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  • EEVblog #284 – Braun Toothbrush Teardown

    Posted on May 30th, 2012 EEVblog 40 comments


    Teardown Tuesday.
    What’s inside a Braun electric rechargeable toothbrush?
    And some basic measurements on wireless power transfer and charging.
    Chips Used:
    EM6682
    TSM7401

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    • robert

      Perfect! I’ve almost got the same model. Saves me the trouble of ripping it apart before it has died ;-)

    • Ross McKenzie

      Dave,

      Did you investigate the effects of returning the two ferrite beads that you removed at the start of the “teardown”?

      Cheers,

      Ross

    • Mickel

      Excellent teardown! I once opened an older model Braun toothbrush and also noticed those ‘ferrite’ beads. I think those are for absorbing hydrogen from the battery (for safety reasons!). I’ve noticed my Pelican torches have similar looking beads and those are designed for use in explosive atmospheres.

    • John

      The “ferrite beads” are actually platinum catalyst pellets for the hydrogen gas from the NiMH cell.

      Also, the IP67 rating stamp on the bottom of the (mains powered) charger should well explain why it’s sealed off as well it is: you generally don’t want your consumers to be electrocuted. :>

      • http://www.eevblog.com EEVblog

        Someone else on Youtube mentioned the pellets too. They look and feel and are placed an awful like like ferrite!
        Missed the IP67 rating stamp. Yeah, makes sense given it’s proximity to basins full of water.

    • Pingback: EEVblog #284 – Braun Toothbrush Teardown | EEVblog – The … | O'hai

    • Jasper

      Dave, didn’t I see *two* LEDs on the board? Your schematic only shows one.

      • http://www.eevblog.com EEVblog

        Yes, another one simply comes from a micro pin.

    • Niklas

      The markings on SOT23s might be checked against this excellent database:
      http://www.marsport.org.uk/smd/mainframe.htm

      6Cs = BC817-40 NPN
      A4 = BAV70 diode

      • http://www.eevblog.com EEVblog

        Ah, nice, thanks.

    • arekm
      • http://www.eevblog.com EEVblog

        I’m convinced the 6683 is a custom job for Braun. Although the asian brokers list it…

    • Angga

      I think that double coil is there to increase current handling like in a normal CT transformer.

    • http://www.christianseifert.net Christian

      Okay, your next project must be a homemade x-ray machine to look inside of the charger stand ;-)

      Many Greetings from Hamburg/Germany

      Homeland of BRAUN equipment :D

      • Niklas

        I opened up a potted toothbrush charging station a few years ago for a work project. From what I can remember, there were no ICs at all in it. It was transformerless with an RC-network to limit the voltage. The oscillator was built with discrete transistors and diodes, perhaps with some feedback from the coil.

    • f4eru

      The EM6682 is probably derived from a specialized microcontroller for watches !!
      This is the reason of the swatch group having buyed that.
      In fact, the swatch group has a local hand on every aspect and every subcontractor for manufacturing watches, so a chip company makes sense :)

    • Hakon

      Hi Dave,

      I’m very sure that Braun just used these antiparralel Coils to get their current rectifies without having two times the voltage drop of the diodes like you have in bridge rectifiers. That might be the best way for efficiency and conserving the battery without a big capacitor.

      Best Regards from Germany,
      Hakon

      • Peter

        I think you are on the money here. I would also be surprised if the EMI is not also reduced due to a balanced current waveform in antiphase – particularly due to the ringing artifacts which seem like they extend to several hundred kHz.

    • f4eru

      look here :
      http://www.emmicroelectronic.com/webfiles/product/asic/sens_act.pdf

      even they use a very low voltage mosfet, they seem to put a charge pump for feeding the gate :) makes sense when the battery is low !

    • Dennis

      It’s quite simple to get all the stuff out of the tube:
      You have to pull the ring at the top around the plastic shaft where you put the brush on.
      On my Braun, it is a metal ring. Once you removed it, you can pull out the whole insides from the tube.

