Enough Voltage for everything.

Discussion in 'General Electronics Chat' started by TheRoman, Oct 13, 2010.

  1. TheRoman

    Thread Starter New Member

    Jul 22, 2010
    Hi, I have got 4 motors which have a Voltage Range of 3V to 6V, I am using an Arduino board which outputs 5v. So my understanding of this is that the board can only drive one motor, because essentially it needs a minimum of 12v to drive all 4 motors. This made sense in my head, so i hope this is correct so far.

    Anyway i was wondering, what would be the best way to supply this 12v so that i can drive all 4 motors? I was looking up H-Bridge's was I barking up the right tree?

    Thank you for your time in advance.
  2. SgtWookie


    Jul 17, 2007
    You don't wire motors in series; you wire them in parallel - that is, each motor has it's own path to +5v and the board power return (ground).

    You most likely cannot drive a motor directly from your uC; you will need some kind of driver circuit, either transistors or MOSFETs.

    For something easy, look at Steve Bolts' H-Bridge:
  3. TheRoman

    Thread Starter New Member

    Jul 22, 2010
    Hi again, thank you, thats make far more sense, i have tried it with 3 transistors and motors and it works fine.

    I have just has some trouble understanding the datasheet for transistors, so i was hoping you could shed some light on all the details. I have been researching transistors and have an understanding of how npn transistor works and how it can be used as a switch and amplifying. But then when i look at the datasheets i get confused. So for the 2N2222A low power transistor, the datasheet states

    |VCEmaxV| VCBmaxV| VEBmaxV| IcMaxmA| PtotmW| hFE@Ic mA| fT MHz|
    ----40-------- 75------- 6--------- 800----- 500----100@150----250---

    I get confused because it has Collector-Base Max voltage and Emitter-Base Max voltage and also the first one is VCEMax voltage. Then i take it the IcMaXMa is the maximum amount of output current...

    Was just hoping you could explain each one if possible.

    Thanks again.
  4. steinar96

    Active Member

    Apr 18, 2009
    |VCEmaxV| VCBmaxV| VEBmaxV| IcMaxmA| PtotmW| hFE@Ic mA| fT MHz|

    VCEmax is the maximum voltage between the collector-emitter junction.

    VCBmax is the maximum voltage between the collector-base junction

    VEBmax is the maximum voltage between the emitter-base junction.

    IcMax is the maximum current in milliampers you can put trough the transistor (current entering the collector junction).

    Ptot is the maximum power the transistor can dissipate in milliwats. This parameter varies a bit with heat sinking and ambient temperature.

    hFE is the typical current gain. Its the ratio between the current flowing into the base and the current that flows into the collector junction (this parameter is highly unreliable for transistors on transistor to transistor basis even if they are of the same type).

    fT is the signal frequency where the gain of the transistor falls to unity. That is if you apply a signal at the fT frequency to a ampifier utilizing this transistor it means the signal won't achieve any gain between the input and the output
  5. Bosparra


    Feb 17, 2010
    Those are more than likely the absolute maximum ratings. Exceeding these parameters will cause the device to fail.
    VCEmax: Maximum voltage between Collector and Emittor.
    VCBmax: Maximum voltage between base and emitter.
    VEBmax: Maximum voltage between emitter and base.
    IcMaxm: Maximum continuous collector current.
    PtotmW: Maximum power dissapation.
    hFE@Ic: Transistor Beta at specified collector current.
    fT: Maximum switiching frequency.
  6. Bosparra


    Feb 17, 2010
    How's that for cross posting.;)
  7. TheRoman

    Thread Starter New Member

    Jul 22, 2010
    Hi, thanks a lot for the explanations.

    I do still struggle to get everything clear in my head, was hoping an example could help me understand all this information, for instance, looking at all that data, i have a couple of questions.

    A) does it mean the max voltage it can recieve is 40v, becuase the VCEmax is V40 max?

    B) for every 100mA you will recieve ~150mA, because the hFE is 100@150, although i understand from your comments that this is unrealiable.

    c) I have a DC Motor with the following:

    Operating Range: 4.5 - 12v
    No Load Current: 0.45A
    At Max Current: 2.1A

    I take it they should work together?
    Also what does "No Load" mean?

    Thanks for your time in advance. Sorry for the amount of questions, but i find i get lots of material talking about transistors etc, but it would be nice to have a couple of working examples, where an explanation of compatability is used with different components.