Enter the steady state current rating of the LED driver and the number of drivers into the calculator to determine the LED inrush current.
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LED Inrush Current Formula
The following equation is used to calculate the LED Inrush Current.
IC = SSC * 100 * #D
- Where IC is the total inrush current (amps)
- SSC is the steady state current rating of the LED (amps)
- #D is the total number of drivers
What is LED Inrush Current?
LED inrush current is the maximum current drawn by a single LED at turn-on. It is caused by the self-heating of the die during turn-on and is usually very short (≤1 ms). The magnitude of the inrush current varies with the technology and size of the device.
For example, an SMD package may have a much lower inrush current than an LDMOS device because SMD packages perform better at higher temperatures. The power supply design should always consider the inrush current as it can be large enough to cause damage to the supply itself or even destroy expensive components.
The value for regular LEDs is typically in microamperes due to their small size. For larger devices such as high-power LEDs, it can be more like milliamperes or even more. Inrush currents for these devices can be orders of magnitude higher than those for regular LEDs, leading to circuit protection and reliability problems.
How to Calculate LED Inrush Current?
LED Inrush Current (aka “LED Turn-on Current”) is the current draw that a circuit or device made from LEDs will experience when the switch is turned ON. It is usually measured in milliamps (mA).
It’s typically calculated by adding the forward voltage drops of all the individual LEDs in the circuit and then multiplying this total by the supply (or battery) voltage. For example, if we have a course with 3 LEDs, each with a forward voltage of 3.0V; and we’re using a 12V supply, then the total LED Inrush Current would be:
3 x 3.0V = 9.0V
9.0V x 12V = 108mA
LED Inrush Current is crucial because it needs to be considered part of an LED circuit’s overall power budget. It also has implications for how a power supply converts AC mains electricity into lower DC voltages; and how much load an inverter can handle before it fails.