Heat Problem of Transistor

Discussion in 'The Projects Forum' started by secretstep, Jun 28, 2008.

  1. secretstep

    Thread Starter Member

    Jun 27, 2008
    17
    0
    Please refer to the attached PSpice pics...

    The load is 10.45 ohms motor, and the voltage and current supply (for stall) sould be around 6V and 0.4A.
    That is around 2.5W... right?

    so the current around 0.6A flows through the NPN transistors...

    The problem is that the heat sinks of both NPN Transistors get too hot (so I cannot touch it). Are they supposed to be that hot?
    I don't see why it gets that hot.

    Here's the spec for the NPN transistors I have... TIP 29C and TIP 41C

    TIP 29C
    Ic (DC) 1A
    Pc, Collector Dissipation (at Tc = 25 C) 30W
    Pc, Collector Dissipation (at Ta = 25 C) 2W
    Junction Temp 150 C
    Storege Temp -65 ~ 150 C

    TIP 41C
    Ic (DC) 6A
    Pc, Collector Dissipation (at Tc = 25 C) 65W
    Pc, Collector Dissipation (at Ta = 25 C) 2W
    Junction Temp 150 C
    Storege Temp -65 ~ 150 C
     
  2. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Your bottom transistor conducts a lot of current all the time, especially when the top transistor conducts.

    The output high voltage of the 741 opamp is about +4V and the emitter voltage of the top transistor is about +3V so the top transistor has 3V across it and a very high current through it. Therefore it gets very hot.

    The bottom transistor gets very hot because it is fighting the top transistor.

    You need an "H-bridge" circuit.
     
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