What is the difference between a linear charger and a switch charger? Which one should I choose?

Linear Battery Charger and switch Adapter Charger are used in a variety of applications: hearing aids, smart watches, sensor nodes, cell phones, laptops...numerable! A Li-ion Battery Charger is required whenever a rechargeable battery is used. However, considering the pros and cons of the different charging topologies available, you may need to consider more factors when choosing a charger.

Each method has its pros and cons. Linear chargers are small, easy to use, and low cost. They can be used in noise-sensitive applications without any switching; however, when the charging current is large, the power consumption is high. Figure 1 shows a schematic of a linear charger.

Switching chargers are known for their high efficiency and can minimize power consumption over a wide range of input adapter voltages. However, additional inductors and capacitors consume more board space than linear chargers, adding BOM cost and design complexity. Figure 2 shows a diagram of the switch charger. Table 1 compares the functions of the two charger types.

Figure 1: Linear Charger Diagram

Figure 2: Switching Charger Diagram

Linear charger

Switch charger

Large power consumption and large charging current

Higher efficiency and lower power consumption

Simple design; small solution size

More complex design

cut costs

More components; this higher

No electromagnetic interference (EMI) problem

Switching noise may require more layout considerations

Suitable for charging small batteries or batteries with <1.5A charging current

Suitable for large capacity batteries and fast charging

Which charger to choose will depend on which factors in Table 1 are most important for a particular design. Typically, linear chargers are preferred due to small solution size, simple design and low cost (such as bq25120), small batteries and low charging current applications such as wearable devices, Internet of Things (IoT) and the like. Some backup battery applications, such as emergency calls and car GPS location trackers, are also more preferred as linear chargers for the bq24081-Q1. High-power and multi-cell battery applications such as smartphones, tablets and laptops will use switching chargers such as the bq24170.

These chargers are custom designed to support different battery chemistries such as lithium ion, lithium polymer, LiFePO4, NiMH, lead acid, and more. Lithium-ion batteries are commonly used in consumer and industrial applications due to high energy density, low maintenance frequency, and low self-discharge characteristics. Due to stability and reliability characteristics, LiFePO4 and NiMH are often found in automotive applications.