Safety regulations are product safety requirements in product certification, including the safety requirements of product parts and the safety requirements after the finished product. Safety is actually a product of the Chinese themselves, and foreign countries generally call it regulatory.

What is safety?

Safety – The best English explanation should be ProducTIon Compliance. It refers to the product's entire life cycle from design to sales to end users, relative to the laws, regulations and standards of the place of sale. This product safety compliance not only includes product safety in the ordinary sense, but also includes requirements for electromagnetic compatibility and radiation, energy saving and environmental protection, food hygiene, etc. She should be more than just a requirement, a standard, a certificate, a test report can replace or can explain, but should be a product safety responsibility and activities throughout the product life cycle.

Simply understanding safety as a certification should be one-sided. Certification is only a means or process for assessing product compliance, but it is not a required means or process. This conformity should be assessed at the beginning of the product design, but not necessarily through third-party testing, to examine the conformity of the product to relevant laws, regulations and standards, to assess the foreseeable or unforeseen risks, to ensure users Avoid as expected or unforeseen personal injury or property damage as much as possible during use.

Safety regulations can simulate electric shock, fire, mechanical injury, thermal injury, chemical injury, radiation injury, food hygiene, etc. that may occur under normal or abnormal use by a series of tests. Such hazards are prevented by the corresponding design before the product leaves the factory.

This safety specification applies to PCB safety design for weak point devices with input voltages below 600V.

Safety specifications for PCB design

The first part of the safety basics

There are fundamental differences between UL and VDE safety standards. UL specifications focus on preventing fire hazards, while VDE specifications are more about operator safety. For power supplies, VDE is the most stringent electrical safety standard.

The following safety parts are required to have a VDE and UL certificate (if the model is also in Canada plus a CUL certificate):

1. Transformer (skeleton, insulating tape, polyester insulation tape)

2. Filter (skeleton, insulating tape, polyester insulation tape)

3. Optocoupler

4. Y capacitor

5. X capacitor

6. PCB material (including the yellow card of the board)

7. Combustible plastic material (including front panel, power board support rubber column, power board insulation PVC, fuse holder, power cord socket VH-3, etc.)

8. Fuse

9. Thermal casing

10. Large capacity electrolytic capacitors.

11. Various types of wire

Clearance / clearance:

The shortest spatial distance measured between two conductive parts or between the conductive parts and the equipment protection interface.

Creepage / creepage distance:

The shortest path between two conductive parts or between the conductive parts and the equipment protection interface measured along the insulation surface.

Protection interface (boundingsurface):

The outer surface of the electrical protective casing, for accessible electrical insulation, can be considered to be a surface on which the metal foil is pressed against the surface of the material.

Dielectric strength:

Also called dielectric strength test, English is the hito test, which is probably the most well-known and frequently executed production line safety test. In fact, it shows that its importance is part of every standard. The hipot test is a non-destructive test to determine that electronically insulating materials are resistant to transient high voltages. This is a high voltage test that is suitable for all equipment to ensure insulation is sufficient. Another reason for the hipot test is that it can detect possible leakage distances and insufficient clearances during the manufacturing process.

The test method is to increase the zero voltage to 3000V AC or 4200V DC between the AC input lines or between the AC input and the chassis, and pass the arc or pass the arc.


Safety standards are very strict with 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 ° C, and the temperature of the power components should be less than 90 ° C. However, in general, both UL and CE-certified tests are based on the temperature tolerances identified by the safety certificate for components (especially safety devices). In the safety test, the temperature unit is K (the thermodynamic temperature scale is also called the Kelvin temperature scale, or the absolute temperature scale, which specifies that the temperature at the time of molecular motion stop is absolute zero, the symbol is K.), it is obtained by subtracting the room temperature. the result of.

Grounding 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 of the product on the product becomes a charged body in the event of a single insulation failure, and that the conductive components that are accessible to the user are reliably connected to the ground point of the power input. In other words, a ground test uses a low current source of high current to the ground loop to verify the integrity of the ground path.

