LC ValuesĬhoosing the value of the inductor and capacitor seems to be a simple process. If it’s hard to achieve, consider using two capacitors in parallel for a lower combined ESR and ESL value. To suppress high-frequency noise efficiently, you’ll want to opt for a capacitor with low ESR and ESL value. Adding an LC filter at the input results in greater suppression. While there’s nothing wrong with that placement, you can achieve better noise reduction by placing the LC filter at the input if you’re using a buck regulator.įor buck regulators, most of the noise stems from switching transition at the input. Naturally, you’ll think of placing the LC filter between the output of the regulator and the load. Here are some tips for proper implementation: Positioning Therefore, you’ll want to ensure that the power supply is designed with an LC low pass filter. Unlike a badly-made cup of coffee, the implications of power supply noise disrupting systems in the field are much larger. You can’t predict how and when it will affect the circuit. Take my word that power supply noise is annoyingly disruptive. Even if the circuit could tolerate the AC noise, it can still be radiated as EMI and affect other electronic products. In one study, it was found that power supply noise reduces the clock frequency of a high-speed microprocessor by 6.7%. Power supply noise doesn’t only affect analog parts. The accuracy of these modules can be compromised, and in some instances, the components may fail to function correctly. Modules like ADC, DAC, and Op-amps are particularly sensitive to AC noise on the power supply. Just like how unfiltered water could ruin a cup of espresso, the AC ripple that bleeds into the regulator output could affect system functionality. Even if you’re sticking with a linear regulator, you’ll also have AC components from the mains frequency or digital interference. The switching and transition frequency produces ripples above 500 kHz, which are often coupled to the output voltage. The DC power supply is susceptible to AC ripple and noise and even more so for a switching power regulator. However, the world is far from ideal and the voltage is never a perfect line. In an ideal world, the voltage from the output of a DC power supply is a perfect horizontal line when observed on an oscilloscope. Why Do You Need an LC Filter for Power Supply? The idea of the LC filter is to prevent high-frequency AC components from flowing to the load. Meanwhile, the capacitor’s impedance decreases and forms a pathway for high-frequency components to pass through. Here’s a typical arrangement of an LC filter.Ī basic LC low pass filter circuit schematic.Īt higher frequencies, the inductor acts as a choke, which blocks AC components from passing through. It is meant to prevent certain high-frequency AC components from passing through the circuit. If you need a basic refresher, an LC filter is a low pass filter built with an inductor and capacitor.
There might be no water filter involved, but you will need to place an LC filter for the power supply.
The experience also highlights a similar and often overlooked aspect when designing a power supply. Witnessing this master was eye-opening in terms of how meticulous you need to be to make a perfect cup of coffee. Apart from the sublime techniques, the water filter determines the end result of the espresso. After watching a world-class barista in action, I realized I was wrong. I have always assumed that high-quality coffee beans and an expensive coffee machine are all it takes to make the perfect espresso. Pick up tips for designing a power supply LC filter.ĪC noise affects the precision, stability, and functionality of various components. Learn why an LC filter for a power supply is important.
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