EEVblog 1406 - DC Circuit Transients Fundamentals

[EEVblog]

The conclusion of the DC circuit fundmentals tutorial series.
How a capacitor and inductor works, parallel and series configurations, exponential rise and decay, time constants, and basic differential calculus. Energy storage in capacitors and inductors and how a collapsing inductor magnetic field can be both a problem and a benefit.

[f4eru]

worst transient i know of after lighning is the unclamped load dump in automotive.
Nasty stuff, it's due to the huge inductances in the generator and the closed loop that takes time to wind the current down when cutting off loads.

[Schwuuuuup]

This video came - once more - just in time for me.

I never studied EE and really struggle with all that analog stuff... so when I got a LED-Strip with a inrush current that could not be handled by the power supply, I was really prod of myself to introduce an inductor into the circuit.... I should add a diode!

Can anyone hint me to calculate an ideal inductor? The LED strip consumes 3,76A at 12V, the power supply is rated at 12V 4,17 A but does not really deliver on that, or better put: the internal protection circuits trip easily before reaching the nominal 50W.
Is there an easy way to calculate an inductor that would limit the inrush current to a reasonably slow curve? I was thinking 500ms until full power is reached (5 or 10T) but I guess the choke would be enormous and expensive.

best wishes
TOM

[f4eru]

you should check or excahnge your PSU.
Normally a LED strip does not consume more as inrush as when in operation, there should not be a need for inrush limiting.
Inductor would be massive, not good.

1) PSU is improper, change it
2) PWM soft-start the strip
3)One non-nice option if everything else fails would be a NTC : like B57237S0229M000 https://www.digikey.com/en/products/detail/epcos-tdk-electronics/B57237S0229M000/652133?s=N4IgjCBcoLQBxVAYygMwIYBsDOBTANCAPZQDaIALAJwCsIAugL6OEBMZIAQjQOysDMPAMoAGVqyoBZETIaMgA

[EEVblog]

Can anyone hint me to calculate an ideal inductor? The LED strip consumes 3,76A at 12V, the power supply is rated at 12V 4,17 A but does not really deliver on that, or better put: the internal protection circuits trip easily before reaching the nominal 50W.
Is there an easy way to calculate an inductor that would limit the inrush current to a reasonably slow curve? I was thinking 500ms until full power is reached (5 or 10T) but I guess the choke would be enormous and expensive.

Maybe look at adding an NTC resistor in series like many mains power supplies do.

[Schwuuuuup]

I think the PSU is VERY delicate regarding Current spikes... and we are talking about 4m of LED strip that is placed with its plus pole along a grounded aluminium bar... so there is a substantial capacitor right there

The NTC is a nice idea, I would like a really slow start like that. I wonder how slow you can get it with that... on Mains it's only milli seconds.. but on 12V ... maybe a nice effect

PWM is out of the question: too many parts. there is not really space for a pcb, I only have the 12V rail, so I would have a specialized part or MCU with DC-DC-Converter. If I went that route, I would throw in a esp to have it WIFI connected... but for right now, I just want to have the lights turn on and stay on