R
Ricketty C
Guest
I thought this was a simple circuit to measure a current on the high side with a lower voltage op amp. Input resistors couple with the feedback resistor to keep the op amp inputs at safe levels. No big deal, seems to work ok. I used a second amp to dig the signal out of the dirt.
Then it appeared I would need some filtering so the current measured would be an average of the PWM signal used to control the device. The caps I added didn\'t seem to do exactly what I was looking for and when I removed them I realized there was something going on that was limiting the band width. Seems it is the basic circuit without filter caps.
With no caps the roll off was around -20dB at 42 kHz. I thought I might get better response using lower value resistors if the parasitic capacitance was causing this (620k is a bit high). Using lower resistor values makes it worse! With 46k4 and 20k resistors the first stage is -110 dB down!
I am missing something very fundamental here. The original resistors are 620k and 215k. I think this zip file contains all the files needed.
http://arius.com/temp/CurrentMon.zip
--
Rick C.
- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209
Then it appeared I would need some filtering so the current measured would be an average of the PWM signal used to control the device. The caps I added didn\'t seem to do exactly what I was looking for and when I removed them I realized there was something going on that was limiting the band width. Seems it is the basic circuit without filter caps.
With no caps the roll off was around -20dB at 42 kHz. I thought I might get better response using lower value resistors if the parasitic capacitance was causing this (620k is a bit high). Using lower resistor values makes it worse! With 46k4 and 20k resistors the first stage is -110 dB down!
I am missing something very fundamental here. The original resistors are 620k and 215k. I think this zip file contains all the files needed.
http://arius.com/temp/CurrentMon.zip
--
Rick C.
- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209