Minimizing Current Consumption in High Voltage Divider Circuit

Zaim01 · ‎2024-07-07

Hello everyone,

I'm working on a circuit for monitoring the bias voltage of a GM tube, which requires a high voltage of 100V. I am currently using a OA1NP22C op-amp configured as a unity-gain buffer to read the divided voltage. To minimize current consumption, I'm considering using a voltage divider with 1GΩ and 12MΩ resistors. However, this configuration still consumes approximately 9.8µA, which is higher than I would like for my low-power application.

Here is a simplified version of my circuit:

100V Bias Voltage (GM Tube)
|
R1 (1GΩ)
|
+----> To OA1NP22C Op-Amp (unity gain buffer) > MCU
|
R2 (12MΩ)
|
GND

My questions are:

How can I further reduce the current consumption of this voltage divider to the nanoampere range?
Would switching out the voltage divider using a transistor be a viable solution? If so, what configuration and components would you recommend for achieving this?
Are there alternative methods or components that could help in significantly reducing the power consumption while maintaining accurate voltage monitoring?

Any insights, suggestions, or examples of similar implementations would be greatly appreciated!

Thank you!

Additional Context:

Control Signal: 2.9V from a microcontroller.
Power Efficiency: Critical to keep the overall system power consumption as low as possible.

Feel free to ask for further details if needed.
Zaim

Zaim01 · ‎2024-07-09

You mean a circuit like the one below:

The issue with this circuit is the leakage of the MOSFET and the current consumption through R1. When increasing the value of R1, the P-MOSFET T1 may not turn off completely, and if R1 is too small, it could draw unnecessary current. Could you please recommend some values based on the schematic above?

Or, if I have misunderstood your point, please clarify.

Thanks in advance,
Zaim

View solution in original post

Peter BENSCH · ‎2024-07-07

Please check your idea again:

at 100V at 13Gohms a current of 7.7nA flows, not 9800nA
the OA1NP22C will surely be connected to GND, right? What voltage does it then see at his input? What happens then?

It would be better if you could insert schematics as a picture, including the opamp, so that we can make suggestions for improvement.

Regards
/Peter

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Zaim01 · ‎2024-07-07

Hi Peter,

Thank you for your feedback. You are correct about the current calculations.

To clarify, R1 is 1GΩ and R2 is 12MΩ. Please find the schematic below for further reference.

Regards,

Zaim

Zaim01 · ‎2024-07-07

Hi Again Peter,

Regarding the voltage divider, the mentioned values were just a preliminary idea. The voltage divider network will only be used once a day to check the output voltage is stable, so it should not consume unnecessary current to help preserve the device's battery.

Regards,

Zaim

MM..1 · ‎2024-07-07

Peter little mix M and G, but still divider current is around 98nA for your values. Then seems uA current is from MCU and OP. Your point 2 is one step use NFET transistor and remove capacitor.

Zaim01 · ‎2024-07-07

Hi MM,

Thank you for your insights.

Could you please illustrate any drawing or a schematic showing how the NFET will be used? Additionally, could you recommend a specific NFET or provide important considerations to check when choosing one?

Thank you for your support.

Regards,

Zaim

AScha.3 · ‎2024-07-07

Hi,

>How can I further reduce the current consumption of this voltage divider to the nanoampere range?

You are there... 100V/1Gohm = 100nA . (100nA x 100V = 10uW - where you wanna go then ?

+ How much uA needs the cpu and all other circuit ? )

>Would switching out the voltage divider using a transistor be a viable solution?

Yes. But to get lower than 100nA, you only could use a mosfet; but at your 3v3 supply, only few mosfets can work at >100V and be switched with < 3V at the gate - so close to impossible.

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BarryWhit · ‎2024-07-07

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Zaim01 · ‎2024-07-07

Hi AScha.3,

Thank you for your insights, I understand your points exactly. Finding a small MOSFET with a low gate voltage is indeed challenging. Therefore, I still think that the voltage divider solution may be the best for our product. I also realized that I miscalculated the current; it should be 89nA, not 9.8uA.

An important consideration for our product is cost, and as you may know, GΩ resistors are very expensive. Thus, the maximum resistance I can use is 1GΩ. So, the question is: are there any other ways to achieve lower current consumption for this circuit, or should we proceed with the current values?

As I mentioned earlier, I will enable the ADC for this feedback once a day. I was considering completely shutting down the circuit and only powering it when I need to read the values. However, if the switching circuit draws more than 100nA, it might be hard to used, and I might have to use the configuration with the 1GΩ / 12MΩ resistors.

Thank you for your support.

Regards,
Zaim

MM..1 · ‎2024-07-07

I mean 98nA with transistor off can be reduced only to DS leakage current for example BSS123N

and is temp sensitive. Primary reduce other corrents.