Connect with us

Electrolytic Capacitor Vs Ceramic Capacitor

Discussion in 'General Electronics Discussion' started by sabahan, Feb 29, 2016.

Scroll to continue with content
  1. sabahan

    sabahan

    31
    0
    Jul 14, 2013
    I build the circuit in the diagram that act as a time delay when the opamp which act as a comparator, when the condition is match, the opamp goes high which charge the capacitor instantly, when it goes low, the capacitor discharge through the resistor slowly, the signal is fed to another OpAmp, when I test the cirrcuit in the breadboard, I uses a aluminium electrolytic capacitor of 10uF, the time that it reaches the trigger point for next stage is about 10sec, but when I build the circuit on a PCB, I uses a ceramic multi layer capacitor with the same 10uF, but the time delay shorten to about 2 second, I wonder why this could happened, all the resistor value are the same on the breadboard and the PCB except that the bread board are using through hole resistor and capacitor and the PCB version are using surface mount capacitor,

    BTW the capacitor on the bread board are polarized and the PCB version are non polarized

    Will the surface mount version have a much lower actual capacitance value than the polarized version?
     

    Attached Files:

    Last edited by a moderator: Feb 29, 2016
  2. Colin Mitchell

    Colin Mitchell

    1,417
    313
    Aug 31, 2014
    Supply photo of 10u ceramic
     
  3. Harald Kapp

    Harald Kapp Moderator Moderator

    11,160
    2,548
    Nov 17, 2011
    Check the real capacitances of the capacitors in both circuits. Electrolytic capacitors often have -20%...+80% (!) tolerance. Ceramic capacitors often have a much lower capacitance than rated, especially when operated at >50% of the rated voltage.
    Also check the resistors used. A ratio of 10s/2s is not easily explained by capacitor tolerances alone.
     
  4. sabahan

    sabahan

    31
    0
    Jul 14, 2013
    all the resistor used are 1% tolerance metal film resistor, after solder on the resistor I have measure all the resistor and all are within tolerance, I have also check the ceramic capacitor value which is 9.8 uF, I than replace the smd capacitor with the through hole capacitor, it work as design, when I replace the capacitor with the ceramic capacitor, the time delay drop back to 2 second.
    The working voltage of the circuit is 12 V, which is way below the rated voltage of the ceramic capacitor which is 50V, can someone explain to me why this happened?

    The photo is the actual circuit on the pcb, I used a 16v 10uF capacitor for the small size, it actual is for a surface mount 1206 type capacitor of 10uF
     

    Attached Files:

    Last edited by a moderator: Feb 29, 2016
  5. dorke

    dorke

    2,342
    665
    Jun 20, 2015
    What is the input resistance of the next op. amp stage?
    Did you test it with both stages in the 2 cases- before and after PCB?
     
  6. sabahan

    sabahan

    31
    0
    Jul 14, 2013
    It fed to a input of a opamp which is at least 1Mohm
     
  7. sabahan

    sabahan

    31
    0
    Jul 14, 2013
    Now the problem is when I solder a electrolytic 10uF through hole capacitor on the pcb, the RC constant is larger, when I replace the electrolytic capacitor with a ceramic non polarized capacitor the RC constant shorten, the whole circuit parameter didn't change except the capacitor, why this happen?
    I have measure the ceramic capacitor before I solder it on, it reads 10.3uF
    The delay time shorten to a significant amount, about 30% of the electrolytic capacitor
     
    Last edited by a moderator: Feb 29, 2016
  8. Harald Kapp

    Harald Kapp Moderator Moderator

    11,160
    2,548
    Nov 17, 2011
    Did you also measure the electrolytic capacitor?
    Imho the only way the observed effect can happen is when the real life capacitances of the two capacitors are very different.
     
  9. sabahan

    sabahan

    31
    0
    Jul 14, 2013
    The tolerance of the electrolytic capacitor is +-20%, which means the largest value it can be is roughly 12uF, the discharge resistor is a 820K 1% metal film resistor, so the time constant on paper is 820000*0.00001, which give 8.2 second. If in the worst case, the capacitor is a 12uF, the time constant will be 9.84 second, and yes the delay time of the electrolytic cap is around 8 second, but why the ceramic cap time constant is around 2 second with a capacitance of 9.8 uF measured
     
    Last edited by a moderator: Feb 29, 2016
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-