Electronics > Beginners
problems controlling voltage spikes when connecting voltage
frich:
Hello
i am new here, and quite new to electronics. as such i am still pretty much at the level of standard passive components, and just play abit with timers and such.
i have a made a small project where i am connecting a small router to the a plug that contains 24Vdc and an ethernet connection. the small router i am using is running on 5Vdc (usb) so i have a small buck converter inbetween to step down the voltage from 24 to 5.
unfortunaly i keep burning up buck converters at random, some times they last 3-400 times, and some times they only last a couple of times.
from what i have been able to figure it, it must be due to a spike during when i plug it in. it is allways at the point of plugging it in that the converter gives up.
i have installed a diode on the negative to protect from reverse polarity connection (1N4007), and i tried installing a zener diode across the supply to cap the spike (1N5360BG).
this also seems to fix the positive spike, but i still get a negative spike from time to time.
i have tried multiple buck converters (all cheap chinese ones) and it is allways the IC on them that blows up, not sure if you can use the markings on them for anything (JWBV 045F, AGCH, 1HRG, MP1584EN, CXW8509) i have tried to look up a datasheet, but without much luck :(
so the big question is, how do i create a proper filter to protect the buck converter or maybe someone can point me towards a better buck converter.
Vovk_Z:
For example, use aluminium electrolites with high enough ESR (at inputs and outputs). They will dump spikes.
frich:
sound reasonable :)
but not quite sure how to calculate that.
if i place something like a 10uF 63v cap parallel across the zener diode, would that be enough ?
found one here with an internal resistance of 2,3ohm
circuit at that point is 24Vdc nominal, with a current draw of 0,03A
terribly sorry about the seemingly stupid questions :( but i am used to working from 100V to 36kV
David Hess:
If the input capacitance is low, then applying power quickly, through a mechanical connection or transistor, can cause any series inductance in the wiring to produce a ringing waveform which exceeds the absolute maximum input voltage of the device. One solution is to add enough bulk input capacitance, typically 10 to 100 microfarads per amp, to absorb the energy.
Alternatively if the module uses a solid tantalum input capacitor, its surge rating could be exceeded.
Deni:
Had similar issues on a project few years ago. Inductance of power supply wires caused spikes, so I added TVS diode in parallel to the input (with rating above normal operating voltage, but below max. input
voltage rating of DC/DC converter - 33V in mycase) and, just in case, added 100uF/35V electrolytic cap. No issues afterwards.
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