about DC-Link capacitors - Page 1
Forum section: electronics / beginners

author: Benjam
author_rank: Regular Contributor
timestamp: November 17, 2021, 05:16:11 am
content: I want to replace all the electrolytic capacitors in the picture with MLCC capacitors. What formula should I replace? If you simply replace it from the perspective of capacitance value, MLCC needs a lot to reach 600uF (C43+C49+C61+C72+C73+C85=600uF). In addition, I have another doubt, why is it 600uF instead of 800uF or 400uF? What are they based on?

author: ledtester
author_rank: Super Contributor
timestamp: November 17, 2021, 06:06:17 am
content: There are a lot of issues to consider here...* Voltage rating: I checked at Mouser -- any MLCC (SMD or leaded) with a voltage rating of > 50V and > 100 uF is very expensive.* Dave did a video on the voltage dependency of high value ceramic capacitors:EEVblog #626 - Ceramic Capacitor Voltage Dependencyhttps://youtu.be/2MQyQUkwmMk* Discussion of the topic on StackExchange:https://electronics.stackexchange.com/questions/43161/can-i-replace-all-electrolytic-capacitors-with-ceramicIt mentions some reasons not to switch from electrolytics to ceramics: some linear regulator designs require the higher ESR of electrolytics for stability; large SMD sizes are prone to cracking.Also check out:https://electronics.stackexchange.com/questions/232631/ceramic-caps-vs-electrolytic-what-are-the-tangible-differences-in-use

author: Benjam
author_rank: Regular Contributor
timestamp: November 17, 2021, 06:57:38 am
content: Quote from: ledtester on November 17, 2021, 06:06:17 amThe problem you mentioned is real, but unfortunately, DUE to the size of PCB, I have to consider MLCC. In addition, I have googled a lot about this problem so far, but there is no clear explanation, so I think this kind of discussion is valuable and necessary.

author: Berni
author_rank: Super Contributor
timestamp: November 17, 2021, 07:21:22 am
content: The size of the capacitors depends on what they are supplying with power, like how much power it needs, how much ripple it can tolerate, what impedance it requires.You can likely take 1/2 of this value and it might still work fine, you can likely make it 10x this value and it will still work.But i don't see how you want to save space with ceramic capacitors here. You are going to need a LOT of ceramic capacitors to reach 600uF 63V. Even more so because of the voltage dependent capacitance falloff nature (as mentioned by ledtester) the most compact ceramic caps are most dependent, up to a 50% capacitance loss even. So you might actually need 1200uF 50V of ceramic caps to get the required 600uF of capacitance at the operating voltage. This is a huge amount of ceramic caps. Only way i see this as a viable space saving is if you have a large flat area available but have very little height to work with. Electrolytic caps are the most energy dense type of capacitor commonly available (apart from dual layer supercaps)

author: dtmouton
author_rank: Contributor
timestamp: November 17, 2021, 08:05:19 am
content: You also have to look at the RMS ripple current the capacitors can withstand. Make sure that your new capacitors can handle at least the same amount of ripple current as the old ones.

author: Keivinstib
author_rank: Newbie
timestamp: November 26, 2021, 01:00:24 pm
content: DC-Link capacitors form an essential stage in power conversion for many applications, including three-phase Pulse Width Modulation (PWM) inverters, photovoltaic and wind power inverters, industrial motor drives, automotive onboard chargers and inverters , medical equipment power supplies, etc. Demanding applications possess cost, harsh environmental, and stringent reliability constraints. Although circuit designs can use different approaches, the long-standing core of power conversion designs includes DC-Link capacitors. DC-Link capacitors can improve system energy density and resolve the physical challenges of ripples introduced by rapid switching that is inherent to switching power conversions.