AC to DC converter

Discussion in 'The Projects Forum' started by aishwarya1404, Dec 29, 2011.

  1. aishwarya1404

    Thread Starter New Member

    Dec 29, 2011
    6
    0
    I'm doing project on transformer testing... i've to give supply to microcontroller... so i've to convert 0-500v supply to 0-5v... like if i give 500v supply it should show output as 5v... for 400v as 4v.. it should be vary linearly.. please give me some ideas..
     
  2. @android

    Member

    Dec 15, 2011
    178
    9
    I'm little confused here! You said you wanted to give supply to microcontroller then...??
     
  3. Santosh_16k

    New Member

    Aug 19, 2011
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    0
    Use comparators to check for values 5V, 4V, 3V, 2V,1V (Use them as reference voltage to the comparator)...
    Send the output of the comparator to the micro controller...depending upon which ports go high you will get the desired output...
    You can increase the number comparators for better accuracy...
     
  4. debjit625

    Well-Known Member

    Apr 17, 2010
    790
    186
    Make it clear what you want to do...

    Are you trying to supply the microcontroller i.e. to power it using transformer ,if yes then use a step down transformer of 6V and then regulate it using any linear regulator like 7805 or using switching regulator like MC34063A.

    Or if you are trying to measure a voltage range from 0 to 500V using ADC (Analog To Digital Converter) module of your mcu,then most mcu’s ADC will accept an ADC input valid voltage range of 0V to 5V,so you can use a step down transformer of 100:1 ratio so that you get the valid input range of ADC ,but don't directly pass the voltage to ADC use a buffer with clipper circuit.

    Good Luck
     
  5. aishwarya1404

    Thread Starter New Member

    Dec 29, 2011
    6
    0
    Thanks for the information........Actually i have variable ac voltage of 0 to 5 volts and i need to vary it to 0 to 5 volts dc and my other condition is the output dc should vary linearly with respect to ac input
     
  6. debjit625

    Well-Known Member

    Apr 17, 2010
    790
    186
    Normally in this kind of circuits we have to consider many things like the AC value you provided i.e.. 5VAC, is it in RMS or peak or peak to peak ? if its in RMS then remember 5VAC RMS is 7.072 Volt peak and 14.144 Volt peak to peak ,normally an ADC input will not accept the negative half cycle. The AC voltage can be converted into DC using a diode ,but normally silicon diodes have a forward voltage drop of 0.7 volt, so for measuring, the minimum voltage will be 0.7 not 0V ,you can use low forward voltage drop diodes like Schottky diodes also known hot-carrier diodes typically 0.25 to 0.4 volts. But still as said earlier you have to use a buffer and a clipper circuit .

    Good Luck
     
    aishwarya1404 likes this.
  7. billbehen

    Active Member

    May 10, 2006
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    aishwarya1404 likes this.
  8. aishwarya1404

    Thread Starter New Member

    Dec 29, 2011
    6
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    Actually i tried using diodes and i got rectified output also but the problem is the output is not linearly varying with input.Actually wt i need is if input is 1 v ac then i need to get 1 v dc...for 2 volt ac i need to get 2 v dc and so on.......or if input is 1 v ac then if i get output 2v dc further if i applied 2v ac then i should get 4 v dc like that it should vary linearly....but using diode im not getting linearity...
     
  9. aishwarya1404

    Thread Starter New Member

    Dec 29, 2011
    6
    0
    I'm thinking to use RC filtering circuit for filtering the rectifier output.....and i need to design it...So pls help me how to calculate that time constant and how to design it
     
  10. roadey_carl

    Active Member

    Jun 5, 2009
    116
    5
    how is the variable ac input being made variable?
     
  11. bwack

    Active Member

    Nov 15, 2011
    107
    10
    Is it required to do all these analog rectifying, filtering stages before the mcu ?

    You could sample the AC at a much higher speed than 50Hz, then calculate Vac from that, then run that value thru a (precalibrated) polynomal function to dampen the linear errors. You would need a voltage divider and a buffer though. Oh btw you wouldn't actually need to sample so very quickly, only long enough to pick up the max and mins.

    Example of polynomal curve fitting: http://www.waitingforfriday.com/index.php/USB_Performance_Monitor
     
    Last edited: Dec 30, 2011
  12. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,788
    945
    You could sample the AC directly with a large cap and a peak detector to sample the voltage and ouput the peak value. If the AC peaks at 4.4 vac then the circuit should make seeing a DC value of 4.4 volts easier. It only needs to hold the peak value for a duration equal to 1/freq of the AC waveform
     
  13. aishwarya1404

    Thread Starter New Member

    Dec 29, 2011
    6
    0
    using potentiometer....
     
  14. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    Using a potentiometer as a voltage divider for 500V isn't quite within their specifications. In some conditions, there will be arcing when the wiper is moved.

    What is the overall intent of the project, meaning, what is supplying the high voltage AC and what needs to be acted on based on that voltage, and why it would vary.
     
  15. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    Buddy , did you even finish reading what OP wrote ?

    As for u, Please do reply properly if you want to help. Otherwise you are confusing the OP.

    Where are we getting these guys. Isn't there any rule to really find that a new member is even qualified to give advice about such circuits.

    This is bad. It confuses a lot of people.


    As for the OP's real problem, she does not give us much about her project.
    And it includes high voltage than mains.

    If you want us to help, give us more details of the project and your experience with high voltage.

    Should this be Moderated before actually giving suggestions.

    Did any body care to ask OP how she is getting the 500V from or where it is sourced and how is it reduced.
    Is it isolated or not ?

    Before replying to such questions, members should take caution about the level of danger involved.

    And n00bs should not be allowed to reply to those specific threads if AAC does not know the qualification of that member.


     
  16. debjit625

    Well-Known Member

    Apr 17, 2010
    790
    186
    Ok remember their are two kind of potentiometer linear and log,if you are using a log type then the voltage will be not divided linearly.
    http://en.wikipedia.org/wiki/Potentiometer#Logarithmic_potentiometer

    I think he/she is using PT(Potential Transformer), its nothing but a step down transformer.Anyway you asked it....
     
    R!f@@ likes this.
  17. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,536
    There is a very real concern about safety issue here. This is the kind of stuff we need moderators for.

    Questions:

    You want to convert line voltage with a transformer to 500V?

    You want to test this with a microcontroller?

    This is a test station?

    What are the current, you give no clue as to the wattages you are talking about?

    Are you manufacturing the transformers in question?

    Intermediate answers:

    You simply haven't given enough information to be able to help you much. This could be a language problem, or it could be a competence problem. If the moderators conclude the latter we will reluctantly have to close this thread.

    So, please, give us the required information before going off half cocked.
     
    R!f@@ likes this.
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