Voltage regulator

Discussion in 'The Projects Forum' started by brain8, Nov 13, 2008.

  1. brain8

    Thread Starter New Member

    Nov 13, 2008
    2
    0
    hello, i have built a voltage regulator circuit (it regulates voltage at 9V)for my project and i'm required to also include current sensing and temperature sensing circuitry. For current sensing the cicruit must limit current to 1A and cut-off when 1A is exceeded. For temperature sensing the circuit must cut-off at 60 degrees centigrade.

    For current sensing i was told to use a RS 304-267 IC but i can't find a data sheet so i don't know operation. if any one can suggest another IC and a location as to how to use it??

    For temperature sensing i was given a LM35 IC but again i don't know how to set it to cut-off at 60 centigrade.

    Any suggestions???

    This is for a school project.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    I'm assuming that 304-267 is a Radio Shack catalog number?
    There must be other numbers on the IC itself.
    Consider using a low-value resistor in the power supply return line to ground. I=E/R (Current=Voltage/Resistance). If you had a current of 1 Ampere flowing through a 1 Ohm resistor, you would measure 1v across the resistor.

    You could use a comparator such as an LM339 to compare a reference voltage against the voltage drop across the resistor.

    If you go to National Semiconductor's website, you can obtain the datasheets for both an LM339 and an LM35.
    http://www.national.com

    If you look at the datasheet for an LM35, you'll find that if it's supplied with somewhere between 4 and 20v, it will give an output voltage that corresponds to 10mV/°C. So, 60° will give 60 x 10mV = 60 x 0.01v = 0.6v.
     
  3. Søren

    Senior Member

    Sep 2, 2006
    472
    28
    Hi,

    Not knoving your regulator circuit, I cannot be too specific, but you need to use the detected values to turn down (or cut off completely) the voltage by its regulating circuitry.

    The current could be handled by a ~0.68 Ohm resistor in line with the positive supply (before the regulator circuit) and a PNP transistor with the emitter connected to the positive side of this resistor and the base to the other end of the resistor. The collector would then be able to power a shut down transistor with its collector.

    With careful transistor selection, the temp. output could control a second shut down transistor in parallel with the first.
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    If you aren't married to the regulator you have, look up an LM723. It will do foldback current limiting.
     
  5. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
    1,438
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  6. brain8

    Thread Starter New Member

    Nov 13, 2008
    2
    0
    thanks guys for your help,i understand what to do with the comparators. when i'm finished designing i'll test it and post the schematics...

    thanks again!!!
     
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