Lavolta BPS305 power supply - Page 1
Forum section: electronics / beginners

author: Ferret
author_rank: Newbie
timestamp: October 26, 2016, 11:22:45 pm
content: Good evening from the Old Dart,My knowledge of electronics is very limited (but I suppose, that's why I posting in the newbie forum). I've bought some cheap One Hung Low brand equipment, and for how often I'll use it, it's worth the money. To buy anything more expensive would be a waste for me. I'll do with what I've got.I've bought a power supply as per the title, and today received a Hantek 6022BE oscilloscope.Anyway, onto the issue... I think Dave has done a video on these cheap Chinese power supplies and scoped them at turn on to discover that you get a voltage spike when turning them on.I too have that issue, I also found a spike when turning off too, a 5.04v spike when the PS was set to 2v. I've added screenshots so you can see that spike.My question is, is there anyway to suppress the spikes, like adding a cap to the output?If I can't, then no wukkas, I can turn the PS on then add my device that I need a voltage to.Thanks,Ferret.

author: singapol
author_rank: Frequent Contributor
timestamp: October 27, 2016, 05:26:43 am
content: Transients and spikes are ever present in real life.http://barktech.com/wp-content/uploads/2012/09/Causes-and-Effects-of-Transient-Voltages.pdfYou have to look at it in perspective. Perhaps the engineer did not pay attention to this aspect as power supply works and left it at that. It is inherent in elctrical and electronic circuits. you can eliminate or reduce transients if you understand how things work..normally the scapegoat is inductance.Circuit or pcb layout,lead dressing and low esr etc. read the following and you should be able to appreciate what is going on. If you manage to tame the spikes please share your findings.Capacitance,esr and resistance to the rescue aka snubbers.Definition of transients/spikes:http://www.sollatek.com/voltage-surges-causes-and-control/Dangerous LC spikes:https://www.pololu.com/docs/0J16/allhttp://www.talkingelectronics.com/projects/ThePowerSupply/Page80PowerSupplyP2.html

author: Kleinstein
author_rank: Super Contributor
timestamp: October 27, 2016, 03:44:52 pm
content: The spike during turn off looks quite short, which suggests there is not much capacitance at the output. It looks so fast that it might even be more like an artifact of the measurement, like external induction.Adding capacitance to the output likely will only make the transients smaller but longer.To really get grid of these transients other changes to the circuit are usually needed. The instructions suggest the manufacturer (or the one who wrote the instructions) is aware of the transients and does not know an easy / cheap way to get rid of them. So it could be a challenge to find a simple fix for this.

author: janoc
author_rank: Super Contributor
timestamp: October 27, 2016, 05:28:36 pm
content: Quote from: Ferret on October 26, 2016, 11:22:45 pmWhich is the only sane thing to do anyway. The same for turning the PSU off. This is also the reason why more expensive supplies have on/off buttons for each rail that connect/disconnect the load that default to off. In that way the startup/power down transients of the supply will not come into play. It is also nice to not have to constantly disconnect the leads.You can try to reduce the spikes, but it would require quite a bit of work and you still can't really rely on that - you get used to your supply being well behaved, then you connect your circuit to some other supply that isn't, don't take the precaution, because you are used to your supply that doesn't have the problem - and, fried hw.After a while it will become completely automatic for you to pull the leads out of the supply before turning it off and to connect your circuit only after the supply is stabilized already (i.e. not power it up with the load attached).