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Md Jony Islam Author
Md Jony Islam
CalculatorToolsProjectExpert
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Małgorzata Koperska, MD Steven Wooding
Last updated: September 24, 2025

Solar Panel Automatic Light Circuit Using BC547 Transistor

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BC547 Transistor

BC547 Transistor

General-purpose NPN bipolar junction transistor (BJT)

10K Fixed Resistor 1/4W

10K Fixed Resistor 1/4W

A 10,000-ohm resistor rated for 0.25 watts

[10k-fixed-resistor-1/4w]
1N4007 Diode

1N4007 Diode

General-purpose 1000V, 1A diode

3V LED 5mm

3V LED 5mm

3V, 5mm round light-emitting diode

3V LED 5mm

Mini Solar Cells

Mini solar cells are small photovoltaic devices that convert sunlight into electrical energy, typically used in calculators, toys, DIY projects, and low-power electronic applications.

*Please note: These are affiliate links. I may make a commission if you buy the components through these links. I would appreciate your support in this way!

Solar Panel Automatic Light

Build a solar panel automatic light using BC547 transistor. Lights turn ON at night and OFF during day, perfect for energy-saving DIY solar projects.

automatic night light using transistor:

A solar panel automatic light, with the help of BC5,47, activates the light at night and deactivates the light when the day arrives. The transistor is a BC547, which detects the changes in the voltage on the solar panel to regulate the lights on the LEDs.

low-voltage solar light circuit:

Solar Panel Automatic Light Using BC547 is a very simple, low-voltage circuit, which switches lights ON at night and OFF during the day. The BC547 transistor is a switch, activated by a solar-powered voltage divider or LDR sensor, which detects the ambient light. This project would suit hobbyists, students, and DIY enthusiasts who want to have energy-efficient lighting. The solar panel, when it is in daylight, will charge a battery and place voltage in the circuit, ensuring that the light is off. During the ark, the voltage is reduced, the BC547 is in operation, and the light is ON. Unlike the other two, the circuit is small and affordable and operates with low-voltage DDC C, which can be easily sourced through solar-powered LEDs. It illustrates the fundamentals of transistor switching and solar power and offers a practical and automatic night lighting to gardens, walkways, or other small outdoor areas.

⚡ Work & Installation (Input → Output):

  • Solar Panel Input → DC voltage to charge battery and provide circuit voltage.
  • Voltage Divider / LDR → Detects ambient light level.
  • BC547 Transistor → Switches LED ON/OFF based on input from LDR/voltage divider.
  • Load → LED or small DC light connected to collector of BC547.
  • Battery Storage → Stores energy from solar panel to power LEDs at night.
  • Installation → Connect solar panel, battery, BC547, and LEDs on PCB or breadboard. Test light switching day and night.

Testing & Final Adjustments:

Once the solar panel has been assembled, put it in the sun and confirm that the battery is charging appropriately. The LED is supposed to be switched on automatically during the night or in the dark. Tune resistor values in the voltage divider circuit or LDR sensor circuit to make the switching point fine. Make sure that the transistor, BC547, is properly oriented to avoid failure. Connect the LEDs with proper polarity and fix all elements to avoid short-circuiting. Test the circuit through multiple day-night cycles to make sure that it works reliably in the automatic mode. The solar-powered automatic light should be tested properly to guarantee efficient, safe, and stable operation.

Frequently Asked Questions - Solar Panel Automatic Light:

What is BC547?

A general-purpose NPN transistor used as a switch in this circuit.

Voltage required?

Typically 6–12V DC from solar panel or battery.

Can it work with LEDs?

Yes, ideal for low-voltage LED lights.

Does it turn ON automatically?

Yes, based on ambient light levels detected by LDR.

Battery needed?

Yes, to store solar energy for night operation.

Is it beginner-friendly?

Yes, simple components and low-voltage DC operation.

Applications?

Garden lights, pathway lights, small outdoor solar lighting.

Can I adjust switching threshold?

Yes, by changing resistor or LDR values.

Safe for indoor use?

Yes, operates on low-voltage DC.

PCB required?

Optional, can be built on breadboard for prototyping.

Md Jony Islam

Md Jony Islam

CalculatorToolsProject

Founder of Earthbondhon.com

a free online tools website designed to make everyday and engineering-related calculations easier for students, professionals, and hobbyists. The site offers a wide range of basic calculators across key categories, including Electrical Calculators, Electronic Calculators, and Time & Date Calculators.