Dumitru Stama wrote:

>Well, i was just asking if the Darlington would be the best sollution
>for my project. The Voltage is ~6v and without heatsinking (at start).
>I don't know exactly which Darlington i was thinking of using but it
>was one than could handle ~1A of current and max. 30v.
>I guess i will try the IRF sollution proposed by Olin and if it works
>like i want i will stick to that. Nevertheless is good to know that
>Darlingtons dissipate a lot of power and they really need heatsinking.
>I was not thinking about this when i started. I am quite new to
>electronics.
>
>  
>
What Olin is saying- and most people here will agree with him- is that 
Darlingtons
are a VERY old solution to driving power loads. The losses when using 
them are
incredible, about 1.8V of lost switching range, and that power turns 
into HEAT..
It isn't that darlingtons cannot be used- they can- but its a solution 
for a bygone
era, and it will never return. Like using leeches to treat a bad cold.

To drive power devices nowadays, we use MOSFET devices, IR makes some, 
Fairchild
now makes a good assortment. These can switch  many amperes without  
measurable
heat being generated. But some care must be taken to protect these 
devices from
transients (high voltage spikes), which motors are notorious for 
generating..

More important for handling motors is handling rotor locks and or jams. 
Power IC's are
now available that contain builtin MOSFETS, protective diodes, and 
circuitry designed
to prevent damage when a rotor is locked. Some are designed in a bridge 
configuration
that  allows you to reverse the motor with a minimum of fuss.

--Bob

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