Is this Schematic correct??

Discussion in 'The Projects Forum' started by jonnyboy24, Mar 5, 2009.

  1. jonnyboy24

    Thread Starter New Member

    Mar 5, 2009
    Hey guys!

    I'm totally new to electronics. I'm working on a little invention but I need help with my schematic drawing and getting this thing working right.

    Is my drawing below correct? My transistor heats up so hot that it burnt my finger when i touched it! I've got to be doing something wrong. My transistor is just a simple one from radio shack. Do you think i'm putting to many volts through it or is the fast on-off (more like pulsing) causing it to over heat? What do i need to do? :confused::confused:

    Thanks for the help! :)

    Schematic Drawing:
  2. mik3

    Senior Member

    Feb 4, 2008
    The diagram is wrong.

    Connect the emitter to ground and the motor between the positive supply and the collector. Also, put a diode in parallel with the motor with its anode on the collector side to absorb the spikes when the transistor is switched off.
    What is more you need to use a resistor on the base to limit the current through it.

    What is the stall and run current of the motor?

    Which transistor are you using?
  3. SgtWookie


    Jul 17, 2007
    Are you sure that your 3v and 6v batteries are connected as you have shown in the schematic? The diodes to the left of them would block any current flow.

    There is no current limiting resistor on the base of the transistor.

    I'll assume for the moment that you bought a Radio Shack NPN transistor assortment, grabbed one out of the bag and used it in the circuit. They should have part numbers marked on the face of them, like 2222, 4401, 3904, etc. What do yours read?
  4. Wendy


    Mar 24, 2008
    You don't have any current limiting on the base. You need a resistor there. That transistor is likely toast.
  5. jonnyboy24

    Thread Starter New Member

    Mar 5, 2009
    Hey thanks guys for replying! :)

    I thought I might have something upside down.

    I bought a bag of 2N4401 NPN Switching Transistors from radioshack. Link:

    Alberto thanks for that diagram! that's what i need. I thought I might need a resistor or something like that. In the drawing you said a 330 ohm. Is that the correct ohm(age) i need for my setup?

    Would i need a higher ohm if the volts increased say instead of the 3v put a 6 volt in there?
  6. jonnyboy24

    Thread Starter New Member

    Mar 5, 2009
    :mad: My transistor is still over heating! :mad:

    Instead of having the 6v hooked up to it I tried just having 3v connected to the collector and it works fine (doesn't over heat). So i'm guessing i'm pumping to much power through it. But what transistor should i use??

    I picked this one (see link above) because it said "switching" transistor on the package. So being the kind of silly newbie at electronics i said ok i'll buy this one! lol. Does it have to say "switching" for it to be used as a switching transistor?

    Could someone recommend a transistor at that I could use? :) Or what should i do? I need all the power from the battery i can get. (both volts and amps)

    Also I have it set up according to the schematic that was posted as the first REPLY to this thread. thanks :)
  7. SgtWookie


    Jul 17, 2007
    A 2N4401 is only good for up to about 100mA, then it starts getting "toasty".

    Try a TIP120:

    Hook it up like this:

    As the schematic shows, you really only need one battery.
    Just for clarification on the TIP120 connections in the schematic; the wire from the bottom is the emitter, the wire from the left is the base, and the wire at the top is the collector.

    When you are looking at a "real" TIP120 transistor, oriented pins down, lettering facing you, left to right:
    1=Base 2=Collector 3=Emitter
    Last edited: Mar 22, 2009