Hi there I'm working on a L298 coupled to a pwm made with a N555) to drive two dc motors 24V 0.3A
unfortunatly the L298 got damaged after just a couple of uses without overheating (I mean that it doesn't burn), anybody can figure out why it happens?
Thanks for every hint

 

You show SB120 diodes in your schematic. Those are rated for a maximum of 20v, and you are using a 24v supply. You will need to use diodes rated for more than 24v.

I don't know why you are using 555 timers for PWM. You should use the L297 IC to drive the L298.

 

well I made a mistake in the schematic, I'm using the right diodes I've on the board SB160, btw I'm using a N555 only because I'm quite new in electronics and I've been hinted so

 

but the combination l297 l298 isn't for stepper motors? i need to drive normal dc motors

 

OK, I missed that (puts on dunce cap).

The first thing I'd suggest doing is from each 555 pin 3 outputs, connect a 470 or 510 Ohm resistor to +5v. This is because a standard bjt (transistorized) 555's output sinks current nearly to ground, but even under light loading, can only get within about 1.3v of Vcc. That's because the output stage has a Darlington voltage follower in it. That means two base-emitter voltage drops between the internal signal and the pin 3 output. Adding the external pull-up resistor helps the output to get near Vcc.

Secondly, did you buy the L298 from an authorized distributor, like Digikey, Mouser, AvnetExpress? If not, that might be a problem. There seem to be quite a few counterfeit components on the "grey market" nowadays. If you purchased the L298 from other than an authorized distributor, you may have a counterfeit part; looks like the real thing, but on the inside it's junk. Auction site sellers are NOT authorized distributors, neither is your local "mom & pop" electronics store.

Thirdly, did you use a large heat sink on the L298? If not, you need to use a heat sink on your next L298. These IC's can dissipate a good deal of power, even with light loading. Yours will need to dissipate about 1.2 Watts of heat per channel, or ~2.5 Watts. Even if you THINK it was pretty cool when it died, it got a good bit hotter than you realize.