Automatic low power switch based on voltage threshold?

Thread Starter

jcun4128

Joined Apr 5, 2021
17
I made this ESP-01 powered by solar cells and super capacitors but it has this problem where I need to "jump it" to get it going... I think it has to do with the slow charge/build up and the ESP-01 doesn't like that... sorry to be vague.

I thought everything was working/all fine but I think it's actually just because of me probing with the DMM/jump starting it.

So I'm looking for some kind of switch that won't turn the ESP-01 on until the 3.3V after the LR is available.

I'm not sure the terminology for it, I'm hoping it's a dumb chip/low quiescent current deal.

See diagram for context.

Thanks

schematic.png
 

Ya’akov

Joined Jan 27, 2019
5,660
What you want is a voltage supervisor like this TI TLV80xE. It holds the RESET pin low until the voltage is in an acceptable rage. There are also other features. There are many, so you can look around to see which looks right for your application,
 

LowQCab

Joined Nov 6, 2012
2,050
First, You need a Low-Drop-Out Voltage-Regulator, ( and your Schematic is incorrectly drawn ),
then You need an Under-Voltage-Protection Circuit with some Hysteresis.

There are probably better ways of accomplishing these ends, but this is what came to mind first.

LDO Regulator ..........
https://www.digikey.com/en/products/detail/microchip-technology/MIC5156-3-3YN/1030134

LDO Regulator FET ( 1.2-Amps ) ..........
https://www.digikey.com/en/products...rEAOALlCAMrcATgEsAdgHMQAX2nFYFEADUAcrFhhG7aUA
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High Current LDO .PNG
 

Thread Starter

jcun4128

Joined Apr 5, 2021
17
Yeah you are right about it being incorrect regarding the LR having 3 pins, was supposed to be an abstraction but I can make that small change.

I think what you have (diagram) might be overkill for my case. The solar cells barely produce any power and the threshold for the LR it's like 1V or more above the minimum eg. 3.3V... I mean it does work... the problem is it does not work from idle up to max sunlight unless I do something like "jumping" (short pos and neg together somewhere briefly during max sunlight).

Updated, I'm using this AMS1117 breakout board, sorry I know these MS paint crayon circuits are terrible, this is not my field.

Also I will point out, there's not much theory behind what I made. I just put it together, it seemed to work and now I'm seeing this problem. So if ther'es something blatantly wrong with what I made please let me know.

I was also shown here how to make a FET switch circuit, not sure if I can use that. At any rate I appreciate the ideas.

Thanks for the links

schematic-updated.png
 
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LowQCab

Joined Nov 6, 2012
2,050
The AMS1117 Regulator drops around 1-Volt no matter the conditions,
( it's just not quite as bad as most "jelly-bean" Regulators that drop ~3-Volts ),
and requires special attention to the Output-Capacitor selection,
and to the Minimum-Required-Current,
both of which can be quite confusing to a newbie.

The MIC-5157 that I suggested has virtually zero Voltage-Drop under any condition less than 1-Amp,
provides adjustable, continuous, Current-Limiting with no over-stressing of anything,
and provides an UVDO, (Under-Voltage-Drop-Out), function, ( at 3.036-Volts ),
and will not restart without adequate Input-Voltage, (3.75-Volts),
this makes for clean starts and stops of your Micro-Controller as the Output of your Solar-Cells varies,
and so will eliminate short-cycling, failure to Boot, and other weirdness that may occur with
a slowly rising or falling, unregulated Input-Voltage.
All this means that your Micro-Controller will see a clean "switch" between zero, or exactly 3.3-Volts,
every time it starts or stops because of Solar-Cell Output fluctuations,
and You gain ~1-Volt from your Solar-Cells instead of wasting it as Heat.

When You have a funky variable Power-Source, additional measures are required for stability.
You would be better-off using your Solar-Cells to charge Batteries, but it's not any less complicated.

BTW, all the little details matter when creating a Schematic.
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Thread Starter

jcun4128

Joined Apr 5, 2021
17
Cleaning this up.

