qusetion about transistors connection

Discussion in 'The Projects Forum' started by bluesky01, Nov 4, 2009.

  1. bluesky01

    Thread Starter New Member

    Jul 13, 2009
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    I want a help about how the connection of transistors in parallel because of i want to connect six transistors of tip35 on parallel please help me
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    What exactly are you trying to do?

    Can you post a schematic of your circuit thus far? .png format is preferred. Use the "Go Advanced" button below the reply box, then click "Manage Attachments" on the following screen.

    If you wanted each transistor to sink 15A current (90A total), you would need a total of 9A current for the six transistors' bases.

    If this is a switching application (on/off), you would be better off to use some power MOSFETs.
     
  3. bluesky01

    Thread Starter New Member

    Jul 13, 2009
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    Dear SgTwookie the circuit i want to do is a ubs inverter as shown below
    [​IMG]
     
  4. bluesky01

    Thread Starter New Member

    Jul 13, 2009
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    it's a ups-inverter circuit
     
  5. SgtWookie

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    Jul 17, 2007
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    You might want to know that the "D313" transistors are 2SD313 transistors.
    Datasheets available here: http://www.datasheetcatalog.com/datasheets_pdf/2/S/D/3/2SD313.shtml

    I'm afraid that the inverter you're looking to build is a poor design.

    The SD313 won't be able to source the base current that the TIP35's will require.

    The CD4047 output is very close to a 50% duty cycle, but there is no "dead time" - and even a small deviation from a 50% duty cycle will result in a phenomenon known as "flux walk" which will rapidly destroy the transistors.

    The schematic has errors; for example the transformer center tap has +12v on it, not 0v. The ends are either ~12v or ~0v, depending on whether the transistors are ON or OFF.
    There are no provisions for regulation of the output voltage.

    But to answer your original question, from the emitters of the D313's, you would need six 22 Ohm resistors connected to the bases of six TIP35's.

    But since there are no current matching resistors in the emitter paths for the TIP35's, one transistor will get warmer than the rest, rapidly overheat and go into thermal runaway before it fries. The remaining transistors will rapidly follow suit.

    It is difficult to connect transistors in parallel due to the negative temperature coefficient; the hotter they get, the more they conduct, which makes them even hotter. Power MOSFETs have a positive temperature coefficient; if they are operated in parallel and a MOSFET heats up, it will start carrying less current until it cools down.
     
  6. bluesky01

    Thread Starter New Member

    Jul 13, 2009
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    dear SgtWookie thanks for illustration but there are 2 heat sinks to fit power transistors
    anyway can you give me a good and simple circuit of inverter thats invert 12 volt to 240 volts with sinusoidal wave, i am student and novice in design. sorry for poor english
     
  7. bluesky01

    Thread Starter New Member

    Jul 13, 2009
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  8. SgtWookie

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    Jul 17, 2007
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    The circuit you have been considering would produce a square wave output.

    A pure sinusoidal inverter would have terrible efficiency; most of the power would be wasted in the transistors.

    Efficient inverters use high frequency PWM to synthesize a semi-sinusoidal waveform.

    A good beginning would be to do research on "class D" audio amplifiers, as very much the same technique is used.
     
  9. bluesky01

    Thread Starter New Member

    Jul 13, 2009
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    OK ,thank you very much dear
     
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