Ground plane isolation question

In summary, using a high value bleed resistor between the digital and output stage grounds can help to prevent static voltage buildup that could potentially damage the isolator IC.
  • #1
Hello All,

I was talking to a friend about how to properly isolate a digital board from a high-powered output stage. The output stage in my application make square wave pulses that can be as high as 500V. So my first thought was to galvonically isolate the output stage circuitry from the digital board which contains a microcontroller to run it all.

Up to this point, I figured that a simple isolator (like the IL710) would work great. They are fast, and have 2500V of isolation between the input and output.

But my friend mentioned that there should be a 10 ohm resistor between the two ground planes of the digital and output stage board to keep a static voltage from building up and poping the isolator IC.

But I'm thinking that if you connect the ground planes at all, then it is kind of defeating the purpose of the isolation in the first place. But at the same time, I recognize the issue with the static voltage buildup. How do I deal with such a problem?

Jason O
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  • #2
The value is just off. He probably meant more like 10 MegOhm, or 1MegOhm would work too. Bleeding off static charge doesn't take a low value resistor.
  • #3
Ok, that makes sense. Is this what is commonly done in isolation situations? Will having the high value resistor still block fast transients from crossing into the digital side and blowing stuff up? I do have a lot of bypass caps and TVSs on the chips to prevent this from happening but maybe I'm just being paranoid...
  • #4
Depends on the isolation requirements (like, is it for UL approval of an AC Mains powered device, or isolation of analog and digital sections of a device for noise coupling issues, etc.).

A high-value bleed resistor is commonly used when you don't want static buildup between two things. Like between the shield and the twisted pair inside shielded twisted pair cable, for example.

Often, just using a star ground configuration, with the two grounds connected only at one point (where the power supply is, for example) is sufficient to prevent noise coupling between two parts of a circuit.

When you're following the UL rules for AC Mains isolation, there are spacing rules, and rules for the allowed resistance (big) and capacitance (very small) between primary and (SELV) secondary circuits.
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  • #5
Ahhh interesting :smile: Thanks for the info

1. What is ground plane isolation?

Ground plane isolation refers to the process of separating the ground plane of a circuit or electronic device from other components or circuits. This is typically done to prevent interference and improve signal integrity.

2. Why is ground plane isolation important?

Ground plane isolation is important because it helps to reduce the effects of electromagnetic interference (EMI) and crosstalk between different components or circuits. It also helps to improve the overall performance and reliability of the device.

3. How is ground plane isolation achieved?

Ground plane isolation can be achieved by physically separating the ground plane from other components or circuits, using isolation materials such as ferrite beads or capacitors, and implementing proper grounding techniques.

4. What are the benefits of ground plane isolation?

The benefits of ground plane isolation include improved signal quality, reduced noise and interference, and increased reliability of the device. It can also help to prevent damage to sensitive components and improve the overall performance of the circuit.

5. When is ground plane isolation necessary?

Ground plane isolation is necessary in situations where there are multiple components or circuits on a single board or device, and there is a risk of interference or crosstalk between them. It is also commonly used in high-frequency and high-speed circuits to improve signal integrity.

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