5V Power supply expectations spikes in voltage. - Page 1
Forum section: electronics / beginners

author: onemanonelaptop
author_rank: Contributor
timestamp: December 13, 2023, 04:53:17 pm
content: I am working on a power supply design and have a few questions i am hoping to get answered.I am seeing the following at the output of the boost converter. the 40mv ripple i am happy with but I am seeing occasional spikes.So my question is this:1. I am currently testing the circuit under no load at all, is this a good idea, could i do damage to the chip..... if so what can i do to protect it if the power supply is turned on with no load connected.edit: actually the led and its resistor is providing some load.2. What might be causing those peaks in voltage up to 100mv, is there anything i can do to get rid of them.The current iteration of the circuit.

author: SeanB
author_rank: Super Contributor
timestamp: December 13, 2023, 05:17:47 pm
content: Easiest is to make the LED current higher, by reducing R52 to 1k, though the small spikes are still well within the ratings for TTL logic to operate in. If you are still concerned add a small inductor, probably a ferrite bead or two in series, or a small SMD inductor capable of handling the output current, between Cout1 and Cout2, which should reduce the ripple as well along with damping out the switching noise. Inductor value not too critical, just has to be rated for the expected DC current, and any value that will have an ohm or ten impedance at the switching frequency.Increased LED current will take care of any no load instability, but the chip should be stable under no load anyway, and a 5mA load will be more than enough for it. Extra LC filter will remove the noise, and if not needed simple to replace with a zero ohm resistor as well, or use as a current test point.

author: MathWizard
author_rank: Super Contributor
timestamp: December 14, 2023, 08:24:38 am
content: I see spikes I don't like on lots of my SMPS's, and they are mostly for consumer grade products with digital circuits.But if money was no concern, how much cleaner can you make things like computer SMPS, with just the idle load on them, so just a constant restive load, if any at all.Also like how much better would my 6.5 digit DMM, scopes and AWG be if they all had 10x more expensive PSU's ?

author: PSR B1257
author_rank: Frequent Contributor
timestamp: December 14, 2023, 08:50:25 am
content: How do you measured this?The 'ripple-band' seems suspicious homogeneous.

author: ArdWar
author_rank: Frequent Contributor
timestamp: December 14, 2023, 08:54:15 am
content: Are you sure it isn't your measurement artifact? Is the 40mVpp signal came from your scope noise or is it actually from the switching?A lot of "light load efficient" converters use PFM instead of PWM at light load, so occasional spike is expected when the load is zero or very low. However, the spike is not supposed to look like that. It should look like exponential decay. The converter also should not switch at high frequency with zero load (it's the whole point of PFM).

author: ArdWar
author_rank: Frequent Contributor
timestamp: December 14, 2023, 09:19:49 am
content: Quote from: MathWizard on December 14, 2023, 08:24:38 amWait, which 6.5 digit (bench?) DMM don't use linear PSU?Or do you mean you want something super low noise ultra low leakage metrology grade PSU like those on 8.5 digits?

author: zrq
author_rank: Frequent Contributor
timestamp: January 01, 2024, 02:28:54 pm
content: A bit off topic but an interesting note: my Agilent/Keysight L4411A doesn't use a linear PSU but a 12 V OEM SMPS. It's just a regular module without specific leakage requirements. (although the in-guard is powered by an additional custom transformer driven by a class-D amp chip).