This thread has been locked.
If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.
Tool/software:
I am looking at a design example for a high side current sense for systems with very high common mode voltage.
https://www.ti.com/lit/an/sboa295/sboa295.pdf?ts=1726922754966
What changed needs to be made to have this work at even higher voltages (650V)?
Hello Appreciated Engineer,
I am looking at you question and will respond shortly.
Best,
Peter
Hello again,
We truly apologize for the weekend delay.
In order to scale the referenced design to higher voltages you need to:
1. Increase R3 to reduce unnecessary power loss.
2. Replace Z1 with a Zener that has a larger breakdown voltage < current sense amplifier's maximum supply/common-mode voltage. So for INA138 Z1's reverse breakdown needs to be < 36V. Using a larger Zener voltage reduces the voltage drop/power lost through R3
3. If 1 and 2 aren't possible, then maybe use a slightly more complicated floating supply voltage circuit that does not require as much regulation current/power loss.
4. Replace Q1 with transistor (or stack of transistors) that can drop the 650V with some margin from drain to source.
I would recommend either using a the largest rated amplifier (INA169 or INA168) to reduce power lost from the Zener regulator. If you need more accuracy you could use a voltage-output current sense amplifier (e.g., INA296B), but convert it into a current-output architecture using a Howland Current Pump as shown in the following documents:
https://www.ti.com/lit/an/sboa358/sboa358.pdf
https://www.ti.com.cn/cn/lit/an/sboa513/sboa513.pdf
The other option is use a an isolated amplifier such as AMC1301.
Sincerely,
Peter