News

News | FiDUS Power

Measuring Power Supply Noise Correctly

Friday, April 13, 2018

When using an oscilloscope to measure the noise output of a power supply, one must utilise the correct return probe attachment. Usually oscilloscope probes come with the crocodile clip return attachment already fitted, which is handy and flexible for most measurements, however for noise measurements it results in an unfavourable or misleading result.

The crocodile return attachment of the probe creates an inductive hoop that induces current from RF (like an aerial) which is then superimposed on the voltage signal that is seen on the oscilloscope.

Below is the oscilloscope image of a power supply when using the crocodile clip attachment

Oscilloscope image of a power supply when using the crocodile clip attachment

Below is the oscilloscope image of the same power supply under the same load, but using the spring return probe attachment

Oscilloscope image of the same power supply under the same load, but using the spring return probe attachment

We can see some subtle differences in the two graphs, which would mislead you in to thinking that the power supply was noisy.

In addition to this it is always important to see how the noise specification is defined on the product datasheet. Often the specification detail states that the oscilloscope must have a 20 MHz bandwidth filter on the probe and is measured with some capacitor across the lines. This may be in the small print notes. On all FiDUS POWER datasheets we state if a bandwidth filter or capacitor(s) are used in defining the specification.Specification


Latest news...

New Medical VPS family offering 600, 800 & 1000W Units with Current Share Expands the Chassis Mount AC-DC Range to 2700W

Thursday, September 26, 2019

The Versatile Power Series offer medical system designers flexible system power solutions from 600 to 1000 watts. The Medical Versatile Power Series allows customers to use this...

Read More...

Universal Medical RHM250 1U, 3 x 5” 250W Natural Convection PSUs

Wednesday, August 21, 2019

The new RHM250 series from FiDUS Power is rated at 250W natural convection and provides 7 different output voltages from 12 to 48VDC. The RHM250P variant is also...

Read More...

Can’t find what you are looking for? Call us 01183 420730 or

Contact Us ›