What safety issues should be paid attention to in switching power supplies?

Due to high efficiency and small size, switching power supply technology is widely used in the production of electronic equipment, products will be put into the market, and to establish a foothold in the market, product safety certification is indispensable. So, what are the safety issues that need to be paid attention to in switching power supplies?

First: safety distance specification

The following issues related to safety regulations are only for primary, secondary and high voltage, high current area PCB layout.

AC input LN, N-GND, L-GND spacing must be greater than 3.5 mm; primary rectification filter capacitor is positive; negative spacing must be greater than 4 mm; primary and secondary spacing must be greater than 6 mm (optical coupling spacing is minimum); When the circuit voltage is less than 48V, the layout is generally not required for safety spacing.

It should be noted here that the electrical clearance and creepage distance should meet the relevant requirements.

Second: the withstand voltage test specification

Test content and standards

Input-output withstand voltage test and standard

AC 3000V, withstand voltage for 1 minute, the leakage current is set to 10mA. The voltage gauge indicates that the leakage current is <10 mA, and no arcing is acceptable.

Input – earth pressure test

AC 1500V, withstand voltage for 1 minute, leakage current is set to 10mA; pressure gauge indicates leakage current <10mA, and no arcing phenomenon is acceptable.

Output – earth withstand voltage test

DC 500V, 1 minute withstand voltage, leakage current set to 10mA, withstand voltage indicator leakage current <10mA, and no arcing phenomenon is qualified.

Note: The earth is the outer casing. The test instrument is a pressure tester.

Third: insulation test specification

Test content and standards:

Input - Earth > 500Mohm is qualified;

Output - Earth > 500Mohm is qualified;

Input-output >500Mohm is acceptable;

Fourth: temperature test specification

Test content: After the switching power supply is stable for a long time, test the temperature values of the switching MOSFET, switching transformer, primary rectifying filter capacitor, secondary rectifier, and filter inductor and record.

Judging Criteria: Comparing the measured temperature value with the relevant standard safety value, the temperature value of the above device must be less than the safe value.