Transistor heating up on 555 output when increasing voltage level.

Discussion in 'General Electronics Chat' started by Fuji, Jan 19, 2015.

  1. Fuji

    Thread Starter Member

    Nov 8, 2014
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    Im using a BC547 on the output of the 555 timer to increase voltage levels. Basically the 555 output turning on the Transistor. Emitter is to +9, Collector is to the load, other side of load to ground, and 100 Ohm resistor from 555 output to transistor Base.

    The amount of current from the Base of the transistor is what causes the transistor to heat up and this is a problem for me. Is a relay better in terms of lower heat dissipation? What is an alternative as I don't want heat dissipation at all.
     
  2. killivolt

    Active Member

    Jan 10, 2010
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    Post your circuit. You'll get more help if someone can see what your trying to accomplish.

    kv
     
  3. Fuji

    Thread Starter Member

    Nov 8, 2014
    100
    1
  4. ronv

    AAC Fanatic!

    Nov 12, 2008
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    That picture doesn't match your description.
    You said you wanted to raise voltage levels - it uses the same voltage.
    You said the load is in the emitter - it is in the collector.
    You said the load goes to ground - the load goes to V+
    The one in the picture will work if the current is not to high.
     
  5. Fuji

    Thread Starter Member

    Nov 8, 2014
    100
    1
    Would you prefer I take a picture of my circuit on the breadboard? I have no schematic made on the computer.

    I'll just go ahead and draw the schematic.
     
    Last edited: Jan 19, 2015
  6. ronv

    AAC Fanatic!

    Nov 12, 2008
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    A schematic would be best.
    But the 547 is a NPN transistor so it's emitter should not be tied to a more positive voltage than the collector. If you want to keep the load in the ground side use a PNP.
     
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  7. JohnInTX

    Moderator

    Jun 26, 2012
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    Also, at Vdd=9V, a 100 ohm base resistor kind of small - you're pushing 75-80ma into the base of the transistor. 5ma (or less) might be closer to what you want.

    EDIT: I'm not really sure why you are using this transistor at all. Its only good for 100ma max Ic. The LM555 is good for 200ma output with a supply voltage of 15+V.
     
    Last edited: Jan 19, 2015
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