Zener for voltage limit - Page 1
Forum section: electronics / projects

author: panoss
author_rank: Frequent Contributor
timestamp: March 03, 2019, 04:27:13 pm
content: I 've made a device with Arduino and Lora RA-01 module.The transmitter is powered by a Li-Ion battery charged at 3.6V because Lora module cannot tolerate more than 3.6V.When I give it to the client, he will charge the battery at full voltage, 4.2V.So, I 'm thinking of putting at the output of the battery a zenner diode of 3.6V.So that when the battery is over 3.6V the voltage will be limited at 3.6V.And when the battery voltage drops at 3.6 the zener will tottaly stop conducting, which is extremelly important as it's a battery operated device and I mind power consumption a lot.On the other hand I could use an LDO regulator, but I don't think I 'll gain anything.What do you think?

author: Kleinstein
author_rank: Super Contributor
timestamp: March 03, 2019, 04:48:05 pm
content: Just a Zenerdiode will not work, as there is nothing to limit the current. A full battery could easily damage the zener diode.Another point is that the corner in a 3.6 zener is not very sharp: it will already conduct a little at some 3 V, and with enough current (e.g. 100 mA) the voltage may be higher than normal.So the better way is to use a low power LDO. If possible more like a lower voltage (e.g. 3.3 or 3 V) as with the AVR µC the current consumption would go down about proportional to voltage. So at 3.3 V one would need something like 10% less than at 3.6 V and this could more than compensate for the little extra current needed by a low power LDO.

author: Cliff Matthews
author_rank: Unknown
timestamp: March 03, 2019, 04:51:33 pm
content: How about just using a barrel jack with an integrated switch? This way customer provided equipment is isolated (or regulated on insertion) rather than doing harm to the uC and Lora modules.

author: tsman
author_rank: Frequent Contributor
timestamp: March 03, 2019, 05:00:32 pm
content: The Zener diode is a kludge and won't work. Use a protected cell if you don't want to add a low voltage cutout to your design. Buy/make a 3.3V output buck/boost module like thisPololuone.

author: panoss
author_rank: Frequent Contributor
timestamp: March 03, 2019, 05:23:02 pm
content: This pololu looks perfect! I supposethisandthisare something similar, right?But because I can't wait till it comes, which LDO regulator would you suggest?Don't they all have the same efficiency?(Arduino consumes at full power I think around 11mA, Lora 120mA)

author: georges80
author_rank: Frequent Contributor
timestamp: March 03, 2019, 06:15:12 pm
content: I designed an STM32F0 based board to solder a Lora module onto. It is also powered by a lifepo4 cell and in my case it is solar charged.My solution was to design in an efficient buck/boost switcher to provide stable 3.3V to the STM and the Lora module. The switcher is capable of handling the few hundred mA 'spikes' that the Lora module will pull when transmitting, especially at 20dB. Transient response of any such regulator is important when you have relatively high current demands that cycle on/off.I'd suggest that is a better solution than trying to 'clamp' higher battery voltages (especially during charging).cheers,george.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 03, 2019, 06:31:14 pm
content: MCP1703 could be a good start. For 150 mA it already needs some cooling copper area.

author: Kasper
author_rank: Frequent Contributor
timestamp: March 03, 2019, 06:39:39 pm
content: I recommend LDO instead of buck because you have small voltage drop and probably want low quiescent (sleeping) current.Switching regulators are usually more efficient than LDOs but with low power devices that are usually sleeping, sometimes LDOs give longer battery life just because they have lower waste when sleeping.

