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can you recommend a good transistor? — Parallax Forums

can you recommend a good transistor?

roboticmaggotroboticmaggot Posts: 12
edited 2005-10-27 17:31 in BASIC Stamp
I need a transistor to hook to a basic stamp for turning on/off a 2 amp current load. The load is 75 superbright LEDs.
Any ideas?
Thanks!

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-10-24 16:33
    A MOSFET might be a better choice here.· There are several examples on the forums here for using one, but basically you'll need the MOSFET and a resistor.· Unlike a transistor, this·resistor actually connects to ground.


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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Robert KubichekRobert Kubichek Posts: 343
    edited 2005-10-24 16:47
    roboticmaggot said...
    I need a transistor to hook to a basic stamp for turning on/off a 2 amp current load. The load is 75 superbright LEDs.
    Any ideas?
    Thanks!

    We would need more info, ie;

    What is the led max supply voltage? Which determines if some of the leds will be in series...

    At 12V you could have 3 leds in series with a resistor for the proper current regulation...

    It all depends on the specs of the led you are going to use, some bright white leds have a vf of 3.6 max at 30ma,
    so 3 x 3.6v = 10.8v at 30 ma plus the proper resistor....

    75 / 3 = 25 25 x .03 = .75 A or 750 ma

    If you do it this way, your power requirements for the solid state switch (mosfet/transistor) will be a lot lower.

    A power mosfet is the best way to go....


    Bob N9LVU scool.gif
  • roboticmaggotroboticmaggot Posts: 12
    edited 2005-10-24 16:55
    I am running the LEDs in series sets of 4 with a 12v supply.


    What about an IRL520N?
  • Robert KubichekRobert Kubichek Posts: 343
    edited 2005-10-24 17:33
    roboticmaggot said...
    I am running the LEDs in series sets of 4 with a 12v supply.


    What about an IRL520N?

    What is the max current of the leds????

    75 / 4 = 18.75 or
    19 strings of 4 each, for a total of 76 leds...
    25 strings of 3 each, for a total of 75 leds...

    19 x 25 ma = 475 ma
    25 x 25 ma = 625 ma

    Also, you would be much safer to put a resistor on each string of leds, as it would be much safer, and the resistor
    would NOT have to handle such a large load...
    Plus each led is not always the same as the next as far as light output, quality..... You will have to match em to get
    an equal output....

    Bob N9LVU scool.gif
  • roboticmaggotroboticmaggot Posts: 12
    edited 2005-10-24 17:47
    I believe the max current is around 25ma.
    19 strings of 4 each, for a total of 76 leds...
  • KenMKenM Posts: 657
    edited 2005-10-25 02:17
    Yes, the 520N is a good choice.
    roboticmaggot said...
    I am running the LEDs in series sets of 4 with a 12v supply.


    What about an IRL520N?
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    Ken
    IRL520 drive circuit.jpg
    869 x 555 - 53K
  • roboticmaggotroboticmaggot Posts: 12
    edited 2005-10-26 03:12
    Thanks!
    is there any real difference between an IRF520 and an IRL520?
  • KenMKenM Posts: 657
    edited 2005-10-26 06:19
    The IRL device is specifically designed to turn on fully with a Logic level voltage (and the stamp 5v does the job nicely), hence the L in IRL.

    The IRF on the other hand will switch only about 2 3 amps at 5 volts to the gate. To switch higher currents more than 5 volts is needed.

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    Ken

    Post Edited (KenM) : 10/27/2005 2:31:26 PM GMT
    IRF520.jpg
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  • Clock LoopClock Loop Posts: 2,069
    edited 2005-10-26 07:31
    Dont forget the ULN2003 chips!!! They can handle high voltage, and high current. You can drive your 12volts at 2 ampere with a single ULN2003 chip set up so the lines are parallel.

    Good luck.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2005-10-26 16:43
    I suspect that you are going to smoke that UNL2003 by trying to drive 2 amps.

    Take a look at the total power output for the package.· I think it is 500milliwatts

    Amps x Volts = watts··· 2ampsX12volts = 2400 milliwatts

    And watts = heat· Heat = smoke and fire.· Hmmmm.


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    ······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
  • roboticmaggotroboticmaggot Posts: 12
    edited 2005-10-26 22:26
    kenm said...
    the irl device is specifically designed to turn on fully with a logic level voltage (and the stamp 5v does the job nicely), hence the l in irl.


    The irf on the other hand will switch only about 2 amps at 5 volts to the gate. To switch higher currents more than 5 volts is needed.

    thanks!!
  • Clock LoopClock Loop Posts: 2,069
    edited 2005-10-27 04:45
    Kramer said...
    I suspect that you are going to smoke that UNL2003 by trying to drive 2 amps.

    Take a look at the total power output for the package. I think it is 500milliwatts



    From the DATASHEET.

    The ULN2001A, ULN2002A, ULN2003 and
    ULN2004A are high voltage, high current darlington
    arrays each containing seven open collector darlington
    pairs with common emitters. Each channel
    rated at 500mA and can withstand peak currents of
    600mA.     Suppression diodes are included for inductive
    load driving and the inputs are pinned opposite
    the outputs to simplify board layout.d

    Combine all 7 channels and you have over 3.5 ampere.
    Natually a DIP package supplying 3.5 ampere WOULD NEED A HEAT SINK.
    But I do not know if this person requires continual supply of power, or a low duty cycle.
    Also I have NOT tried it myself so I cannot say for certain that the DIP package can withstand this kind of power.
    The data sheet suggests it can, when its within its thermal limits...

    If sustained ampere is required, most likely a transistor is better, as it is made to withstand MUCH higher thermal limts.
    Plus who wants to put a heatsink on a DIP.. I dont even know how one would go about it.
  • Bruce BatesBruce Bates Posts: 3,045
    edited 2005-10-27 06:44
    Gents -

    Aavid-Thermalloy makes plenty of different heat sinks for DIP packages:
    http://www.aavidthermalloy.com/cgi-bin/standarda.pl?PgNum=1&thermalresist=40.5&HeightMax=7&HeightMin=2&SortBy=TR&NumPerPage=all&Device=12&x=28&y=9

    Regards,

    Bruce Bates
  • Clock LoopClock Loop Posts: 2,069
    edited 2005-10-27 07:05
    If I put wiings on my DIPS will it make it go faster?

    580200w00000.jpg

    LoL, just kiddin.. But wow, I guess now I know....
  • KenMKenM Posts: 657
    edited 2005-10-27 14:33
    I wonder what the value of theata case to sink is with those dip heat sinks? Can't imagine it is too good, but some heat sink is better than none.

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    Ken
  • Paul BakerPaul Baker Posts: 6,351
    edited 2005-10-27 17:31
    If you know you'll need a heat sink on a chip, try your best to find a ceramic packaged chip instead of plastic, it has better heat conduction and can withstand higher temperatures. Most "need to sink" components have means for heat conduction through the ground pins the TO-220 package is a good example but there are several other packages that do it via wider center pins for ground.

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    ·1+1=10
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