0
\$\begingroup\$

I have a question about the need of the use of the X2 capacitor. I have a simple design which can be connected to AC line and I not use an X2 class capacitor but I m using an SMD capacitor from Murata (GA255DR7E2104MW01L) (size much more compact than THT X2 capacitor). However somedays, I discover that the SMD capacitor C1 is damaged (cc) which cause the damage of the two resistors (R1 and R2). For this circuit I use also a unidirectionnal TVS diode which is the P4SMA400A, to avoid overvoltage. So is there any need to use an X2 capacitor for my case? Otherwise what can be the real cause of the failure of this capacitor. I thank you for your help. enter image description here

Best regards

\$\endgroup\$
  • 1
    \$\begingroup\$ What is the purpose of your circuit? What are you trying to achieve? \$\endgroup\$ – Peter Karlsen Jul 5 at 8:01
  • \$\begingroup\$ @Peter Karlsen: It's a non isolated power supply \$\endgroup\$ – geek225 Jul 5 at 8:17
  • \$\begingroup\$ You should definitely use a safety capacitors rated for mains voltage (X2). By not using the right components you risk starting a fire. Be careful when playing with mains. It might kill you. \$\endgroup\$ – Peter Karlsen Jul 5 at 9:33
  • 1
    \$\begingroup\$ The capacitor you are using is rated to 250V. What is the voltage across it in the circuit. Usually a capacitor breaks at over voltage. \$\endgroup\$ – Peter Karlsen Jul 5 at 10:16
  • 1
    \$\begingroup\$ Please don't shout. \$\endgroup\$ – Hearth Jul 5 at 11:28
1
\$\begingroup\$

Considering you are applying a low loss 2k source R to a 50k Load with a nominal input of 339Vp to a 250V 0.1uF ceramic cap, it is no wonder that it failed. The only choice here is an X2 rated film cap which attenuates 1kV To 3kV lightning transients as per your unstated CE requirements.

Start with worst case power & transient specs, then your choices become clear using your regional power standards.

\$\endgroup\$
  • 1
    \$\begingroup\$ Don’t use SMD since the Dk is far less than ceramic. you can also use much lower C values with a line filter type toroidal choke. Look up line Pi filter after you define safety standard and transient attenuation for Vimpulse. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 5 at 12:08
  • 1
    \$\begingroup\$ Keep looking as I suggested. Leaded film cap or Pi CLC line filter but do what I asked 1st. define specs.. Your homework.! \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 5 at 12:19
  • 1
    \$\begingroup\$ who knows what line tolerances you have , enclosure temp rise and Arrhenius Law reduction on MTBF. caps have short finite lifespan at rated temps from which You can extrapolate based on specs for actual vs expected and temp rise. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 5 at 12:27
  • 1
    \$\begingroup\$ No the Line filter replaces the 1k R’s and 0.1uF with a LPF using chokes and smaller C. where are your specs? \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 5 at 12:47
  • 1
    \$\begingroup\$ All PC PSU’s (SMPS) use them before the bridge diodes. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 8 at 0:00

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.