Wiring up two 2n3055 transistors

Discussion in 'General Electronics Chat' started by br0ns0n77, Aug 10, 2013.

  1. br0ns0n77

    Thread Starter New Member

    Aug 10, 2013
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    Hi all,

    I have a joule ringer circuit setup using a 2n3055 transistor and it's pulling around 1amp with 2 7.5w LEDs. The 2n3055 is rated for 6amps I believe and it's mounted on a small heat sink but is running fairly hot. I would like to balance the load using multiple transistors.

    Any idea on how to wire that up so that one transistor isn't doing most of the work?

    I'm a newbie to electronics and circuits so lamens terms would be appreciated :) Thank you!
     
  2. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Post your schematic, including power supply voltage(s).
     
  3. br0ns0n77

    Thread Starter New Member

    Aug 10, 2013
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    [​IMG]

    Input is 12v.
     
  4. ian field

    Distinguished Member

    Oct 27, 2012
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    The usual trick is to give each transistor its own emitter resistor, whichever transistor tries to hog the current, develops a greater volt-drop on its emitter resistor - which cancels some of the Vbe drive.

    If by Joule-ringer you mean "joule-thief" or blocking oscillator - the pulses are large and narrow - the emitter resistors should be pretty small, maybe less than 0.1 Ohm.
     
  5. Ron H

    AAC Fanatic!

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    What is the purpose of your circuit? Is it a flasher?
     
  6. br0ns0n77

    Thread Starter New Member

    Aug 10, 2013
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    an inverter to run lights. just wanting to know how to wire up and load balance two 2n3055 transistor.
     
  7. ian field

    Distinguished Member

    Oct 27, 2012
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    That circuit doesn't look right - usually the CT of the 2 windings goes to B+ and the base winding is fed to the base via a current limiting resistor.

    And that circuit is only suitable for 1.5V single cell operation - for higher B+, one end of the base winding would be grounded and it would be AC coupled to the base, you then need a start-up resistor from base to B+ to get the current flowing.
     
  8. Ron H

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    I agree. It looks like a smoke machine to me.
     
  9. #12

    Expert

    Nov 30, 2010
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    Suffering from a bit of ignorance, I ask, shouldn't the transistor be rather cool because it is being used as a saturated switch? What is wrong with this picture? Slow shut-off due to the massive size and antiquity of the 2N3055 transistor? And, if that be true, wouldn't putting 2 in parallel make the problem worse?
     
  10. Ramussons

    Active Member

    May 3, 2013
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    2N3055 is rated for 15A and Pd of 115W. Do you really need more than 1 transistor for this operation?

    Ramesh
     
  11. br0ns0n77

    Thread Starter New Member

    Aug 10, 2013
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    That's what I was wondering... 115w and 6A. If the circuit draws 1A @ 12v = 12 watts that's no where near the max for the 2n3055.

    The circuit works and has been working for quite sometime at or below 1A, but much beyond that the transistor on a heat sink gets hot to the touch.

    Please are there any simple suggestions to modify this inverter circuit to reduce the transistor heat?
     
  12. Ramussons

    Active Member

    May 3, 2013
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    Driven transistors can be operated in parallel using current balancing resistors in the emitter path.

    This is a self excited oscillator and hooking up more transistors for parallel operation is very tricky and not likely to work.

    The total power dissipation by the transistor(s) is going to be, more or less, the same.

    I would say - Use a bigger heat sink.

    Ramesh
     
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