LED Power Supply – Philips 9 W Luminaire Quotes 7 A for 300 ms Inrush!

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In his answer to Will repeatedly turning a light bulb on and off damage it? @Bradicul stated,

An example of inrush current is an LED downlight fitting with 9 W (0.0375 A at 240 V) will have any average inrush current of 7 A for 300 ms.

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Figure 1. The 220 – 240 V, 9 W Philips downlighter has an overall diameter of 84 mm.

I thought he was mistaken but he linked to the Philips DN135B LED6S/830 PSR-E II WH datasheet and it states that the inrush for this 9 W lamp is 7 A for up to 300 ms.

Can anyone think of a reason the PSU in these luminaires could draw 1.75 kVA for up to 300 ms when the lamp is only 9 W with a 0.9 power factor? Where is the juice going?

Best Answer

I don't see much contradiction. Inrush current is usually an exponentially decaying spike. The "7A" nameplate value is certainly the peak current. The "300ms" is likely a nameplate for spike duration, probably defined at 10% level, so the total energy is much lower than the bold estimation. Here are "definitions" from Murata:

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where the duration looks like is defined at 0% level :-)

There is a line-up of technology and tutorials that deals with inrush current measurement, like Keysight

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Let me guess some numbers from the Philips datasheet.

If the input has 7A at 240 V peak, the ESR looks like about 35 Ω. If the 300 ms is defined as RC constant, then the capacitor might be (35 * C = 0.3) C =8,500 uF, which sounds too high. So the 300 ms is likely defined differently in the area of industrial lighting.

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