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Wondering why you would choose to use smaller capacitors in parallel vs one bigger one. Here's an example:

Multiple in Parallel

Page 4: One larger C

Is this a component size and track width choice? Thanks!

jgaro
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  • This is speculation on my part, but perhaps reliability could also play a factor. It depends on the failure mode of the cap, but perhaps if one one of three capacitors fails as an effective open circuit, the remaining two of three capacitors could function acceptably, if not necessarily idealy. – Dan Jun 07 '16 at 23:12
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    Dave Jones did an entire program on this exact question: https://www.eevblog.com/2015/05/09/eevblog-742-why-electrolytic-capacitors-are-connected-in-parallel/ – Richard Crowley Jun 08 '16 at 01:55

2 Answers2

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A couple reasons come to mind.

  1. Lower ESR. The effective ESR of the capacitors follows the parallel resistor rule. For example, if one capacitor's ESR is 1 Ohm, putting ten in parallel makes the effective ESR of the capacitor bank ten times smaller. This is especially helpful if you expect a high ripple current on the capacitors.

  2. Cost saving. Let's say you need a large amount of capacitance. A single large capacitor might be more expensive than several smalls ones that add up to the same amount.

  3. Filtering. Capacitors of different values have different impedance characteristics as a function of frequency. If you're trying to filter out a range of frequencies (noise, EMI, etc), it's helpful to put a range of different capacitors next to each other to present low impedance to as much undesirable frequencies as possible.

  4. Stock availability. Distributors don't carry every possible value of capacitance. You may need to combine multiple caps that add up to a specific capacitance you need.

  5. Board Layout. The physical constraints of the PCB or enclosure may allow multiple small parts to fit where a single large part will not.

Dan Laks
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  • Since this appears to be a direct replacement of one 10uF cap with seven 10uF parallel caps, I would have to imagine 2, 3, and 4 are ruled out here. – jgaro Jun 07 '16 at 23:19
  • Board Layout. The physical constraints of the PCB or enclosure may allow multiple small parts to fit where a single large part will not. (also ruled out if replacing one 10uF with seven).
    • – Mark Jun 07 '16 at 23:46
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  • Packaging Style. A design may require something like a 120 uF cap but the design must be done with all very low profile SMT components. (Try to find an SMT multilayer ceramic cap of 120 uF for any reasonable price; if at all).
    • – Michael Karas Jun 08 '16 at 03:07