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# amc1301

hii alex

how are u doing

i want to use the amc1301 to sense a power ac line that has an amplitude ranges from 0 to 700 volts with frequency of 60 hz

as i see i need to use resistor divider  network at the input of the AMC1301 so when the ac line is 700v the max amplitude at VINP pin is 250mV .(i connect the VINN to ground )

but i have a problem with this design and my problem is when the power line amplitude reduces down to 100 volts or less i get very low input voltage at VINP about 5mV and its not very big swing at the input of the isolation amplifier .

do have any recommendation of how to sense high ac voltage like in my case

i can solve this issue by connecting a different resistor network  so when the amplitude voltage gets down to 100volts i start to use another resistor divider network that give me 250mV at the input of the amc1301

but i want to see if you have another approach  for sensing an voltage with an amplitude of 700 AC volts using the amc1301

• Hello Aied,

Thanks for your post! I am well and I hope the same to you.

Can you post a schematic that shows your resistor divider network?

The voltage should be proportional, so if 700V on the AC line corresponds to 250mV, then 100V on the AC line should be 35mV; not 5mV.

Having a second resistor network is an interesting idea but I believe that it may lead to problems if it doesn't switch back correctly - either physically or in the code.

Best regards,

Alex Smith
Applications Engineer | Precision Delta-Sigma Converters

• In reply to Alexander Smith:

hii alex

good morning

yes you are right 100v  is equal to 35mv

the resistor network is 10K and 3.5ohm

do you have a recommendation for other resistors values?

and yes i intend to change the resistor network by hardware but i wanted to see if there is another idea for doing this measurement?

• In reply to AIED BEBAR:

hii alex
one more question the phase of the output signal does it have any drift relatively to input phase ?
cause i consider the output phase to have the same phase as the input ?
• In reply to AIED BEBAR:

Hi Aied,

Thank you! I hope you have a good afternoon.

These resistor values are not safe for dropping 700Vac - the voltage will be dissipated as heat and I doubt that these resistors could handle such a drop. When you choose the resistors to use here, make sure you look at their thermal ratings to ensure that they can handle the heat that will be generated. Please be safe when working with voltages this high!

Take a look at this thread, I believe they are performing a measurement very similar to yours: e2e.ti.com/.../2281751

And this TIDesign for reference: www.ti.com/.../tidubx1b.pdf

Let me know when you change your schematic and if you have any other questions!

Best regards,

Alex Smith
Applications Engineer | Precision Delta-Sigma Converters

• In reply to Alexander Smith:

hii alex

i did a simulation using TINA for the reinforced amc1301 circuit that is in tidubx1b.pdf

for sensing the DC bus input voltage.

i wanted to sense a 566 AC volts with 50 hz frequency

and i got the following results

the peak value of the input signal is 322mv

and the minimum value is -124mv

and  the output of the opamp was clamped at the maximum and not a full sin wave

i expected to see +/- 250mv at the input  and a full sine wave at the output i tried of biasing the input but the output was still clamped ,do you have any idea why?  how to correct the circuit in order to utilize the range of the 250mv input  566volt main line sense1.TSC

i attached the Tina design

• In reply to AIED BEBAR:

the output of the op-amp320 was clipped at 3.24
the output of the opamp320 is feed into the mcu ADC
• In reply to AIED BEBAR:

hii alex ,how are you doing

did you see my question?

• In reply to AIED BEBAR:

Hi Aied,

Apologies for the delay in response, it was a Holiday in the US last week.

Are you calculating the 322mV peak and -124mV minimum using the DC transfer characteristic?

Using Analysis -> AC Analysis -> Calculate Nodal Voltages, I am seeing 224mV Amplitude and 186mVrms on the input.

The output of the OPA320 should be 0 to 3V, correct?

Best regards,

Alex Smith
Applications Engineer | Precision Delta-Sigma Converters

• In reply to Alexander Smith:

hii alex

hope you had a good refreshing holiday :)

i attached a screen shot of the simulation

as you can see the input is with 322mv max amplitude and -124mv   when i take the deference between this values  its about 340mv which is much higher than 250mv input swing of the device this is one problem

and the second one is this input sine wave is not centered around 0v

from the resistor divider network at the input should be 250mv once there is 566v at the input line .

and the out put op the opamp is clipped at the max peak of the output wave  , and yes the output should be between 0 and 3v cause i feed it to my ADC e output of the opamp should be between 0 to 3v cause i feed to my adc

• In reply to AIED BEBAR:

hii i also attached the schematic that shows the resistor network that i use at the input

by voltage division if there is 566 VAC by phase i should sense 250mv

and this is not happening in the simulation the amplitude  as i mentioned above 322mv and -124mv

and i suspect that is whats causing the clipping at the output on the op amp.