Insulation protection requirements for PD Charger

Insulation protection requirements for PD Charger
 
1. Insulation type
Insulation materials and insulation protection must be used to ensure the normal operation of the circuit and when there is a voltage higher than the dangerous voltage inside the circuit. UL60950 divides insulation into five categories: functional insulation, basic insulation, additional insulation, double insulation, and reinforced insulation.
 
① Functional insulation: It is necessary for the correct operation of equipment and does not provide safety protection against electric shock, but can reduce ignition and combustion. For example, the lacquer skin of enameled wire.

 
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② Basic insulation: The most basic insulation to avoid electric shock. It is not safe to rely solely on basic insulation, and safety requirements must be met through additional insulation and protective grounding secondary protection, such as coil interlayer insulation.
③ Additional insulation: Insulation independently added to the basic insulation to ensure secondary protection against electric shock in the event of accidental failure of the basic insulation. The minimum thickness of the additional insulation single layer material must be greater than or equal to 0.4mm.
④ Double insulation: It is a secondary insulation system composed of a combination of basic insulation and additional insulation.
⑤ Enhanced insulation: A single insulation system that prevents electric shock, equivalent to double insulation. The minimum thickness of the single layer used inside is greater than or equal to 0.4mm. There may be several layers, but each layer cannot be tested separately.
 
2. Equipment level and insulation requirements
Different types of circuits require different types of insulation:
① Class I equipment. This type of equipment adopts protective grounding, that is, the metal chassis is grounded to a protective ground as a level 1 protection. Only basic insulation is required between any hazardous voltage component and the chassis, such as the communication power supply of the station.
② Class II equipment. Use double insulation and reinforced insulation, without metal chassis and grounding screws, such as portable chargers.
③ Class III equipment. The power supply is generated by the SELV source and there is no potential hazardous voltage inside, so only basic insulation is required, such as circuit board power supply. Figure 8.2.3 shows a simple functional block diagram of the power supply. From the block diagram, first distinguish whether the internal circuit functional blocks are LCC, SELV, TNV, ELV or hazardous voltage, and then determine the insulation level and quantity between the functional blocks and between internal components and usage. From the figure, it can be seen that at least two poles of insulation are required between the hazardous voltage and the parts that can be contacted by the user.

For example, the ELV path of a floating ground must have two pole insulation, and there must be at least one level between the ELV and the user, otherwise the ELV circuit will be unsafe once a single stage fails. However, if ELV circuit grounding protection is provided (providing level 1 protection), only adding level 1 is sufficient. Similar situations such as heat sinks and metal enclosures must use Class 2 insulation to isolate users from hazardous voltages. Class 1 can only be used if the metal is grounded.
 
 
3. Insulation material
Solid insulation materials should be selected based on working voltage, electrical strength, temperature requirements, mechanical strength, and working environment, and these materials should be moisture resistant and flame retardant; If it is a wire insulation material, the flexibility of the material is also required.
 
Semiconductor devices and other components are molded into solid insulation materials, and their insulation is evaluated and tested separately during the factory manufacturing process. The film, tape, and sheet of solid insulation materials have thickness requirements: if single-layer insulation is used, the minimum thickness is greater than or equal to 0.4mm; If it is a two-layer insulation, there is no thickness requirement, but each layer must meet the electrical strength requirements; If it is three or more layers, there is no minimum thickness requirement, but every combination of two layers must meet the corresponding electrical strength requirements. There are no thickness requirements for basic or functional insulation.