LED Power Supply Testing Methods and Precautions

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On 02/11/2025

Testing the performance and reliability of power supply units (PSUs) is critical to ensure they meet industry standards and function as expected in various operating conditions. This article outlines several key testing methods, including ripple & noise, efficiency, insulation resistance, and short-circuit tests, as well as the necessary precautions to ensure accurate and reliable results.

Table of Contents

1.Ripple & Noise Test

Purpose: The ripple & noise test measures the variations in the output voltage of a PSU to ensure it meets the specified ripple and noise limits.
Equipment: AC Source, Electronic Load, Oscilloscope, Chamber (optional)
Test Procedure: The connection should follow figure 1: AC source – PSU – Electronic load, Connect a test fixture to the output terminals of PSU, then connect the oscilloscope probe to the test fixture to check the waveform.

Note:
1. As defined in the standard test specification, the wire of test fixture is a twisted pair with a length of 30±2cm;
2. The test fixture must be connected with 10uF electrolytic capacitor and 0.1uf film capacitor to eliminate high-frequency interference;
3. As shown by the circle in figure 1, the clamp attached to the oscilloscope probe needs to be removed to avoid antenna interference; Set the oscilloscope mode to AC peak detect mode;
4. When testing ripple and noise under condition of high or low temperature, you need to place the 10uF and 0. 1uF capacitors outside the chamber to avoid inaccurate results.

2.Efficiency Test

Purpose: The efficiency test evaluates whether a power supply meets its efficiency specifications.
Equipment: AC source, Electronic Load, Power analyzer, multimeter.
Test Procedure: Connect the PSU and equipment in the following order: Ac source – Power Analyzer – PSU – Electronic Load. Set the test conditions, turn on the Ac source, then record the input power, output voltage and output current after PSU operating stably, And calculate the efficiency by the equation below:
Efficiency= Output Voltage * 0utput Current / Input power * 100%.
Notes:
1. The efficiency of power supply products may vary due to different test conditions, so it is necessary to check the test conditions such as input voltage, output voltage and output current before the test;
2. LED power supply usually has a large output current and line loss. So you need to measure the output voltage at the terminals of the PSU to get a accurate result instead of reading the value on the electronic load(refer to fig. 2):
3. When calculating efficiency of power supply with multiple outputs, the total output power is the sum of power of each output. And the efficiency is equal to the total output power divided by the input power.

3. Insulation Resistance Test (HI-POT Test)

Purpose: This test checks whether the PSU meets the required insulation resistance specifications to prevent electrical hazards.
Equipment: HI-POT Tester, Bakelite or other insulating materials
Test Procedure:
1. Connect the HI-POT tester to the appropriate PSU ports based on the test setup (primary-to-secondary, primary-to-ground, secondary-to-ground).
2. Set the tester parameters according to the specification and initiate the test. Verify that no arcs occur, and the current does not exceed specified limits.
Notes:
1. The rubber sheet is not fully insulated, so place the PSU on Bakelite or another insulating material to prevent interference during testing.
2. Before testing, short the primary terminals (L and N), short the secondary outputs, and ensure the PE terminal is properly connected to ground. Refer to fig. 3.

4.Short-Circuit Test

Purpose: The short-circuit test verifies that the PSU will enter self-protection mode if a short circuit occurs in the external circuitry.
Equipment: AC Source, Electronic Load, Breaker or low-impedance short-circuit fixture
Test Procedure:
Short V+ and V- by using breaker or other short- circuit fixtures with low impedance while the PSU is operature normally and check if PSU can realize self-protection, (Refer to the Specification For Approval for protection type).
Notes:
1. Ensure that the wire connecting the short-circuit fixture to the PSU is at least AWG 4#.
2. The impedance of the short-circuit fixture should be less than 0.1mΩ.
3. For multiple outputs of power supply, each output cannot be shorted to each other.