It is considered to be satisfactory by measuring the impedance connected between the protective earthing connection terminal or the grounding contact and the part to meet the standard requirements, and the impedance does not exceed a certain value determined by the product safety standard. It is important to remember that conductors used as protective earths should not contain any switches or fuses from a structural and design point of view.

Leakage current measurement

In the UL and CSA standard specifications, all exposed fixed metal components must be connected to the earth terminal, and the leakage current is measured via a 1500 Ω resistor connected to the ground; the VDE standard specification specifies a 1500 Ω resistor at 1.06 times the rated voltage. The leakage current is measured in parallel with a 150nF capacitor.

The current meter is connected in series between the live or neutral line of the power supply and the accessible metal through the isolation transformer. The leakage current of the switching power supply should not exceed 3.5 mA at 260V AC input.

InsulaTIon resistance

In the VDE standard specification, a minimum resistance of 7.0 MΩ is required between the input terminal and the SELV output circuit, and a minimum resistance value of 2.0 MΩ is required between the input terminal and the metal component that is more susceptible to variation. The applied voltage is 500Vac for 1 minute.

SELV: A safety extra-low voltage circuit is defined as a secondary circuit with an appropriate protection design, ie grounding protection between any two potentially touching components or the human body may touch any component or product. The secondary circuit between the terminals does not exceed 42.4Vacpeak or 60Vdc;

ELV: an extra-low voltage circuit is defined as a secondary circuit in which the peak value of the alternating voltage between the conductor and the conductor or between the conductor and the ground does not exceed 42.4 Vac or the DC voltage does not exceed 60 Vdc;

Hazardous voltage: A voltage with an AC peak exceeding 42.4Vac or a DC exceeding 60Vdc.


1. Under normal conditions, if the power available at a certain point exceeds 15W or the working voltage exceeds 50V, the flame retardant level needs to be V-1 or more; if a point can exceed 15W when the working voltage exceeds 400V, the flame retardant level needs to be V-0, and the manufacturer needs to have the certification of the injection process (UL6500 standard);

Under normal conditions, if a working voltage exceeds 50V and is less than or equal to 400V, the available power exceeds 15W, then the flame retardant level needs to be V-1 or more; if a certain point exceeds 400V, the available power exceeds 15W. , the flame retardant grade needs V-0 (EN60065 standard).

2. The fuse rating must 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. Mark the safety device next to the circuit diagram

5. For class I products, use a Y2 capacitor between the primary and secondary; for class II products, use two Y2 capacitors in series or one Y1 capacitor.

6. a. The insulation between the primary and secondary is to be reinforced, and the distance from the surrounding casing must also meet the requirements for reinforced insulation; between L and N, there must be basic insulation between the two legs of the fuse. The specific value needs to be determined according to the operating voltage. (UL6500 standard);

For the EN60065 standard, it is generally the same as the UL6500 standard, but since the voltage is generally about 230V, the distance required for reinforced insulation is generally 6mm, and the basic insulation is generally 3mm. The specific value is still determined according to the operating voltage (EN60065 standard).

The distance between the primary and secondary on the power board must be designed with a minimum safety distance of 6mm.

b. Fix all the wires in the low-voltage area 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 for powering the decoder board in my driver type is basic insulation. The wire body, therefore its safety distance from the primary area on the power strip must be such that a distance of at least 6 mm can be applied when a force of 2 N is applied to the wire. Similarly, all devices belonging to the low-voltage region can be placed at a minimum distance of 6 mm from the high-pressure region when applying an external force of 2N.

