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Variable current power supply with varying duty cycle

Discussion in 'Power Electronics' started by Raiyan, Apr 4, 2018.

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  1. Raiyan

    Raiyan

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    Apr 4, 2018
    I need to build a power supply whose voltage having limits 6v-45v and current ranging from 0.5- 5 amp can be changed according the need.
    Plus it can also provide varying duty cycle
    For example i want the power to be on for 23ms nd off for 2 ms , or on for 12ms nd off for 13ms and so , as per the testing requirement . How can i accomplish that? Any suggestions?
    Can i use a solid state relay with any microcontroller to serve the latter part? By just just giving the on nd off commands in a loop after a certain delay in ms ?
     
  2. ramussons

    ramussons

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    Jun 10, 2014
    I think these are 2 different projects.

    The power supply is one and the "duty cycle" will be an oscillator with adjustable duty cycle, which in turn drives a "driver" or "bridge".
    Is your "power supply" to give a fixed power pulses or free running ?
     
  3. duke37

    duke37

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    Jan 9, 2011
    AC or DC?
     
  4. Raiyan

    Raiyan

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    Apr 4, 2018
    Yes, they are two different parts , u got that right . Once set the duty cycle it should be free running!
    i have tried using LM317 as a voltage and current regulator , but not being able to incorporate the second part . Or i am trying to look for a single circuit that can do both the parts !
    Please suggest something if you have an idea. How can i do it easily and efficiently
     
  5. Raiyan

    Raiyan

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    Apr 4, 2018
    It should be DC but with varying duty cycle , like on for 12ms and off for 13ms . Where this on and off time can be changed and set according to the need
     
  6. duke37

    duke37

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    Jan 9, 2011
    I bought a dual power supply at a junk sale in 2009. This is analog and uses a pair of L200C chips, it controls voltage and current.
    The L200C could perhaps be a basis of a switched mode supply
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,411
    2,779
    Jan 21, 2010
    An LM317 is not going to do the job for you. It has a maximum input voltage less than your choice of output voltage (let alone the higher input voltage which would probably have to be 50V or so).

    In addition, an LM317 had a maximum output current of 1A.

    Even if you found a 5A adjustable regulator, at 6V at 5A the regulator would be dissipating more than 200W.

    For the power supply itself, you would need a transformer rated at around 40V at 7A.

    Then you would want to look at one of the many designs for current boost circuits for 3 terminal regulators. (Or better, roll your own with an op-amp, a voltage reference, and pass transistors).

    Then you would want to add a circuit to provide a variable current limit (this is easier with a regulator not based on a 3 terminal regulator.

    After you have that working, a circuit based on a 555, and a P channel mosfet can easily be designed to chop the output the way you want.
     
    Raiyan likes this.
  8. Raiyan

    Raiyan

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    Apr 4, 2018
    I mistakenly mentioned LM317 actually it was LM138 because even 30V was enough for me and current specification was more crucial .
    I calculated the max power dissipation would be 100W according to my usage limits and can use a heat sink for that.
    I got most of the things you mentioned, i just need more elaboration and help in the last 555 timer part .
    even if i got a controlled DC voltage and current supply , how can i turn it into a square wave supply with adjustable on and off time ??
     
  9. Raiyan

    Raiyan

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    Apr 4, 2018
    I checked L200C but it doesn't meet my power requirements! Outputs upto 2Amps only
     
  10. Hopup

    Hopup

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    Jul 5, 2015
    What kind of application are you going to use this power supply for?
     
  11. Raiyan

    Raiyan

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    Apr 4, 2018
    Basically it is needed to power the Electromagnet . Its actually a research topic and we need to test different readings on different current and duty cycle
     
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