Check power supply

Discussion in 'Homework Help' started by simo_x, Jan 24, 2011.

  1. simo_x

    Thread Starter Member

    Dec 23, 2010
    200
    6
    Hi all, I have to check, without any measuring instrument (voltmeter and ampermeter) if a power source can supply 13,2 Vcc and at the same time 5,5A & 50A.

    I was thinking about using 2 schottky (with little voltage drop) for a 12V - 65W bulb (5,5A) but I don0t know what use for the 50A..
    However, I am trying to find a way for it.. Do you have some idea??
     
  2. Georacer

    Moderator

    Nov 25, 2009
    5,142
    1,266
    I would say zener diodes and current division networks and LEDs. One circuit for each ampere rating.
    Then again, power isn't really my thing.
     
  3. Wendy

    Moderator

    Mar 24, 2008
    20,764
    2,535
    Dealing with a bad power supply I have found a oscope to be critical. This is because a meter (such as a DVM) can not see if the power supply has dropouts, where the voltage goes from the regulated level to ground and back in a narrow pulse. HP power supplies were very bad about this.

    You can cobble together an electronic load, using a power BJT transistor on a heat sink in a constant current mode to make a easily programmable current sink.
     
  4. simo_x

    Thread Starter Member

    Dec 23, 2010
    200
    6
    I am not so expert about transistors.. How to deal with it???
    Could I use two thyristors?
     
    Last edited: Jan 25, 2011
  5. Wendy

    Moderator

    Mar 24, 2008
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    No, thyristors will stay on once they conduct. You need a basic constant current sink. Power transistors of the BJT variety are easy to thermally heat sink, they have many package styles such as the TO3 (google it) that are meant to make it easy.

    I have a half way designed project for an electronic load, I'm working on getting an adequate chassis for it.

    Electronic Loads

    I find it unusual you have not studied basic BJT transistors, but have studied TRIACs. I highly recommend you put the hours in understanding transistors, as they are not going away, and have a lot of uses left in them still.

    A much simpler version than what the link shows is possible.
     
  6. Wendy

    Moderator

    Mar 24, 2008
    20,764
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    I went ahead and drew up some simplified versions. The transistors will get extremely hot, at 1A R2 will barely heat up (and the transistors might scorch wood). The second drawing is slightly better, but both are constant current sinks, vary the voltage into them collector to ground and the current shouldn't change much. R1 adjusts the current setting.

    [​IMG]
     
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