profdc9 ud2.7c THT question

[costas_p]

Looking at the BoM of profdc9 for ud2.7c through hole design, it says to use ceramic disk caps.

Is there any problem to use polyester/polypropylene ones rather than ceramics?

I am not fond of ceramics, also the local electronic market ceramic caps range a lot in value (eg. bought 20 104 ceramic, and the values are ranging between 60 and 85 nF)

[Da_Stier]

I can't speak for the specific circuit you are building.
But in general, this way around is definately no problem, as long as the replacement has the same or better voltage, etc. (obviously).

The other way around (using ceramics as a replacement of other types) is often difficult, since ceramic capacitors have a huge dependency between capacity and voltage.
They also tend to be pretty microphonic which might be a problem in some cases.

So I'm pretty sure you will be fine.




Greetings,
Michael

[johnf]

I'm not familiar with the actual design but disc ceramics tend to have the best high frequency response (SRF) ie they have very little stray inductance
polypropylene / polyester caps tend to be of wrapped construction adding significant self inductance hence much lower high frequency SRF before turning into an inductor

[Mads Barnkob]

I have not yet had any problems using MKT/MKP only on DRSSTC drivers, instead of ceramic capacitors, on the through-hole drivers.

Remember that many hobby designs are not based on optimum choices, but rather what you have in stock already

[davekni]

Agree that ceramic caps generally have lower inductance (ESL), but film will likely work.  The key to choosing ceramic caps is the dielectric material.  Z5U and Y5V materials are worthless - huge capacitance loss with temperature and DC bias voltage.  X7R and X5R are much better with temperature, but often still suffer huge capacitance loss with DC bias voltage, sometimes down by 90% at full rated voltage.  Only way to tell is look for parts who's specifications include capacitance vs. voltage graphs or measure yourself.

NP0/C0G ceramic caps are close to ideal.  Insignificant change with temperature and with voltage.  Usually have +-5% tolerance too.  Down-side is high cost and larger size for large capacitances.  I personally use mostly NP0 (also called C0G) for values of 100nF (0.1uF) and below in spite of the cost.  For lower voltage and larger value bypass caps, I've found a few Murata 4.7uF 1206 X7R parts that are reasonable for <=25V (in spite of their 50 and 100V ratings):
    GRM31CR71H475KA12
    GRM31CC72A475ME11
    GRM31CZ72A475KE11
    GRM31CZ72A475ME11
    GRJ31CC72A475KE0
    GRJ31CC72A475ME0
    GRJ31CZ72A475KE01
    GRJ31CZ72A475ME01