Disc capacitor //Electrolytic polarised capacitor

Discussion in 'Analog & Mixed-Signal Design' started by sohamkul, Aug 2, 2016.

  1. sohamkul

    Thread Starter Member

    Jun 24, 2016
    43
    2
    Hello Everyone ,
    Few days back i had posted a question related to an instrumentation amplifier ,
    As per suggestions and advice from forum members..i made the circuit...and it works like charm !!!
    Now i had ordered 0.47microfarad disc type capacitors and i got 100 electrolytic polarised capacitors ...supplier wont take it back ..:(
    Please review and suggest if i can use 0.47 electrolytic polarised capacitors.
    Images :
    1) circuit (capacitors C3 and C4)
    2)type of capacitors i expected
    3)the ones that i got ...

    Thank you !! IMG-20160628-WA0006.jpg 474-500x500.jpg
    EL.CA0.1433682.jpg
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,123
    3,048
    Since one end of C3 is grounded, a polarized cap will be OK if circuit voltages never drop below ground. I didn't take the time to study your circuit to verify that is true. The situation at C4 is even less clear to me. But if the cap is always charged with one polarity, the polarized cap will be OK.

    The supplier is acting very badly, if in fact you can prove what you ordered. Most suppliers I've dealt with would let you keep the wrong part and ship the proper ones to you. Otherwise, you'll never go back to them.
     
    Sinus23 and sohamkul like this.
  3. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,951
    387
    If the op-amps are supplied with positive and negative supply rails with the circuit ground being half-way in between then, no, you can't use electrolytics in those positions as the input and output of that last amplifier may be either positive or negative depending on the input.
     
    sohamkul likes this.
  4. crutschow

    Expert

    Mar 14, 2008
    13,014
    3,234
    It's problematic to use those electrolytics in those two spots.
    Afraid you will need to buy some non-polarized caps for that.
     
    sohamkul likes this.
  5. hp1729

    Well-Known Member

    Nov 23, 2015
    1,954
    219
    Help us avoid dealing with that supplier in the future. Who from? What part number did you order?
     
  6. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,058
    3,819
    Use four of the caps you have, connected as follows to make one non-polar cap assembly of .47uF. Be sure to connect + to + on the caps.

    image.jpg
     
    sohamkul likes this.
  7. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    1,145
    204
    (Below is incorrect as suggested)
    474 = 47 with 4 zeros pF or 47 000 e-12, or 47 nf (e-9) or 0.047 uF (e-6) not 0.47 uf

    0.47 uF is a little high for a ceramic cap. Polyester caps are non-polarized and have better tolerances.

    Edit:
    Thanks Guys. (Migraine): Corrected version.
    474 = 47 with 4 zeros pF or 470 000 e-12, or 470 nf (e-9) or 0.47 uF (e-6) or 0.47 uf
     
    Last edited: Sep 9, 2016
  8. hp1729

    Well-Known Member

    Nov 23, 2015
    1,954
    219
    Well 47 and 4 zeros is 0.47 uF alright (470 000 pF). Not unusual for a ceramic cap.
     
    KeepItSimpleStupid likes this.
  9. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,058
    3,819
    Wrong.
    A cap labeled 474 = 0.47uF (470 nF).

    470000 pF
     
    KeepItSimpleStupid likes this.
  10. OBW0549

    Well-Known Member

    Mar 2, 2015
    1,310
    885
    There is an error in the schematic in post #1: the inputs of U3 are reversed. As drawn, the circuit will not operate; rather, the positive feedback through R10 will force U3 to latch up, with its output stuck at either the positive or negative supply rail.
     
    GopherT likes this.
  11. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,058
    3,819
    OBW0549 likes this.
Loading...