"non-polar" capacitor?

Jim Brain brain at jbrain.com
Mon Aug 1 02:30:24 CDT 2016

On 7/31/2016 12:37 AM, Ian McLaughlin wrote:
> Jim,
> These are non-polarized (or bi-polar) electrolytics.  An example is the following digikey part number: 493-12697-3-ND
> You can always whip one up out of your junk box - just put 2 normal (polarized) electrolytic in series with the polarities alternating (for example, connect the two positives together).  Each capacitor has to be twice the value of the result - so for example, to replace a 1uF 50v non-polarized, you can put two 2uF in series.
> Hope this helps.
> Ian
Thank you (and Chuck) for the response.

I guess it brings up more questions for me:

  * Why would Tandy spec such a cap in the design?
  * As I look at the specifications of the design, it looks like the
    rest of the design assume mac .250W of power on the audio line
    (given the selection of resistor networks and other parts) .  I
    noticed the Digikey unit you referenced has 17mA of ripple current
    capability.  I realize audio is not truly a ripple current, but the
    disparity between 17mA and 250mW seems like a problem... (Again, my
    analog is severely rusty, so maybe I am looking at this wrong.  I
    spent all night trying to find a way to determine the power of a R2R
    ladder given 5V logic and 8mA output drive of the 74ls374 IC, to no
    avail, so maybe I am looking at this wrong)
      o you'd think with the prevalence of R2R ladder logic, someone
        would have whipped up a power calculator, if nothing else, to
        determine the wattage of the resistors in the R2R, but I came up
        empty... I'll have to either calculate it longhand by summing
        all of the currents or sim it; not sure I can assume that since
        the effective impedence is 10K, the amperage would be .5mA @ 5V
        and thus the power would be 2.5mW

Sometimes, I wish I'd cared more about analog in college...


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