Multiple output DC-DC converter.

Discussion in 'General Electronics Chat' started by Rydaholic, Jul 15, 2014.

  1. Rydaholic

    Thread Starter New Member

    Feb 4, 2014
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    Hi,
    I am trying to make a single variable input dc-dc converter with multiple outputs(Buck-Boost). I have succeeded in making single output dc-dc converter(Buck). In which Voltage is stablized or regulated by means of closed loop feedback system (Simple P-Control is implemented). In which a micro-controller is used to take feedback voltages from load, converts it into digital signal through ADC, and this ADC value changes the duty cycle of PWM which is feeded to MOSfET, MOSfet driver IC (IR2110) is used to drive the mosfet. The more the duty cycle, the more the output voltages. A reference voltage is set to maintain the output voltage at some certain level, if the load varies, then ADC value will also change according to it and thus by increasing or decreasing the dutycycle of PWM, the voltage is again maintained or regulated to the reference value. Note that, I made Asyncronous BUCK, so that only one MOSfet is used as a High-Side Switch. There is no problem in this circuit.
    But I want to make a multiple output DC-DC converter. What should I do? If I make similar circuit and only changes the reference value of duty cycle of PWM and then applied to the other one MOSfet driver, and the input is taken from the same power rail, will it work? Please Guide me.
    Thanks
    (The working Circuit of Single Output DC-DC converter Buck is attached).
     
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  2. ronv

    AAC Fanatic!

    Nov 12, 2008
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    To answer your question. Yes that would work.
    A couple of observations on your circuit:
    I don't know your pwm frequency, but L1 & C6 seem very small.
    R1 very big - more like 20 ohms.
    D2 is not needed.
    Unless your micro is very fast the response to transients will be poor.
     
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  3. Rydaholic

    Thread Starter New Member

    Feb 4, 2014
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    Thanks ronv,
    My practical circuit is differ from it in terms of values. While making circuit in proteus, I just forget to alter the values of these components. Don't worry about the values of L1 and C6. They are big enough and works fine.
    L1= more than 2mH, C6= in uF @ PWM frequency of 20 KHz.
    And the value of R1 is 10 ohms.
    One more thing, the other output should also be a regulating voltage, so that the feedback voltage is taken from second output and applied on ADC channel(1), note that first output is applied on ADC channnel (0). Also check my new approach to implement code for Mutli-output.
    x=read_ADC(0) ; x=OCR1A (for first output)
    y=read_ADC(1) ; y=OCR2A (for second output)
    Is it the effiecient way? will only one uC is enough or my application? Because now ADC register has to perform calculations on two variables and vary the duty cycle a/c to different feedback voltages. I want that there is no conflict b/w the two output and there PWM is isolated from each other. One more thing, I think current is divided into two because of paralleling of this circuit with the first one?
     
  4. alfacliff

    Well-Known Member

    Dec 13, 2013
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    as in pc supplies, the main output is regulated in pwm supplies, the other outputs unless low current, are just set by the transformer ratios. thats one reason that you have to put a load on the +5 volt output to use the other outputs.
     
  5. Rydaholic

    Thread Starter New Member

    Feb 4, 2014
    15
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    Dear alfacliff,
    I don't want to use transformer. I want to implement different technique, explained above.
     
  6. ronv

    AAC Fanatic!

    Nov 12, 2008
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    It is difficult to say. In theory it will work if the micro is fast enough.
    You will loose phase margin due to the delay for the micro to process the ADC. This may cause some instability. Think about when the voltage goes to low because the load increased. In hardware you can correct this very fast, but in code not so fast.
    I'm not sure I understand your last question about the current.
     
  7. Rydaholic

    Thread Starter New Member

    Feb 4, 2014
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    0
    I think, implementing code on PID can remove the instability issue.?
     
  8. ronv

    AAC Fanatic!

    Nov 12, 2008
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    Yes, it will help.
     
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