extend a led circuit

Discussion in 'The Projects Forum' started by markosillypig, Sep 15, 2010.

  1. markosillypig

    Thread Starter Active Member

    Jul 21, 2008
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    hi all i have a circuit that works ok but i would like to modify it a little so need some help i have included the scamat.
    i want to replace the leds with a transistor ??? to make them switch 12v 500ma so i can add replace led with smd led strip pic attached
    can any one help
    thanks
     
  2. wayneh

    Expert

    Sep 9, 2010
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    For switching that much juice you should use MOSFETs, eg. N type rated to 2A or higher. Ground the "source" pins and connect the low side of your loads to the "drains". The high side of the load is connected to +v. The gates are like the base of a transistor and connect to your controller. Finally, you may need to pull the gate up or down with a 1-10k resistor if the controller is not doing that.
     
  3. markosillypig

    Thread Starter Active Member

    Jul 21, 2008
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    any suggestions on the mosfet ?
     
  4. R!f@@

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    Apr 2, 2009
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    search for logic level FET's
     
  5. markosillypig

    Thread Starter Active Member

    Jul 21, 2008
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    i have some irf530's will they do the job
     
  6. R!f@@

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  7. wayneh

    Expert

    Sep 9, 2010
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    You want logic level FETs so that they are fully on - almost no resistance = no heat generation - when the gate goes to +5v.

    A regular FET needs ~10v to go full on, and thus will show some resistance, voltage drop and heat generation at only 5v. However it'll be "nearly" on and would probably work. Half an amp probably wouldn't cook it too fast, and you could use a resistor to adjust the LED brightness to compensate for voltage drop. Maybe try one (530) with a heat sink and see how it goes. If you're patient, go ahead and get a logic level FET.
     
  8. marshallf3

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    Jul 26, 2010
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  9. markosillypig

    Thread Starter Active Member

    Jul 21, 2008
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    would a IRL320 or a IRLZ14PBF or evan this one witch sounds better IRLZ34NPBF
    do the job just been surfing the net ??
     
  10. R!f@@

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    Apr 2, 2009
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    I think they will suffice as Vgs rating given is around 4.5V & 5V
    If you have it, try it. But be careful of heat dissipation.
    If the MOSFET get's too hot to touch, mount it on a heatsink and try again.
    If the heatsink get's too hot to touch then try a bigger one :)
     
  11. markosillypig

    Thread Starter Active Member

    Jul 21, 2008
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    my brother has some IRL3202PBF would they be better
    Max Voltage Vds:20V; On State Resistance:16mohm; Rds Measurement Voltage:7V; Max
    thanks
     
  12. R!f@@

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    Apr 2, 2009
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    this will definitely do ur job. But do keep in mind the heat generated
     
  13. markosillypig

    Thread Starter Active Member

    Jul 21, 2008
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    circuit as this ??
     
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  14. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Don't use 10KΩ for gate R, Use a value between 47Ω to 100Ω

    FET gate needs to charge quickly to turn on. Don't worry uC can handle fet gate currents
     
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