Re: [CAD_CAM_EDM_DRO] Re: L297/L298

In a message dated 8/4/2006 3:26:02 P.M. Central Daylight Time,
johnd@... writes:

The L298 is a bi-polar device and consequently generates more heat in
operation than its FET counterparts<<
I think someone should clarify "bipolar" as used here for the non-techie
types:

There are basically TWO realms of semiconductors, those like diodes and NPN
and PNP transistors are called "bipolar;" and the other kind, "FET's"
(Field-Effect Transistors).

This should NOT be confused with "bipolar steppers and drivers!" "UNIpolar"
stepper-drivers have four transistors that alternately connect two
motor-wires to negative, the positive "always" supplied via center-taps in the two
windings in "UNIpolar" motors.

"BIpolar" motors have two windings with NO center-taps, and the two wires
per winding (four such wires in all) are "fed" positive and negative by the
driver, and this polarity is simply SWAPPED to negative and positive,
respectively, first in ONE winding for ONE step and then in the other winding for the
NEXT step, and so on.

A "Bipolar driver" can be made with EITHER "bipolar" or "FET" transistors!
Sorry if I've confused you all by my poor explanation! JRR




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