New material ceramic capacitors and applications on LED bulbs

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[Content Guide] In recent years, as the demand for electronic devices has evolved beyond just being compact, energy-efficient, and quiet, there's now a growing need to meet ecological standards in order to combat global warming. This shift has made LED bulbs, which became popular since 2009, even more appealing due to their slim design and long lifespan, making them highly eco-friendly. As a result, the components used in these devices also need to be smaller, thinner, and more durable.

LED bulbs typically use small power supplies of around 10W, often relying on electrolytic and film capacitors for smooth operation. However, ceramic capacitors are becoming increasingly popular due to their compact size and extended life. These new ceramic capacitors offer higher capacitance compared to traditional materials, and this article will explore their unique characteristics and how they can be applied in various power supply circuits, especially in LED-based systems.

Advancements in New Material Ceramic Capacitors

Compared to conventional ceramics, the new material has a Curie point shifted to a lower temperature, allowing it to remain in a paraelectric phase at room temperature (25°C). This change results in several performance improvements over traditional products:

The reduction in capacitance when DC voltage is applied is significantly lower, ensuring a high effective capacitance value. For example, under DC600V, the capacitance is twice that of conventional materials. This makes them ideal for applications where stable and high-capacity performance is critical.

The new material also exhibits low loss and can handle large ripple currents. At a frequency of 250 kHz, it can tolerate approximately 1.6 times the current compared to traditional capacitors. Murata’s standard allows for a self-heating temperature of up to 20°C at ambient temperatures below 25°C. For a 1µF product, the allowable RMS current is 4.7A, which is significantly higher than the 2.9A of traditional materials.

When DC voltage is applied, the mechanical strain is minimal, resulting in reduced noise levels. The sound pressure level of the new material is only one-fifth of that of conventional capacitors. Additionally, its piezoelectric effect is much lower, reducing the likelihood of mechanical vibrations caused by electrical signal changes.

A reduction of 6 dB in sound pressure means the noise is halved. The new material's sound pressure level is 15 dB lower than that of conventional capacitors, meaning the noise is only 1/5 as loud.

Product Overview and Circuit Applications

In October 2010, the commercialization of new material capacitors was completed, as shown in Figure 5. Two stacked capacitor products have been introduced, offering different ratings. For DC250V, the maximum capacitance is 2µF (1µF × 2), while for DC450V, it is 1.1µF (0.56µF × 2), and for DC630V, it is 0.54µF (0.27µF × 2). The temperature characteristic of the new material is X7T, compared to X7R for conventional materials.

The general power circuit diagram for an LED bulb is shown in Figure 6.

As summarized, the key benefits of the new material include:

1. Higher effective capacitance than traditional products.
2. Ability to handle larger ripple currents and higher power.

These features make them suitable not only for smoothing functions but also for noise suppression. For instance, in the Japanese market, when the input voltage is AC100V, the peak-to-peak voltage of the rectifier circuit is 140V, so a 2µF capacitor rated at DC250V is ideal. For global markets with AC240V input, the peak-to-peak voltage is 340V, and a DC450V-rated capacitor with 1.1µF is appropriate. For DC630V, a 0.54µF capacitor would be the best choice.

In addition to LED bulbs, PFC (Power Factor Correction) circuits are often added after the rectifier to improve harmonics and power factor. The new material’s low loss and high ripple current tolerance make it an excellent choice for PFC input capacitors.

Other capacitors, such as C1 and C2, can also benefit from using these advanced ceramic capacitors. The following figure illustrates some examples.

These new ceramic capacitors have been developed with a focus on low loss and high capacity. Beyond noise suppression, they are particularly well-suited for smoothing applications. In the future, we plan to provide more technical data and support to help you make the most of these advanced components.