I will get the MIC5157, and other parts I might need. I think I understand that circuit for the most part except:

  1. what is NC and 3R? (referring to your annotations)
  2. does the voltage on the capacitors matter

Thanks
 
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LowQCab

Joined Nov 6, 2012
2,050
1) "NC" is a universal acronym for "Not-Connected".
( Or it could be "Normally-Closed" when applied to a Switch )

2) "3R" ,
"R" is used when there are less than 3-zeros following the value of a Resistor,
"R" simply means "Ohms", "K" means thousands of Ohms, "M" means millions of Ohms,
so the Resistor has a value of 3R or 3-Ohms.
R, K or M may also take the place of a decimal-point, for example- 3K3 = 3.3K, or 3,300 Ohms .
( This Resistor is for monitoring Current, and
will reduce the Output-Voltage if the Output-Current exceeds 1-Amp ).

3) The Voltage-rating of Capacitors always matters.
In this case, there are no Voltages in the entire Circuit that exceed ~5-Volts,
so the Capacitors may have any Voltage-rating in excess of ~6.3-Volts.
( 6.3-Volts is one of the "standard" Voltage-ratings for Capacitors )
( 16-Volts is the next higher "standard" Voltage Rating, and
will provide slightly better overall performance at the expense of larger size,
it will be almost twice as large in physical dimensions )
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Thread Starter

jcun4128

Joined Apr 5, 2021
17
Alright thanks for the additional info, I think I have everything I need to know to order the right parts and assemble this thing.

Edit: question, I saw you put VN2210N3 but they have IRLZ44 does it matter? Seems like it does if you made that distinction.
I only mention it because VN2210N3 seems to be out of stuck but they have VN2210N3-G and I have some IRLZ44's.
Well I'll get the VN2210N3-G for now since the non-G one seems to be obsolete, not sure where to get it.
 
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LowQCab

Joined Nov 6, 2012
2,050
Sometimes Transistor numbers can get out of control, so sometimes they are abbreviated.
The "G" on the end has only to do with some odd specification that is usually not significant
in a simple application such as this.
If You do a search on most Electronics Suppliers websites,
anything related to the root part-number will pop-up.

DigiKey has a bazillion of them ......
Here is a search on DigiKey's site with just "VN2210N3"
https://www.digikey.com/en/products...3-G/4902400?s=N4IgTCBcDaIGoDkxgIwAYEGYQF0C+QA
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As for the IRLZ44 , yes You can use it with zero problems,
but a ~50-Amp-rated part is total over-kill, it's also in a much larger TO-220 package,
while the VN2210N3 is in a much smaller TO-92-package which is completely adequate for your application.
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Thread Starter

jcun4128

Joined Apr 5, 2021
17
Well my fate is sealed, placed the order, hope I got the right stuff. I also bought the TLV803E that Yaakov mentioned, will try that.

I really wanted something "stupid simple" and this MIC-5157 is a bit beyond that but perhaps it simply won't work unless you have something like this or use a charger. I just thought the supercap approach would be simpler than batteries.

Thanks a lot for both of your time.

Edit 04/15/2022

Wow... note to self: check the physical dimensions of the parts, look at how insanely small these capacitors are
Conversely these 3 Ohm resistors are enormous, I thought they'd be the size of grain of rice but it's like an almond

Mouser's packaging is crazy, the circuit supervisor chips are in this sealed moisture sensitive bag dang. It's like an MRE.

OMG this voltage supervisor is also very small. It's not impossible (for me) to work with but dang.

Well now I know, lesson for next time.

Well, that did not go well. I open the ribbon package immediately lose one, flies somewhere, gone. 4 left. I solder some wires on, not working, eventually the wires break off (yeah dumb to solder 24gaug wire to a 10th of a mm sm tab). I am not equipped to work with this small stuff right now. I will revisit this again.

Thanks for the help, my bad for not paying attention to the sizes.
 

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