    • axel12p

      How to disassembly a Braun electric toothbrush:
      http://www.blinkenbyte.org/braun-battery-replacement/index.html

      Tried in mine, because original battery has gone completely off.

    • kiu

      Out of fun I measured my Braun 3757 after this episode. It’s a newer model and it uses 31khz. http://dump.501gu.de/braun_3757_scope.png

    • http://hackedgadgets.com Alan Parekh

      Great digging. Next time I need a few million custom chips I know where to go.

      I wonder how long some gold contacts would last to couple the base to the toothbrush? I am thinking that they would probably last the expected life of the brush. It would sure simplify things tremendously.

      • Trui

        The problem is that the gold contacts would collect dirt (e.g. dried up toothpaste) and stop working properly.

    • Grapsus

      I disassembled my borken toothbrush (almost same model) after your teardown. Circuit layout was different, but still using TSM7401 and an EM micro. The coil had only two leads. Mine stopped working because it wasn’t sealed properly, so moist got in there and everything got rusty, the motor shaft wasn’t even able to turn anymore.

    • http://www.RedResistor.com Rob

      I did a teardown on a oral-b toothbrush. Wasn’t too exciting since it was a $2 non-electric one, lol.

      Ok, it was electric and I’m glad I didn’t make a video of it, because getting it open wasn’t pretty. It involved a hammer and diagonal cutters. I’m pretty sure it was glued shut, or maybe I’m just an idiot.

    • http://www.danielbjohnson.net Daniel

      Can someone explain thet micro to us a bit. I assume this is not a one time programmable device, it looks like its more of a you buy it preprogrammed from the factory kind of deal. Am I correct, that hobbyist can’t play with these?

      • Tony

        That’s correct, you supply the factory with the program and they make the chips with that program in ROM. If you want new software, you’ll have to order new batch of chips with new ROM.

        Based on datasheet page shown that chip isn’t even available in flash version, so for development they most likely have some kind of in-circuit emulator.

        Mask ROM isn’t really that uncommon; for example Microchip also can provide you with ROM-masked PICs, but if I remember correctly, you’ll need to meet some quality criteria, buy a lot of chips and whatnot before they even consider selling them to you.

      • http://www.eevblog.com EEVblog

        Correct.
        I think they have a special dev version of the chip is reprogrammable some way, or allows you to do the development. But this brand and style is likely very much not hobbyist friendly. I doubt a hobbyist could even get them.

    • Bearman

      Definitely keep up the tear Down Tuesdays. I like the variety of products and their associated technologies you are discussing.

      Big THUMBS UP!!!!!!!!!!

      B

    • Bruce

      WTF?

      Double coil to increase current handling? antiparralel coils? conserving the battery without a big capacitor? balanced current waveform in antiphase?

      Are you kidding me?

      None of you recognise a simple full-wave rectifier circuit?

      Really?

      The two parts of the appliance form a simple transformer with a centre tapped secondary winding (that’s the ‘two’ coils thingy).

      The rectifier diodes are connected across the winding in opposite polarities with the cathodes connected together to form the ‘output’ connection.

      The centre tap is the 0V (common or return) line.

      During each half of the A/C cycle, one of the diodes will be forward biased and conducting, allowing current to flow from the ‘output’ to 0V. The other will be reverse biased and non-conducting.

      This sort of circuit is very common in these sort of low voltage ‘wireless charging’ appliances due to the voltage drop across the two conducting diodes in a bridge circuit (the only thing you did get right). For silicon that drop can be between 1.2V ~ 1.4V.

      • Jonathan

        I wasn’t going to tell them :)

        BTW, Cost is also a factor. The manufacturing costs for this configuration are less than half that of a single winding with a bridge rectifier chip or four diodes.

    • jopki

      Time to open my Braun – it has seized mechanically after 12-15years of daily service, the battery was still decent…

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    • Pete Higgins

      Presumably the charge pulsing is to enable the microcontroller to measure the battery voltage without any charging ripple in order to determine when the battery is fully charged. It would need a better ADC than the one in the EM6682 to determine state ofcharge from battery voltage.

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