L298 help

Discussion in 'General Electronics Chat' started by endaya_walatch, Sep 9, 2010.

  1. endaya_walatch

    Thread Starter Member

    Sep 13, 2009
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    Hi...

    I'm currently using L298 to drive a dc motor.. My problem is that L298 heat up excessively... is this normal? By the way, the duty cycle is 50% and the frequency is 1Khz.. I also posted the schematic that I used.. please help me.. thanks in advance..
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    What is the current requirement for the motor you are using?

    You realize that each output is limited to 2 Amperes, right?

    You also realize that if you are going to be passing that much current through it, you need to have a LARGE heat sink on the IC, right?

    L298 H-bridges are old technology. They are not very efficient. You lose several volts across the bridge; if your motor requires 2A current, about 2.7v is dropped in the IC itself, which at a 50% duty cycle and 2A load, will dissipate 2.7 Watts of power.

    But, you haven't said what your motor requires, or if you are using a heat sink.
     
  3. endaya_walatch

    Thread Starter Member

    Sep 13, 2009
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    thanks for the reply.. ahm, in that set-up alone, we're not using a heat sink.. also, at least we require 2 A current for the motor.. So is it still normal to heat up excessively??
     
  4. marshallf3

    Well-Known Member

    Jul 26, 2010
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    2.7W isn't going to dissipate itself into ambient air, that's a fair amount of power to get rid of.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    You're running the IC at maximum continuous current without a heat sink, and you are wondering why it is getting hot?

    You need a large heat sink. Otherwise, you will very quickly let the smoke out of the L298. Once you let the smoke out, it will not work anymore.
     
  6. endaya_walatch

    Thread Starter Member

    Sep 13, 2009
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    0
    the motor requirement is 3A current. Actually, we're using 2 L298 IC in our quad-rotor project. As you can see in the schematic provided, the other output is for another motor. Also, we doesn't know the dc motor that we're using since we just get it in a mini helicopter. Is it normal to heat up excessively?The motor is connected to a propeller, do you think it is a reason why L298 heat up?

    Lastly, do you have any suggestion/alternative for driving motor?Can a MOSFET be use?
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    Yes, a MOSFET can be used.

    Consider using something like an IRLU8721 logic-level N-ch power MOSFET to sink current from the motor, rather than sourcing current. That is not a random suggestion by the way; it is very well-suited to your application, and should not require a heat sink. Digikey and Mouser stocked them the last time I looked.

    You will also need a diode for the reverse-EMF across the motor; it should be rated for more current than the motor; Schottky preferred, or a fast-recovery rectifier. Standard diodes do not fare well unless your PWM is a very low frequency - and then you have a lot of inefficiencies.
     
  8. endaya_walatch

    Thread Starter Member

    Sep 13, 2009
    33
    0
    ]

    thanks for the advise.. we will try it.. I'll return to share the results.. thanks again.. ^^
     
  9. BONNYONE

    New Member

    Mar 30, 2010
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    Hi all, To start with I'm not an electronics person, I happened on this site whilst reserching electronic components,I Invented a switch to reconise wether a power sorce was wired the right way round ie reverse polarity,and if it was to automaticly reverse it,this is used in the caravan & motorhome sites, we found that sites in Europe were not always round the right way hence the switch. The company that was building this for me went bust & as soon as I heard this I made an offer through the receiver for the stock so as to get all the parts which made up my PCB's, which I got & ended up with about a million parts which I had no idea what they were, through sites like All About Circuits I have learned a great deal about components & through the advice that is given on not only this site but all the sites I've visited have been able to Identify about 85% of the components. I would like to thank all for their help & if anyone is interested in thousands of parts ?
    Again thanks, bazzer (bonnyone)
     
  10. Rbeckett

    Member

    Sep 3, 2010
    205
    32
    In addition to wasting a lot of energy as heat, the flight time on that circuit is going to be very small due to the current draw/voltage draw from the available battery pack. MOSFETs are definately the way to go to reduce heat and improve flight time and lift ability. At those limits, the circuit will fail and then you have an out of control heli to contend with also. NOT a good way to start the day!!!
    Bob
     
  11. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
    201
    Contact http://www.goldmine-elec.com and they may make you an offer for the whole lot of parts.
     
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