How were engineers charging Li-ion batteries before today's highly integrated charger modules? Back in 2007, Elektor published a compact MAX745-based lithium charger that combined an efficient buck-converter design, adjustable charge current, and support for up to four Li-ion/LiPo cells.
How were engineers charging Li-ion batteries before today's highly integrated charger modules? Back in 2007, Elektor published a compact MAX745-based charger that combined an efficient buck-converter design, adjustable charge current, and support for up to four Li-ion/LiPo cells.
The Design
At first glance, Paul Goossens’s project looks straightforward: a charger for Li-ion and LiPo battery packs containing one to four cells. But the real story is in the circuit design. The charger uses a step-down (buck) converter architecture, making it more efficient than many chargers of its era. The design features a Maxim MAX745, a dedicated lithium-battery charging controller. The IC continuously monitors battery voltage and controls the charging current through an external MOSFET and inductor-based power stage.
The complete charger controller is inside IC1.
“In our case the charger uses a step-down converter,” Goossens noted. “In this way very little power is wasted in the charger and it can operate without the use of a heatsink. The complete charge controller is inside IC1. A few external components are required for the step-down converter. These are FET T1 and its surrounding components.”
Another clever feature is the use of jumper-selectable cell counts. Two jumpers configure the charger for one, two, three, or four series-connected lithium cells. The circuit then adjusts the target charging voltage accordingly, ensuring each cell receives the correct maximum voltage.
The PCB
Looking at the PCB, it's also a reminder of how practical power-electronics layouts were approached before today's highly integrated charger modules became commonplace. A large toroidal inductor, a handful of discrete components, and a carefully designed double-sided board deliver a complete charging solution.
Nearly two decades later, this project remains a great example of analog and power-electronics design.
The Lithium Charger Project
The original article, “Lithium Charger,” appeared in Elektor July/August 2007. Here is the article.
Editor's Note: The article first appeared in a 2007 issue of Elektor Magazine. Due to the project’s age, some parts and components might not be available. But we still think the project will inspire you to start a new design.
Elektor Magazine has been one of the leading sources of information on electronics for engineers, designers, start-ups and companies for 65 years. Our magazine is powered by an active community of electronics engineers – from students to professionals – who are passionate about designing and sharing innovative ideas.
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