hi im running a dc 12 water pump with ~15V with pwm from a pic.
im using the l298 for it, and its in parallel mode (until 4A), i made a small board for the l298 (schematics attached), and this is my first time driving big motors, now the l298 get very hot even at 20% by the pwm (i cant touch it for more then a second) so is that normal? and i must use a heatsink? and if i do i would like it to be a small as possible so how would i know what big enough?

olso any comment on how to improve the circuit will be great, cus i made it up by myself from date sheet i dont know if its the best way....

thanksss

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If I calculated the power dissipation properly for 0.7A, it's either running at 40C or 80C without a heatsink. If you can touch it for a second then my guess it would be 40C (maybe?). Anyways, use a heatsink. THe only way to size a heatsink is to hunt through the thermal resistance info in the datasheet and the power dissipation of the driver, and then find a heatsink with the power dissipation and thermal resistance that you want.

Technically "being too hot to touch" is a fairly poorly measure as to how hot is too hot for drivers (a lot of them can run at 85C and even higher which is quite a bit too hot for a human anyways).

 

Also there is a difference between the temperature of the die and the case. You can calculate the difference from the figures on the datasheet.

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thx for ur replays so il get a heatsink on it, but i have a different problem.
the pic is controlling the motor by pwm and as you can see it totally isolated from the pwm circuit not even applying the pwm directly rather then by the tip41 transistor. it has its own 5v regulator and is getting only the 15V... but strangely the pic circuit is influeced and for example when i blink leds at a rate it makes them act very strangly like turn on and off and blink at will or turn slightly on.

the only common spots for the 2 circuits are the 15V the GND and the PWM output, and i have the diodes there and the caps, and still its effecting the circuit somehow, the pic circuit has a its own voltage regulator.
when i run the system without the motor unit it works ok but with it strange things happen.

pic circuit attached below. and btw its happned also when simply conected a single 5V led with a resistor to the pic....

help meh thakzz

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Well that diagram makes no sense at all!.

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it dose when it with the full circuit with picture1 up there in my first post heres the full diagram with few corrections.

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