TIP120 Not Saturating

Discussion in 'General Electronics Chat' started by binsky3333, Oct 2, 2012.

  1. binsky3333

    Thread Starter New Member

    Oct 2, 2012
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    Hello everyone!

    I am currently using an Arduino to trigger a tip120 darlington transistor.

    I have a pin from the Arduino hooked up to the base. I have a 12v hooked up to the collector and then the emitter goes to a solenoid valve. The problem i am having is the arduino is supplying a full 4.5V to the transistor, but the transistor is only outputting 3.5V out of the 12v it is getting supplied. I am not sure what is going on? The transistor has a HFE of 1000, so i only need to supply 5ma(arduino can putout 40) to saturate the transistor. I believe the solenoid is drawing around 4 to 5 amps as the transistor gets pretty warm.

    After doing some more research i read you can put a resistor between the arudino and the base of the transistor. I put a 1k resistor between the two, but it was still a no go.

    I then used this website http://kaizerpowerelectronics.dk/calculators/transistor-base-resistor-calculator/

    to calculate what value resistor i need. Collector current 5A, HFE 1000, Supply Voltage 5, Voltage drop 1.4, came out to 720 ohms. Do you think my resistor is too big? Why would only 300ohm make that much of a difference?

    Any help would be apprecaited, thanks!
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,999
    745
    your using it as an Emitter follower. Put the solenoid on the collector and the +12v supply, and put the emitter to 0v, put your 1k resistor to the base and the arduino output, then it will work.
     
  3. binsky3333

    Thread Starter New Member

    Oct 2, 2012
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    I also read that. The problem is this solenoid is in my car, already prewired. I only get 1 wire (+) and i must apply 12v to that, the other side is grounded to the chassis.

    I tried hooking 4XAA batteries up to the tip120 and i got 10 volts and it worked. Idk why the microcontroller cant get it to work.
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    Just curious, you do know the lowest Collector-Emitter drop of a Darlington pair can go is 0.6VDC, right?
     
  5. binsky3333

    Thread Starter New Member

    Oct 2, 2012
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    Are you talking about when i hooked up the 4 AAs to the base?

    I guess i need a high side switch transistor. AKA a PNP. like a TIP125.

    Wow, duh.

    Actually a TIP125 would not work b/c in order to turn it off i would still need 12+ volts. I dont get it? If i use a PNP will i need 12+ v or can i just use the 5V the arduino is supplying?

    Anyone know of a good High Side Switch IC? Will a mosfet be better than a darlington?
     
    Last edited: Oct 2, 2012
  6. crutschow

    Expert

    Mar 14, 2008
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    3,244
    Yes, you need a high side switch. Here are many hits on that.

    You could also make your own using a small NPN, such as a 2N2222 driving the high side PNP or P-MOSFET switch. I would go with a P-MOSFET.

    Edit: Here is a schematic for the switch using an NPN and a P-MOSFET. The transistors can be any devices that meet your voltage and current requirements.
     
    Last edited: Oct 2, 2012
  7. binsky3333

    Thread Starter New Member

    Oct 2, 2012
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  8. ScottWang

    Moderator

    Aug 23, 2012
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    I just designed a driver circuit for you, but not try it yet, you can check it first, if you want to try it, you should according to your tests and adjust the value of resistors.

    Mj15003 - 140V/20A, The heatsink about 10x10 cm.
    Tip42 - 40V/6A, The heatsink about 5x5 cm.
    2SC1384 - 50V/1A, Maybe it doesn't need the heatsink, it depends on your tests.

    You can search the datasheet here.
    http://www.datasheetcatalog.com/datasheets_pdf/T/I/P/4/TIP42.shtml

    [​IMG]
     
    binsky3333 likes this.
  9. binsky3333

    Thread Starter New Member

    Oct 2, 2012
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    Wow awesome! Thank you so much! I will definitely take a look at that!

    Right now im leaning towards a high side switch automotive IC, seems easier and requires less space.

    Thanks guys!

    Can someone confirm this IC will work?

    http://www.mouser.com/ProductDetail...GAEpiMZZMuCmTIBzycWfI4m8xJauJbqY/xk9%2bdhbjE=

    I know of someone who used a BTS409L1IN.

    The one i linked looks like a updated one that can handle more as the BTS409L1IN is no longer produced.
     
    Last edited: Oct 2, 2012
  10. crutschow

    Expert

    Mar 14, 2008
    13,050
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    That's a low side switch. The OP needs a high side switch to apply 12V to a grounded solenoid.
     
  11. crutschow

    Expert

    Mar 14, 2008
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    binsky3333 likes this.
  12. binsky3333

    Thread Starter New Member

    Oct 2, 2012
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    Awesome, i will be ordering those then. Pretty simple IC.

    +12V in, connect the in pin to the microcontroller, GND to gnd and then output to the solenoid.
     
  13. binsky3333

    Thread Starter New Member

    Oct 2, 2012
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  14. ScottWang

    Moderator

    Aug 23, 2012
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    I designed another driver circuit using Low Internal Resistance Nch MOSFET IRF3205.
    IRF3205,Nch,55V/110A,8mΩ
    IRF3710,Nch,100V/57A,23mΩ

    If you need the high side switch, the we should find a P type MOSFET with Low Internal Resistance.

    [​IMG]

    I post the P type MOSFET driver circuit, but I can't find a P type MOSFET to suit your need.

    [​IMG]

    Maybe you can use two parts inside of BTS50080-1TMA, make them to parallel in and out to increase the current.
    Using the P type MOSFET that I drawed.
     
    Last edited: Oct 2, 2012
  15. crutschow

    Expert

    Mar 14, 2008
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