Adding 'Oomph' to the Garden Solar Light

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Introduction: Adding 'Oomph' to the Garden Solar Light

Tired of the feeble light from your Solar-rechargeable Garden lights? You can more than triple the light output with this new circuit. Works even with red or orange lights - as long as it runs off a single AA rechargeable battery!

Step 1: Remove the Old Circuit Board.

Cut the wires as close to the board as possible. We'll need the wires from the solar cell and the battery holder, so cut them as close to the circuit board as possible. If there are wires from a light sensor (colored Green here) we can cut those too - it's not needed anymore.

The board can go and join the others we removed from other projects.

Step 2: The New Turbo Circuit.

The new circuit uses fewer parts than the original but can deliver over 80mA, almost 4-times the current to a White or Blue LED while using about 250mA, which is double the efficiency of the original design.

We will need to use 1/2W LED, which are readily available on eBay:
here, or here. They each have slightly different products, but I've used both and they're both reliable.

The real star of this circuit is the driver transistor, FJN965, from Fairchild Semi. Capable of handling up to 5-amps of current in a TO-92 case, it will start at .9v and run the light until the battery drops to under 0.3-volts. You can get them from

Resistors, capacitors and inductors can be obtained from your local supply houses (eg Radio Shack, The Source), Sure Electronics, or at online surplus stores, like

The second image shows the layout using a Perfboard. S+ and S- indicate the wires from the Solar cell.

Step 3: Perfboard? or Try Just Winging It Freehand...

We will be using a 100mA white LED with a 140-degree spread. Start by slipping the leads through a scrap piece of perfboard to keep it upright.

If you want to follow the perfboard assembly, do that now, then solder the leads to the finished board.

The circuit is simple enough that the whole thing can be assembled freehand, which I will show you here.

Start by flipping the case over and bend the shorter (-) lead of the LED flat against the plastic. Then push it INTO the plastic by holding a hot soldering iron against the end of the lead until it melts it. Now it's SOLID!

Step 4: What IS This Sh*t???

Making our many legged creature.

Start by holding the 'C' lead of the 2N3906 to the 'B' lead of the FPN965 and soldering them together.

When you have attached the 2 capacitors and the diode to the transistors, this section is done.

Let me emphasize the need to COOL the parts after applying solder. The rule-of-thumb is to blow on the solder for TWICE as long as you apply heat. So if the joint took 2 seconds, cool it for 4 seconds. Heat is the second highest cause of failed circuits. (Number one is operator/designer stupidity.)

A few more images of the process of building our amorphous creature. Fine needle nose pliers are a must-have for little circuits like this. As is a GOOD soldering iron with a 1/16" or 1/32" tip.

Step 5: Attaching to the LED

I've trimmed and cleaned up all the little solder joints and I've bent into small hooks the 3 leads which require attachments.

Step 6: A Quick Test, And...


The green wires from the Light Sensor is left unconnected.

A 'feature' of this circuit is that once on, it will not be 'distracted' by flashes of light, from passing cars etc.

Here's another approach to make your garden light more effective - by adding Bling to the Oomph!

If you like this, see other LED ideas on my website:

Step 7: Another Option.

I have a light which sits on a gate surrounded by tall trees, with perhaps a max of 3 hours of sunlight in the afternoon. I added a small 2v, 30mA solar cell which is glued on facing West. It is simply added in series with the existing one. I also put a 2000mAH Sanyo battery in. Now even on overcast and rainy days, I get a good light showing the gate.



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    So do I use the 2SD965 in place of the FJN965? This will actually be the first circuit I'll ever have built from scratch, so I'm very new to all the different parts and what they are called/do.


    Yes, they are identical. Fairchild had a licence to make them and decided to call them by a different name.

    So how much illumionation time do you get from a half-decent days sun????

    Hello QS; still love yer designs. I am having trouble geting yer OOmph circuit to start reliably. Could you please describe the mechanism that begins the whole converter process? I have read all the comments and replies; but no joy.

    I am using 2SC3202 specd at 2A: schottky diodes both places; and a 2N2907 with 22uH. Help


    Hi OldGuy,

    Very briefly, the circuit starts when the PNP begins conducting, which turns on the NPN, and this starts charging the coil. At the same time, current is drawn through the 150pF capacitor, which further increases the drive to the PNP and, subsequently, the NPN. When the capacitor is charged, the drive is cut off, and the magnetic field built up in the coil collapses and cause a voltage to appear across the ends. This voltage is placed in series with the NiCd battery to turn on the LED. Simultaneously, a small portion of this voltage is diverted through the diode (D2) to charge the 1uF cap. This provides about 3.5v to drive the PNP, which improves the brightness and efficiency. The cycle then restarts.

    As far as your circuit, double check the specs for the transistor you're using - the datasheet I have rates the C3202 for 500mA, not 2A. And the gain at that level may be a tad low. This may be offset by reducing the 1M-ohm to 720K, which will likely help with the startup reliability. If the output is low, you can try to increase the drive to the NPN (by going down to 680k), but remember you are already pushing the transistor to its operating limits. Fwiw, the FJN965 is also available as the 2SD965 on Ebay  The 2SC2500 also works here.

    Another thing I'd watch for is that the pinouts for the 2SC series is different from the BC series, which is different from the 2N series!

    Good luck!

    Here is a spice simulation of the new turbo circuit. I have substituted an FZT849 for the FJN965 being the closest type available in the simulator (8 amp) and I needed to reduce the 1meg resistor down to 100k before it would operate properly. I also found that increasing the 1 microF cap to 2 microF in the peak detector arm improved its voltage stability but takes slightly longer to startup.

    However, I also found that this circuit will not start if the voltage is below 1.1 volts (!). It should work down to at least 0.8 volts to be usable.

    ltspice simulation3.jpg

    Can you emulate a circuit to use a lithium instead and i can wire up 6 solar cells in series instead of the normal two? Id like to have the batteries cycle from 3.9v to 3.2v if possible. I just do not know how to use that program.


    Even if SPICE is getting close to real-world performance, it's not a valid emulation if you substitute a part that has less than 1/2 the gain of the FJN- / 2SD965. The 2SC2500 is also acceptable.

    Your observation about the 10uF cap is a valid one - it does improve the operation somewhat.

    This circuit was designed to make use of the power curve of the NiCad cell, so operation below 1-volt was not a consideration. However, for other applications, substituting a Schottky diode for the 1N4148 / 1N914 will allow the circuit to start at 0.7-volt and continue running until 0.4-volt.


    Are the diodes both the same kind?