Re: L297/L298

--- In CAD_CAM_EDM_DRO@yahoogroups.com, JanRwl@... wrote:

>
> 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

All:

Yikes! Both John and Ballendo are correct. I was
using the "techie" terminology for silicon transistors.
The first transistors that were invented are called
PNP and NPN silcon transistors (actually they used
Germanium first; but I digress.) Silicon transistors
drop .2 volts when they are saturated and consequently
radiate .2V * (current) watts of heat. For the L298,
if you have 4 coils turned full on, that 4 (coils) *
(2 amps) * .2 volts = 16 watts. This is quite hot and
needs a heat sink.

FET (field effect transistors) are newer and have
a lower voltage drop when the are "on". Thus, they
radiate much less heat. I'm not as comfortable talking
about FET's, since most of my experience is with the
older silicon NPN/PNP transistor techonology. I'll
let other more experienced people on the list chime
in about FET transistors.

-Wayne

P.S. I'm out on vacation, and my internet access is
kind of spotty; hence, the delay in my responses.