Hi everyone

I have a problem of current filtering with my controller of brushless dc motor (BLDC).

the problem that the current is PWM and i want to read it and show a fixed value like the multimeter process.

so what's the filter that can be used to prevent this problem , or specially what's is the filter inside the multimeter ( i know that a Low Pass Filter!!).

thanx in advance

 

Hello,

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Bertus

 

Hi

Sorry

 

why not just measure the supply current to the pwm output stage? should be dc.

 

What, exactly are you trying to measure?

 

Hi Mr Crutschow

if you see the image there's 2 resistor to measure the current ( pwm command) my goal is to measure it like a dc ammeter . so my question what's the type of this filter ??

thanx in advance

 

Sorry Mr alfacliff

no i want pwm current on the source pin of mosfet .

the supply current isn't practical

 

A single-pole RC filter should work to smooth the PWM signal into the average value. The RC value should be at least 5 times the period of the PWM frequency.
The trade-0ff is between ripple voltage and the time to respond to any change in the current level.

 

Hi

in my circuit this filter is implemented

don't you think this filter is good for this (mission) ? ?

thanx

 

That is a differential circuit followed by a 1st-order low-pass RC filter with a corner frequency of 159Hz.
If the bottom of R32 goes to ground then you don't necessarily need a differential circuit.
What's VREF?
What is the PWM frequency?
Are you having a problem with that circuit?

 

R=1k, C=1n -> corner frequency is 159kHz

 

R=1k, C=1n -> corner frequency is 159kHz

Correct. The characters are very small and I mistook the n for a μ.

 

Hi

thanx Mr jjw for your help.

Mr crutschow , no i don't have any problem with this circuit but i told about the filter and you're right this is very little .

but is there any other digital filter without changing the pcb board ?

 

...............................
but is there any other digital filter without changing the pcb board ?

Why do you want to change the filter?

 

hi

to change the cutoff frequency , because pwm freq = 20 khz
for 159 khz , this is not a good LPF

so my question can i add a digital filter in the mcu instead of analog ?