In the production site of switching power supply adapters, electrical safety testing is a critical step. The basic electrical tests include the Electrical Strength (Insulation Withstand Voltage) Test and the Contact Current (Leakage Current) Test. These tests ensure that the adapters meet safety standards and are safe for consumer use.
Electrical Strength (Insulation Withstand Voltage) Test
The Electrical Strength Test, also known as the withstand test or high-voltage test, is designed to verify the insulation integrity of the switching power supply adapter. This involves applying several times the rated working voltage between live parts and the casing, as well as between primary and secondary circuits. The goal is to detect any grounding or insulation breakdown of live components.
During this test, the part undergoes non-normal voltage stress testing. If any part of the insulation fails due to manufacturing processes, components, or materials, a breakdown will occur. Additionally, if the electrical gap becomes smaller for some reason, it may not cause issues under normal working voltage. However, over time, dust or moisture accumulation in too small a gap can lead to gap breakdown and potential electric shock hazards. The withstand test helps identify these hidden dangers early.
If an insulator does not break down under several times the working voltage, it is deemed safe under normal operating conditions. The withstand test also inspects too small conductor gaps and process defects, which other tests cannot match.
Withstand tests specify both the applied voltage value and duration. According to IEC335-1(GB4706.1), for AC below 250V, the insulation must withstand a 1-minute application of a 50Hz/60Hz sine wave voltage. The specific values and positions for the applied voltage can be found in GB4706.1-1998. For SELV circuits, basic insulation should withstand 500V, other basic insulations 1000V, additional insulation 2750V, and reinforced insulation 3750V.
At the beginning of the test, the applied voltage does not exceed half of the specified value and is gradually increased. No breakdown should occur during the test; otherwise, the adapter fails the test.
UL60950 requires similar specifications. If using DC testing, the test voltage amplitude should be the corresponding AC voltage peak value. For example, if reinforced insulation requires 3750V AC testing, then the DC test voltage should be 5303V.
For Class I equipment:
- Apply a minimum test voltage of 2500V between AC high voltage input and safety ground, with a minimum leakage current of 30uA.
- Apply a minimum test voltage of 5000V between input and DC output, with a minimum leakage current of 60uA, and the test time is 1 minute.
- The leakage resistance between input and output is 9 megohms, setting a minimum leakage current of 300uA.
For Class II equipment:
- Apply a minimum test voltage of 5000V between AC high voltage input and DC output, with a minimum leakage current of 60uA, and the test time is also 1 minute.
- The leakage resistance between input and output is 9 megohms, setting a minimum leakage current of 600uA.
The above domestic product test leakage current is higher than the specified value but must not exceed 10mA.
Contact Current (Leakage Current) Test
The maximum allowable values for different types of devices vary:
- The maximum allowable contact current for Class I devices is 3.5mA.
- For Class II devices, it is 0.25mA.
Switching power supply adapters developed or improved must undergo safety certification before entering the market. Depending on the certification body, type of power supply, and usage scenarios, the steps may vary but generally include:
- Opening or unpacking test samples for structural analysis.
- Insulation arrangement.
- Gaps, creepage distances, and body insulation dimensions.
- Accessibility.
- Protective grounding.
- Mechanical structure assessment.
- Determine internal working voltage through analysis and testing.
- Conduct worst-case scenario testing under input voltage and load variation limits.
- Test single faults and overloads, including short circuit tests.
- Thermal testing under rated operating conditions.
- Moisture testing.
- High-voltage leakage current testing.
- Flammability testing.
- Any other necessary additional tests.
Certification starts from the application of all parts and materials provided by the manufacturer of switching power supply adapters, along with documentation. It also requires submission of multiple tested switching power supplies. For low-power switching power supplies, typically 5 units without casings and 5 complete power supply adapters are submitted, along with a certification fee worth
600010000. The certification process takes about 6-8 weeks, and if the certification includes product design flaws, it will take even longer.
By ensuring these rigorous tests and certifications, switching power supply adapters can guarantee consumer safety and compliance with regulatory standards.
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Post time: Nov-15-2024