how define the ESR in Capacitors

2024-08-07

ESR stands for Equivalent Series Resistance. It is a measure of the effective resistance that appears in series with an ideal component, such as a capacitor, inductor, or sometimes even a resistor or semiconductor device.

Here's a breakdown of ESR in different contexts:

Capacitors: In capacitors, ESR refers to the resistance that exists in series with the capacitance. This resistance is due to the internal construction of the capacitor, including the resistance of the conductive plates, leads, and the electrolyte in the case of electrolytic capacitors. ESR affects the capacitor's efficiency, frequency response, and stability.

Inductors: ESR in inductors is the resistance associated with the wire windings and core losses. It affects the Q factor (quality factor) of the inductor, which determines its efficiency in storing and releasing energy. High ESR in inductors can lead to greater power dissipation and reduced performance in high-frequency applications.

Resistors: Although resistors are defined by their resistance value, they also have ESR, which accounts for any non-ideal characteristics such as temperature coefficient and parasitic inductance or capacitance. In precision applications, minimizing ESR is important to maintain accuracy and stability.

Semiconductors: ESR can be relevant in semiconductor devices like diodes and transistors, where it represents the parasitic resistance in their internal structures. It affects power dissipation, voltage drop, and switching characteristics.

Circuit Analysis: ESR is crucial in circuit analysis, especially in power supply filtering, decoupling capacitors, and high-frequency circuits. It impacts the overall performance, efficiency, and stability of electronic systems.

ESR is important in ceramic capacitors:

1. Losses and Efficiency: ESR causes power dissipation in the capacitor due to resistive losses. In applications where efficiency is critical, such as in power supply filtering or high-frequency circuits, lower ESR is preferred to minimize these losses.

2. Frequency Response: ESR affects the frequency response of the capacitor. At higher frequencies, the ESR can significantly impact the performance of the capacitor, especially in circuits requiring stable capacitance over a wide frequency range.

3. Stability and Performance: ESR influences the stability and performance of circuits, particularly in applications involving decoupling and filtering. Lower ESR capacitors help maintain stable voltage levels and reduce noise in power supply lines.

4. Capacitor Selection: When selecting ceramic capacitors for a specific application, engineers often consider the ESR along with other parameters like capacitance, voltage rating, and temperature stability. Different ceramic capacitor types (e.g., X7R, Y5V) have different ESR characteristics which must be matched to the application requirements.

5. Temperature Dependence: ESR can vary with temperature. Ceramic capacitors typically have a more stable ESR compared to electrolytic capacitors, but this parameter can still change with temperature variations, affecting circuit performance.

6. Impedance Matching: In RF and high-frequency circuits, matching the ESR of capacitors to the characteristic impedance of the circuit is crucial for minimizing reflections and optimizing signal integrity.

Overall, understanding the ESR of ceramic capacitors helps engineers design circuits with better performance, efficiency, and stability across various applications. Different types of ceramic capacitors (such as NP0/C0G, X7R, Y5V) offer different trade-offs in terms of ESR along with their other electrical characteristics.

ESR in Aluminum Electrolytic Capacitors

For medium and high voltage applications, low loss aluminum electrolytic capacitors are required. Low ESR capacitors have fewer power losses and internal heating problems as compared to high ESR capacitors. Apart from lowering performance, high ESR values reduce the life of an aluminum electrolytic capacitor. In addition, a low ESR value allows a greater ripple current capacity to be achieved.

In an aluminum electrolytic capacitor, the aluminum anode, cathode foils, electrolyte, and tabs contribute to the overall ESR of the capacitor. The value of resistance from each source mainly depends on frequency and temperature. At low frequencies and low temperatures, the aluminum oxide makes the largest contribution to the overall ESR. On the other hand, at high frequencies and high temperatures, the largest contribution to the overall ESR comes from the electrolyte. Generally, under application conditions, paper combinations and the electrolyte are the primary sources of equivalent series resistance in these capacitors.

Polymer and hybrid (combining polymer and wet electrolyte) electrodes with significantly lower and more stable ESR are available on the market as well, that address most of the disadvantages of the wet electrolytic capacitors reducing the ohmic losses, dry out effect (reliability and stability improvement) and ESR temperature dependency.

The ESR value of an aluminum electrolytic capacitor is dependent on the thickness and density of paper separators. To minimize equivalent series resistance, thicker and denser separators are not recommended. Use of many tabs and high conductivity electrolyte material helps to reduce ESR in aluminum electrolytic capacitors. The tab connections, foils, and paper separators can be tailored to produce a specific resistance contribution to the overall equivalent series resistance.

ESR with frequency capacitor technologies comparison

Comparison of different capacitor technologies 220uF 6.3V ESR with frequency

ESR is used to characterize capacitors losses mainly in the higher frequency domain with standard reference frequency at 100kHz. ESR with a frequency chart is illustrating losses in the entire frequency spectrum. As discussed above, the low-frequency losses below around 1kHz are driven by “slower” polarization and losses in dielectric layers, mid frequencies (~ 1kHz to 10kHz) are driven by internal construction losses (such as conductivity of internal structure and electrolyte), the high frequencies >100kHz are driven by mostly ohmic losses of terminations, contacts, etc.

Referring to MLCC capacitors are exhibiting lowest ESR values compare to other technologies referred to a standard specification frequency 100kHz thanks to its multilayer structure. This is beneficial for smoothing of higher frequencies and fast spikes for applications such as switching power supplies. However, at low frequencies, MLCC class II capacitors are featuring higher ESR(and DF) compare to other technologies. it is more efficient to use the MLCCs in parallel with some aluminum or tantalum electrolytic capacitors.

Reducing ESR is often desirable in electronic design to improve performance and efficiency, especially in circuits where high reliability and low power loss are critical. Different types of components have different methods for measuring and minimizing ESR, depending on their construction and intended application.

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