LM2596 Controllable Buck Converter Switching Noise on Signal - Page 1
Forum section: electronics / projects

author: syntax333
author_rank: Regular Contributor
timestamp: May 01, 2019, 04:16:14 pm
content: Hi, I am using LM2596 Power Module to convert 18V to 10V for my application.However, signal that I am working on has spikes with constant frequency. I checked everything on circuit and found out my cheap power module has the same switching frequency.In attachment you can see both my signal and switching of LM2596.Power output of LM2596 is connected do decoupling capacitors of the ICs which outputs this signal.Is there a way to get rid of this noise? or better converter suggestion which has better characteristics?Thank you.

author: madires
author_rank: Super Contributor
timestamp: May 01, 2019, 04:33:55 pm
content: The LM2596 has a switching frequency of 150kHz. Maybe a poor counterfeit?

author: syntax333
author_rank: Regular Contributor
timestamp: May 01, 2019, 04:43:41 pm
content: ProbablyI was thinking plugging a linear L7809CV regulator to output of power module.Do you think this will help the situation?Can you suggest other regulators with better performance?

author: wraper
author_rank: Unknown
timestamp: May 01, 2019, 04:44:16 pm
content: Quote from: madires on May 01, 2019, 04:33:55 pmNot maybe but certainly counterfeit. 99% of these modules on ebay and aliexpress use counterfeit IC.

author: mariush
author_rank: Super Contributor
timestamp: May 01, 2019, 04:47:36 pm
content: It's probably a clone of LM2576 ... which in theory is supposed to be a 52 kHz switching regulator.

author: syntax333
author_rank: Regular Contributor
timestamp: May 01, 2019, 05:24:16 pm
content: So do you think signal disturbance is due to power supply?

author: Le_Bassiste
author_rank: Frequent Contributor
timestamp: May 01, 2019, 05:44:42 pm
content: can speak for waveform in 2nd picture only. perfectly fine for a buck converter that's running under lighter load than it was designed for.this is called "discontinuous mode", because the inductor is "running out of steam" during the free-wheeling phase, and then resonating with the circuit's stray capacitances.if fast step response is not an issue in your circuit, you can basically increase the inductance to a value such that the inductor current still hasn't fully vanished at the beginning of the next ON phase. then the inductor current is never going back to zero, and the buck converter will run in "continuous mode". in continuous mode, the voltage in the 2nd picture will change to a clean (if pcb layout is good) square wave.

author: syntax333
author_rank: Regular Contributor
timestamp: May 03, 2019, 11:02:16 pm
content: Is this ringing on signal normal for a buck converter or is this due to power module being a counterfeit?

author: ptricks
author_rank: Frequent Contributor
timestamp: May 04, 2019, 03:09:10 pm
content: My experience has been that the cheap power modules , the 5 for $10 ones sometimes ship with open inductor vs the shielded type and you can see all sorts of noise in the outputs from it depending on load.You can try putting an LC filter on the output and see if that helps.

author: madires
author_rank: Super Contributor
timestamp: May 04, 2019, 03:40:23 pm
content: Switching power causes ringing. The amount of ringing depends on several factors, for example the buck converter's operation mode, load, the components chosen and so on. A poorly designed buck converter can make things worse (controller IC and complete circuit). ptricks' suggestion to add an LC filter is the standard way to reduce switching noise.

author: Le_Bassiste
author_rank: Frequent Contributor
timestamp: May 05, 2019, 06:23:57 am
content: Quote from: syntax333 on May 03, 2019, 11:02:16 pmno, this is not indicative of a counterfeit part. its telling you that the buck is running in discontinuous mode (DCM).of course, your power module may still be consisting of counterfeit parts, though