PWM DAC For Programmable DC Power Supply

Discussion in 'The Projects Forum' started by calvin0908, Mar 17, 2010.

  1. calvin0908

    Thread Starter New Member

    Mar 9, 2010

    I am doing a project of a programmable DC power supply, the programmable resolution is 1mV/1mA, PWM DAC is a low cost solution, but I am a litter worrying about the PWM DAC resolution, many microcontrollers have a 16-bits PWM integrated, but I am a little worry about the real performance like settling time, ripple noise, transient response. is there any expert can give some suggestion?
  2. DickCappels


    Aug 21, 2008
    Yes, there probably is an expert who can answer, but he apparently is not here right now.

    How about getting the datasheet for the microcontroller you are thinking of using and comparing the specs with the performance you will need.

    The good news is that with a little are, PWM DACs are inherently monotonic. In general, the higher the frequency and the lower the cutoff of the filter, the less ripple you will have. The lower the cutoff frequency of the filter, the longer the settling time.

    If you can post your desired specs, such as the output range in millivolts or milliamps, and if you have a favorite controller in mind, maybe you can receive some more helpful information.
  3. calvin0908

    Thread Starter New Member

    Mar 9, 2010
    Thanks DickCappels.

    The specs of the power supply are probably like this:

    Voltage output range: 0-50V
    Current output range:0-4A
    Programmable voltage : 5mv+0.1%
    programmable current :10mA +0.2%
    Programmable Resolution: 0.5mV/0.5mA
    Voltage/Current Programming speed <12ms
    Ripple and Noise (20Hz to 20Mhz): <350uVrms/2mvVpp

    I am planning to use a 8-bits microcontroller to generate PWM DAC signal, most of 8-bits MCU has a 16-bit resolution PWM, but the problem I am wonderring is : most of 8-bits MCU's clock frequency is less than 20Mhz, so the PWM frequency is less than 20000000/2^16=305Hz, to suppress this low level ripple noise, the settling time is very long and unacceptable.more longer settling time, more slower programming speed.

    Does this mean I need have to turn to a more higher speed MCU?