I am interested to learn more about wireless power, and decided to break open a generic electric toothbrush, to find out how it works. (There was a moment of irony when the lady called me back saying "Sir, you forgot your receipt, you need this otherwise our warranty does not cover your purchase")
So I am going to document the process here, and If anyone wants to pitch in, give feedback on the way, that would be cool.
So these are the guts.
The toothbrush part is simple enough. There is a zener diode for voltage regulation, Ni-Mh battery at 1.2V, a regular DC motor and some gear which convert the rotary movement to an oscillatory movement.
The charging circuit is a bit more complex though:
I'm trying to figure out what exactly is happening here. I thought that all I would find here would be some voltage regulation circuit, i.e. two coupled zener diodes and some resistors.
So, I did some photoshopping (well, actually I used Gimp, which I dont know how to use, so the results are mediocre... but here goes:)
So, what parts are there?
(using the pcb's markings)6 regular resistors
R2 = 43k Ohm (5%)
R4 = 3.3k Ohm (5%)
R5 = 820 Ohm (5%)
R6 = 1.8k Ohm (5%)
R7 = 51 Ohm (5%)
R9 = 82k Ohm (5%)1 blue resistor
R3 = 13.6M Ohm (0.05%)1 big light blue resistor (R8)
R8 = F1/2J D5K 820 Ohm3 Transistors
Q1 = MPSA 44 G8 C
Q2 = BC 547B G5 E
Q3 = BC 547B G5 E1 Diode
D1 = (400 013)? (cant read it propperly)3 Dark Brown Squarish Ceramic Caps:
C2 = CL21 682 k 400
C3 = CL21 154 K 250
C4 = 333JA 4001 Light brown Roundish Ceramic Cap (?) or big ass Resistor?:
R1 = TVR 07471 (is this a resistor array? is it mislabelled?)1 Electrolytic Capacitor
C1 = KM(M) Z 6 A 105° C8
So, some of these parts I vaguely understand, some I have no clue what they do.
Can anyone shed some light in this? In theory all this circuit should be doing is drop the voltage to safe levels and then (while maintinging the AC signal) power the coil. I guess some of the resistors are required to keep the current down and not burn out the whole thing... maybe thats what R1 is for?)
I have to do some stuff for university, but I plan on eventually drawing a schematic to help me understand this. Can anyone recommend some software for the schematic? Fritzing does not appeal to me that much, and eagle is too complicated for what I want to do... anything simple out there?
Anyway, I will continue on this later. Any input you can give me would be appreceated