The safety standards of UL and VDE are essentially different. UL specifications are more focused on preventing the risk of fire, while VDE specifications are more about the safety of operators. For power supplies, VDE is The most stringent electrical safety standards.
The following safety parts require VDE and UL certificates (if the model is shipped to Canada, a CUL certificate will also be added):
1. Transformer (skeleton, insulating tape, polyester insulating tape)
2. Filter (skeleton, insulating tape, polyester insulating tape)
3. Optocoupler
4. Y capacitor
5. X capacitor
6. PCB material (including board manufacturing yellow card)
7. Flammable plastic materials (including front panel, power board support plastic column, power board insulation PVC, fuse holder, power cord socket VH-3, etc.)
8. Insurance management
9. Heat shrink tubing
10. Large-capacity electrolytic capacitor.
11. Various types of wires
Spatial distance (clearance) / electrical clearance:
The shortest spatial distance measured between two conductive parts or between a conductive part and the equipment protective interface.
Creepage distance (Creepage) / Creepage distance:
The shortest path between two conductive parts or between a conductive part and the equipment protection interface measured along the insulating surface.
Protective interface (bounding surface):
The outer surface of the electrical protective enclosure. For accessible insulating materials, it can be considered as a surface with metal foil pressed on the surface of the material.
Electric strength:
Also called dielectric strength test, hipot test in English, it is probably the most well-known and frequently performed production line safety test. In fact, showing its importance is part of every standard. The hipot test is a non-destructive test to determine the adequacy of electronic insulation materials to withstand transient high voltages. This is a high voltage test applied to all equipment to ensure that the insulation material is adequate. Other reasons for performing hipot testing are that it can detect possible defects such as insufficient creepage distances and clearances caused during the manufacturing process.
The test method is to increase the zero voltage between the AC input lines or between the AC input and the chassis to 3000V AC or 4200V DC, and it will be qualified if there is no breakdown or arcing.
Temperature:
Safety standards are very strict for electronic appliances and require materials to be flame retardant. The internal temperature rise of the switching power supply should not exceed 65°C. For example, the ambient temperature is 25℃, the temperature of power supply components should be less than 90℃. But generally speaking, whether it is UL or CE certification testing, the temperature resistance limit marked on the safety certificate of the component (especially the safety device) is used as the standard. The temperature unit expressed in safety tests is K (the thermodynamic temperature scale is also called the Kelvin temperature scale, or the absolute temperature scale, which stipulates that the temperature when the molecular movement stops is absolute zero, and the symbol is K.), which is obtained by subtracting the room temperature. result.
Ground test:
Also known as ground continuity test, ground test must be performed on all Class I products. The purpose of the test is to ensure that all conductive parts on the product that would become live in the event of a single insulation failure and that can be touched by the user are reliably connected to the ground point of the power input. In other words, a ground test uses a high current, low voltage source added to a ground loop to verify the integrity of the ground path.
Measure the impedance connected between the protective ground connection terminal or ground contact and the part to determine whether it meets the standard requirements. If the impedance does not exceed a certain value determined by the product safety standard, it is considered to be in compliance with the requirements. It must be remembered that from a construction and design point of view, the conductor used as protective earth should not contain any switches or fuses.
Leakage current measurement (leakage current measurement)
UL and CSA standard specifications require that all exposed fixed metal components must be connected to the earth terminal through a 1500Ω resistor connected to the ground terminal. The leakage current is measured by a resistor; the VDE standard specification stipulates that at 1.06 times the rated voltage, a 1500Ω resistor and a 150nF capacitor are connected in parallel to measure the leakage current.
Use an isolation transformer to connect the live or neutral line of the power supply to the easy Connect an ammeter in series between the touched metals. The leakage current of the switching power supply should not exceed 3.5mA under 260V AC input.
Insulation resistance (insulation resistance)
In the VDE standard specification, a minimum resistance value of 7.0MΩ is required between the input terminal and the SELV output circuit, and the input terminal is more susceptible to Between the changing metal components, a minimum resistance value of 2.0MΩ is required, and the applied voltage is 500Vac for 1 minute.
SELV: safety extra-low voltage circuit (safety extra-low voltage circuit) It is defined as a secondary circuit with appropriate protection design, that is, the voltage between any two components that may be touched or the human body may come into contact with the ground protection terminal of any component and product will not exceed 42.4Vacpeak or 60Vdc. ;
ELV: Extra-low voltage circuit (extra-low voltage circuit) is defined as an AC voltage peak between conductors or between conductors and ground does not exceed 42.4Vac or a DC voltage does not exceed 60Vdc Secondary circuit;
Hazardous voltage: voltage with an AC peak value exceeding 42.4Vac or a DC voltage exceeding 60Vdc.
For PCB
1. Under normal conditions, if the power available at a certain point exceeds 15W or the working voltage exceeds 50V, the flame retardant grade needs to be V-1 or above; if the power available at a certain point exceeds 15W when the working voltage exceeds 400V, the flame retardant grade needs to be V-0, and the manufacturer needs to have injection process certification (UL6500 standard);
Under normal conditions, if the working voltage at a certain point exceeds 50V and is less than or equal to 400V, the available power exceeds 15W, then the resistance The flame retardant grade needs to be V-1 or above; if the power available at a certain point exceeds 15W when the operating voltage exceeds 400V, the flame retardant grade needs to be V-0 (EN60065 standard).
