Inside a twisted LED bulb

I chose this lamp to take apart because it has an interesting style. It's very similar to a fashionable (and expensive) designer compact fluorescent lamp called Plumen that was very popular with architects and designers because it "made a statement".

This one is based on two shaped plastic tubes with two parallel flexible LED filaments running through them. Each filament is based on a flexible PCB strip with a series parallel array of LEDs to give a high operating voltage from one end of the strip to the other. That means they can use a fairly standard linear driver inside.

There's another of those mysterious inline regulating chips to add an extra layer of current regulation to the LEDs. These seem common in dimmable lamps, and I think it's a way of regulating the LED current based on ripple from the current limited supply to the capacitor, that will be affected by the duty cycle of the dimmer output.

It could be that the chip detects when the voltage across its internal sense resistor has dropped too low and then regulates the current down to the point it can maintain an acceptable level continuously, with its external capacitor acting as a simple analogue memory.


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