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Power dissipation is the voltage across something times the current through it. To reduce the amount of heat then simply reduce the voltage, the current or both.
There are some ways to reduce power dissipation, please see it as below:
1. Use a Proper DC Input Source
A low voltage input reduces the power dissipation. In order to charge the single-cell Li+ battery, we need a well regulated 4.2V±1% or 4.1V±1% (depending on battery chemistry) output. The input voltage needs to be higher to cover the voltage drops between the battery positive terminal and the input DC source. Figure 1 shows these for a typical charger.
2. Optimize Charge Current and Power Dissipation
Figure 3 shows the circuit used for testing. It is a linear charger with a 500mA charge current and a 6 hours timer limit.
Conclusion
We can deliver a safe and reliable linear charger for a single-cell Li+ battery by optimizing the DC input source, the charge current, and the power dissipation with proper heatsinking method. Figure 4 shows an actual test result using the MAX1898 charger with a 4.2V, 900mA Li+ cell and a regulated 5V/1A MAX5021 AC adapter.
By Optoroute, please see more technical solutions from optoroute blog.
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