2． The fuse rating needs to be marked next to the fuse holder, in a format such as "T315mA L125V"
3. The transformers and filters on the board should be labeled with the manufacturer's name (or trademark) and model number
4. The mark should be added next to the safety device in the circuit diagram
5. For class I products, use one Y2 capacitor between primary and secondary; for class II products, use two Y2 capacitors in series or one Y1 capacitor
6. a. The insulation between primary and secondary should be reinforced insulation, and the distance from the surrounding shell should also meet the requirements of reinforced insulation; there should be basic insulation between L and N, and between the two pins of the fuse. The specific value needs to be determined according to the working voltage. (UL6500 standard);
For the EN60065 standard, it is roughly the same as the UL6500 standard. However, since the voltage is generally around 230V, the general requirement for reinforced insulation is a distance of 6mm. For basic insulation it is generally 3mm. The specific value still depends on the operating voltage (EN60065 standard).
The distance between the primary and secondary stages on the power supply board must be designed with a safety distance of at least 6mm in mind
b. All wires in the low-voltage area must be fixed to ensure that the creepage distance and electrical clearance from the high-voltage circuit (including components and wiring) must be greater than 6mm. For example: the cable that supplies power to the decoder board in our driver model belongs to basic insulation. The wire body, therefore, the safe distance between it and the primary area on the power board must ensure that there is at least 6mm distance when an external force of 2N is applied to this cable. Similarly, all devices in the low-voltage area can maintain a safe distance of at least 6mm from the high-voltage area when an external force of 2N is applied.
c. For models that require insulating gaskets (PVC), the position of the insulating gasket must ensure that the electrical gap from the high-voltage area circuit (including components, wiring and the basic insulation section at the end of the power cord) to the upper cover (or bottom plate) is greater than 6mm, for example: When a force of 20N is applied to the upper cover of the casing, the shortest distance from the exposed basic insulated wire body at the end of the power cord (and switching power cord) plugged into the power board to the upper cover of the casing cannot be less than 6mm. If this The shortest distance may be less than 6mm, then an insulating gasket PVC needs to be added. When adding the insulating gasket PVC, it must be ensured that the exposed basic insulated wire body is close to the nearest chassis cover conductor (that is, the edge of the PVC ) cannot be less than 6mm;
7. If the fuse is listed, you can report it at will; if it is recognized, it needs to be tested before reporting
8. UL and CSA specifications also provide flammability standards, that is, all PC boards must be recognized by UL as 94V-2 or better materials, and VDE specifications also accept these standards. Flammable materials include board supports such as panels and power boards. Glue pillars, various fixing tapes, etc. .
Note: Fire protection grade pros and cons
Foam plastic materials: HF-1 grade is better than HF-2, and HF-2 grade is better than HBF;
General materials: 5V is better than V-0, V-0 is better than V-1, V-1 is better than V-2, V-2 is better than HB.
For the shell
The flame retardant grade of the main part needs to be V-0, and the manufacturer needs to have injection process certification (UL6500);
The requirements for the flame retardant grade of the shell generally depend on the distance between the fire source and the shell. OK (EN60065).
The openings of the shell should be designed to ensure that suspended foreign objects will not become dangerous electrified objects when entering the ventilation holes or other holes. The EN60065 standard requires a diameter of 4mm and a length of A 100mm metal test pin is inserted into the hole to check whether it is qualified. One end of the test pin is freely inserted and the insertion depth does not exceed its length.
For transformers
In the VDE standard specifications, there are strict regulations on the design, manufacturing and utilization of transformers to meet the safety needs of most other countries. In the UL standard The specification requires that all materials used in the transformer structure must have a rating of 94V-2 or better.
(1). Transformer insulation
The windings of the transformer must be physically separated by insulation according to requirements. The lacquer, enamel or foreign paint coating on the winding wires, as well as other metal components, asbestos and moisture-absorbing materials, are among the purposes of this requirement. Insulation is not considered within.
(2). Transformer dielectric strength
When using the insulation thickness of the composite layer, any two layers must be able to withstand Dielectric strength, tested when the insulation layers are in contact and the test potential is applied to the external surface.
(3) Transformer insulation resistance
Insulation is used in the structure of the transformer There must be a minimum resistance value of 10MΩ between the windings, and between the windings and the core and frame metal plates, and provide 500Vac voltage within 1 minute.
(4). When designing the transformer Please ensure that the creepage distance between the secondary winding and the primary pin of the transformer, and between the primary winding and the secondary pin, must be a safe distance of 6mm (you can increase the width of the white insulating tape Margintape or add casing Tube to all pins) to achieve), and there should be two layers of insulating tape between windings of the same polarity.
The label of the transformer needs to be marked with a trade mark or manufacturer's name.
For insulating materials
To ensure the anti-shock protection of the switch, a reliable insulating structure is necessary, and the safety of insulating materials is the basis for ensuring the reliability of the insulating structure. Therefore , the selection of insulation materials should consider:
1. Components that support, cover or wrap live parts must not endanger their safety due to heat, and must be made of materials with sufficient heat resistance;
2. a. For double insulation, the thickness of basic insulation or supplementary insulation should be at least 0.4mm.
b. The minimum thickness of reinforced insulation shall be 0.4 mm when it does not withstand any mechanical stress that may cause deformation or deterioration of the insulating material at temperatures under normal operating conditions and fault conditions.
c. Internal conductor insulation between hazardous live conductors and accessible parts in a wire or cable, or between hazardous live parts and conductors connected to accessible conductive parts in a wire or cable, if made of polyvinyl chloride , the thickness should be at least 0.4mm.
d. In DVDs, the following parts should have double insulation between them:
— between accessible parts and conductors of wires or cables that are conductively connected to the mains power supply;
——Between conductors in wires or cables that are connected to accessible conductive parts and parts that are conductively connected to the power grid.