Mains power filter - Page 1
Forum section: electronics / projects

author: Pack34
author_rank: Frequent Contributor
timestamp: February 28, 2018, 03:31:56 pm
content: I want to be sure I'm designing these right and providing enough protection.Basically, I just feed everything through a CMC, and follow that up with a LC filter and a zener for over voltage protection. Since it's a barrel connector I haven't added a polyfuse for reverse protection. This is all being fed by a certified power supplies rated for up to 5x typical current.Should the LC filter be more aggressive? I thought this was all that was needed when using a certified desktop power supply.This isn't the exact brick we're using, but close:https://www.digikey.com/product-detail/en/sl-power-electronics-manufacture-of-condor-ault-brands/TE60A1202Q01/TE60A1202Q01-ND/7403203Is there anything on my end I could do more to protect from things like surges and an unstable mains?The current choke is rated for 2A and 1 kOhms @ 100MHzThe current LC filter is 100uH and 2.2uFThe current Zener is rated for 18VCMC currently used:https://www.digikey.com/products/en?keywords=490-4018-1-ndInductor currently used:https://www.digikey.com/products/en?keywords=SRN1060-101MCT-NDCapacitor currently used:https://www.digikey.com/products/en?keywords=587-1351-1-nd

author: BrianHG
author_rank: Super Contributor
timestamp: February 28, 2018, 03:47:26 pm
content: You do realize that the 12 v DC source (usually not called mains), it's GND may be connected to the GND pin on your power AC outlet. Now, that bottom half or your common mode choke is connected on the other side to your GND. If that GND on that side is connected to or with, for example, a PC or Laptop supply, which may have their GND wired to an AC outlet's GND pin, that filter may introduce rings and current noise with power consumption which may corrupt data on a shared data bus GND between hardware. This may cause problems elsewhere or potentially blow shared data ports.For DC power filters, all you need is a single choke inductor and cap with stiff good grounding. You may potentially kill your zener diode by accident depending on currents in your circuit. Common mode choke are only good if you designed the DC power supply yourself and you know exactly what you are doing, or the common mode choke is on the AC side.Get rid of the CMC and place filter caps, something like 1000uf or more after L2. Add a .1uf and 10uf in parallel with the 1000uf to lower ESR at higher frequencies. (Well, I don't know how much current your circuit draws, I'm going on 1 amp.)I don't think using the zener diode will do anything.

author: CopperCone
author_rank: Super Contributor
timestamp: February 28, 2018, 04:04:28 pm
content: Well your filter and common mode choke are basically applying transfer functions to the input waveform. You will attenuate harmful energy impulse by some amount with the filter if the energy is contained within the filter stopband. A higher order filter will attenuate more energy but only if its within the stopband. Nothing prevents you from designing a 15th order brickwall low pass filter then cost.You do need to take the source impedance of the transient into account though when calculating the filters effect.

author: BrianHG
author_rank: Super Contributor
timestamp: February 28, 2018, 04:10:57 pm
content: Quote from: CopperCone on February 28, 2018, 04:04:28 pmOMG, get out the bank of 1F caps and batteries, huge transformer sized inductors, and shielded cases.... We will kill all power noise if like it's the end of the worldBut in the process, his 1 amp 12v DC adapter will take 24 hours to power up the device.

author: Pack34
author_rank: Frequent Contributor
timestamp: February 28, 2018, 04:56:18 pm
content: Quote from: BrianHG on February 28, 2018, 03:47:26 pmI meant filtering a wall-wart power supply, just worded it oddly.The circuit typically only pulls an amp at most.