How it works?

Discussion in 'General Electronics Chat' started by wkyong, Apr 29, 2008.

  1. wkyong

    Thread Starter Active Member

    Apr 29, 2008
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    Pls see attached ,can anyone explain how R1 & Q1 contribute to this high current power supply?
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    If you read the data sheet for a 78xx regulator, you would know, too.

    The regulator is limited to 1 amp current (that is the usual limit for TO-220 packaged regulators). In order for more regulated current to pass, an external transistor has to do the work. That is Q1. R1 makes a small voltage drop so the 78xx IC can control base current in Q1.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Nice explanation, Beenthere - I could practically swear you acquired your knowledge in an environment similar to mine... ;) But then again, I might swear anyway :rolleyes:
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
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    Well, considering your misguided background....
     
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