Minimizing Current Consumption in High Voltage Divider Circuit

[Zaim01]

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:

1. How can I further reduce the current consumption of this voltage divider to the nanoampere range?
2. 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?
3. 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!

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Additional Context:

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

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Feel free to ask for further details if needed.
Zaim

[Zaim01]

Hi Barry,

Thank you for your concern and valuable insights.

I understand the importance of safety when dealing with high-voltage circuits. Yes, I do have experience designing HV circuits and I did before, and I am also consulting with experts in this field to ensure the design's safety and reliability.

This boost converter is very low power, so the current is minimal. The technique I'm using is called biasing, which is commonly used to bias LCDs, APDs, photodiodes, GM tubes, and more. The circuit is designed with safety in mind, and the PCB will be assembled and insulated with conformal coating.

Using GΩ resistors is still common in medical devices. In the event of a failure, our software algorithms are designed to detect anomalies and immediately shut down the oscillator, effectively closing the high-voltage system.

I appreciate your advice on seeking additional guidance from forums dedicated to HV applications. It's always good to get a wide range of inputs to ensure the design is both effective and safe.

Thank you again for your concern and advice.

Regards,  

Zaim

[AScha.3]

Hi,

i think, if you really need to measure the voltage, the 1GΩ / 12MΩ resistor is best, simple solution.

All photocouplers (AQVxx series) or mosfet at 100V have 100nA or more leakage current - so useless here.

Just - afaik - most ("professional" ) circuits anyway producing a regulated HV , so there is a point with some divider there, to check the voltage ; if you can access this, it would be the best solution, consuming no extra power.

btw  GM working at only 100V ? typical is 400...700V .

[Zaim01]

Hi,

You raise some good points. Since my voltage is 100V, I can't use a MOSFET with a Vds of 100V; it should have some margin, so at least 120V is necessary. I searched for a suitable MOSFET on Digi-Key but couldn't find one that meets these specifications with low leakage current.

Regarding the GM tubes, you are correct; their working voltage plateau is typically from 350V to 2000V. In my design, the boost circuit initially steps up 3.3V to 100V, and from there, I use a 4-stage Cockcroft-Walton voltage multiplier to reach the required biasing voltage of 400V.

To minimize current consumption, instead of using a voltage divider at 400V, I take feedback from the input of the first stage of the multiplier, which is 100V. This approach reduces the power consumed by the divider resistors significantly.

Given that all photocouplers and MOSFETs at 100V have leakage currents of 100nA or more, the 1GΩ / 12MΩ resistor solution appears to be the best and simplest approach for this application.

Thank you for your insights and suggestions.

Regards,
Zaim

[BarryWhit]

Would a N.O. Solid-State Relay (SSR) work in your application instead of a FET? (I've never used one, but it looks like a maybe)

[AScha.3]

Hi,

>To minimize current consumption, instead of using a voltage divider at 400V, I take feedback from the input of the first stage of the multiplier, which is 100V.

Now i know. 🙂

+ Yes, here the most simple solution is the 1GΩ / 12MΩ resistors .