I use the 0.12uF metallized polyester film capacitor Model ECQE2124JB which
has 250VDC rated voltage. I have a sine wave across the capacitor, then can I
think that the maximum AC voltage is 250/1.414=176.8 Vrms? But from the characteristic datasheet, the permissible voltage is less than 40Vrms at sinewave. What's the difference? If I use the capacitor in a LC resonant circuit, does it mean the RMS resonant voltage cannot exceed 40Vrms?
In my opinion, the permissible current is calculated as I = 2*pifC*V, for my application f = 10KHz, so I = 2*3.14*10kHz*0.12uF*250V=1.884Ap = 1.33Arms. Is it right? But from the characteristic datasheet, the permissible current is only about 0.2Arms. Why that?
In my LC resonant application, the mearsured current across the capacitor reaches 3.5Arms, but the peak voltage will not exceed 250VDC. It also conflicts with Vrms = Irms *Xc, where Xc is the impedance of the capacitor.
Electronic – how to understand the permissible voltage and current of film capacitor
capacitorcurrent-limitingvoltage
Related Solutions
I'm assuming we are talking in terms of DC here to keep things simple.
Voltage is a measure of how much a single electron's energy changes across the circuit. Current is how many electrons are flowing through a circuit. Multiply those two values to get the rate of energy transfer, or power. If all you have is a measure of current, you know how many electrons are flowing through the circuit, but not how much their energy is changing.
You are correct that voltage induces current, and that voltage and current are interrelated. Ohm's law is the simplest case of that. You can derive a circuit's power from current and it's resistance using known formulas. And even more simply, if you know current is flowing you know the circuit is dissipating power, even if you don't know how much (as the other commenters have said)
According to wikipedia the letter at the end of the resistor part number is its the MIL tolerance designation. Copied table below:
±5% J
±20% M
±10% K
±2% G
±1% F
±0.5% D
±0.25% C
±0.1% B
This page indicates that the letter is also the tolerance code for inductors.
Unfortunately I haven't got a clue what the extra L for capacitors is for (perhaps ask TI support?).
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Best Answer
Excess voltage will cause the capacitor to fail due to dielectric breakdown.
Excess current will cause the capacitor to fail due to overheating (because of the equivalent series resistance of the capacitor). Since an AC voltage implies an AC current as the capacitor charges and discharges, an AC voltage can lead to overheating failure at a lower voltage than the DC voltage that would cause dielectric breakdown.
So you have two different failure mechanisms, and you need to consider different limitations to avoid these two types of failure.