Mylar Capacitor: Its Unique Performance Explained

Introduction to Mylar Capacitors and Their Performance

Mylar capacitors, also known as polyester film capacitors, are a type of capacitor that utilizes thin layers of Mylar (polyethylene terephthalate) as the dielectric material between the conductive plates. These capacitors have gained popularity due to their unique performance characteristics, which make them suitable for a wide range of applications in electronics and electrical systems.

In this article, we will delve into the details of Mylar capacitor performance, exploring their key features, advantages, and applications. We will also compare Mylar capacitors with other types of capacitors and provide insights into their selection and usage.

Understanding the Construction and Working Principle of Mylar Capacitors

Construction of Mylar Capacitors

Mylar capacitors are constructed using thin films of Mylar as the dielectric material. The Mylar film is sandwiched between two conductive plates, typically made of aluminum or metallized Mylar. The plates are wound together in a cylindrical or oval shape, forming a compact and stable capacitor.

The thickness of the Mylar film used in these capacitors typically ranges from 0.9 to 100 microns. The thinner the film, the higher the capacitance per unit volume, allowing for smaller capacitor sizes.

Working Principle of Mylar Capacitors

Mylar capacitors work on the same basic principle as other capacitors. When a voltage is applied across the conductive plates, an electric field is created in the Mylar dielectric. This electric field causes the dielectric to polarize, storing electrical energy in the form of an electrostatic field.

The amount of energy stored in a Mylar capacitor is proportional to the applied voltage and the capacitance of the capacitor. The capacitance, in turn, depends on the surface area of the conductive plates, the thickness of the Mylar dielectric, and the dielectric constant of Mylar.

Key Performance Characteristics of Mylar Capacitors

Dielectric Constant and Dielectric Strength

Mylar has a relatively high dielectric constant compared to other common dielectric materials used in capacitors. The dielectric constant of Mylar ranges from 3.0 to 3.25, which allows for higher capacitance values in smaller package sizes.

Moreover, Mylar exhibits a high dielectric strength, typically around 580 V/μm. This means that Mylar capacitors can withstand high voltages without experiencing dielectric breakdown, making them suitable for high-voltage applications.

Capacitance Stability and Temperature Coefficient

One of the notable advantages of Mylar capacitors is their excellent capacitance stability over a wide range of temperatures. The temperature coefficient of capacitance (TCC) for Mylar capacitors is relatively low, typically ranging from -5% to +5% over a temperature range of -55°C to +125°C.

This stability in capacitance ensures consistent performance across varying operating conditions, making Mylar capacitors a reliable choice for temperature-sensitive applications.

Dissipation Factor and Equivalent Series Resistance (ESR)

Mylar capacitors exhibit low dissipation factors, typically in the range of 0.1% to 0.5% at 1 kHz. The dissipation factor represents the energy loss in the capacitor due to dielectric absorption and leakage currents. A lower dissipation factor indicates higher efficiency and lower power loss.

Additionally, Mylar capacitors have low equivalent series resistance (ESR), which contributes to their excellent high-frequency performance. Low ESR allows for faster charging and discharging cycles, making Mylar capacitors suitable for high-frequency applications.

Frequency Response and Self-Resonant Frequency

Mylar capacitors exhibit excellent frequency response characteristics. They maintain stable capacitance values over a wide frequency range, typically from a few Hz to several hundred kHz. This flat frequency response makes them suitable for audio and signal processing applications.

Furthermore, Mylar capacitors have a relatively high self-resonant frequency (SRF) compared to other types of capacitors. The SRF is the frequency at which the capacitor’s inductive reactance becomes equal to its capacitive reactance, resulting in a resonance peak. A higher SRF allows Mylar capacitors to be used effectively in high-frequency circuits without experiencing significant performance degradation.

Insulation Resistance and Leakage Current

Mylar capacitors offer high insulation resistance, typically in the range of 10^6 to 10^7 megohms. This high insulation resistance minimizes leakage currents, which are the small currents that flow through the dielectric when a voltage is applied.

Low leakage currents are essential for maintaining the charge stored in the capacitor and preventing unwanted discharge. Mylar capacitors’ excellent insulation resistance ensures stable and reliable performance over time.

Comparison with Other Types of Capacitors

Mylar vs. Ceramic Capacitors

Ceramic capacitors are another popular type of capacitor known for their high capacitance density and low cost. However, compared to Mylar capacitors, ceramic capacitors have some limitations:

• Ceramic capacitors have a higher temperature coefficient of capacitance, which means their capacitance can vary significantly with changes in temperature.
• They are more prone to microphonic effects, where mechanical vibrations can cause changes in capacitance.
• Ceramic capacitors have lower voltage ratings compared to Mylar capacitors.

Mylar capacitors offer better temperature stability, lower microphonic sensitivity, and higher voltage ratings, making them a preferred choice in certain applications.

