How to get the best low power while in sleep mode

Thread Starter

Omri284

Joined Apr 18, 2020
21
Hi,
My goal is as said, run my system at the lowest power I can.
I have an esp32, a dc-dc boost converter(from 3V battery to 3.3V) and some sensors.
These are 2 schematics I am considering:

1. Powering the esp32 from the 3V battery always and the sensors from the 3.3V - is it possible and correct to do so? Using an efficient dc-dc converter what magnitude of current do they take with enable off?
Screenshot 2022-01-18 223011.png

2. Switching between the power sources - when in active mode - esp32 is on the 3.3V, and when in sleep mode esp32 is on the 3V battery.
Screenshot 2022-01-18 223035.png

Which is better? Or there is a simpler alternative?
Thanks!
 

Thread Starter

Omri284

Joined Apr 18, 2020
21
Hi, Thanks for the reply.I am looking at the video. Meanwhile I'll say i'm already using esp32 in deep sleep mode. My problem is I don't want the dc-dc converter to add its quiescent current while in sleep mode(to be completely off or en off).
What do you think of my solutions?
 

Thread Starter

Omri284

Joined Apr 18, 2020
21
I want to clarify my question. The ESP32 already consumes the least power can be(~10uA) and it doesn't matter if its ESP32 or another micro controller.
The dc-dc converter in the best cases I found consumes ~20uA - that is I want to reduce.
There is no need for the ESP32 to run on the dc-dc's output voltage, it can run only on the battery and will be fine.
Therefore I am trying to find the best way to use the dc-dc converter only while awake, and not use it when in deep sleep mode.
Thanks
 

Papabravo

Joined Feb 24, 2006
18,070
I want to clarify my question. The ESP32 already consumes the least power can be(~10uA) and it doesn't matter if its ESP32 or another micro controller.
The dc-dc converter in the best cases I found consumes ~20uA - that is I want to reduce.
There is no need for the ESP32 to run on the dc-dc's output voltage, it can run only on the battery and will be fine.
Therefore I am trying to find the best way to use the dc-dc converter only while awake, and not use it when in deep sleep mode.
Thanks
This is not an uncommon problem. The usual solution is to use low forward drop diodes to combine power sources. this may require you to reconfigure either your battery arrangement or you DC-DC converter to get the required voltage output.
 

Thread Starter

Omri284

Joined Apr 18, 2020
21
This is not an uncommon problem. The usual solution is to use low forward drop diodes to combine power sources. this may require you to reconfigure either your battery arrangement or you DC-DC converter to get the required voltage output.
Could you elaborate where the power source combination is? Is there a schematic close to what I need?
 

michael8

Joined Jan 11, 2015
272
The 2N7002 source follower switch isn't likely to do what you want -- the output when "on" won't get to the supply voltage,
The Vgs threshold voltage is typically 2 volts for the 2N7002 so the output to the sensor will "typically" be 2 volts less than your supply voltage. You likely need a P-MOSFET or PNP transistor...
 

Thread Starter

Omri284

Joined Apr 18, 2020
21
Ok, made some changes according to what you guys suggested(Changed to P-FET and put diodes for 2 sources):
Screenshot 2022-01-19 193938.png
What diodes are most recommended for this(least voltage/noise)?
Thanks!
 

Papabravo

Joined Feb 24, 2006
18,070
Ok, made some changes according to what you guys suggested(Changed to P-FET and put diodes for 2 sources):
View attachment 258175
What diodes are most recommended for this(least voltage/noise)?
Thanks!
Schottky diodes, but remember the forward voltage drop is a function of the current drawn. This means you may need adjust the battery arrangement and/or the DC-DC converter. I'm puzzled about why the DC-DC converter is required. Can you enlighten us?
 

Thread Starter

Omri284

Joined Apr 18, 2020
21
Schottky diodes, but remember the forward voltage drop is a function of the current drawn. This means you may need adjust the battery arrangement and/or the DC-DC converter. I'm puzzled about why the DC-DC converter is required. Can you enlighten us?
I am using a very sensitive to voltage sensors such as a load cell and capacitive sensor.
Also I think it is crucial that the sensors will get the same voltage as ESP32 gets.
In active mode I am using 1 50-150mA current, I assume the diode will "ruin" my stable voltage out of the dc-dc converter.
Is there a way I can make it stable? some capacitors after the diode?
What arrangement would you recommend in order to reach this goal?
Thanks
 

ericgibbs

Joined Jan 29, 2010
15,332
hi Omri.
Ref the 3V battery, what type and life cycle discharge curves do you have for it.?

E
BTW: I guess you are aware that DC DC converters outputs are electrically noisy.

Do you have a circuit showing the sensors connections.?


Added:
PDF
 

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Thread Starter

Omri284

Joined Apr 18, 2020
21
hi Omri.
Ref the 3V battery, what type and life cycle discharge curves do you have for it.?

E
BTW: I guess you are aware that DC DC converters outputs are electrically noisy.

Do you have a circuit showing the sensors connections.?
The battery(which is optional and can change in the future though it works fine):
https://jm.pl/gfx-base/s_1/orgs/18/CP502440-HCB.pdf
I have a lot of sensors of all kind of types connected, that's why I tried to simplify the question.
I know it is noisy, but the bottom line is with 3.3V regulator(and not a good one), they work consistent enough, and with battery they get very unstable.
 

Thread Starter

Omri284

Joined Apr 18, 2020
21
I'm kind of worried about the voltage instabilty of the diodes, so I replaced it with P-fets.
Will this be a better soultion?
Screenshot 2022-01-20 112748.png
Just to be clear it divides into 2 states:
1. EN on - ESP32 and sensors get 3.3V off the dc-dc converter, battery goes only to the converter.
2. EN off - ESP32 gets voltage off the battery only, converter and sensors are disconnected.
 

Papabravo

Joined Feb 24, 2006
18,070
You seem to be adding unnecessary complexity and problems for no apparent reason. Just run the whole thing from the battery and be done with it.
 

ericgibbs

Joined Jan 29, 2010
15,332
Unfortunately running the circuit with the battery's voltage gives me bad data Unfortunately running the circuit with the battery's voltage gives me bad data
hi Omri,

Please explain, how is the data bad.?

I guess you know that the ESP32 ADC has a non-linearity problem.?
E
 

Thread Starter

Omri284

Joined Apr 18, 2020
21
hi Omri,

Please explain, how is the data bad.?

I guess you know that the ESP32 ADC has a non-linearity problem.?
E
Yes, i.e when sampling the load cell with the battery I get jumps in values that are not logical(equal to hundreds of grams) while with rectifier I get logical values(jumps of single grams). I know the fall backs of ESP32's ADC but it is not an analog sampling, it is a sampling of a wheatstone bridge with an amplifeir - what makes it really sensitive to small change of currents and not very consistent if using a battery's voltage(that can changes by >0.5V).
 

ericgibbs

Joined Jan 29, 2010
15,332
hi Omri,
The ESP32 ADC's are ratio metric, if you power the Wheatstone bridges with the same power source as the ESP the bridge readings will track accurately.
I am assuming that you are using the Vsupply of the ESP as the ADC reference voltage and not an external reference.?

That's why I was interested in seeing your sensor bridges and IA OPA's etc ..

E
 
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