Electrical – Limit inrush current

inrush-currentledpower supply

I'm looking into a LED driver and I'm quite curious about the inrush current.
Where does it originate from? Is it to load up the input/output capacitors?

Can I limit the inrush current? What's the most simple way to do this, inrush current limiters (ICL), PTCs, or any other way?

Can the inrush current be limited by starting the luminaire in a dimmed mode?

Best Answer

The inrush current would be commonly caused by the charging of power supply capacitors. These loads would not appreciably change depending on any other circuit setting (such as dimming).

The common ways to limit inrush current are:

  1. Using a passive inrush current limiter (basically a resistor whose impedance quickly goes down as it heats up, i.e. an NTC thermistor).
  2. An inductor that limits the dI/dt on the line (but care must be taken to avoid ringing and other issues).
  3. Using active circuitry that sequences the power up and reduces operational losses. This active circuitry could be a resistor or NTC in parallel with a relay, a pass transistor, or an SCR that is activated some time after power up.

In some cases, some components of the inrush current could be reduced by staggering (i.e. sequencing) the multiple power supplies in a system (the large filtering capacitors at the output of the supply also have to be charged).

This document might provide some more pointers.

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