Dumitru Stama <list <at> mirosat.com> writes:

> 
> 
> Hi guys,
> I implemented a small motor driver (forward only) and i tried it with
> two motors. One small one which sucks about 500 mA of current and one
> which sucks about 4A at normal load; probably more when starting.
> Now, if i am varying the duty cycle the smallest motor works from half
> the duty cycle to the max width of duty cycle (in time).
> The largest motor is not working at all and what is worst, itmakes the
> driver so hot i can barely touch it.
> What is the proper way of using PWM to control the speed of the motor?
> Should i vary the period and keep the duty cycle fixed or exactly the
> opposite? Also is there a proper way of calculating this ?
> 
Dumitru,

this sounds like the controller cannot sink (or source) enough current.  What 
is your output stage? It should be rated for at least 5 A continuous.  Use 
larger MOSFET, I believe IRL510 will do. 

As for PWM control, most people use fixed period and vary duty cycle, but I 
have seen fixed duty time and variable period.  It does not really matter most 
of the time.  The use of fixed period allows one to select PWM frequency such 
that the mechanical parts will not resonate.

Sergey

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist