variable DC Power supply question.

Discussion in 'General Electronics Chat' started by qaisershah, Nov 21, 2014.

  1. qaisershah

    Thread Starter New Member

    Nov 21, 2014
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    Hi friends...
    I am working on this circuit in Picture..i have downloaded from internet.
    This in variable DC Power Supply of 5A and 0-30V.
    i want to ask some question from experts
    1. The Resistors from R1 to R8 are of what wattage?
    2. Any alternate for BD140?
    3. 2N3055 requires any heat sink?
    help me out plz i had completed its PCB.
    Thanking all of you.
     
  2. Brownout

    Well-Known Member

    Jan 10, 2012
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    You can try something like 2n3809's for the BD140's, as this looks like a general purpose NPN transistor. And heat sinks might be a good ides, as this appears to be a high current supply, though it will ultimately depend on the load you plan to connect. Resistors are probably 1/8 - 1/4 W, but try to simulate the circuit to get accurate power numbers. (ltspice is a good sim program)
     
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  3. Brownout

    Well-Known Member

    Jan 10, 2012
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  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    You will need a HUGE heatsink. Say you have the supply loaded with a 1Ω resistor, and you have adjusted it to deliver 5V (it is supposedly rated for this). The voltage across the filter cap will be ~30V, so the transistors/emitter resistors will be dissipating P=IE = (30-5)*5 = 125W! This makes a pretty good room heater, and will likely need a fan...
     
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  5. qaisershah

    Thread Starter New Member

    Nov 21, 2014
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  6. qaisershah

    Thread Starter New Member

    Nov 21, 2014
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    can i use 2SA1195 or 2SA 1220 inplace of BD 140?
     
  7. qaisershah

    Thread Starter New Member

    Nov 21, 2014
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    Thanks friend...that was informative
     
  8. Brownout

    Well-Known Member

    Jan 10, 2012
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    Heck if I know. What are those? Are they general purpose NPN's? Check the specs against the ones specified and that will tell you.
     
  9. qaisershah

    Thread Starter New Member

    Nov 21, 2014
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    2SA1195 and 2SA1220 are transistor i found these details:-
    Type Designator: 2SA1195

    Material of transistor: Si

    Polarity: PNP

    Maximum collector power dissipation (Pc), W: 10

    Maximum collector-base voltage |Ucb|, V: 40

    Maximum collector-emitter voltage |Uce|, V: 40

    Maximum emitter-base voltage |Ueb|, V: 5

    Maximum collector current |Ic max|, A: 3

    Maksimalna temperatura (Tj), °C: 150

    Transition frequency (ft), MHz: 50

    Collector capacitance (Cc), pF: 35

    Forward current transfer ratio (hFE), min: 80
    Can i use this inplace of transistor BD140?
    Thanks
     
  10. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    The two resistors and one pot, all in series and between two common. What is that? R2 R3 and VR1. A common divider?
     
  11. Brownout

    Well-Known Member

    Jan 10, 2012
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    They might work, but that wouldn't be my choice.
     
  12. ScottWang

    Moderator

    Aug 23, 2012
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    2SA1195 is ok, the Ic current of 2SA1220 has a little less then DB140, for the replacement if the values is great that is better than less.
     
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  13. Brownout

    Well-Known Member

    Jan 10, 2012
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    You're right. I take back what I said in post #11.
     
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  14. qaisershah

    Thread Starter New Member

    Nov 21, 2014
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    Thanks
     
  15. qaisershah

    Thread Starter New Member

    Nov 21, 2014
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    hi friends..i found BD140 and used it. everything in circuit is working perfectly except that it gives variable voltage only between 18V to 24 V instead of 0V to 30V. Is this some problem with IC?
     
  16. ScottWang

    Moderator

    Aug 23, 2012
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    I have also had some power supply used the LM723, although it was an old chip, but it still good to use, you can adjust the VR1 and measuring the P.11, if the voltage of P.11 no change or just a little changing, it could be some thing happened in LM723, check all the circuit for LM723, if you was used the socket for LM723 then you can change another new LM723 to try.
     
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  17. qaisershah

    Thread Starter New Member

    Nov 21, 2014
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    P.11 means IC pin at R4?
     
  18. qaisershah

    Thread Starter New Member

    Nov 21, 2014
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    P.11 means IC pin at R4?
     
  19. ScottWang

    Moderator

    Aug 23, 2012
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    P.11 - Pin 11 of LM723.
     
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  20. qaisershah

    Thread Starter New Member

    Nov 21, 2014
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    I checked at pin11 , the vvoltage regulates between 18 to 25V.
     
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