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Current ADC

  1. Apr 13, 2010 #1

    How do i feed the current information in to micro-controllers ADC input to calculate the total power?

    Please help. I am using atmel tiny45 and its a boost converter output current i want to measure for output power.

  2. jcsd
  3. Apr 13, 2010 #2


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    Science Advisor
    Homework Helper

    ADCs measure voltage, just connect the ADC across a suitable resistor with the current flowing through it.
    It's a balance between a resistor that's small enough not to use too much power and to produce a voltage difference big enough to measure accurately
  4. Apr 13, 2010 #3


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    Staff: Mentor

    Does your boost DC-DC use a current-sensing resistor for current liminting? If so, you can do a differential voltage measurement across it (like with an opamp), and drive that voltage into the ADC to sense the current. You may want to do some filtering of that signal, to lowpass to get the average current.
  5. Apr 14, 2010 #4
    No i don't have a current sensing resistor. Although i have two resistors in series to measure the output voltage. But how do i measure the current at the output?
  6. Apr 14, 2010 #5


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    Staff: Mentor

    Without a series current sensing resistor, you won't be able to calculate power (barring a CT). Can you post your schematic? We can't do your student work for you, but we can post hints and suggestions for you to consider to solve your problem.

    Quiz Question for extra credit -- how is the duty cycle of your boost related to the output voltage?
  7. Apr 14, 2010 #6
    Lol i know i need a resistor but i need more information i guess what i have to do is measure the voltage drop then divide by the resistor to get the current value? i have searched the net but haven't found anything. Well my goal is to extract maximum power so all i am planning to do is measure the output voltage and measure the output current multiply them to get output power than increase the duty cycle and measure the output power again. Then compare them if power increased then increase duty cycle further then compare again if power decreased than decrease duty cycle to change the output voltage. It's pretty simple. But how to get the current information into micro controller is the problem right now.

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