I am performing a Load test on an LDO. I will be measuring:

  • Input current
  • Input voltage
  • Output current
  • Output voltage.

In the oscilloscope measurement settings I can see MAX, MIN, MEAN, RMS, PK-PK etc. Which one is the most appropriate one for measuring the above parameters, and why?

  • 1
    \$\begingroup\$ What do you want to know about your LDO - what is wrong with the spec sheet? \$\endgroup\$
    – Solar Mike
    Jan 26 '18 at 6:42
  • 1
    \$\begingroup\$ Those measurements give exactly what they state. Maximum voltage, Minimum voltage, Mean voltage, RMS voltage and Peak to Peak voltage. They are all parameters of a voltage signal. Without knowing what characteristic of your listed measurements are important to you, it's quite hard for us to give any advice. \$\endgroup\$
    – MrGerber
    Jan 26 '18 at 6:44

I would consider a load test on an LDO a DC test, meaning static voltages and currents.

So my test could for example be:

  • apply input voltage of 5V, 6 V and 7 V
  • for each input voltage load the output with 1 mA, 10 mA and 100 mA and measure the output voltage and input current.

For that I would use current and voltage meters, an oscilloscope isn't really needed. Still, you could use an oscilloscope as well if that is all you have.

The min, max, mean, rms and peak-peak measurements on an oscilloscope are intended for AC signals. For example a 50 Hz sinewave could have:

  • a maximum of +1 V
  • a minimum of -1 V
  • a mean voltage of 0 V (there is no DC present)
  • an RMS value of 0.7 V
  • a peak-peak value of 2 V

All of these, except the mean value, are not very useful for a DC voltage or current. On the oscilloscope you could select mean but it is not really needed especially if the voltage isn't that noisy as then the standard value (no min, max etc.) is good enough already.

Things are different if you want to do a dynamic load test so for example applying a sinewave on top of the DC input voltage of the LDO. Then the scope's min, max etc. settings can become more important depending on what you want to measure.

  • \$\begingroup\$ Hi,May I know for static load tests simply putting RMS in oscilloscope will give us the noise content of LDO \$\endgroup\$
    – Hari
    Jan 28 '18 at 17:02
  • \$\begingroup\$ Only if you switch on AC coupling (so filter out the DC) and then change the Volts/div setting so that you see the noise. But you will only get an indication of the noise. You cannot measure noise properly with an oscilloscope. For that you'd need a spectrum analyzer because noise is defined in a certain frequency bandwidth. A spectrum analyzer can filter the signal so that only that Bandwidth is taken into account. An oscilloscope cannot do that. \$\endgroup\$ Jan 28 '18 at 20:20

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