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Driving heavy duty relays with a TIP110 Darlington transistor. — Parallax Forums

Driving heavy duty relays with a TIP110 Darlington transistor.

LoopyBytelooseLoopyByteloose Posts: 12,537
edited 2009-07-06 05:16 in General Discussion
I'd like to use a TIP110 to drive relays. Some of the 12 volt relays for 10amp at 240VAC are 210ohms and that is roughly 60ma current. But I imagine that if I build a board, I may end up wanting to drive even heavier relays occasionally with higher demand for current. Of course I could use a 2n2222A transistor, but the idea is to get the input current as low as possible so that 16 relays in all coils ON does not overheat the microprocessor.


I am thinking that the TIP110 might be good with a 5600ohm resistor on the base to limit current to it. Of course there will be a diode across the relay coil as well.



What am I overlooking?



The project is to build a board that will allow an SX28 to demodulate remote control IR and toggle 16 relays.

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Ain't gadetry a wonderful thing?

aka G. Herzog [noparse][[/noparse] 黃鶴 ] in Taiwan

Post Edited (Loopy Byteloose) : 7/5/2009 7:47:13 PM GMT

Comments

  • LeonLeon Posts: 7,620
    edited 2009-07-05 18:26
    ULN2803A?

    Leon

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    Amateur radio callsign: G1HSM
    Suzuki SV1000S motorcycle
  • CounterRotatingPropsCounterRotatingProps Posts: 1,132
    edited 2009-07-05 19:20
    > ULN2803A

    Loopy, Leon's suggestion is what I'm using to do about the same thing with fewer relays - for motor, pump, and large fan control. They're pretty beefy --- about 1/2Amp if I recall --- and you can parallel them by physically stacking them on top of each other. (Though I tried that only once as a curiosity test - wonder if the bottom chip might get too hot if really pushed?)

    - H

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  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2009-07-05 19:35
    I have my doubts- 500ma at tops. The ULN2803A could burn up if I turn on 8 relays that are pulling 60ma each and leave them on. Switching relays may actually pull more amps momentarily. There is an overall limitation as the heat from 8 channels will build up in the package. Darlingtons run hot. That is exactly why I am wanting to use an individually packaged Darlington pair. In my approach, the board might easily be used for driving other coils that are more power hungry, like stepper motor coils.

    I just want to confirm that the microprocessor can properly switch the TIP110 if the current is limited to less than 1ma. As the microprocessor has an internal limitation on the total millamps each 8 bit bank can draw. If you exceed it, you burn up the I/O. Sure, you can get 20 to 30 ma out of one pin, but not all 8 pins at the same time.

    Everyone seems stuck on that tiny little chip. I'd like to be able to handle up to 1amp at 12volts in each coil. It just easier to build a heavy duty board and use it for lighter loads than it is to build a light load board and then have to build a second board later.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Ain't gadetry a wonderful thing?

    aka G. Herzog [noparse][[/noparse] 黃鶴 ] in Taiwan

    Post Edited (Loopy Byteloose) : 7/5/2009 7:45:58 PM GMT
  • LeonLeon Posts: 7,620
    edited 2009-07-05 19:47
    It's actually 500 mA per output (600 mA peak). Eight relays at 60 mA each is negligible.

    Leon

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    Amateur radio callsign: G1HSM
    Suzuki SV1000S motorcycle

    Post Edited (Leon) : 7/5/2009 8:08:57 PM GMT
  • stamptrolstamptrol Posts: 1,731
    edited 2009-07-05 20:57
    While physically larger than the ULN, and 2n2222 or TIPxxx, my usual general purpose relay driver is a IRL510 MOSFET which switches nicely at 5 volt, can switch several amps at appreciable voltage and draws no measureable current from the Stamp.

    Cheers,

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    Tom Sisk

    http://www.siskconsult.com
    ·
  • CounterRotatingPropsCounterRotatingProps Posts: 1,132
    edited 2009-07-05 21:00
    Loopy, grab the datasheet on the ULN - it can handle some inrush surge too. I've been driving a pair of healthy-sized steppers 16 hrs / day with it too.

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  • CounterRotatingPropsCounterRotatingProps Posts: 1,132
    edited 2009-07-05 21:04
    stamptrol said...
    my usual general purpose relay driver is a IRL510 MOSFET
    Vdss = 100V
    Id = 5.6A

    not too shabby for < $0.75 !

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  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2009-07-06 05:16
    I think you all really missed the point of my request.

    I was asking to verify how to use the TIP110 and not for other choices. This is an engineering question of how to properly restrict the base current and still get adequate full on of the TIP110. This particulary darlington will output a steady 2 amps per i/O. Admittedly, a MOSfet might run cooler, but it has more capacitance and is harder for me to purchase over the counter in Taiwan.

    If you always use a UNL2803A, your designs are limited by its capacity and heat build up. There comes a point when you want more power and have to use individual components rather than ICs in order to dump the excess heat - especially with Darlington Pairs.

    Stacking two ICs does work to increase power, but is not really the right way to build anything that is intended for long use and service. Beam designers do it with experimental toys. But as you mention, the bottom IC may get very hot.

    What I want to deal with is properly getting the TIP110 to fully switch on and off efficently. I'd rather not build the board and then discover that I've relay chatter.

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    Ain't gadetry a wonderful thing?

    aka G. Herzog [noparse][[/noparse] 黃鶴 ] in Taiwan
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