5v regulator

Discussion in 'The Projects Forum' started by monkeyhead, Jan 26, 2008.

  1. monkeyhead

    Thread Starter Active Member

    Mar 5, 2007
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    Hi,
    I've got this diagram from a book which says its a 5v regulator!
    I've built it in workbench and on breadboard yet for some reason I get 8.38 volts out :S

    Is there any reason for this? Have I made an error some where?

    Many thanks
    Matt
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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    You need to add a load on the circuit. Try putting around 1K across the output terminals and then let us know what the voltage is.

    The zener diode does not indicate a voltage. What value is it?

    hgmjr
     
  3. Søren

    Senior Member

    Sep 2, 2006
    472
    28
    Hi,

    The values you mention point in the direction of the zener being out of circuit or above 8.3V at least - try moving it around to see if it's connected to the rest of the circuit.
     
  4. monkeyhead

    Thread Starter Active Member

    Mar 5, 2007
    45
    0
    I added a load of 1K ohms like suggest but its only knocked the voltage down by about 200mV. No reading from the diode on the simulation for some reason.

    Many thanks,
    Matt
     
  5. Søren

    Senior Member

    Sep 2, 2006
    472
    28
    Hi,

    Try to remove the zener diode and insert it once more.
     
  6. monkeyhead

    Thread Starter Active Member

    Mar 5, 2007
    45
    0
    Still the same readings :( But ive added a voltmeter to the where the the line of the diode is and in reference to ground and gives a reading of : 8.934v

    Many thanks

    Matt
     
  7. Søren

    Senior Member

    Sep 2, 2006
    472
    28
    Hi,

    Didn't know sims could have faulty components :D

    Anyway, haven't used workbench since like forever (I hate sims), so don't know if you have to select the voltage value of the zener or if you just grab one with the wanted value?
    You'd need a 5.6V zener for 5V out, since the tranny will drop around 0.65V

    If anything else fails, breadboard the circuit :)
     
  8. hgmjr

    Moderator

    Jan 28, 2005
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    In view of the subsequent posts in which were able to report the voltage across the zener to be 8.93 volts the added resistor should have not had any serious effect on the output.

    You could increase the input voltage to 12 volt and notice that the output of the circuit would continue to regulate at around 8.3V.

    hgmjr
     
  9. monkeyhead

    Thread Starter Active Member

    Mar 5, 2007
    45
    0
    Oh noooooo! It appears my Zener on breadboard is a BZV85C 10V... :(
    This is why the voltages wont be right, correct?

    Matt
     
  10. hgmjr

    Moderator

    Jan 28, 2005
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    That is bound to cause a problem with your simulation.

    hgmjr
     
  11. monkeyhead

    Thread Starter Active Member

    Mar 5, 2007
    45
    0
    Hmmm. Is there any recommended zener diodes at 5.6v then?
    I'm gutted :( Ah well learn by our mistakes :)
    Matt
     
  12. hgmjr

    Moderator

    Jan 28, 2005
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    A 1N4734A is a 5.6V zener.

    You could go to Digi-key and see what zener-diode part numbers they have on hand. Then you could try to see if you could find one for which you have a model.

    You could take several ordinary diodes and put them in series to get near the voltage you are looking for. For example, 8 standard diodes should get you pretty close to 5.6V.

    hgmjr
     
  13. monkeyhead

    Thread Starter Active Member

    Mar 5, 2007
    45
    0
    Ok Thanks.
    I've simulated with the 1N4734A zener and I still get the same results. I'm not really sure whats going wrong here

    Thanks for your help

    Matt
     
  14. hgmjr

    Moderator

    Jan 28, 2005
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    In that case, I would exit the simulator and then go back in and start a fresh simulation from scratch knowing what you now know about zeners.

    hgmjr
     
  15. monkeyhead

    Thread Starter Active Member

    Mar 5, 2007
    45
    0
    Same issues, it must be a workbench issue!Thanks though.

    If I replace the diode with a 1N4734A zener in theory it should regulate to 5volts right?


    Matt
     
  16. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    The simulation will be reasonably accurate; just not what you expected.

    Computers can't read your mind (yet) - but they can translate garbage in to garbage out quite readily, and have been doing so for many years now. ;)
     
  17. hgmjr

    Moderator

    Jan 28, 2005
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    That is a good point, sgtwookie. I should have stated my reply more clearly. Thankfully, you captured the essence of my meaning nicely.

    Thanks,
    hgmjr
     
  18. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    OK, I got off my dead arse and on my dying feet to put together a circuit. ;)

    No, it's not wonderful - but it's very similar to what the OP posted, and it does give a simulated output of 4.97V; the 2N2222A transistor leaves much to be desired for current capacity, etc etc ad nauseum - but at least it's a working model.

    What's needed is to come up with something much better than what I threw together in a few minutes.

    [eta] Output is taken across R2.
     
  19. Søren

    Senior Member

    Sep 2, 2006
    472
    28
    Hi,

    Correct, you just had a wee case of selective blindness :D

    Now try with a proper zener, just to convince yourself.
     
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