Help me calculate the value of C for a RC filter for which the supply is 12volts

[rahul.6sept]

i need to calculate the value of C for a RC filter for which the supply is 12volts,current is 500mA,R is 24 ohms.The output should be 90 percent of input i.e 10.8 volts in 10msec.i'm using the relation Vr=RC dv/dt, but then i need dt which is to be determined from the transient.i'm using the relation V=VoSinwt, but it is not giving the result.What should i do?

 

[bigkitty]

Re: RC filter

You can calculate it by step response:Vo=Vin(1-exp(-t/RC)). If at to=10msec,Vo=0.9Vin,(1-exp(-to/RC))=0.9,then,you can find proper C.

 

[Kral]

Re: RC filter

rahul.6sept,
Let Vo = specified voltage at time t
Vf = the final voltage (= the input voltage)
Vo/Vf = 1-exp(-t/(RC))
1-Vo/Vf = exp(-t/RC)
ln(1-Vo/Vf) = -t/RC
RC[ln(1-Vo/Vf)] = -t
C = -t/{R[ln(1-Vo/Vf)]}
.
Plug in specified values of R, Vo/Vf, t, and calculate C. Be sure to use consistent units, e.g., t in seconds, C in farads, R in Ohms.
Regards,
Kral

 

[rahul.6sept]

Re: RC filter

i determined the value of dt=8.564msec from the transient and substituted in the relation Vr=Vo RC dv/dt to determine the value of C.