Philips Sonicare

Philips Sonicare

I found a Sonicare toothbrush from 2012 with a brush sanitizer and charger base.




Inside the sanitizing compartment is a UV-C light source together with a lot of reflective metal-plated plastic and a tray that supports the brush heads.  The surfaces look very metallic but there is hardly any metal here just the electrical contacts to the UV bulb.  A feature I found of both the brush and the charger is an intricate mechanical design of the parts. The reflective interiors can be with some effort unclipped to reveal the bulb and (Another plastic) screen.This is a 5W UV-C bulb (On the base of the charger the power is quoted as 1.0-1.4W Charge Mode Only and 5.8-6.5W (UV and Charge Mode).  These bulbs are a low pressure mercury vapour lamp emitting 254nm UV light (UV-C) which has a germicide function that destroys the DNA in bacteria, preventing it from replicating.  I measured the voltage to the bulb as 18V DC.

The charger is a non-contact magnetically coupled inductive charger. Unscrewing the base you can see a small board and a resin packed enclosure that houses the mains transformer and bridge rectifier.

The board is quite simple perhaps surprisingly simple, with 18V (for the bulb) and 23V input.  Around the coil are wrapped two coil wires (And a sense wire) that are switched by a couple of small 667 power transistors.  I believe they are switching at relatively high frequency ~80kHz this creates a magnetic flux that is picked up by a coil in the base of the toothbrush.


The toothbrush is sealed with an o-ring, that if you break the seal all around the inside slips out of the housing.






The magnetic flux is picked up by a coil (100 turns of 30AWG copper wire around a 12mm diameter spool.) This generates a voltage which is rectified and then regulated to charge a Li-ion battery. I measured a battery voltage of 3.8V (But this was an old battery so it might be a higher voltage.)

The mechanical aspect of the brush is also a very intricate mechanical design.

It functions by energizing a pair of electromagnets (at 15.5kHz) that literally rock a permanent magnet which is in turn connected through a small metal bar to the head. This oscillates up/down but with a small degree of lateral movement.  The drive enclosure is has a welded case and inside are several pieces of metal and plastic that transmit the motion and confine the desired rotational freedom.

The PCB board is somewhat unusual for a consumer device in that it does not have any custom devices, just using off the shelf components.

Underneath the contact switch are 6 gold plated pads that are used to program the 8-bit Microchip PIC16F726 MCU.  There are two MOSFET drivers connecting to the magnet coils and voltage regulators and some LED’s together with 22 circular test pads on the board.

There are quite a few Sonicare teardowns online, this one and this one  are very good (A lot better than mine.)  But since this blog is about getting inside the silicon chips…

Microchip PIC 16F726

The PIC micro-controllers are very common but as usual could find very few die photo examples on-line. The die is not very large at 2.64mm x 2.03mm
Microchip PIC 16F726It has both a 44 pin and 28 pin versions. This is the 28 pin version but you can see the die is the same and contains 44 bond pads. I have attempted to identify some of the key functional blocks in the layout of the die.  The analog block down the left side contains a 16 channel capacitive touch sensing oscillator module, a 14 channel 8 bit ADC, a 3.2V regulator, 16MHz and 500kHz precision oscillator. I think I identified the touch sense oscillator and ADC but could not find the regulator.

The technology used for this is I believe a 3 metal 0.25μm CMOS process. Large by todays standards but still pretty dense for an optical microscope.  This is a focus stacked image from the corner of the Flash memory array taken with my 80x objective. You can see the memory interconnection, but cannot make out the transistor cells.

This is the 8 bit ADC block (Taken with 20x objective)

And this is the capacitive touch sensing oscillator region

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