基于單片機(jī)的智能手機(jī)充電器的設(shè)計(jì)-文庫(kù)吧
2025-06-03 18:28 本頁(yè)面
【正文】 e. Historically, there have been some noise issues with these kinds of ICs. In addition, some early generations of switch mode devices have required several external ponents. However, the benefits of the switched mode battery topology are clear. They include higher efficiency and lower power dissipation, along with fast charging cycles. These devices also are capable of charging from higher input voltages, which allows the use of lower cost unregulated adapters. They can increase the charging current from current restricted sources. The noise from switching chargers usually es during light load operation, particularly during preconditioning. As it decreases, many switching chargers move into an operation known as pulse skipping. In pulse skipping, the PWM frequency changes asynchronously. There have been battery charger ICs developed that supply high charge current with minimal thermal impact to the system using a switching charger, then switch into a linear charger during low current charging modes to minimize noise. This type of PWM switch mode charger with a linear mode has been a good development, providing high efficiency at the full constant current (fast charge) rate. The switching charger controls large constant current charge (up to 2A) with a PWM switching regulator. It automatically moves to linear mode while the battery is preconditioning and near the end of constant voltage taper charge mode, which lowers the noise while the switch mode speeds up charging. Once the charge current level dips below 300 mA, the linear mode kicks in pletely and noise generated by the switching converter is eliminated. But now there are further advances. For example, an ideal solution for new handhelds is a plete charger for single cell Li+/ Polymer batteries with up to 1A charge current and advanced indication capabilities for full charge system monitoring. USB Compliant 100mA/500mA charge current settings are beneficial as are programmable precharge and fast charge. Many products also include battery temperature monitoring, which ensures safe charging. Companies such as Intersil are leading the development effort for new generations of charger ICs. These fully integrated solutions serve pact applications and provide charge controllers for higher power applications. Charge voltage accuracy is now at percent, an improvement over just a few years ago, when an accuracy rating of 1 percent was considered good. Switching frequencies are up to 3 MHz and new switching chargers now provide up to 2A charge current, with one recent example being the ISL9220, which is suitable for both 1 and 2 cells Li Ion applications. In addition, new designs restrict leakage there is no less than typical leakage current off the battery when no input power is attached. These improvements also have bee available in smaller and smaller packages, such as 4 x 4mm QFNs or 2 x 2mm CSPs, which save real estate in spaceconstrained handheld equipment. The latest battery charger ICs also are able to monitor the input voltage, the battery voltage, and the c
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