Verry noisy step up converter, how to make it quiet? - Page 1
Forum section: electronics / projects

author: Michaelaudio
author_rank: Regular Contributor
timestamp: December 29, 2022, 09:08:05 pm
content: I have bought a Boost converter for a mobile Headphone amp, but it is so noisy, that i can hear music on a low Volume, bc its so horrible loud. Its a tiny module from eBay, based on the SDB628 Sot-6 Chip.Since i only need around 100mA max, by 15V Out, i added a RC Filter to its Output (150ohm, 33uF), which worked pretty Well (from 200mV ptp to 30mV ptp). The Problem is, the voltage breaks down, when i draw about ~60mA and i dont know why. I couldnt find much more Boards, who are 23*16mm, so i would like to modify this one as good as possible.What else can i do?

author: Slh
author_rank: Regular Contributor
timestamp: December 29, 2022, 09:43:40 pm
content: More details about the module would be useful - power rating, input/output voltage ranges, maybe some photos.I'm going to make some assumptions and assume that the module is designed for more than 1A out with 5V in? At low power out it switches to pulse frequency modulation which might be low enough to hear. It also doesn't give much information about it so I can't say exactly how it behaves. Another option is whatever is supplying the input voltage is struggling to keep up. It could be that the ripple from the boost converter is high enough to screw up the supply to it so it is hiccoughing. If this is the case then you might have an issue as you may not be able to increase the boost converter input capacitance. It you're using a usb port for power supply, I think the max spec for capacitance on a usb device is only 10uF so there aren't any simple fixes if that's the case (if I'm incorrect about that then please will someone let me know. I just read it on a usb charger ic datasheet but haven't checked the standard)The Rx filter doesn't work because of Ohms law. You pull 60mA out of it and the voltage on the output will drop I times R volts which is around 9V.

author: dobsonr741
author_rank: Frequent Contributor
timestamp: December 29, 2022, 11:19:05 pm
content: Just to clarify, is your complaint about the audible noise the module produces at low loads?If so, the converter not getting enough load, and operating in bursts. The ceramic capacitors, specially the weaker quality with high voltage dependence tend to show piezo effects. Second suspect is the inductor. The better ones are the epoxy filled, so that the winding can not move.I suggest two changes:1. Apply a pre-load resistor, to see if the audible effects reduce after a certain load current.2. Replace the ceramics on the output with tantalum caps, or if space allows low ESR Alu electrolytes.

author: jonpaul
author_rank: Super Contributor
timestamp: December 30, 2022, 02:13:13 am
content: Suggest you find specs and schematics boost conv and HP amp. Expect cheap Chinese converters to have lots of EMI, both CM and DM. Filters and compliance cost $!What's the converter F, wideband noise?amplifier power supply input noise rejection?check converter noise with a scopeSuggest you replace RC filter with EMI filter, a series L shunt CJon

author: Michaelaudio
author_rank: Regular Contributor
timestamp: December 30, 2022, 12:45:22 pm
content: Its this Module:https://www.ebay.de/itm/2-5PCS-SX1308-Converter-Step-up-Adjustable-DC-DC-Power-Module-Booster-Board-NEW-/264331100824?mkcid=16&mkevt=1&_trksid=p2349624.m46890.l49286&mkrid=707-127634-2357-0I tried a parallel 33uF electrolyte, but nothing changed at all. The converter is powered from a 9V battery. It doesnt make a huge difference If loaded or not, on the Output i have a 200mV ptp noise. I havent tried to heavily load it, but even If that worked, it would obviously not be a good solution.The Headphone amp is Selfmade, it uses a Split supply. It works almost with No noise when i power it from my bench PSU.Yes i know its a cheap chinese converter, but i must be able to improve it dont i?

author: jonpaul
author_rank: Super Contributor
timestamp: December 30, 2022, 03:01:10 pm
content: Schemati and photo your DIY Amp and the module ?Scope pix the DC bus ripple/noise?Jon

author: Niklas
author_rank: Frequent Contributor
timestamp: December 30, 2022, 04:50:23 pm
content: 9V batteries are usually a series combination of small coin cell batteries and they typically have a large series resistance that makes the output voltage drop at higher currents.The step-up converter draws current through the inductor until it reaches a certain current and then turns off the switch transistor. The peak current can be much higher than the 100 mA that you want. With 100% efficiency you will get 100mA×15/9 if you assume DC current. With switching and lower duty cycle you will get more current for a short period of time, if the battery allows that. Variation of the input voltage can also affect the stability of the output voltage.You can try to power the step-up converter from your power supply and see if the output current and ripple improve. Also try with more input capacitance to offload some of the peak current from the battery.

author: SiliconWizard
author_rank: Super Contributor
timestamp: December 30, 2022, 06:51:44 pm
content: Quote from: jonpaul on December 30, 2022, 02:13:13 amYep. This will form a Pi filter with the output cap. Note that this will attenuate high-frequency noise but not so much the low-frequency ripple. (Unless the inductor is huge which is not really practical.)The usual approach is to add a Pi filter at the output of the switching converter, and then a linear regulator which will reject low-frequency ripple. Select an inductor with low ESR to avoid unacceptable voltage drop.Since it's a step-up converter, just set the output voltage slightly higher than the target voltage and add a LDO.

author: langwadt
author_rank: Super Contributor
timestamp: December 30, 2022, 07:06:18 pm
content: Quote from: SiliconWizard on December 30, 2022, 06:51:44 pma capacitance multiplier might do

author: dobsonr741
author_rank: Frequent Contributor
timestamp: December 31, 2022, 02:41:17 am
content: So it's the ripple that's bothering you. Adjust the boost converter to 2V higher and add an LDO after it.

author: Terry Bites
author_rank: Super Contributor
timestamp: December 31, 2022, 01:04:53 pm
content: Its very hard to say without seeing the wiring arangement.Well impossible really!You may well have current loops radiating large amounts of garbage.Is your input voltage high enough to enure correct operation?

author: dobsonr741
author_rank: Frequent Contributor
timestamp: December 31, 2022, 07:04:41 pm
content: Michaelaudio, just wanted to show the guts of a Topping headphone amp. It's dead silent. The +/-7V rails are directly from a TPS65130. The power supply ripple is around 5mVpp.It's possible, but not with Ebay parts. Take a look at the PCB routing too, and the inductors. And the rest of the amps (AD8610A, BUF634) have pretty good PSRR, too. All over a proper ground plane.

author: Michaelaudio
author_rank: Regular Contributor
timestamp: January 02, 2023, 06:38:01 pm
content: I hooked the PCB straight Up to my psu, so there wont ve mich current loops.The LDO is a quite nice solution, however it adds some extra 10mA of load, which id like to avoid.The capacitance multiplier didnt do much at all, strangely. I did it with a single Transistor (around 100hfe) with 1k, 33, and 470uF. I guess its bc its Not really a ripple, attached are some pics of the noise, after the cap multiplier. The big ringing are the spikes, zoomed in.@dobsonr741 Looks pretty neat, but my Board is like 1/5 of the size of yours, but i'll keep that in mind when i maybe Update my design soon or later.

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: January 02, 2023, 07:04:33 pm
content: You need another LC filter on the output. If you look at the other design, they have another filter after the boost converter with the ferrite bead and capacitors.