Safety requirements for switching power supply structures
Abstract：Space requirements. The UL, CSA, and VDE safety codes emphasize the requirements for exterior and space spacing between live parts and between live parts and non-live metal parts. UL, CSA requirements: between high-voltage conductors with an inter-electrode voltage greater than or equal to 250VAC, and between high-voltage conductors and non-charged metal parts (excluding wires here)
1) Space requirements. The UL, CSA, and VDE safety codes emphasize the requirements for exterior and space spacing between live parts and between live parts and non-live metal parts. UL, CSA requirements: between the electrode voltage is greater than or equal to 250VAC between the high-voltage conductor, and between the high-voltage conductor and the non-charged metal part (here does not include the wire), whether in the outer space or in the space, there should be 0.1 inch spacing; VDE requires 3mm creep or 2mm clearance between communication lines; IEC requirements: There is a 3mm clearance between the communication wires and a 4mm clearance between the communication wires and the ground conductor. In addition, VDE and IEC require a space distance of at least 8mm between the output and input of the power supply.
2) Dielectric test method (high voltage: input and output, input and ground, input AC between two stages).
3) Leakage current detection. Leakage current is the current flowing through the ground wire of the input side. In the switching power supply, it is mainly the leakage current of the bypass capacitor through the squelch filter. UL and CSA require that the exposed non-charged metal parts should be connected to the earth, and the leakage current detection is through the direct resistance of 1.5K ohms between these parts and the earth, and the leakage current should not be more than 5 mA. The VDE promises: a 1.5K ohm resistor and a 150nP capacitor are connected. And apply 1.06 times the additional use voltage, for data processing equipment, leakage current should not be greater than 3.5 Ma. It's usually about 1 mah.
4) Insulation resistance test.
VDE requirements: There should be a 7M ohm resistance between the input and the low voltage output circuit, and a 2M ohm resistance or 500V DC voltage continued for 1 minute between the accessible metal part and the input.
5) Printed circuit board requirements. The requirement is UL certified 94V-2 material or better.
2. Safety requirements for power transformer structures
1) Insulation of transformer. The copper wire used in the winding of the transformer should be enameled wire, and other metal parts should be coated with porcelain, paint and other insulating substances.
2) Dielectric strength of transformer. Cracking of insulation layer and flaring should not be shown in the test.
3) Insulation resistance of transformer. The insulation resistance between the windings of the transformer is at least 10M ohms, and 500 volts DC voltage is applied between the windings and the magnetic core, skeleton and shielding layer, and the phenomenon of breakdown and flarc should not be shown for 1 minute.
4) transformer humidity resistance. The transformer must be placed in a wet environment, immediately after the insulation resistance and dielectric strength test, and meet the requirements. The humid environment is generally: the relative humidity is 92% (2% for public service), the temperature is stable between 20 and 30 degrees Celsius, the error is allowed by 1%, and the above test should be carried out immediately after being placed inside for at least 48 hours. At this point, the transformer's own temperature should not be 4 degrees Celsius higher than the test before entering the wet environment.
5) VDE requirements for transformer temperature characteristics.
6) Requirements of UL and CSA on transformer temperature characteristics.
2) Dielectric test method (high voltage: input and output, input and ground, input AC between two stages).
3) Leakage current detection. Leakage current is the current flowing through the ground wire of the input side. In the switching power supply, it is mainly the leakage current of the bypass capacitor through the squelch filter. UL and CSA require that the exposed non-charged metal parts should be connected to the earth, and the leakage current detection is through the direct resistance of 1.5K ohms between these parts and the earth, and the leakage current should not be more than 5 mA. The VDE promises: a 1.5K ohm resistor and a 150nP capacitor are connected. And apply 1.06 times the additional use voltage, for data processing equipment, leakage current should not be greater than 3.5 Ma. It's usually about 1 mah.
4) Insulation resistance test.
VDE requirements: There should be a 7M ohm resistance between the input and the low voltage output circuit, and a 2M ohm resistance or 500V DC voltage continued for 1 minute between the accessible metal part and the input.
5) Printed circuit board requirements. The requirement is UL certified 94V-2 material or better.
2. Safety requirements for power transformer structures
1) Insulation of transformer. The copper wire used in the winding of the transformer should be enameled wire, and other metal parts should be coated with porcelain, paint and other insulating substances.
2) Dielectric strength of transformer. Cracking of insulation layer and flaring should not be shown in the test.
3) Insulation resistance of transformer. The insulation resistance between the windings of the transformer is at least 10M ohms, and 500 volts DC voltage is applied between the windings and the magnetic core, skeleton and shielding layer, and the phenomenon of breakdown and flarc should not be shown for 1 minute.
4) transformer humidity resistance. The transformer must be placed in a wet environment, immediately after the insulation resistance and dielectric strength test, and meet the requirements. The humid environment is generally: the relative humidity is 92% (2% for public service), the temperature is stable between 20 and 30 degrees Celsius, the error is allowed by 1%, and the above test should be carried out immediately after being placed inside for at least 48 hours. At this point, the transformer's own temperature should not be 4 degrees Celsius higher than the test before entering the wet environment.
5) VDE requirements for transformer temperature characteristics.
6) Requirements of UL and CSA on transformer temperature characteristics.
