Lithium (Li-Ion) Battery Charger using LP2951 IC + PCB

Fig. 1 - Lithium (Li-Ion) Battery Charger using LP2951 IC + PCB

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This is a complete and compact Li-Ion battery charger circuit, composed of Integrated Circuit LP2951. 

The circuit performs assisted and controlled charging, and this represents a longer life for your battery and a full charge giving more autonomy in the circuits powered by these batteries.

It is a very simple circuit to assemble, because the external components are minimal, due to the IC having integrated in its encapsulation all the necessary components to perform the task.

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LP2951 Integrated Circuit

The LP2951 is an adjustable micro power voltage regulator suitable  for  use  in  battery-powered  systems.  

This  regulator has  various  functions  such  as  alarm  which  warns  of  a  low output voltage, often due to falling batteries on the input, the external   shutdown   which   enables   the   regulator   to   be switched on and off, current and temperature limiting.

Additional Features

The LP2951 has three additional features: 

• 1st - Error output that can be used to signal external circuits of an out-of-regulation condition or as a microprocessor reset trigger. 

• 2nd - Allows the output voltage to be preset to 5.0 V, 3.3 V or 3.0 V (depending on the version) or programmed from 1.25 V to 29 V. It consists of a fixed resistor divider along with direct access to the Error input on the internal operational amplifier feedback. 

• 3rd - It has a shutdown input that allows a logic level signal to turn the regulator output off or on.
  
  

What it is used for

Due to the low specifications for input to output voltage differential and bias current, this device is ideal for computers, consumers, and battery powered industrial equipment where extended battery life is desirable, battery charger. 

The LP2951 is available in eight-pin dual-line, SOIC-8 and Micro-8 surface mount packages. Devices with an 'A' suffix have an initial output voltage tolerance of ± 0.5%.

Features

• Low Quiescent Current 
• Low Dropout Voltage
• Low Temperature Coefficient
• Tight Line and Load Regulation
• Guaranteed 100mA Output Current
• Internal Short Current & Thermal Limit
• Error Signals of Output Dropout (8 pin Versions only)
• External Shut Down ( 8-Pin Versions Only)
  
  

The Circuit

In Figure 2 below we can see the schematic diagram of the Li-Ion battery charger, the LP2951 IC is responsible for measuring the state of the battery through the voltage divider, at the charging voltage output of the battery, and thereby control it to not emit an unnecessary charge.

Fig. 2 - Schematic Diagram Lithium (Li-Ion) Battery Charger using LP2951 IC

Capacitor C1 and C2 act as an RF filter to eliminate spurious, capacitor C3 is for stability of the feedback system, the 50K potentiometer RP1 is to adjust the system according to the operating voltage of the cell.

The Li-Ion battery charger circuit can be powered by a DC voltage between 6 to 10V with a current equal to 1.5 times the capacity of the cells to be charged.

Charger Operation

When we connect the power supply to the circuit and insert the battery, the LP2951 IC checks the charging status and, when it detects a charge below the programmed one, it triggers the charging to complete the charge.

After the battery is fully charged, the circuit goes into sleep mode, it keeps checking periodically the status of the battery and if necessary it activates the continuity of charging. 

Components List

• Semiconductors
• U1 .......... LP2951 Voltage Regulator Circuit
• D1 .......... 1N4007 Silico Diode
  
  
• Resistor
• R1 .......... 2MΩ 1%  Precision Resistor (red, black, yellow, brown)
• R2 .......... 806KΩ 1%  Resistor (gray, black, blue, orange, brown) 
• RP1 ........ 50KΩ Potentiometer
  
  
• Capacitor
• C1 .......... 0.1uF or 100nF Polyester/Ceramic Capacitor
• C2 .......... 2.2uF / 16V Electrolytic Capacitor
• C3 .......... 470pF Polyester/Ceramic Capacitor
   
  
• Other
• B1, B2 ... 2-pin PCB soldering terminal blocks
• Others .... Printed Circuit Board, tin, wires, etc.

Printed Circuit Board

In Figure 3, we provide the PCB - Printed Circuit Board, in GERBER, PDF and PNG files. These files are available for free download, on the MEGA server, in a direct link, without any bypass. 

All to make it easier for you to do a more optimized assembly, either at home, or with a company that prints the board. You can download the files in the Download option below.

Fig. 3 - PCB - Lithium (Li-Ion) Battery Charger using LP2951 IC

Files to Download, Direct Link:

Click on the link beside: GERBER, PDF and PNG files

If you have any questions, suggestions or corrections, please leave them in the comments and we will answer them soon.

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