Re: [CAD_CAM_EDM_DRO] H bridge progress

Chris,

Great to hear the progress! Keep us posted.

I built a pwm servo drive with 2104's and 8-irf540 mosfets that runs a 110
volt, 2 hp brush dc motor with a buss voltage of 75 for the spindle motor on
a minimill.

The data sheet was not much help to me on a few points. The gate resistor
in the data sheet gave me much more of a problem than it sounds like you
had. I messed around for a long time before I found out a gate resistance
less than 20 ohms worked best. I also put reverse polarity clamping diodes
from each gate drive pin to ground to keep the 2104 from latching up. I
still don't have things perfectly designed because I blew a mosfet and a
2104 yesterday, and the thing has been working perfectly for 3 months, so I
am confused by this. I need to keep working on it.

I have this same design working on all three axis of a small minimill.
They run 24 volt 33 watt servos with a buss voltage of 40 volts. I have not
had any problems with these axis drives, but they operate at a much lower
voltage and current level than does the spindle drive. All the axis drives
run cool heat sink temps too.

I am driving all the pwm servo drives with pic-servo's. I can tell the
pic-servo not to run the servo drive at 100% full on, thus I did not need to
deal with putting a charge pump on the high side to help the bootstrap caps
maintain gate drive voltage. Keep this in mind if your circuit will be
operating at 100%.

Also be carefull with the circuit layout. Keep the gate circuit away from
large current areas of the board. I fear I may not have done this part
correctly.

I am no circuit designer, I just poke around until I find something that
works, so I could learn a lot from some one who knows what they are doing,
and from your rapid progress it sounds like you do.


Thanks

Andrew



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