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switch a 2amp load with a 555 timer — Parallax Forums

switch a 2amp load with a 555 timer

jonwjonw Posts: 67
edited 2006-10-07 05:04 in General Discussion
I want to switch a 2amp load with a 555 timer.·· Using one transistor I have a base current of aprox 200 ma. At 12 volts this is 2 watt. Can the 555 handle 2 watts? I know it can handle the 200 ma.
····· Even if I use two transistors( is this connection correctly called a darlington pair) with one transistor switching the base for the next transistor, I still·· waste· 2 watts.·· Would a mosfet be more efficient? ie less gate current.

Post Edited By Moderator (Chris Savage (Parallax)) : 10/6/2006 7:50:02 PM GMT

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-10-06 19:49
    This thread is being moved from the·BASIC Stamp·Forum to the·Sandbox Forum.

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    Chris Savage
    Parallax Tech Support
  • metron9metron9 Posts: 1,100
    edited 2006-10-06 20:41
    Would a mosfet be more efficient? ie less gate current.

    Yes and nano current to drive it.

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    Think outside the BOX!
  • Mike GreenMike Green Posts: 23,101
    edited 2006-10-07 04:50
    The 555 is specified to handle 200ma and can run easily off voltages up to 12V. The datasheet indicates that the device should be able to handle 1/2 watt for short periods of time. Given that the voltage drop across the device can be as much as 2.5V, that comes out to 1/2 watt at 200ma. If you want to switch a 2A load, you're going to need something else to take the load. Most power transistors have a gain of at least 20-30. You should be able to turn on/off pretty much any switching transistor in this range with 100ma base drive which is certainly doable but seems wasteful when you can get a Darlington transistor with a gain of 1000 for much the same price. The TIP122 can switch 5A up to 100V and is $0.60, comes in a TO-220 package. You can run the 555 off 5V with the Darlington and use a 220 ohm base resistor (to limit the base current). If you want to run the 555 off the 12V supply, you could use a 680 ohm to 1K ohm base resistor. You want 5-10ma of base current to really saturate the Darlington.

    Post Edited (Mike Green) : 10/7/2006 5:03:40 AM GMT
  • Mike GreenMike Green Posts: 23,101
    edited 2006-10-07 05:04
    You can use a HEXFET and those are much easier to use in general these days than conventional (bipolar) transistors with microcontrollers. A Darlington will work fine.
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