I’m designing a DC voltage measurement circuit using the HCPL-7800A for isolation and MCP6002 as the op-amp. I’m wondering if it’s necessary to add an offset to the DC signal before feeding it to the ADC.


From my understanding, DC voltage does not require an offset since it doesn’t swing around 0 like an AC signal. My circuit will measure the DC bus voltage directly, with a voltage divider to scale it appropriately for the IC’s Vin.


Has anyone experienced using HCPL-7800A or MCP6002 for DC measurements? Are there any papers or references showing that adding an offset is required for DC measurement?

 

I have used the HCPL-7800A many times. Most of the time Vin- is at ground and the signal is at Vin+.
In your schematic pin-4 should be the ground that matches 5V_ISO1. Not SGND. I can't see all the information. Probably pin-4 should be GND.
What country are you in? I am in the US.

 

The MCP6002 works with voltages from Vee to Vcc for both inputs and outputs. (R-R) It will work well as you drew it.

 

I have used the HCPL-7800A many times. Most of the time Vin- is at ground and the signal is at Vin+.
In your schematic pin-4 should be the ground that matches 5V_ISO1. Not SGND. I can't see all the information. Probably pin-4 should be GND.
What country are you in? I am in the US.

The signal ground (SGND) corresponds to the ground of the isolated 5V supply designated as 5V_iso1. This supply is provided by an external switching power supply, and it remains entirely independent from the main circuit ground to maintain proper electrical isolation, minimize the risk of ground loops, and ensure accurate and reliable operation of the control circuitry.

 

Something is wrong here. Pin-4 and pin-5 are connected together. There is no isolation this way.

Back during COVID we had some very bad part shortages. I purchased parts for 5x the normal price to keep the company going. Also I purchased parts that are slightly different. I don't remember which parts I have but more than I will ever need.

 

The MCP6002 works with voltages from Vee to Vcc for both inputs and outputs. (R-R) It will work well as you drew it.

Thank you, I now understand where I went wrong. May I exchange information with you so that I can learn more about circuit design in the future?

 

May I exchange information with you so that I can learn more about circuit design in the future?

Yes. There are many good people on the forum that can help. Post questions and someone will respond and all can learn.

 

Thank you, I now understand where I went wrong. May I exchange information with you so that I can learn more about circuit design in the future?

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