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Discussion in 'General Electronics Discussion' started by BHARGAV SHANKHALPARA, Feb 15, 2014.

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    Nov 6, 2013
    Hello Everyone...

    I decide to make automatic cradle for baby's, for that i use magnet attraction and repulsion property. for that i attech 2 powerful magnet on movable pipe of cradle and put one coil near this magnet.

    Now to obtain movement we need to energy's coil such a way that moment of cradle can be obtain.

    for that i directly connect two terminal of coil with 12V DC power supply and make switching with hand. Current Rating was 2.5A when turn on. This way i obtain movement in one direction. as i increase coil voltage large movement can be obtain.

    after that i decide to switching it with micro-controller so i can obtain movement in both direction by changing current flow direction. for that i use H-BRIDGE concept.

    i make h-bridge using Relay but it make noise as TICK TACK.
    To Avoid this problem i use power mosfet 55NF06.

    Circuit diagram is attached with this post...

    Problem with mosfet is, after starting circuit mosfet start heating and after minute it become fry.

    please help me, what should i do to avoid this kind of problem....?

    Thank you..!!

    Bhargav Shankhalpara India.

    Attached Files:

    Last edited: Feb 15, 2014
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Always useful to link to the datasheet so people don't have to go looking for themselves.

    It's a logic level mosfet -- good.

    I assume your logic ground (negative supply to the microcontroller) is connected to the negative terminal of the magnet power supply (essentially the source of Q2 and Q4.

    I'll also assume that you're switching one lot of mosfets off (and then waiting a short time -- maybe a millisecond) before switching the other ones on.

    If I'm right, it's Q1 and/or Q3 that gets hot, and that neither are heatsinked.

    If this is true then the problem is that the gates of Q1 and Q3 cannot be raised high enough to turn them hard on. They are operating in their linear region acting as a voltage divider. If your logic runs at 5V and your electromagnet at 12V, then about 7V (12-5) is dropped across the mosfet.

    You need to modify the circuit so that Q1 and Q3 get at least Vmagnet+3 volts appled to their gates, or you use P Channel mosfets and a slightly different driving circuit.
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