c. For models requiring insulation gaskets (PVC), the position of the insulation gasket shall be such that the electrical clearance between the high-voltage zone circuit (including the components, wiring and the basic insulation section of the power cable tail) to the upper cover (or the bottom plate) is greater than 6 mm, for example: In the case where a force of 20 N is applied to the cover of the casing, the shortest distance from the bare insulated wire body of the power cable (and the switching power supply wire) at the end of the power supply board to the upper cover of the casing cannot be less than 6 mm. If the shortest distance may be less than 6mm, it is necessary to add insulating gasket PVC, and in the case of PVC with insulating gasket, it must be ensured that the bare basic insulated wire body is farther to the nearest casing upper cover conductor (ie the edge of PVC) ) can not be less than 6mm;

7. If the fuse is listed, it can be reported 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 UL recognized as 94V-2 or better materials, and VDE specifications also accept these standards, combustible materials including surface shell, power board and other board support Rubber column, various fixing tapes, etc. .

Note: Pros and cons of fire rating

Foamed plastic materials: HF-1 grade is better than HF-2, 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, and V-2 is better than HB.

For the outer casing

The flame retardant rating of the main part must be V-0, and the manufacturer must have the certification of the injection process (UL6500);

The requirements for the flame rating of the enclosure are generally determined by the distance from the source of ignition to the enclosure (EN 60065).

The opening of the outer casing shall be designed so that the foreign objects suspended during the operation do not become dangerously charged when entering the vents or other holes. The EN60065 standard requires the insertion of a metal test pin having a diameter of 4 mm and a length of 100 mm. The hole is inspected for compliance, wherein the test needle is freely inserted at one end and the insertion depth is not more than its length.

For transformer

In the VDE standard specifications, there are strict regulations on the design, manufacture and utilization of transformers to meet the safety requirements of most other countries. In the UL standard specifications, all materials required in the transformer structure must have 94V. -2 or better rating.

(1) Transformer insulation (transformer insulaTIon)

The windings of the transformer must be physically separated by insulation, lacquer on the winding wire, enamel or lacquer coating, and other metal components, asbestos and moisture absorbing materials, for the purpose of this requirement. Then insulation is not considered.

(2) Transformer dielectric strength (transformer dielectric strength)

When using the insulation thickness of the composite layer, any two layers must be able to withstand the dielectric strength, the insulation layers are in contact with each other during testing and the test potential is applied to the external surface.

(3) Transformer insulation resistance (transformer insulaTIon resistance)

Insulation used in the construction of the transformer must be between the windings, and between the windings and the core and the frame metal plate, must have a minimum resistance of 10 MΩ, and provide 500 Vac voltage in 1 minute.

(4) When designing the transformer, please ensure that the creepage distance between the secondary winding of the transformer and the primary, primary and secondary pins must be 6mm safe distance (can be increased by adding white insulating tape Margintape width or all tubes) The foot is connected to the casing Tube), and there should be two layers of insulating tape Tape between the windings of the same polarity.

The label of the transformer must be marked with a trade mark or the manufacturer's manufacturer name.

For insulating materials

To ensure the protection against electric shock of the switch, a reliable insulation structure is required, and the safety of the insulation material is the basis for ensuring the reliability of the insulation structure. Therefore, the selection of the insulation material should be considered:

1. Parts that support, cover or wrap the live parts shall not be dangerous due to heat, and materials with sufficient heat resistance must be used;


a. For double insulation, the thickness of the basic or additional insulation shall be at least 0.4 mm.

b. When the reinforced insulation is not subjected to any mechanical stress that may cause deformation or deterioration of the insulating material under normal operating conditions and fault conditions, the minimum thickness of the reinforced insulation shall be 0.4 mm.

c. Insulation between hazardous live conductors and accessible parts in wires or cables, or between internal conductors in hazardous live parts and wires or cables and conductors that are accessible to conductive parts, if made of polyvinyl chloride In order, the thickness should be at least 0.4mm.

d. In DVDs, there should be double insulation between the following components:

– accessible parts between conductors of wires or cables that are electrically connected to the mains supply in the wires or cables;

—— Between the wires or cables and the conductors that are accessible to the conductive components and the components that are electrically connected to the mains power supply.

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