Mylar vs. Polypropylene Capacitors

Polypropylene capacitors are known for their low dissipation factor and excellent high-frequency performance. Compared to Mylar capacitors:

• Polypropylene capacitors have a lower dielectric constant, resulting in larger capacitor sizes for the same capacitance value.
• They have a slightly better temperature coefficient of capacitance and lower dissipation factor.
• Polypropylene capacitors are more expensive than Mylar capacitors.

While polypropylene capacitors offer some performance advantages, Mylar capacitors provide a good balance of performance and cost-effectiveness.

Mylar vs. Tantalum Capacitors

Tantalum capacitors are known for their high capacitance density and low ESR. However, compared to Mylar capacitors:

• Tantalum capacitors have a higher leakage current and are more prone to failure if exposed to voltage spikes or reverse polarity.
• They have a higher temperature coefficient of capacitance and are more sensitive to temperature changes.
• Tantalum capacitors are typically more expensive than Mylar capacitors.

Mylar capacitors offer better stability, reliability, and cost-effectiveness compared to tantalum capacitors in many applications.

Applications of Mylar Capacitors

Audio and Signal Processing

Mylar capacitors are widely used in audio and signal processing applications due to their excellent frequency response and low distortion characteristics. They are commonly found in:

• Audio coupling and decoupling circuits
• Filters and crossover networks
• Tone control circuits
• Microphone and preamp circuits

Power Supply Filtering and Decoupling

Mylar capacitors are used in power supply filtering and decoupling applications to reduce noise and ripple voltages. They help to smooth out the DC voltage and prevent high-frequency noise from propagating to other parts of the circuit.

Timing and Control Circuits

Mylar capacitors are used in timing and control circuits, such as oscillators, timers, and Pulse Generators. Their stable capacitance and low leakage current ensure accurate and consistent timing performance.

Motor Run and Start Capacitors

Mylar capacitors are used as motor run and start capacitors in various electrical motors, including AC motors and compressors. They help to improve motor starting torque and efficiency by providing a phase shift between the main and auxiliary windings.

High-Voltage Applications

Due to their high dielectric strength and voltage rating, Mylar capacitors are suitable for high-voltage applications, such as:

• Voltage multipliers
• Pulse forming networks
• X-ray and laser equipment
• High-voltage power supplies

Selecting the Right Mylar Capacitor

When selecting a Mylar capacitor for a specific application, several factors should be considered:

1. Capacitance Value: Choose the appropriate capacitance value based on the circuit requirements and the desired frequency response.

2. Voltage Rating: Ensure that the voltage rating of the capacitor is sufficient to withstand the maximum voltage expected in the circuit, including any transient spikes.

3. Temperature Range: Consider the operating temperature range of the application and choose a Mylar capacitor with a suitable temperature coefficient of capacitance.

4. Tolerance: Select a capacitor with an appropriate tolerance based on the circuit’s sensitivity to capacitance variations.

5. Packaging and Mounting: Consider the physical size and mounting requirements of the capacitor, such as radial or axial leads, surface mount, or through-hole mounting.

6. Quality and Reliability: Choose Mylar capacitors from reputable manufacturers who follow strict quality control processes and provide reliable performance data.

Frequently Asked Questions (FAQ)

1. What is the main advantage of Mylar capacitors over other types of capacitors?

Mylar capacitors offer a combination of high dielectric strength, excellent temperature stability, low dissipation factor, and good high-frequency performance, making them suitable for a wide range of applications.

1. Can Mylar capacitors be used in high-voltage applications?

Yes, Mylar capacitors have a high dielectric strength and can withstand high voltages, making them suitable for high-voltage applications such as voltage multipliers and pulse forming networks.

1. How does the temperature affect the performance of Mylar capacitors?

Mylar capacitors have a relatively low temperature coefficient of capacitance, typically ranging from -5% to +5% over a temperature range of -55°C to +125°C. This means their capacitance remains stable across a wide temperature range, ensuring consistent performance.

1. Are Mylar capacitors polarized or non-polarized?

Mylar capacitors are non-polarized, meaning they can be connected in either direction in a circuit without affecting their performance or causing damage.

1. What are the typical applications of Mylar capacitors?

Mylar capacitors are commonly used in audio and signal processing circuits, power supply filtering and decoupling, timing and control circuits, motor run and start applications, and high-voltage systems.

Conclusion

Mylar capacitors offer a unique combination of performance characteristics that make them a versatile choice for various electronic and electrical applications. Their high dielectric constant, excellent temperature stability, low dissipation factor, and good high-frequency response set them apart from other types of capacitors.

By understanding the construction, working principle, and key performance parameters of Mylar capacitors, engineers and designers can make informed decisions when selecting the appropriate capacitor for their specific application requirements.

When choosing Mylar capacitors, it is essential to consider factors such as capacitance value, voltage rating, temperature range, tolerance, packaging, and reliability. By carefully evaluating these factors and selecting capacitors from reputable manufacturers, designers can ensure optimal performance and reliability in their circuits.

As technology continues to advance, Mylar capacitors are likely to play a crucial role in supporting the development of new electronic devices and systems. Their unique performance characteristics, combined with ongoing research and improvements in materials and manufacturing processes, make them a promising choice for future applications.