Li-ion battery charger with low status battery LED indicator - Page 1
Forum section: electronics / projects

author: tapasxplore
author_rank: Contributor
timestamp: February 02, 2018, 06:39:03 pm
content: I am using MCP73831 from microchip, Li-ion battery charger IC. I am looking for a IC which has low power indicator, built into the IC via status LED. Then I got to know about STBC08 from STmicroelectronics, it has two status LED. But it has no low battery indicator.Its datasheet says:1) POWER ONOpen drain. When the STBC08 detects an undervoltage lockoutcondition or when the external adapter provides an input voltagehigher than 7.2 V or less than the battery voltage, POWER ON goesto high impedance state2) CHRGOpen drain. This pin goes to low impedance when the STBC08 is inpre-charge or charge mode.Can any one help in choosing the right IC for my application.Design Requirement:1) Status LED should turn ON when the battery is charging.2) LED should turn ON when the battery is in low power mode.Regards,

author: Paul Price
author_rank: Super Contributor
timestamp: February 02, 2018, 07:11:36 pm
content: What do you mean to indicate by lighting a LED with "low battery mode" and seemingly different, "low battery indicator"?These indications seemingly relate to the battery while in use in a circuit, rather than in its charging, and so are not the responsibility of a charger IC.Adding these features to a charger IC can easily be accomplished with a cheap 8-pin MCU with an internal reference for its internal A/D and use only micropower, yet wake itself up periodically to make an accurate check of the battery voltage and indicate it with a LED. Additionally, the LED can indicate a fully charged or low-battery condition and your circuit running in low-power mode with different LED modes of being on, off or blinking in one or more patterns. With a MCU a single LED can serially display the actual battery voltage in a parsed series of numbered blinks, perhaps periodically or by pressing a multi-purposed switch for a certain length of time, and the same MCU can also be used to create a step-down converter to charge the battery as well, eliminating the charger IC.Also, depending on the battery voltage and acceptable accuracy and your visually acceptable precision of indicating a low-battery voltage state, and in consideration of your current use requirements, a circuit can be created with maybe two transistors two LED's and about 3 to 4 resistors.Of course there are dedicated IC's aplenty to do this job as well.If the voltage is >2V then a single LED or LED + PNP transistor and a LED's brightness can indicate a low-battery condition. A high-efficiency LED can give a bright indication with <1mA of current use. Using two transistors and high-valued resistors, a low-battery threshold can light a LED and further save battery use and only light the LED when the battery is low.If you are adverse to the complexity of getting a MCU to do this job, you can also use a CMOS 555 timer and get it to slowly blink a LED by using a single PNP transistor to keep the 555 timer in a 60uA low-current state until a low-voltage threshold of the battery is detected..takes just one more transistor and a resistor or two.

author: tapasxplore
author_rank: Contributor
timestamp: February 04, 2018, 06:58:04 pm
content: Hi Paul,I am planning to go for STM1061 (http://www.st.com/en/reset-and-supervisor-ics/stm1061.htmlfrom ST microelectronics which is a low voltage detectors. I am not planning to use micro-controller in my circuit, hence need standalone system.Regards,

author: Peabody
author_rank: Super Contributor
timestamp: February 04, 2018, 11:44:43 pm
content: Quote from: Paul Price on February 02, 2018, 07:11:36 pmWhat would a one or two-transistor circuit look like to have an LED light up when a lipo battery voltage goes below 3V?