On 15/12/2017 09:33, Brian Gaff wrote:
If you are worried, then get an lm317 three terminal regulator and a
suitable pot and get it just right on a charger with more volts out, like
one of those beefier usb ones.
It might get a bit warm. Seems odd to me if its AC though, as leds are most
definitely DC.
Brian

Not worth the effort for such low power. Dropping 0.6v across a cheap
silicon diode or two in series will bring a 5v supply down to 4v.

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Regards,
Martin Brown