Capacitor choice for 200KHz

[akis]

Re: Capacitor choice for 200KHz

I did not see the question in time, sorry it has been a while, this has been made in a PCB and works quite well with tiny changes needed to the PCB. Now designing version 2

[budm]

Re: Capacitor choice for 200KHz

You should put the Bias pot in series with the Bias diode, when you put it in parallel with the Diode, voltage across the Diode/pot combo will always be 0.6V because the diode will try to maintain Vf of 0.6, the diode will turn off when the pot value is set so low that it does not have 0.6V to turn on the diode any more. You may ending up with 1 or 2 diodes depend on how much the bias you want to get. I.E.

[PeteS in CA]

Re: Capacitor choice for 200KHz

FWIW, Wima's MKS4 series has a 22uF, 50VDC (30VAC) part that is 31.5mmL x 13mmW x 24mmH, with a 27.5mm lead spacing. It's metallized polyester film. I would be surprised if Roederstein and Evox-Rifa - one, the other, or both - do not have similar parts. Being European companies, they may be reasonably available to you in the UK.

As folks here can confirm, I take a jaundiced view of large form-factor SMT MLCCs. They are a necessary evil, IMO, and have to be used judiciously. First, do not use parts with temperature coefficients worse than X7R or X8R. Parts with worse tempcos vary extremely with temperature. Second and similar, if possible, use X7R (etc.) parts with voltage ratings 10X (or greater) the circuit DC voltage. While parts with horrible tempcos, such as Z5U and Y5V also have horrible voltage coefficients, that characteristic can also become relevant with X7R parts. Third, large form-factor SMT MLCCs are quite brittle. Soldering using two irons simultaneously is advisable (or preheat with a heat gun if you only have one soldering iron) to avoid mechanical stress due to uneven heating. Also, take care that the PCB is not flexed when mounted in whatever chassis you have.