Battery Circuit Diagrams

Constant Voltage Schematic Circuit Diagram

When batteries are used to power a circuit, there is always the problem that the battery voltage drops during operation. A National Semiconductor type LM3354 IC (www.national.com/ 0ds/LM/LM3354.pdf) can provide a solution to this problem. It contains a dc/dc converter that operates as a buck converter in the step-down mode when the input voltage is too high, and which can also handle input voltages that are too low by operating as a boost converter in step-up mode. All of this works without any coils using switched-capacitor technology.

Constant Voltage Schematic Circuit Diagram 1

Constant Voltage Schematic Circuit Diagram 2

Several capacitors are charged to the input voltage and then connected by an internal matrix switch either in series (step-up) or parallel (step-down). The output voltage is regulated by varying the duration of the switch-on phase. The LM3354 is available in several versions for various voltages. The IC is clocked at 1 MHz and works with input voltages between +2.5 V and +5.5 V. At maximum output current, the minimum input voltage is 2.9 V (3.4 V for the 5-V version). A Low signal level applied to the Shutdown input can be used to disable the converter. The efficiency of the IC ranges from 75% to 85%. Thermal overload protection prevents damage to the IC from overloads.

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