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  1. The resistors are on the boards but they don't do current limiting, they are sense resistors that provide a voltage proportional to the winding current, typically 0.5v per amp. This is used to drive comparators that turn off the drive for a short period of time, the so-called 'chopper' action. This is done most easily with the L297 companion chip or a dual op-amp, a dual flipflop and a clock pulse e.g. 555 timer. There are several examples on the web.

    There are other ways to do the necessary current limiting but not with the L298 chip.

    (thanks for the PM btw, appreciated).
    Last edited by irving2008; 23-03-2014 at 07:24 PM.

  2. #12
    Hi Irving,

    Thanks for the above info. The penny has dropped !
    I am working on a PCB using the L297 and L298, which is quite inexpensive in south Africa.
    The size of the desktop engraver is only 400mm x 400mm with a Z movement of around 50mm.
    I will first do a lot of testing and measuring before final set-up.
    The next engraver is already planned. For that I will use more conventional drivers, maybe from the UK.
    (the Rand Pound exchange rate is now around 18 / 1.)
    Your remarks and positive information is very much appreciated.

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