Braun Toothbrush Schematic

alfa88 · Dec 1, 2010

I'm trying to resurrect a dead Braun toothbrush and have the circuit partially figured out. It uses inductive coupling to charge the battery. One half of the circuit is for charging and the other half is used to control the motor. What I found so far is that there was a open from the motor body to one of the motor contacts. They (Braun) did that to complete a switch path. There is a mystery part that has me stumped. It is a 6 pin surface mount part that ultimately outputs to the base of a NPN power transistor. I can power up the moter by supplying base current. No useful part numbers are to be had and the index dot is on pin 6. The purpose of the circuit is to prevent the motor from operating when it is being charged. So what I'm looking for is a 2 transistor switching circuit that will output low when the input is high and it should operate down to 2.5 volts. Attached is what I came up with. The rectangle in the middle is the mystery component.

dawsrobe · Jun 24, 2011

Did you have any luck?

Hi:
I'm in the same boat. Initially, I thought it was a dying battery, so I replaced it.
Now the problem is it won't hold a charge. The primary coil in the base gets nice and warm, but the charge isn't making it through to the battery. Perhaps an internal short?
Do you think there is a choke up where the positive terminal of the battery is? The band on it would indicate that perhaps it is a diode, which is conducting both ways presently... but what value to replace it with.
Thanks for posting the schematic... but could you possibly post a larger one? As a thumbnail, I can't make out the details.
Thank you.

(*steve*) · Jun 24, 2011

dawsrobe said:
but could you possibly post a larger one? As a thumbnail, I can't make out the details.
Thank you.

Try clicking on it

dawsrobe · Jun 24, 2011

Silly me!
Thanks.

alfa88 · Jun 24, 2011

Diode

The diode will appear shorted if the motor is still attached. If, indeed, the diode is shorted just try squeezing in a 1n4xxx . we're only dealing with 3V and any 4xxx series diode should be able to handle the current. One Problem I came across was a poor connection to the motor's body.

dawsrobe · Jun 24, 2011

Yeah, I'm feeling kind of dumb today. No sooner had I sent that off, when I realized the continuity check was probably going through the motor.
I guess what has me going is that the batteries are getting something, it's taking 24 h to get a charge that lasts about 30 s. Yet the whole time, there is a load on the primary coil, because it's warm.
Might help to know what the chips were.