battery charger using lm317

LM317 Battery Charger

According to the battery manufacturers, a battery should be charged with only 1/10 current (in ampere), of its Ah value.

For example, if a battery is of 7Ah value, then it should be charged with 0.7 Ampere current. Charging a battery using this rule, extends the battery life.

battery charger using lm317 voltage  regulator ic

R1 0.56Ω 5W
R2 470Ω
R3 120Ω
R4 100Ω
VR1 220Ω
D1 5A Diode Bridge
C1 1000 µF 50V
C2 0.22 µF
C3 0.22 µF
T1 BC140
IC1 LM317
T1 Secondary 15V, 3AMP Transformer
Other Good Heat sink

LM317 Regulator IC Pin Configuration

BC140 transistor pin Configuration-pinout-bc-140-npn

BC140 Transistor Pin Configuration

  • Charging current is controlled by T1, R1, and R4. VR1 is used to set the charging current.
  • As the battery gets charged, the current flowing through the R1 increases. This result in increase in the current and voltage from the LM317.
  • When the battery becomes fully charged, charger reduces the charging current to the battery, and the battery is charged in trickle charging mode.
  • The input at LM317 should be around 3 volts higher than the output voltage from the LM317. As this IC requires minimum 3-volts for its operation.
  • As this IC gets very hot during operation, a good heat sink should be used with this IC.

Please send your ideas, those are very important for our success…

Tags: ,

Leave a Reply

Your email address will not be published. Required fields are marked *


Electronic Circuits


Enter your email address: