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How to Test a Power Supply

In the paragraphs below, we will review more in detail some of the most common types of testing for a power supply.


Testing a power supply does not only ensure higher long-term reliability. Benchmark testing is also a needed step to ensure that the power module suits the power requirements and quality standards for its intended application.

Certain issues – such as problems with noise and stability – might not be severe enough to cause a power failure in the power supply. However, they might still impact the power module’s lifespan and long-term efficiency.

In the paragraphs below, we will review more in detail some of the most common types of testing for a power supply.

1. Output Voltage Accuracy Test

Voltage accuracy is usually measured by connecting the measurement device in parallel with the power supply. First, we use the oscilloscope probe’s ground wire to connect the power supply’s ground, and then use the probe of the oscilloscope probe to connect the voltage under test. The voltage accuracy needs testing when the board is unloaded and fully loaded.

We first tune output at a full load at a nominal input voltage. Next, we record the nominal output voltage required by the specification as Vnom and measured output voltage as Vout. Then, we can calculate output voltage accuracy by using the following formula: Output Voltage Accuracy =(Vout – Vnom) / Vnom * 100%

2. Ripple and Noise Test

The ripple and noise are the periodic and random AC variations superimposed on DC output and affect the output accuracy. Ripple and noise are generally calculated with peak to a peak value (MVP-p).

Before testing ripple and noise, we should first set the oscilloscope bandwidth to 20MHz to eliminate high-frequency noise. There are three methods to measure ripple and noise: parallel cable, twistedpair cable, and contact measuring method.

• Parallel cable measuring method

There are two pieces of copper foil tape on the AC/DC power supply under test. First, we connect a 1uF high-frequency ceramic capacitor and a 10uf electrolytic capacitor in parallel on the copper foil tape. We should pay attention that the distance between the two parallel tapes is 2.5mm, and their total voltage drop less than 2% of the output voltage. Next, we can connect the oscilloscope probe to the ends of the copper foil tapes and record the test value.

pic for How to Test a Power Supply

• Twisted-pair cable measuring method

In the beginning, we connect the twisted-pair cable composed of 30cm long and #20AWG to the Vo and OV of the switching power supply that needs to be tested. Then, we add a resistance dummy load between Vo and OV. Next, we connect a 10uF electrolytic capacitor at the end of the twisted-pair cable. Pay attention that when the point of measurement connects, one end is connected to the Vo, and the other is the grounding ring.

• Contact measuring method

As the variety of high-frequency noise received by the oscilloscope’s ground clamp can interfere with the measurements, the contact measuring method can be used to eliminate the interference.

We can directly insert the grounding ring of the oscilloscope into the Vo and OV ends of the AC/DC Under Test. From the results, we can find out that the actual measured ripple and noise vary depending on the circuit and external components.

MORNSUN’s Power Supply Solutions

MORNSUN has over 23 years of experience in providing reliable, efficient, cost-effective power supply solutions for a wide range of applications. Our wide selection of power supplies has already been employed in various industries, including healthcare, railway, IoT, renewable energy, and industrial applications. MORNSUN had built
a UL/ CSA/ TUV Certified Lab, which can implement multiple related test items of power supply, including IEC/EN 62368, IEC/EN 60035, IEC61000-4-4, IEC/EN 60950, IEC61000-4-2, IEC61000-4-5, UL 1741, UL/CSA 60950, UL/CSA 60065, UL/CSA 60601. With the lab, MORNSUN helps verify and maintain the reliability of power products and meets the requirements of the standards. Here you can find more details on some of our testing methods for higher power supply reliability.


Benchmark testing is not only important to improve the efficiency of a power supply’s design while also maintaining specified performance over a range of input and load conditions. Testing a power supply also helps engineers reduce re-runs and expensive design changes or board revisions close to release.

Contact us if you would like to enquire about MORNSUN’s power supply solutions or receive a sample.

For more information, please visit


BiS Team

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