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Help selecting n-channel mosfet for analog-region use...

Discussion in 'General Electronics Discussion' started by bvanpelt, Mar 21, 2015.

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  1. bvanpelt

    bvanpelt

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    0
    Mar 21, 2015
    I have a 1920's self-winding master clock from a school. Its movement closes contacts once a minute, for one second, to energise it's winding electromagnet. It's powered from 24V dc. The coil resistance is about 240 ohms, so it's 'on' current is about 100ma.

    It's 'wind' and 'release' actions are pretty noisy - my neighbors complain!

    I'm planning to replace the existing contacts with a Raspberry Pi and a DAC (3.3v output max) to drive a n-channel mosfet, which would in turn drive the existing coil. This approach would let me drive the coil with a waveform, rather than the existing square wave (per the existing contacts). I expect to experiment until I find a waveform that gives me a quiet wind and a nearly silent release.

    I need help choosing the mosfet! I want something in a to-220 case, rated at 100v S/D, that I can drive with 3.3v from the DAC. Most of the specifications I see on the internet discuss devices that are expected to operate in switching mode, and I'm having trouble identifying a suitable general-purpose part.

    Any thoughts?
     
  2. Arouse1973

    Arouse1973 Adam

    5,165
    1,087
    Dec 18, 2013
    Hello
    Thats not a problem but you say T0220. Do you know this pin out of the device you want to use?
    Adam
     
  3. bvanpelt

    bvanpelt

    3
    0
    Mar 21, 2015
    I'm looking for suggestions regarding the device. I like the to-220 package as I can mount it to the clock's movement, close to the winding coil. Mounted to the brass movement, and with the once-a-minute duty cycle, should solve any thermal issues. Once I have ideas on the particular device to use I can locate it's pin-out.

    Any ideas?
     
  4. Arouse1973

    Arouse1973 Adam

    5,165
    1,087
    Dec 18, 2013
  5. bvanpelt

    bvanpelt

    3
    0
    Mar 21, 2015
    I'm planning n-channel. I looked up the part you mentioned - it might be a great fit for me! I've just ordered four of them. Thanks for your help!
     
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