Battery Charger Circuit using IC LM317

Battery Charger Circuit using IC LM317 is an useful project in electronics.

It charges rechargeable batteries well.

Main part is LM317 IC which is a voltage regulator.

It is used in power supply and battery charging.

It is good for 12V lead-acid battery charging.

This post show how LM317 IC charger works, what calculations to use and how to make it.

Circuit Working:

Parts List:

This circuit uses 18V DC input.

LM317 IC control voltage for charging and BC547 transistor give extra current when needed.

LM317 keep voltage stable so its charging is safe and good.

Resistor R1 limit current to battery.

Adjustable resistor R5 set charging voltage as per battery need.

Capacitors C1, C2, C3 remove ripples and make voltage smooth for better working.

Formulas with Calculations:

Below are formulas for simple LM317 battery charger:

Output Voltage:

LM317 give output voltage by:

Vout = 1.25V × (1 + R5 / R3) + Iadj × R5

Iadj is very small of about 50µA, so we ignore.

If R3 = 120Ω and R5 = 0 to 220Ω:

Vout = 1.25V × (1 + 220 / 120)

This give voltage around 1.25V to 6V which is good for many batteries.

Current Limit:

Use ohms law:

Icharge = VR1 / R1

R1 = 0.56Ω

Voltage drop on R1 sets the current.

This stops too much current and protects the battery.

How to Build:

To build a Battery Charger Circuit using IC LM317 follow the below mentioned steps for connections

• Collect all parts from circuit diagram.
• ADJ pin (pin 1) of IC1 goes to collector of Q1.
• Base of Q1 goes to resistor R4 and emitter of Q1 go to GND.
• ADJ pin also connect between R3 and R2.
• OUTPUT pin (pin 2) of IC1 connect to one side of C3 and other side to other end of R4.
• OUTPUT pin also go to R2, R3 and VR1 in series to GND.
• INPUT pin (pin 3) of IC1 goes to C2 and GND.
• C1 positive connect to INPUT pin and negative to GND.
• INPUT pin connect to +18V DC and negative to GND.
• R1 connect to control charging current and protect battery.

Conclusion:

This Battery Charger Circuit using IC LM317 is good for many batteries.

Change R5 to set voltage as needed.

Use good parts and manage heat for safe working.

The circuit is easy to make, cheap and is best for DIY lovers.

References:

Adjustable 3-Terminal Regulator for Low-Cost Battery Charging Systems