introduction
No matter where you are, when you look around, you're likely to see someone using a portable device. Whether at home, in the car, or plugged into a computer, USB-powered portable devices require intelligent methods to determine the proper power for proper operation and charging. Due to the wide variety of portable devices, the wide variety of USB ports, and the complex nature of rechargeable batteries, the USB Battery Charging Specification Version 1.2 (abbreviated as BC1.2), promulgated in 2010, is a key criterion for establishing the right way to charge a battery through a USB port. However, even with the BC1.2 specification, some portable device manufacturers still use proprietary chargers, making the USB battery charging field more complicated.
This article discusses the driving forces of the latest industry standards for USB battery charging and the technical specifications defined, as well as a simple strategy for implementing USB ports for high current charging of various proprietary portable charging devices.
The urgency of battery charging standards - before the BC1.2 specification was enacted
USB is widely used because it can power peripherals. USB was born in the mid-1990s, and the original purpose was to connect external devices (such as keyboards, mice, printers, external drives, etc.) to computers. As more and more portable devices are favored, they also need to be powered. The ability to power from a data transfer connector gives USB a direct and significant advantage in the portable market.
Before the first battery charging specification was promulgated in 2007, trying to charge the battery was essentially an adventure – the results were very unpredictable. When USB 2.0 appeared in 2000, the peripherals absorbed 100mA by default unless the current was explicitly negotiated to increase the current to a maximum of 500mA. If there is no data activity after a delay on the bus, the bus will enter "suspend" mode, which will allow the sink current to be limited to 2.5mA. If the battery of the portable device is completely exhausted, you can only reliably absorb 2.5mA when trying to charge with the standard port!
In fact, many electronic device manufacturers do not strictly adhere to the USB 2.0 specification and do not use these current limits in the USB ports they provide. Some (most) USB ports allow 100mA current regardless of enumeration or continuous activity; some ports even provide 500mA current, regardless of the necessary power negotiation. Some portable devices require more than 100mA of current, and it is a mistake to assume that the USB port always provides 500mA.
A good charging solution must know how to tell the portable device how much current is being drawn from the USB port is safe. While logical, there is a major problem with the previously ambiguous USB “state of affairs†– how will the USB port respond if the current draw exceeds expectations? Some ports will be completely shut down and remain off until the peripherals are removed and reinserted; some ports will trigger a USB system reset and restart the enumeration process.
Launch of the BC1.2 specification
Battery charging is not the original feature of USB. Therefore, before the BC1.2 was promulgated, the official did not make any regulations on the battery charging of the shutdown device. The BC1.2 specification improves many of these issues by establishing a clear USB port power capability communication method.
Regardless of the materials used in the rechargeable battery, special consideration is required during operation and charging. For example, Li+ battery manufacturers sometimes specify a minimum discharge level; deep discharge batteries that exceed this threshold need to be charged first in pre-processing mode before starting full charge. After the battery reaches the nominal condition, a higher current can be used to shorten the charging time, which is commonly referred to as constant current mode. When the battery is almost full, it may be harmful to continue using the constant current mode. The smart charging solution will switch to constant voltage mode to “float†the battery. Due to the complex nature of the battery, customization is required to achieve reliable charging, and most portable devices now include a dedicated battery charging controller in the final product.
An additional advantage of the BC1.2 specification is the provision of charging for depleted or weak batteries. A battery below the “weak battery threshold†allows charging with a current higher than 2.5 mA, regardless of port type. Once the battery reaches the nominal level, the device is required to enumerate for a specific amount of time in order to maintain a higher current draw from the USB port that is required to be enumerated.
Description
It's a press laminated wood veneer in crosswise direction, based on high quality and selected birch veneers, stick together with Electrical thermosetting synthetic resins under high pressure and temperature.
Property
Good Electrical properties
Excellent absorption of transformer oil
High mechanical strength
Low and high temperature resistance
Good resistance to the abrasion and wear
Application
The product is mainly use in the electrical oil transformers applications as high electrical insulation material, like Pressure Beams, step blocks, pressure spare parts, top and bottom support coils, potential rings, pressure rings , spacers, etc. For his mechanical strength, laminated wood can be also use for many applications as abrasion resistance material under stress.
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