author: georges80
author_rank: Frequent Contributor
timestamp: March 03, 2019, 06:56:52 pm
content: An efficient buck/boost switcher (e.g. RT6150) can operate in sub mA quiescent range when providing minimal current to a sleeping uC/Lora module. This is comparable to most LDO and obviously the buck/boost will keep 3.3V available even when battery voltage drops to 3V and below. And of course will be more efficient with higher input voltage from a li-ion where a LOT of it's capacity is in the 4.2 - 3.6V range.With some basic voltage sensing, the uC can warn of low battery/state of charge and even report battery voltage in its comms (I do that on my stm/lora design).In my case I went with a lifepo4 cell and a buck/boost made most sense due to the lifepo4 voltage profile. I chose the lifepo4 since I wanted a durable battery (years) that was not 'fussy' about charging profile. For li-ion only, an efficient buck would be fine - one that remains efficient at light load (sub mA loads), there are plenty to choose from.All depends on what the OP requires in terms of runtime/features. Right now he has off the shelf modules and is thinking of a zener (which I agree is the wrong solution for the problem). If the OP can't design his own solution, then a small LDO 'board' may well be the best bet.cheers,george.

author: panoss
author_rank: Frequent Contributor
timestamp: March 04, 2019, 08:39:15 am
content: (what is the 'OP'?)I have a few MCP1640 step-up converters. So I'm thinking of, instead of Li-Ion(till this step-up step-down converter comes), using 2 plain 1.5V AA batteries.

author: beanflying
author_rank: Super Contributor
timestamp: March 04, 2019, 08:51:26 am
content: These are a good option. 3 & 5 V nominal, charger and BMS cutout in a battery holder for Arduino/Wemos etchttps://www.aliexpress.com/item/ESP32-ESP32S-For-Wemos-For-Raspberry-Pi-18650-Battery-Charge-Shield-Board-V3-Micro-USB-Port/32843629344.htmlPlenty of other sellers too.

author: panoss
author_rank: Frequent Contributor
timestamp: March 04, 2019, 08:57:19 am
content: This is good! But it doesn't have a 3.3V output, it has 3V!Ok, my ICs work with 3V but I don't know if Lora 's range (crucial for the project) is reduced due to lower voltage.

author: beanflying
author_rank: Super Contributor
timestamp: March 04, 2019, 09:00:43 am
content: When it doubt consult the oracleAndreas's channel is well worth a very careful look at if you want to play with Lora in particular. It is his fault I brought 6 of them to have in the stash.

author: guimtl
author_rank: Contributor
timestamp: March 07, 2019, 01:57:05 am
content: I'm curious if the buck/boost will not create noise that could potentially harm the lora operation.I think either great Scott or the guy with the Swiss accent mentioned it in one of their video.

author: beanflying
author_rank: Super Contributor
timestamp: March 07, 2019, 03:11:17 am
content: I don't have anything in particular to test one of these on but loaded one up to have a look at the Regulator Noise. First screen capture is simply probe as shown in the photo with the DUT producing 5V @ 500mAApproximately 500mA on the 5V rail for testing and a 300mA load (10 ohm Resistor) on the 3V rail with the 5V unloaded for the other. Looks like the 5V Boost is a bit more rough than the 3V. Easy fix to drop the noise is if you are running Lora or other noise more noise sensitive gear and only need 3V then cut the power to the 5V Boost.Little to no science was used in these tests and no bandwidth filtering was used on the scope. For really low noise apps then Linear all the way for charging and regulation but for a simple solution these work great.

author: panoss
author_rank: Frequent Contributor
timestamp: April 14, 2019, 09:35:23 am
content: I received themodule beanflying had suggested.It looks nice.But because I think my power needs are a bit high(Arduino, sleepinΓ for an hour and then waking up and transmitting using a Lora RA-01. Then back to sleep. The transmition takes the most of the energy I guess even though it lasts only 2-3 seconds every hour), I'm thinking of adding a small solar panel.Can a solar panel get connected directly on this module? (with a 5.1V zener diode at the output of the panel?)It does have a charger with theTP4056ic.I see there are solar chargers using this ic:https://maker.pro/arduino/projects/diy-solar-battery-chargerI 'm thinking of it this way (in the picture you see the bottom side of the module):