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I have an iPhone 6 with no backlight. Figured out it's the coil. The coil is rated at 15UH .72A 0.9ohm

I didn't have a replacement so out of curiosity I used a random coil off a donor board part of another circuit, but the specifications are different at 2.2UH 1.2A .15ohm

It worked and I got backlight again. Can even adjust brightness.

But I'm curious how this will effect the circuit in the long run. Will it make the switching ic work harder? Will the coil burn out?

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  • \$\begingroup\$ Inductors aren't specified in Farads... \$\endgroup\$
    – uint128_t
    May 21, 2017 at 23:10
  • \$\begingroup\$ Aren't coils? My question says coils and that's what they're called in circuit \$\endgroup\$
    – user140123
    May 21, 2017 at 23:11
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    \$\begingroup\$ The unit of inductance is the Henry. Assuming 15uH vs. 2.2uH, yes, the IC might be working harder, the inductor may be saturating, and there may be severe ripple on the backlight supply (which may make the backlight die sooner, or kill the caps with high ripple current). But it's hard to say what will happen without a more in-depth understanding of the circuit. \$\endgroup\$
    – uint128_t
    May 21, 2017 at 23:14
  • \$\begingroup\$ Yes UH typo on my end. It's a boost circuit taking 3.8v up to 20v. So you're saying the smaller coil will create more current and the current being filtered through the caps could cause them to die out? \$\endgroup\$
    – user140123
    May 21, 2017 at 23:17
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    \$\begingroup\$ @user140123 No way of knowing the likely problems without lots more detail about the backlight circuit. The new coil has lower resistance and lower inductance. If the circuit uses fixed on-times, this means radically higher peak currents. But it is hard to know much at all without any detail. \$\endgroup\$
    – jonk
    May 21, 2017 at 23:30

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