Safety Specification for PCB Design (II)

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.

temperature:

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.