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EEVblog #284 - Braun Toothbrush Teardown

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Thanks so much for doing this Dave.  I've wondered for a long time what was inside my toothbrush!

A question on the inductive charge coils tho.  At one time you had the CRO hooked up to both coils, and the waveforms were a mirror of each other.  How is it that the induction effects don't cancel each other out?

Cheers ! Geoff


Here's some more data ;-) I've got the same charger, only my "pickup coil" was inversed.

Exactly what I have been wondering about, inductive charging.. thanks (I'm still searching out research material)

I believe the nearly flat bottom is from a transistor turning on. I have taken apart a similar toothbrush and it basically used a self oscillating converter.

I also suspect the motor was also operating as a boost converter, since 1.5V is not enough to effectively switch a typical MOSFET. High quality pictures would help.

I haven't watched the video yet, but I HATE electric toothbrush designs (really hate). The reason? Somehow they don't seal them properly and moisture (condensation) gets inside and stops the electronics working. I mean, they know that electric toothbrushes are going to be subjected to immersion and steam, so why don't they make absolutely sure the enclosure is hermetically sealed?

Alright, I have to admit this invective is directed towards Philips toothbrushes, and Braun may be better. I just have to hope that Braun have got it right. But with the ridiculous prices of rechargeable brushes I can't afford to experiment. Gaaarrrhhh!


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