Why are LED Lighting Capacitors So Famous Today

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LED Lighting is one of the most famous form of lighting today. The market for such products is large; Virtually any conventional lighting method can be replaced with an earth-friendly LED version. LED lights are an excellent source of lighting for the home due to their long lifespan and excellent energy efficiency.

LED lighting design components must be carefully selected to ensure they meet the lifespan and energy efficiency requirements of the final products. These can be demanding: LED lighting products can have a lifetime of over 40,000 hours, for example. Therefore, it is essential that all parts of the circuit can meet these requirements.

Ceramic capacitors in this type of circuit can be subjected to higher voltages and conditions than typically seen in appliance applications. These conditions can negatively affect the life of ceramic capacitors, which can mean that they fail before reaching the minimum life of the final product. This article explains the root of the problem and provides recommendations to ensure that ceramic capacitors do not cause problems over the life of LED lighting products.

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Typical conditions in LED circuits

A typical LED lighting circuit is shown in Figure 1. For C1, C2 and C3, safety recognized lightning capacitor rated at 250 Vrms a.c. C6 is a snubber capacitor for the diode; Parts rated to withstand 250V to 630V DC. They are required and may have X7R temperature characteristics. For C7, snubber capacitor for FET, rated voltage greater than 630 V at 1 kV DC. It is essential, and Murata recommends U2J type temperature compensated capacitors. C8 is the secondary circuit smoothing capacitor, any part rated for 100 volts should do the trick.
The circuit capacitors subjected to the harshest conditions are C4 and C5, which act as AC filter capacitors or noise filter capacitors for the primary circuit. Typical working voltage on these capacitors is the full wave rectified waveform shown in Figure 2. X7R capacitors rated at 250 VDC. They are often (wrongly) chosen for C4 and C5. The problem is that when such high dielectric constant capacitors are subjected to full wave rectified voltages, they succumb to the electrostatic effect, which can cause fatal cracks in the dielectric.

The electrical effect applies to all insulating materials. When an AC voltage is applied, the capacitor effectively expands and contracts in various dimensions, as shown in Figure 3. Mechanical distortion and stress concentration around the outer electrode edge of the capacitor. If the AC voltage is large and the material has sufficient dielectric properties, after a while cracks may form under the external electrode which can lead to catastrophic short-circuit failure of the component.

Reduction of the effect of piezoelectricity

There are several ways Murata mitigates electrical shock with a specially designed capacitor structure.

The first factor to consider is the thickness of the dielectric material between the internal electrodes of the capacitor. This has a direct effect on the magnitude of the electrical contraction phenomenon. When creating high voltage capacitors, it is necessary to ensure that the dielectric layer is thick enough to reduce the internal mechanical stress of the wafer capacitor.

Second, the structure of the internal electrodes can contribute to the electrostatic effect. A typical internal electrode structure is shown in Fig. 4(b). For comparison, Figure 4(a) shows one of several types of high-voltage Murata capacitors. The central region of this structure (highlighted in red in the figure) is inactive and therefore free from the effects of the electrospinning phenomenon. This is one of the many ways Murata can protect its capacitors from internal mechanical stress.

Also, the thickness of the outer layer of the dielectric (the “ghost” layer) can affect crack formation. This layer is where cracks usually start, so increasing its thickness, and therefore its mechanical strength, can help extend the life of these products.

Last but not least, the properties of the insulating material itself may play a role, as only materials with a high dielectric constant experience this effect. Murata carefully studies the properties of its materials to ensure that specific high voltage products are made with suitable insulating materials.

Factors

Taking all of these factors into account, Murata recommends GRM series parts for multilayer ceramic capacitors for C4 and C5 that can exceed the minimum required lifespan while subjected to the operating conditions described above (see Table 1 for part numbers). suggested piece). These parts have the X7R temperature characteristic and come in a range of values; 630V DC Rated parts come in capacities between 0.001 and 0.22 μF and 1 kV d.c. Nominal fractions range from 0.00047 to 0.1 μF.

Conclusion

In general, the conditions that ceramic capacitors experience in LED lighting circuits should not be underestimated. In Murata’s experience, the incorrect selection of capacitors can negatively affect the life of the final product due to the formation of cracks in the dielectric material of these capacitors. When designing this type of product, designers must ensure that they use properly rated ceramic chip capacitors with superior structure to mitigate the electrostatic effect described above.

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