Electronics Revision

Discussion in 'Homework Help' started by tom6123, May 31, 2014.

  1. tom6123

    Thread Starter New Member

    May 31, 2014
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    Hello everyone,
    Im trying to catch up on some revision but i have no clue how to do it, so ill just give the question.

    A Circuit containing a transformer, Bridge rectifier, Reservoir capacitor and an additional resister/Capacitor (RC) filter circuit, is the be used to construct a dc power supply. the input voltage is 240V@ 50Hz.
    The output voltage is to be 12V Dc and designed to drive a 1k Ohm load resistor.

    Can anyone help me with this?
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    What is the question?
     
  3. tom6123

    Thread Starter New Member

    May 31, 2014
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    I have to make a circuit from this. im currently trying to draw one. i will post it in a second for suggestions. or corrections
     
  4. MrChips

    Moderator

    Oct 2, 2009
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    There is a significant piece of information missing in the specifications:

    What is the amount of output ripple allowed?
     
  5. tom6123

    Thread Starter New Member

    May 31, 2014
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    well to be honest. the information given is all that is given. the diagram that is meant to be produced isn't going to be placed into practical form and is just meant to be bare basics.
     
  6. tom6123

    Thread Starter New Member

    May 31, 2014
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    i have attached a circuit of what i think the circuit is. Im probably wrong but thats why im here. Untitled.png
     
  7. Sparky49

    Active Member

    Jul 16, 2011
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    I think you have mistaken the load resistance for the R in the filter. If it's the load, it should be across the output.

    What puzzles me from the context is that it gives a set DC output (12V), but no other parameters. Is this for a coursework or just a practice question? I would consider asking your tutor if components are required to have values, or just the layout is all that is required.

    I had a similar (slightly more complex) question in my end of year exam, where we were tasked to create a +-12V supply. Was a bit easier as we weren't limited to components, so I could just wack in a couple of regulators and that was that, lol.

    What do you think? If the layout is all that's important, I would simply leave component values out, otherwise, I would recommend you choose and output voltage from your transformer.

    Regards,

    Sparky.
     
  8. tom6123

    Thread Starter New Member

    May 31, 2014
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    Thanks for your reply.
    This is one of the past electrical and electronic principles questions. i have been revising past papers to get a feel of the exam.
    But I've been told there is a similar question to this, yet I've not been able to learn this subject because i was sick when this was meant to be taught, so i had a stab in the dark and tried to work it out myself.

    but the question has some subs, for instance
    "Draw the appropriate circuit using relevant component values"
     
  9. Sparky49

    Active Member

    Jul 16, 2011
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    Okay, I would suggest starting with an output value for your transformer. The exactly value isn't too important in this case, just so long as it is a bit higher than your output.

    Then using a bit of simple parallel/series resistor equations you should be able to calculate the ratio of resistances needed, and from there you can choose their values.
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    One vital piece is your secondary should be no higher than 8.5vac.
    R1 is high for a Pi filter, normally an inductor would be used in place of R1.
    Is R1 what you call your 'Load' resistor?
    Max.
     
  11. tom6123

    Thread Starter New Member

    May 31, 2014
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    well i have been trying to get the circuit right and try to get the values right. here is an update on the circuit. suggestions will be great http://postimg.org/image/7yyc85yrp/
     
  12. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    In your diagram, label the parts according with the names in your problem statement.
     
  13. tom6123

    Thread Starter New Member

    May 31, 2014
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    Im hoping this is what you meant, maybe you can shine some light on my problem
    Untitled2.png

    sorry forgot output voltage
     
    Last edited: May 31, 2014
  14. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    Correct, except that R1/C2 is the RC filter ... not additional resistor/capacitor.

    Also, the load connection on the ground side is not connected to the ground ... see the circled area.

    Now, check your instructions carefully or check with your instructor, to find out the ripple .... or a figure could be determined here.


    what do you think the ripple frequency is?
     
    Last edited: May 31, 2014
  15. tom6123

    Thread Starter New Member

    May 31, 2014
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    it is kind of the values of the circuit that are over my head, i was regrettably sick of pneumonia when i was meant to be taught this.
    would it be possible for you to give me a step in the direction?
     
  16. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    Did you read that section of your text book? What text book are you using?

    http://www.zen22142.zen.co.uk/Design/dcpsu.htm is an easy read that can help you.

    To make it easier and ensure we are on the same page,

    Select your transformer from your favorite webstore ... like mouser, Newark, farnell, whatever, and create the bill of materials list. Select the resistor value from the E24 series (5%) in the pdf below and select the capacitor value from the aluminum electrolytic from the pdf below. Design for the ripple below 5 percent without the RC filter circuit.
     
    Last edited: May 31, 2014
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