ONE_CELL_CONVERTER

Published:2009/7/16 21:33:00 Author:Jessie | From:SeekIC

The regulator generates a 5-V output from a single lithium-ion cell. Initially, the lithium-ion cell is at 4.2 V, which is greater than the 3.75-V undervoltage-lockout (UVL) limit of the LM2587 Simple Switcher. Once it starts up, the boost circuit will continue to regulate-even when the battery voltage drops lower than the UVL limit. The level that the input voltage can drop to depends on the maximum load current desired. Of course, the source can be any type of battery-three alkaline, four NiCd, or even two lithium batteries. When power is applied to the circuit, the 10-kΩ resistor charges up the 47-μF input capacitor and supplies the startup current to the LM2587. After startup, the LM2587 input and the input capacitor draw current frorrt the switch node through the 1N914B boot-strap diode. When that happens, the IC input pin gets charged up to the output voltage minus a diode drop. In the circuit, with a 5-V output, the IC input voltage is 4.5 V after startup. It stays at 4.5 V-even when the input voltage drops to below 3.75 V. The input voltage can drop to 1.25 V when the regulator is supplying 250 mA. At 2.4 V, the regulator is 84 percent efficient if the 1N914B bootstrap diode is replaced with a 1N5817 Schottky diode.



Reprinted Url Of This Article:
http://www.seekic.com/circuit_diagram/Power_Supply_Circuit/ONE_CELL_CONVERTER.html

Print this Page | Comments | Reading(3)