l298 and pwm

Discussion in 'The Projects Forum' started by venividifoto, Nov 1, 2010.

  1. venividifoto

    Thread Starter New Member

    Nov 1, 2010
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    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
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    1,728
    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.
     
  3. venividifoto

    Thread Starter New Member

    Nov 1, 2010
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    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 :)
     
  4. venividifoto

    Thread Starter New Member

    Nov 1, 2010
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    but the combination l297 l298 isn't for stepper motors? i need to drive normal dc motors
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    OK, I missed that (puts on dunce cap). :rolleyes:

    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.
     
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