Ripple is the alternating component of voltage from a rectifier. It is a AC factor that residually retained when the rectifier convert ac input power to dc output power. Lower ripple means the DC output is more steady. Using DC output with low ripple for plating can get a better quality. The value of the ripple depends on the design of the rectifier and the charaecteristics of the componenet used. Ripple measurement is an AC measurement at the output of the DC rectifier at rated load and 25 oC ambient temperature. The measurement is always specified as millivots peak-to-peak value.


Demonstration of ripple measurement

Probe connection across the terminal should be
as short as possible
    To measure the output ripple, a 20 MHz bandwidth oscilloscope is normally used so that all significant harmonics of the ripple spikes are included. The time base selected in the oscilloscope should be close to the AC input frequency. For example if the AC input of the rectifier is 50Hz, the time base in oscilloscope should be 10ms/div or 5ms/div. Beware that if the time base selected is too small, for example about 5μS/div, the high frequency content of the ripple may be measured. That is the switching ripple of the rectifier, not the output ripple.

    The measurement must be carefully made in order not to induce error voltages in the test equipment. Conventioal ground clip on an oscilloscope probe should never be used sinces it acts like an antenna or inductive pickup loop, creating an extraneous voltage which is not part of the output noise of the rectifier. To eliminate this noise pickup, the connection of the probe that across the output terminals should be as short as possible. The probe with an external ground band or ring can be used. The measureing method is pressing the band directly against the output common terminal of the power converter while the tip contacts the voltage output terminal during measurement.

    Below is the measuring method commonly use:


  • Measuring Equipment

  • Oscilloscope
  • Probe with ground ring
  • 300mm twisted 16 AWG copper wire
  • 47uF capacitor


  • Measuring Instruction

    1. Switch on the DC rectifier with maxinum current output.

    2. Connect the DC output terminal to the 47uF capacitor and Scope probe using the twisted 16 AWG copper wire.
      (As shown in the digaram below.)


    3. Set the oscilloscope to the following setting:
    4. Coupling: AC coupling
    5. Volt/div: 10mV/div
    6. Time base: 5ms/div
    7. Trigger: Auto triggered

    8. The waveform found in the oscilloscope is the ripple waveform. Its peak-to-peak value is the ripple of the DC output.