Battery charger control circuit diagram

Photocoupler

The conventional battery charger relies on a transformer to step down the voltage and initiate charging. While this method is effective, it comes with several drawbacks such as bulky size, susceptibility to overheating in the transformer, and the need for manual intervention to prevent overcharging. However, this particular charger circumvents these issues by incorporating thyristors and integrated circuits into its design. Below is the accompanying circuit diagram.

Battery Charger Control Circuit

Working Principle: Once the battery to be charged is connected, the IC powers up, sending out a pulse current from pin 3 to activate the unidirectional thyristor. RP1 adjusts the frequency of the pulse current, which in turn modifies the conduction angle of the thyristor and regulates the charging current. Meanwhile, RP2 triggers pin 4 of the IC when the battery reaches full capacity, causing pin 3 to cease emitting pulse currents and halting the charging process.

Component Selection: Both RP1 and RP2 are adjustable resistors, while R1 and R2 are carbon film resistors. C1 is a ceramic capacitor, and C2 is an electrolytic capacitor. The IC used here is the NE555. For the unidirectional thyristor, any intergranular tube with a withstand voltage of at least 40 Ω and a current rating of I ≥ 0.5A can be chosen, such as the MRC-100-6 model. Additionally, VZ is a 14V zener diode. After assembling the entire unit, simply fine-tune RP1 to set the desired charging current, followed by adjusting RP2 to ensure the battery stops charging once it's fully loaded.

This device is ideal for charging batteries within the 6–14V range. However, it is not compatible with high-resistance batteries, as it cannot handle their unique requirements. Furthermore, since the charger operates directly from the mains power supply, users should refrain from touching any components while in use to avoid electrical hazards.