automatic solar garden light circuit schematic

Automatic Solar Garden Lights with LEDs

Efficient automatic solar garder lights circuit with minimum components the best deal is that is completely auto and the Solar panel acts as a light detector. Switches the Lamp off at Dawn, charges the battery during daytime and switches the LED lights ON at dusk providing 100 Lumens illumination during the night.

The solar panel must provide 5.5V and 150mA. Assuming a 3.7V/1500mAh battery the charging will be complete in 8 hours at 200% capacity @ 180 mA. With 10 LEDs the power consumption would be 90 mA/hour providing a 10 hours illumination with light levels of 50 lumens to 60 lumens. With 20 LEDs the light intensity will be 100 to 120 lumens.

You can use any number of LEDs and battery capacity too. This would directly provide you the amount of illumination and time for illumination. If you use higher capacity battery than that recommended the solar panel current should be increased proportionately. Current provided by solar panel should be 10% of battery capacity.

Solar garden lights circuit schematic

automatic solar garden light circuit schematic

automatic solar garden light pcb

Bill of material for the solar garden lights

  • Resistor (1) 4K7 or 5K6
  • Resistor (1) 47E or 56E or any value ( Current Limiting )
  • Transistor 2N3906
  • Diode  1N4001/7/ 1N4148 (Any)
  • Solar Panel 5.5v/200mA
  • Battery 3.7v/1500mAh
  • Switch SPST


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  • zafer

    its not working

  • Colin Mitchell

    I see it took 5 months for you to reply. The internet must be very slow in India.
    Just because you get a small glow out of a LED, does not mean a successful circuit. The circuit is just a DISASTER and obviously not produced by someone with any electronics experience.
    See my website for the number of mistakes in Electronics For You magazine.
    Indians have a very limited understanding of electronics and even the Indian Professors have a disastrous number of mistakes in their designs.
    You need to listen and be wise.

    • Nalaka


      Could u pls send me a simple circuit with more LEDs. May be10 or 15. I already got a solar panel of 6v/2w and two batteries of 4v. I made two circuits available in the web but even 10 LEDs are very dim.

  • Raj

    I guess after making the circuit Colin now agrees that it does work. That is the type of circuit we hobbyists like to have – simple but working!

  • Colin Mitchell

    I built the circuit. It took 10.5mA.
    That’s 1.25mA per LED There’s no skill in delivering 1.25mA to a LED.
    Why use a 2 watt panel?
    Why use a 1500mAHr cell?
    How much illumination do you think you will get with 1.25mA?

    I will let the other readers judge the success of the circuit.

  • Sebastian Kushero

    Colin has to actually make the circuit to take his prejudice against the asian his entire life has been spent in denigrating Asian and Indians in particular opicking faults through his theory . Well if he is sych an expert what is he doing on this site other than pciking faults on things that actually work or maybe he like to keep things complex so that he can exhibit his therotical prowess

    He is surely a racist and i believe that they actually bashed Indians in Australia

  • T.K.Hareendran

    While surfing, just got a near-similar circuit with 5K base resistor & only one LED.

    Please refer this

    • maulik patel

      Hello Sir,

      Please suggest me the complete circuit diagram of automatic garden solar led light for:

      * Super Bright 8mm Straw Hat 0.5W/3.2V-3.6V (100-120mA) X 2 Nos.
      * Lithium Battery 18650. : 3.7V/2600 mah
      * SOLAR PANEL Cell: 5V/ 500mW


  • Colin Mitchell

    Let me answer the NON TECHNICAL reply from Jim Keith.
    1. 4k7 will not saturate the transistor. It will turn it ON and allow a collector current flow. But the transistor will not be saturated.
    2. Cree LEDs require 100mA or more and this circuit is simply not suited to high-power LEDs.
    The biggest mistake with the circuit is the impedance of the solar panel when not illuminated. This is an unknown value and the whole circuit is “left up in the air” as to its ability to work.
    Finally we come to the value of the 56R. This will allow a very small current to flow as the characteristic voltage of a white LED is 3.2v to 3.6v and you have 0.2v drop across the transistor. You don’t have any voltage left for the current-limiting resistor.
    There are so many faults with this circuit that saying “but my prototype circuit worked” does not create a good circuit-design.
    You can see that some of the readers could not get the circuit to work and no answer from the designer was forthcoming.
    That’s because the circuit is SUCH A BAD DESIGN.

  • Jim Keith

    Note that the max hFE for the 2N3906 is 300. This would provide a total LED current of 19.5mA. This is likely an empirical design involving a “hot” high gain 2N3906 device. While not optimum, 19.5mA provides useful illumination. Simply reducing the 47K resistor to 4.7K will easily saturate any 2N3906 –in this case the 56Ω resistor limits max load current to approx 30mA –yes brighter, but perhaps not a big difference.

    So my recommendation is to simply drop the value of the 47K resistor to 4.7K or so.

    Regarding the LEDs, two ultrabright Cree LEDs should work well –no need for 8 devices in my opinion.

  • Colin Mitchell

    You say the circuit works. How could it possibly work?
    The base current is 3.1/47,000 mA = 0.065mA
    If the transistor has a gain of 200, the collector current will be 13mA for 8 LEDs – less than 2mA each !!!!

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