Simple Battery Charger Circuit using IC LM317

A Simple Battery Charger Circuit using IC LM317 is an important device that helps recharge rechargeable batteries effectively.

One of the key parts used in these chargers is the IC LM317 which is a versatile voltage regulator.

It is commonly found in adjustable power supplies and charging circuits.

This specific setup is great for charging 12V lead-acid batteries.

In this post we will look closely at how a battery charger circuit using the IC LM317 works, the math needed to figure out the right components and the process to build it.

Circuit Working:

Parts List:

This article is powered with 18V DC input.

The IC LM317 is really important because it controls the voltage when charging a battery and the BC547 transistor helps the circuit provide extra current when needed.

By keeping the output voltage steady the LM317 makes sure that the charging is both controlled and efficient.

The resistor R1 is crucial for limiting the current that goes into the battery while it is charging.

Additionally, the adjustable resistor R5 which allows users to set the charging voltage based on what the battery needs.

Capacitors C1, C2 and C3 work hard to smooth out any ripples in the direct current voltage making sure the circuit runs smoothly without interruptions.

Formulas with Calculations:

Below are the formulas with calculations which are used for simple Battery Charger Circuit using IC LM317:

Output Voltage Calculations:

The LM317 output voltage is determined by:

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

Since Iadj is small 50µA it is often ignored.

Assuming R3 = 120Ω and R5 (variable from 0 to 220Ω):

Vout = 1.25V × (1 + 220 / 120)

This results in an adjustable voltage range of approximately 1.25V to 6V, suitable for charging batteries of different ratings.

Current Limiting Calculation:

Using ohms law the charging current (Icharge) is:

Icharge = VR1 / R1

Given R1 = 0.56Ω the voltage drop across R1 controls the current.

This ensures overcurrent protection preventing battery damage.

How to Build:

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

• Gather all the components as mentioned in the above circuit diagram.
• Connect the ADJ pin 1 of IC1 to collector of transistor Q1, base of transistor Q1 to resistor R4, and emitter of transistor Q1 to GND
• Connect the ADJ pin of IC1 between resistor R3 and R2
• Connect OUTPUT pin 2 of IC1 to one end of capacitor C3 and other end of capacitor to other end of resistor R4.
• Connect from OUTPUT pin of IC1 to resistor R2, R3 and VR1 in series and GND.
• Connect INPUT pin of IC1 LM317 to capacitor C2 and GND.
• Connect positive of capacitor C1 from INPUT pin of IC1 and negative of capacitor to GND
• Connect the INPUT pin of IC1 to positive of +18V DC input and negative of input to GND.
• Connect resistor R1 to control the current and overcurrent protection preventing battery damage.

Conclusion:

This Simple Battery Charger Circuit using IC LM317 is a great way to charge different types of batteries.

You can change the resistor R5 to set different voltage levels which makes it flexible for various batteries.

It is really important to manage heat and choose the right parts to keep everything working smoothly.

This circuit is easy to build, affordable and perfect for people who love DIY electronics.

References:

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