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LED electronic display capacitance related knowledge
LED electronic display capacitors come in a variety of sizes, voltage ratings and other characteristics to meet the specific requirements of different applications. Common dielectric materials include oil, paper, glass, air, mica, polymeric films, and metal oxides. Each dielectric has specific properties that determine its suitability for a particular application. Here are a few of the commonly used ones.
Voltage-controlled oscillators (VCOs), phase-locked loops (PLLs), RF power amplifiers (PAs), and other analog circuits are very sensitive to noise on the supply rails. In VCOs and PLLs, such noise appears as phase noise; in RFPA, it appears as amplitude modulation; in ultrasound, CT scans, and other applications that process low-level analog signals, it appears as display artifacts. Although ceramic capacitors have the above drawbacks, they are used in almost every electronic device because of their small size and low cost. However, when regulators are used in noise-sensitive applications, designers must carefully evaluate these side effects.
Multi-layer ceramic capacitors (MLCC) are not only small in size, but also combine the characteristics of the LED large-screen temperature range. It can be said that the bypass capacitor is the choice. However, such capacitors are not perfect. Depending on the dielectric material, the capacitance value changes dynamically with temperature, DC bias, and AC signal voltage. In addition, the piezoelectric properties of the dielectric material can convert vibration or mechanical shock into an alternating noise voltage. In most cases, such noise is often measured in microvolts, but in extreme cases, mechanical forces can produce millivolt-level noise.
Solid tantalum capacitors are relatively less sensitive to temperature, bias, and vibration effects than ceramic capacitors. A new type of solid tantalum capacitor uses a conductive polymer electrolyte instead of the common manganese dioxide electrolyte, which has improved surge current capability and does not require current limiting resistors. Another benefit of this technology is the lower ESR. The capacitance of the solid tantalum capacitor can be stabilized with respect to temperature and bias voltage, so the selection criteria only include tolerances, buck conditions over the operating temperature range, and maximum ESR.
A disadvantage of solid polymer electrolyte technology is that such tantalum capacitors are more sensitive to high temperatures during lead-free soldering, so manufacturers typically specify that the capacitor should not be soldered for more than 3 solder cycles. Neglecting this requirement during assembly can lead to long-term stability problems.