MPK&CBB capacitance differentiation method

What are MPK & CBB capacitors? How should they be distinguished? In various circuits, different devices are used to play specific roles, and you are wandering in the selection of specific parameters of various components. Are you a little confused? This article will help you understand There are several aspects to help you distinguish between MPK & CBB capacitor selection.

Differences in performance

The main difference between safety capacitors and CBB22 capacitors is the outer packaging method. The box-type structure of safety capacitors has relatively better flame retardant performance and sealing performance, but now CBB22 is basically impregnated type, and its sealing problem is solved. Some manufacturers of the intrinsic electrical performance structure CBB22 series use aluminum films, and some use zinc-aluminum films. The electrical properties of capacitors produced using zinc-aluminum films are similar to those of safety regulations. It is characterized by its strong ability to withstand DC voltage. Aluminum film structure products are characterized by smaller losses than zinc-aluminum films and strong ability to withstand high-frequency AC voltage, but their DC voltage resistance is not as good as that of zinc-aluminum films.

The difference in usage is that CBB22 costs less than MKP. In many places (almost all places), its electrical performance can replace MKP as long as it meets the actual DC withstand voltage. If the output power of the upper and lower half-bridge circuit is 0.47UF, the power can be approximately considered to be 0 in the DC state.

Its AC power is very simple to calculate, P=U*U/XC=U*U/(1/2πfC)

In the formula, U is the effective value of the AC voltage, XC is the capacitive reactance, f is the frequency corresponding to the AC voltage U, and C is the capacity. As for the power that various capacitance capacitors can withstand, refer to the AC voltage and frequency in the figure below and calculate it according to the above formula.

Differences in use

MKP capacitors are mainly used for EMI incoming line filtering, and CBB capacitors are mainly used for oscillation, coupling, resistance-capacitance step-down and other circuits; CBB22 has a lower cost than MKP and can replace MKP in terms of electrical performance as long as it meets the actual DC withstand voltage. The nominal rated voltage of the MKP capacitor is 250/275VAC (x2), but its DC withstand voltage must reach 2000VDC2S; while the CBB22 capacitor voltage standard is only 1.6 times the rated voltage, etc.

frequency

Another problem is frequency. The MKP capacitor of the induction cooker is marked with a frequency (50KHZ). It is found that this capacitor is often used in the electromagnetic induction half-point bridge circuit. And the price is much more expensive than using CBB22, but the capacitance of using CBB22 is much larger than using the MKP capacitor 0.47UF. For example, if you use two MKP0.47 (50KHZ) at the top and bottom for 3000W power output, and you use two CBB22 (3.3UF each) at the top and bottom for 3000W, which of these two methods of use is reasonable?

The key to power output is determined by the AC voltage (mainly AC component), DC voltage, and frequency on the capacitor. The concepts of working power on the capacitor and load power cannot be confused, and one power cannot be generalized. Regarding the frequency issue, many signs are 50~60Hz, but they can also be used at 20~60KHz and some lines are higher. The difference lies in the AC voltage endured under different frequency conditions, which mainly depends on the power borne by the capacitor. Do not exceed standard value. If the power on the working capacitor (MKP61 and CBB22) is 3000W, the capacitor itself will heat up very much, and the iron capacitor (MKP61 and CBB22) will be damaged.

Differences in selection

When selecting and distinguishing CBB22 capacitors and MKP61 capacitors, attention should be paid to the thermal insulation performance of the capacitors. MKP61 and CBB22 capacitors use polypropylene film dielectric, which has less loss and low self-heating. In actual circuits, the temperature rise should not exceed 6°C. (higher than the ambient temperature). After actual testing, the temperature rise on many circuit boards is within 4°C. If the temperature rises above this condition, it indicates that the working power of the capacitor itself is too large, and both types of capacitors are more likely to fail.

Because the MKP61 capacitor uses flame-retardant shell and potting material, its thermal insulation and heat dissipation properties are better than CBB22. If the capacitor is located close to a power transistor or other heating components, it is safer to use MKP61. If it is far away from the heat source, use CBB22 more economics. Through experiments, it was found that the capacitor is close to the power transistor (the temperature on the heat sink exceeds 115°C after the transistor heats up), and the CBB22 capacitor is prone to failure, while the MKP61 is safer. When we increase the distance between the capacitor and the power transistor (heat source), there is no obvious difference between the CBB22 and MKP61 capacitances.

Formula explanation

P=U*U/XC=U*U/(1/2πfC)=U*U*2*π*f*C

U is the effective value of AC voltage, the unit is "volt";

XC is capacitive reactance in ohms;

The π value in 2πfC is 3.14; f is the frequency of the AC voltage and its unit is Hertz; C is the capacitance and its unit is Farad (pay attention to unit conversion when calculating).

Example calculation

VDE certification requires the MKP61-275VAC-105 (1μF) capacitor to withstand an AC withstand voltage of 1500V (50HZ) and its power calculation: P=1500×1500×2×3.14×50×1×0.000001=706.5 watts.

In a test, CBB22-400V-104 calculated its power under 40KHZ, 60VAC conditions: =60×60×2×3.14×40×1000×0.1×0.000001=90 watts

This article starts from several aspects to explain the differences and usage of CBB capacitors and MPK capacitors in some aspects, and provides formulas and example calculations to help everyone further understand the differences between these two capacitors. I believe that through the introduction of this article, friends who have a vague concept of the distinction between the two capacitors should be able to get a clear answer. The above is the method of distinguishing MPK & CBB capacitors. I hope it can help you.