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Original question:
Hi ,first thank you for reading my question.
This is problem I met:
L1 and N1 are the input AC voltage-220VAC.
I acquire the voltage through AMC1200-Q1 ,then I amplify the diffirential signal through OPA2171 ->for PFC control
But when the AC Vin rised up to 200VAC (3kW),I increased the operating frequency of MOSFET which is in the LLC,not in PFC, the AC voltage signal PFC_IN_Uac had a DC offset.
I dont know why the sensed AC voltage signal had a DC offset, however I suspect that the increasement of frequency had an influece in it.
How should I design the AC voltage sample circuit?
Should I add an OPA in front of AMC1200 like the figure in www.ti.com.cn/.../tidrv40a.pdf
What is the reason the lead to the DC voltage bias?
Thank you again.
Good luck!
Vac_max=220*2^0.5=311V
VINP-VINN=311*460/(150k*8+460)=120mV <250mV
VINP-GND=60mV
so I think it didnot violate the common mode range and differential mode range.
The operating frequency of MOSFET in LLC can reach 120kHz~170kHz.
I measured it again and 1.65V rised up with the increasment of Operating frequency of Mos in LLC .
I dont find the reason why 1.65V rised up .
The only link between 1.65V and frequency is GND1.
GND1 is the groud of isolated gate driver(UCC27424), is 1.65V influend through GND1?
Thank you for your reply first.
I had changed it in 2 ways.
1. short voltage follower
In fact, I had shorted off voltage follewer like the picture below,it did not work well
2. change the value of R27 from 1k to 100Ω
It did not work well either.
The phenomeno that +1,65V rised up tinily had a big influence of final resuit.
