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I need to replace a popped capacitor. Externally, it looks almost like

enter image description here (source)

except for the first letter: in my case it is R and not B.

It is in the power supply board of a TV. I would like to replace it with an equivalent one, or even with a stronger one (with the same features, but better materials), to avoid this problem to reappear.

  • Is there a difference between B 221K 1KV in the photo and my R 221K 1KV?
  • May these alternative 1 and alternative 2 be equivalent to R 221K 1KV for my purposes? Why?

As far as I know, they differ at least in the ceramic insulator, being X5F in alternative 1, and Y5P in alternative 2.

According to the Capacitor Letter Codes Table in this page, the 221K mark could refer to a 220 pF capacitace.


Edit

I am sure it is a capacitor and not an MOV because the electrical symbol of a capacitor is printed on the PCB, referred to this component.

Before thinking about modifying the circuit with a line filter, I would like to find a suitable capacitor, which is electrically equivalent to the original one.

This product suggested in the comments has a different capacitance value. In the same site, I found instead:

Both of them are 220 pF. After a first look at the datasheet, they seem to differ only as regards the external dimensions.

My question is still: from the PCB electrical perspective, given the original one marked as R 221K 1KV, are they able to replace it? Why?

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  • \$\begingroup\$ The colour often indicates material ESR & temp stability qualities of ceramic inside so C0G is best for ceramic digikey.ca/products/en/capacitors/ceramic-capacitors/… \$\endgroup\$ Jan 10, 2020 at 19:55
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    \$\begingroup\$ the colour is not consistent among suppliers so that is meaningless but if you cannot recognize burnt part , how certain that it is a cap and not an MOV. If line voltage induced, you may want to consider a line filter. and/or surge protector. \$\endgroup\$ Jan 10, 2020 at 20:02
  • \$\begingroup\$ @TonyStewartSunnyskyguyEE75 Thanks for the suggestions. I edited my question to reply to your comments. \$\endgroup\$
    – BowPark
    Jan 11, 2020 at 16:37

1 Answer 1

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Any cap might replace this one rated for 1kV 100 220 pF but NP0/C0G are best for ESR and temp stability. However, I would have chosen 3kV.

  • It takes a poor design, unusual conditions or a defective kV rated part to blow a 100pF cap which cannot store much energy (50 uJ) due to small capacitance. Possibly a secondary failure next to another.

    • Normally line filters should attenuate peak voltage surges.
  • Where used, may be important to know but for AC power maybe not.

    • If used with SMPS possibly for PFC compensation filter at 1.4 * line Vrms. .
  • To improve reliability, choose a cap with 3kV rating which is more standard for consumer grid impulse protection, but in truth , Power meters have only arc gaps rated for 6kV and external lightning protection is above this. This ionization takes a 1us or so to trigger.

Opinion

This means all the electronics in Florida will fail unless that device has a good line filter to reduce peak voltage below cap ratings. Or it means this why why Floridians and Mariners unplug their sensitive electronics before a lightning storm when they should be getting better line filters and OVP. (next to central Africa, Florida has one of the highest lightning strokes / year.)

enter image description here

This is a much better part but expensive, which is why it was not used.($1 /10k)

The part see rapid discharges and is used as an EMI snubber so is under very high stress as I expected.

So choose 220 pF 3kV (low ESR)

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    \$\begingroup\$ Thanks. A clarification: my capacitor is 220 pF, not 100 pF. I think it may have been damaged for both a poor design or some unusual voltage spike. Yes, it is used in an SMPS: it connects pins S/OCP and DRAIN of IC STR W6052S. It may be AC, even if I am not 100 % sure about this. If I correctly understood, even choosing a 3 kV rating, there is still a risk for lightning damage (without an external protection like a line filter or ... a disconnected device like in Florida). \$\endgroup\$
    – BowPark
    Jan 11, 2020 at 18:05
  • \$\begingroup\$ As I recall some Co's use this color for NP0/C0G, but the 3kV rating also improves ESR. \$\endgroup\$ Jan 11, 2020 at 19:28
  • \$\begingroup\$ Thanks for even adding the IC scheme and some considerations. This all makes more sense now. And if the ESR is low, the transient power is more about Rocp than on the ESR. Just out of curiosity: where/what is this Rocp? And, you said in the comment above: «some Co's use this color for NP0/C0G», but I'm not sure about what color you are referring to. \$\endgroup\$
    – BowPark
    Jan 13, 2020 at 15:30
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    \$\begingroup\$ Rs.ocp connects S/OCP & GND .. turqoise blue = low ESR? or coincidence \$\endgroup\$ Jan 13, 2020 at 15:32
  • \$\begingroup\$ Ok, got it! About turquoise, I am not sure, but I guess the image in my question is related to a very cheap capacitor (not NP0/C0G), so it could be just a coincidence. \$\endgroup\$
    – BowPark
    Jan 13, 2020 at 15:36

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