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self-induction recuperation diode, what is it???

Discussion in 'Electronic Basics' started by ErikBaluba, Feb 21, 2006.

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  1. ErikBaluba

    ErikBaluba Guest

    Hi,

    What is the benefit/usage of a "self-induction recuperation diode" ?

    I saw a motor driver schematic with an L298N motor driver, and two diodes
    were used at each of the four outputs, connected to VDD and GND
    respectively. Is this to clamp negative and positive spikes generated by the
    motors to GND and VDD respectively? If so, what does the self-induction mean
    in this context?

    erik
     
  2. Any magnetic (inductive) device stores energy in proportion to the
    square of current passing through it. If you break connection to both
    ends of the inductive load, you can recover most of the stored energy
    back into the supply with two diodes. If you charge up and dump the
    inductive load often, this can amount to a considerable energy
    savings. The alternative is to just turn that energy into heat to get
    rid of it.
     
  3. ErikBaluba

    ErikBaluba Guest

    ....
    Thanks for sharing your valuable knowledge John,

    I do understand how an inductor behaves but as often happens I got confused
    about the terminology. So the self-induction part is not referring to a
    special kind of diode, but rather to a specific use of a diode, meaning
    recuperating self-induction from a inductive load, in this case the motor.

    But what would really happen if the diodes weren't there? Assuming that the
    output ports on the 298 driver do not zink any current caused by
    self-induction in the motor, without the diodes would the self-induction be
    dissipated in the motor's coil-windings? Also, are the diodes there to also
    protect the outputs of the 298 driver IC from spikes caused by
    self-induction in the motor?

    erik
     
  4. That is my guess.
    The inductive load will produce whatever voltage it takes to get the
    inductive current to go somewhere, either into driver breakdown
    voltage losses or into the stray capacitance of the winding and driver
    devices. The voltage across an inductor is proportional to the
    inductance and the rate of change of current. In order to have the
    current go from some finite value to zero in zero time (an infinite
    rate of change of current) requires that there be an infinite voltage
    across the inductance. That never happens, because something else
    happens, first.
    No. More likely in the eddy current losses of the iron parts of the
    motor (they are just shorted secondaries inside the windings) and in
    the switching devices trying to turn off.
    Definitely. Putting the energy back into the supply is just a bonus.
     
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