Band Reject Filter OR Band Elimination Filter


Band Reject Filter ( Band Elimination Filter ) ( Band Stop Filter )

  • It is a filter in which frequencies below lower cut off frequencies and above higher cut off frequencies are passes whereas stop band frequencies are attenuated.

Range of frequencies

f < fL

fL < f < fH

f > fH

Allowed to pass

Not allowed to pass

Allowed to pass



Band Pass Filter

  • The band pass filter allows frequencies to be passed between lower cut off frequency ( fL ) and higher cut off frequency ( fH ) whereas it reject all other frequencies below fL and above fH.


fL = Lower cut off frequency

fH = Higher cut off frequency


High Pass Butterworth Filter

 First order High Pass Butterworth Filter

  • The high pass filter is obtained by changing frequency determining component – resistors and capacitors in the low pass filter. 
  • The first order high pass filter is obtained by interchanging R and C in the first order low pass filter. 
  • Figure shows first order high pass Butterworth filter.


Low Pass Butterworth Filter


First order Low Pass Butterworth Filter

  • It is a filter which has nearly ideal response, flat passband as well as flat stop band. 
  • As both passband and stop band are flat, it is also called as flat – flat filter.


Types of Filter


  • An electronics filter is a circuit which allows specific band of frequencies whereas blocks frequencies outside of the band.

Classification of Filter






Variable Frequency Drive

The frequency converter is also called as variable speed drive or variable frequency drive. 

This drive basically consists of two parts

( 1 ) First part which converter AC to DC and

( 2 ) converts DC into AC.


Hydrogen Cooling of Alternators


The alternator in the large power plant consists of conductor with high electrical current flowing through them, which generates large amount of heat. If this heat is not dissipate in the surrounding area, alternator winding can quickly degrade and eventually damaged. When selecting cooling gas of alternator, several points to be considered.