature with a lin regulator.

author: Seekonk
author_rank: Super Contributor
timestamp: April 12, 2017, 01:46:28 pm
content: I wasn't doing nuttin and it just broke. That works when you are 5 and cute. Run the numbers and it will be obvious.

author: Ian.M
author_rank: Super Contributor
timestamp: April 12, 2017, 01:52:26 pm
content: Start by building a low voltage heavy duty fast crowbar circuit using a TLV431, a battery powered CMOS flipflop (so it latches even when the rail goes away), and a bipolar driver to slam current from the offending rail into the gate of a beefy low Vgs threshold MOSFET. Adjust it to 3.45V. Temporally connect it directly across the output of any new regulator you are testing before connecting valuable 3.3V loads. Use a fast acting fuse upstream to cut the power before the MOSFET smokesOn the input side of a LDO or low voltage switcher, ceramic decoupling caps can be absolutely lethal. Due to their low ESR and low losses they can form a high-Q resonant circuit with the supply lead inductance and at switch-on, the inrush current can cause the voltage at the regulator to be momentarily doubled. If you are running off a 12V SLA that is on charge, any regulator with an input voltage rating under 35V may blow instantly if you don't clamp across its input capacitor at below its max input voltage rating. Shunting the ceramic with an Aluminum electrolytic (not low ESR) of ten times its value usually helps by adding damping. If you must use only ceramics, add a cap of 10% of its value in parallel, then in series with ONLY the original cap add a low ohm resistor to approximate the typical ESR of an electrolytic of that value.

author: danmcb
author_rank: Regular Contributor
timestamp: April 12, 2017, 01:55:26 pm
content: and yeah, transients from the charger could deffo make things worserer than they already were ... ;-) chalk it up to experience, I think.

author: sleemanj
author_rank: Super Contributor
timestamp: April 12, 2017, 01:58:52 pm
content: Yes I have posted here before about some chinese ams1117-5's i got a few years back that would fail short with more than 10v input. I always test one of each batch when i buy them now to make sure, although i have not come across any more like it since.

author: kolbep
author_rank: Frequent Contributor
timestamp: April 12, 2017, 02:05:53 pm
content: Just measured the Load on the Regulator (with the ESP and DHT11 powered)It starts off at 82mA, then settles to 79mASo, If I plug those values in : 13-3.3=9.7v*.082=0.795wSOT Thermal Resistance (Added all the Tresistances up) works out to 127.7d/wIt is just the sot on the PCB, no heatsinking.Shouldnt these regulators shut down if they get too hot. Or might it just have gotten too hot too quickly.I guess it could still be the fake that is causing it.Well, at least I am now on my last regulator, then I think I might avoid them in future

author: danmcb
author_rank: Regular Contributor
timestamp: April 12, 2017, 02:10:55 pm
content: Quote from: kolbep on April 12, 2017, 02:05:53 pmsome do. Classic LM317 etc are pretty good. But I wouldn't rely on it. I never trust electronics that is at all marginal where power/temperature is concerned. Things can go tits up faster than a drunk stripper at an ice rink.

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 12, 2017, 02:22:47 pm
content: Quote from: kolbep on April 12, 2017, 02:05:53 pmdont do that. this is a nightmare teaching kids. the proper way is..13-3.3=9.7v9.7v*.082=0.795whow could you say:9.7=9.7*0.082?btw. 0.795w is lot of heat for small package. otoh +1 for the fake part.

author: Ian.M
author_rank: Super Contributor
timestamp: April 12, 2017, 02:36:04 pm
content: Nitpicker! Would you rather:13e 3.3e f- fdup f.9.7 ok0.182e f* f.0.795 ok