Would like to build this with existing NPN TO-3's

Discussion in 'General Electronics Chat' started by DanAir, Jul 24, 2007.

  1. DanAir

    Thread Starter New Member

    Jan 31, 2007
    7
    0
    Gentlemen,

    I would like to try this circuit using the 2N3055's (NPN TO-3 with heat sinks) that I scrounged from a discarded organ. They test good with an Ohm meter.

    The transistors he listed are PNP's, but from what I've read here and on data sheets, it looks like the NPN's would plug right in, with the collector towards the left (resistor and the bridge) and the emitter towards the right (output and the load). Base remaining the same (towards the regulator).

    Before I release da smoke from da parts, I be needin' some input from you-all.

    Have I got this bass ackwards? What's the correct way to do this?

    Already have most of the parts including huge multi-tap transformer and two meters. Sure would be nice to use existing stuff.

    Any thoughts, advice, or corrections would be greatly appreciated!!!

    Best Regards,

    DanAir
     
  2. cumesoftware

    Senior Member

    Apr 27, 2007
    1,330
    10
    It seems to be OK to me, except that you should put the capacitor at the outpul located before the fuse. A longer path will increase the chance of a possible ground loop to happen. Alse, you didn't specified the resistor values, since their relation is important.

    There is another way of doing this, and it seems a more ortodox approach to me: http://www.mitedu.freeserve.co.uk/Circuits/Power/boosti.htm
     
  3. n9352527

    AAC Fanatic!

    Oct 14, 2005
    1,198
    4
    I don't think it's going to work with NPN transistors. It'd be emitter follower, and the emitter voltage would be close to the unregulated supply voltage.
     
  4. DanAir

    Thread Starter New Member

    Jan 31, 2007
    7
    0
    Cumesofware and n9352527,

    Thank you both for your input.

    The specified resistor values are: R-1 through R-6= .1 Ohm 5 watt..........and R-7= 100 Ohms .5 watt. The bridge is 35A 1000piv. The transformer secondary voltage is 24V and at 35A it will be lightly loaded. It's 6.8KVA wound 10 to 1. The diagrams provided with this transformer clearly approve this usage or I wouldn't use it.

    I'm not an electronics expert, but have wired just about everything used in the HVAC industry up to 460V 60 cycle. Therefore I'm not likely to hurt myself or start a fire. This is just a fun project and will never likely be fully loaded or even used for that matter. Have three 12V battery chargers up to 10A.

    If someone can direct me to a better diagram using these NPN's or show me how to alter this one, I would be grateful.

    Thanks again,
    DanAir
     
  5. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    I agree with n9352527 that the use of NPN transistors is really not a good way to go. Using PNPs works because they act as current sources and so they do not try to buck or fight the voltage output from the 7812. NPNs will serve as voltage sources and they will fight or conflict with the voltage output of the 7812 and the outputs from the other NPNs.

    hgmjr
     
  6. DanAir

    Thread Starter New Member

    Jan 31, 2007
    7
    0
    hgmjr,
    Thanks for your explanation! Transistors are pretty cheap, so I can just order some PNPs which are available in TO-3 style, so I can reuse the sinks. Will put the NPNs in the e-parts box for future use. The help you guys provide is greatly appreciated!!!!!!
    DanAir
     
  7. DanAir

    Thread Starter New Member

    Jan 31, 2007
    7
    0
    Built this using PNP's and it works (12VDC out) as long as the input voltage is 12VAC.
    When input is 24VAC the volt meter pegs at 30VDC and smokes 12VDC lamp (load). Used all the parts on diagram except used TO-3 style transistors.
    Have I missed something here? Any thoughts on this?
    Thanks!!!!!!
    DanAir
     
  8. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    The style of package should not have any bearing on the performance of the transistor. In fact, a TO-3 package should provide the added benefit that comes with a package that can handle more power.

    You are aware that the case of the TO-3 is the collector of the transistor so take extra care that the cases are not accidently shorted together due to mounting the devices onto a common metal heatsink.

    hgmjr
     
  9. DanAir

    Thread Starter New Member

    Jan 31, 2007
    7
    0
    hgmjr, thanks for the responce.
    The TO-3's are on separate sinks, but I have the extended wires from the collectors intentionally tied together at the connection to the rest of the circuit. Looked to me like they were wired together commonly on the diagram. Please advise.
    Thank you!!!
     
  10. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    You are correct. In this circuit, the collectors are tie together.

    hgmjr
     
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