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My bedside table lamp is plugged into a powerboard and is using a 9.5W Mirabella LED bulb on a 240V circuit - in Australia, i.e. with the Australian plugs.

We can't buy incandescents here as they are banned for environmental carbon emission reduction reasons so for many years I have been using either CFLs and halogens but this is an LED this time.

Over the last few months I have noticed that if I turn out the lamp and then change my mind and need to turn it back on again soon after, the light will be dim for a long time. There is no dimming switch. Also when I then turn it back off again as it is too dim, it will take a few seconds to black out completely.

Is this normal, i.e. I think I have never used LEDs before so haven't noticed this with the CFLs and halgen bulbs, or is this a possible wire fault? I had to clear small dead insects from the holder as they build up from time to time, but it made no difference, and I stupidly touched the pins with my finger to wipe there and gave myself a small electrical shock because I didn't turn the lamp off as it was difficult to do as I was in the dark except for trying to juggle my phone's flashlight to see a bit. Won't make that mistake again!

Should I buy a different bulb and see if it still happens, and if it does, should I replace the power board? Or do you think something more sinister is going on? It only happens if I need to turn it back on soon after turning it off.

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closed as off-topic by PeterJ, laptop2d, RoyC, Finbarr, Bimpelrekkie Apr 8 at 14:08

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Questions on the use of electronic devices are off-topic as this site is intended specifically for questions on electronics design." – PeterJ, laptop2d, RoyC, Finbarr, Bimpelrekkie
If this question can be reworded to fit the rules in the help center, please edit the question.

  • \$\begingroup\$ It seems likely that there is a power conversion circuit that enters a mode where the converter is locked in a low output regulation mode. Events of this sort are not overly common but are well enough known in many devices. When you turn the power an internal voltage falls over a period of typically seconds to tens of seconds. If it is above some threshold the circuit behaves abnormally when repowered. \$\endgroup\$ – Russell McMahon Apr 5 at 5:41
  • \$\begingroup\$ I would try a different lamp, ideally from a different manufacturer. It could be poor design or just an individual lamp that's out of spec. I've never noticed this happening with any of the many LED lamps I've used. \$\endgroup\$ – Finbarr Apr 5 at 7:47
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The following is likely but not certain as the cause.

Events of this sort are not overly common but are well enough known in many devices.
When you turn the power off an internal voltage falls over a period of typically seconds to tens of seconds. If it is above some threshold when the device is repowered the circuit behaves abnormally.

In this case it seems likely that there is a power conversion circuit that enters a mode where the converter is locked in a low output regulation mode. eg a possibility is that the output current is seen as beeing too high due to a spurious interaction at turnon, and until the voltage falls into its normal range the converter acts to minimise current.

I have seen a video card that would fail to restart for tens of minutes if repowered soon after turn off.

The ISD2590 voice storage and playback IC would lockout for minutes if certain pins did not fall to below about 0.2 volts before restart. I encountered this in a commercial design and as the IC had to be used I provided a "workaround" which shorted the 5V rail for some seconds once it fell below about 4 volts. This served to overcome the problem.

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  • \$\begingroup\$ A corollary situation are supplies that use a NTC R for inrush limiting. If you turn them back on right away the resistor is still hot and doesn't provide much limiting. The takeaway here is always wait to turn any modern appliance back on. And probably the only solution available to Natty B. \$\endgroup\$ – EinarA Apr 5 at 6:59

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