Battery Charger Circuit Using MAX1737
There are three methods to charging Li+ batteries: switch-mode, linear and pulse. Each method has its advantages and disadvantages. Switch-mode charging minimizes power dissipation over a wide range of AC adapter voltages, but consume more board space and add complexity compared to linear and pulse charging. Linear chargers are small and great for noise sensitive equipment, but power dissipation is high. Pulse chargers are small and efficient, but require a current-limited AC adapter. Select the charging method based on the prioritization of cost, space and efficiency. Charging Li+ batteries in mobile phones and PDAs is a balancing act. On one hand, high current is needed to quickly replace the energy drained from the battery while transmitting voice or data. On the other, a charger needs to be small, to fit inside ever-shrinking mobile-phone and communicating-PDA form factors. Knowing the types of chargers that are available and the tradeoffs between them allows a designer to choose the right charger for a specific application.
Circuit Of Battery Charger Circuit Using MAX1737
A Li+ battery charger must limit the charging current and the battery’s maximum voltage. Designers should consult the battery manufacturer to determine what’s required to safely charge a particular battery. Other features are often added to improve the life of the batteries or the operation of the charger. These include reduced charging current for over-discharged cells, detection of faulty cells, battery voltage monitoring and/or fuel gauging, input-current limiting, turning off the charger after charge completion, automatically restarting charging after partial discharge, charge state indication, and external charger enable/disable control.
These features can be implemented in the charger itself, in an ASIC or a discrete circuit, or possibly within the software found within a microcontroller. Circuit designers decide which features to include and how to implement them based on the specific application and the level of cost or complexity that is tolerable.
Li+ battery chargers come in three types: switch-mode, linear, and pulse. The major difference between these topologies is the size and cost vs. performance tradeoff they offer. Switch-mode chargers tend to be larger and more complex and require a large passive output LC filter; the extra board space buys added efficiency. Linear and pulse chargers take up little board space and require a minimum of external components. Although a linear charger may not require much board space to accommodate the IC and its external components, it may need additional board area to dissipate the heat generated by the charger’s pass transistor. Pulse chargers don’t present this problem. However, they do require a current-limited AC adapter, which is usually more costly.