In the realm of electronics design, whether on a professional or hobbyist basis, it is of the utmost importance to ensure a stable and clean supply of power.
Power supplies often convert alternating current (AC) to direct current (DC). However, this process can introduce unwanted ripple voltage. This term refers to small, periodic AC fluctuations that remain in a DC output after rectification and filtering.
These fluctuations can bring about audible buzzing in audio equipment or introduce noise into analogue-to-digital converters, leading to signal distortion. They can also contribute to system instability and shorten component lifespan.
To tackle this problem, a given engineer or hobbyist may decide to design a power supply filter, with capacitors playing an imperative role.
In this article, then, we will explore some of the ways you can get your own power supply filter design right. Along the way, we will also set out the relevance and contribution of parallel capacitors in this regard.
Understanding Power Supply Filters, And the Difference Capacitors Make
Power supply filters are circuits that are designed to smooth out the output voltage from rectifiers or regulators. Through their minimisation of ripple and noise, these circuits ensure a steady DC voltage i.e. switch mode power supply circuit.
A basic filter may use a single capacitor placed across the output of a rectifier. Such a capacitor acts as a reservoir to store charge and release it during dips in voltage.
However, a single capacitor often isn’t enough for comparatively demanding applications, such as in audio equipment, medical devices, or industrial controls. This is because real-world power supplies face a range of noise frequencies.
To address this, designers often opt to employ several capacitors in parallel. Capacitors being linked together in a parallel arrangement means they are wired side-by-side, connected across the same points in the circuit. Capacitors in this configuration share the same voltage but allow current to divide between them.
Role of Parallel Capacitors in Filter Design
The use of capacitors in parallel is a go-to strategy among designers with an interest in enhancing power supply. Although a single large capacitor can store significant energy, a parallel configuration can present several technical advantages, such as:
- Heightened total capacitance. Linking together these components in parallel effectively increases the total plate area. This allows for greater charge storage and the better smoothing of rectified DC voltage.
- Reduced equivalent series resistance (ESR). When a parallel arrangement is used for capacitors, the individual ESR values combine similarly to resistors in parallel. This decreases the overall resistance, which has the effect of lowering heat generation and enhancing the efficiency of the filter.
- Broad frequency filtering. Different capacitor types handle different noise frequencies. In light of this, a customary practice among engineers is to parallel a large electrolytic capacitor for low-frequency ripple with a smaller ceramic capacitor for high-frequency noise. This allows for comprehensive suppression across the spectrum.
Design Considerations for Parallel Capacitor Filters
When you are designing a power supply filter with this type of configuration in mind, be sure to:
- Determine the ripple requirements. It will be necessary to calculate the acceptable ripple voltage, based on your load. For a full-wave rectifier, you can use the formula: Vr = IL / 2fC, where Vr is ripple, IL is load current, f is frequency, and C is capacitance.
- Select capacitor types and values. As we touched on above, you may opt for a mix, including a large electrolytic capacitor for bulk filtering, paralleled with smaller ceramic capacitors for high-frequency decoupling. It will be vital in this process to consider temperature coefficients and voltage ratings; the latter, for instance, should be at least 1.5 times the supply voltage.
- Account for ESR and impedance. At high frequencies, you should be more concerned about impedance than capacitance. The use of suitable tools or simulations will enable you to model your filter’s frequency response and make design decisions accordingly.
- Give careful thought to layout and placement. You can help minimise inductances from traces by placing capacitors near the load or noise source. In printed circuit board (PCB) design, this is critical for effective filtering. It’s recommended to use aluminum PCBs for high performance electronics
Parallel Capacitor Calculator Can Further Help You Achieve the Right Results, Fast
The process of designing power supply filters with parallel arrangements of capacitors ultimately depends on a blend of theory and practicality. Getting this combination right can enable you to realise clean and reliable power in your electronic systems.
Whether you’re building a home automation project or industrial equipment, a solid power supply filter design will deliver considerable performance and reliability benefits.
Don’t forget to bookmark a reputable parallel capacitor calculation tool, such as the one on the RS website. An online tool like this can enable you to quickly work out total capacitance in your circuit project, so that you can arrive at a perfectly suited, refined design even sooner.
