Power Management Solutions: Battery Chargers
The huge increase of portable devices during the last 10-15 years has lead to numerous companies seeking (and succeeding) to make significant profits in this market. Many consumer applications are now powered by accumulators, ranging from the omnipresent cellular phones to media players, handheld gaming devices, and navigation systems (that is to name only a few categories). “Portable” means lightweight, low power and of course, battery or accumulator that needs to be charged. Charging an accumulator is not rocket science, but doing it in an energy efficient manner, with tiny circuits that provide provision for many types of batteries and charging modes, represents a design challenge accepted by quite a few semiconductor companies, one of which is Freescale.
Out of all portable devices, the most numerous are the mobile phones (Figure 1). Most of them feature Li-ion or Li-polymer accumulators and Freescale has a broad range of charger ICs dedicated to supporting all the phases of a complete recharge cycle. Generally speaking the charging of a mobile phone is performed by taking energy from:
a) from a wall outlet
b) from the USB port of a computer
c) from the 12V output of a vehicle
The purpose of the battery charger IC is to take energy from this wide range of sources and to deliver this energy in a controlled manner to the battery. The controlled manner means that the IC is capable to operate in all the necessary modes of charging a battery for portable device: trickle mode, constant current (CC) mode and constant voltage (CV) mode. As it may be seen from the block diagram of figure 2 (as example the MC3467x battery chargers family from Freescale), the central point in such a battery charger is a transistor which is backed up with sophisticated control and feedback circuitry.Although batteries seem common to anybody, charging them is not as straightforward as we would like it to be. To maximize life of the battery and to prevent any physical damage due to heating, a precise charging cycle has to be employed for totally depleted batteries and these Freescale battery chargers provide just the means to do that. The logic control logic ensures a minimal circuit diagram for the hardware developer, allowing for a battery charger to be made as a standalone unit, without any supervisory microcontroller or processorThe complete charging cycle is shown in figure 4, with the three states that have to be controlled by the circuit: trickle mode, CC mode and CV mode.
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