Micro-usb 30F Supercapacitor Flashlight





Introduction: Micro-usb 30F Supercapacitor Flashlight

This is an example of a supercapacitor flashlight that can be charged with a standard 1A smartphone charger.

French people can find the entire description here :


Step 1: You Will Need

- perfboard

- micro-usb connector

- 1.1A Polyswitch

- 4.8 ohm 1 Watt resistor

- 1000 ohm, 82000 ohm, 220 ohm and 11.4 ohm 1/4 Watt resistors

- buck converter (RC Airplane Module Mini 360 DC Buck Converter Step Down)

(4.75V - 23V to 1V - 17V)

- 1N5817 diode

- Supercapacitor 30 Farads 2.7V

- TL431 (adjustable shunt regulator with 2.5V Vref)

- green LED 3mm

- button

- boost converter (mini DC DC 0.8 - 3.3V to 3.3 V Step UP Boost converter)

- white LED 5mm (20000 mcd, 3.1 to 3.4V)

- soldering iron with solder and flux

- jumper wires

Step 2: Adjust the Buck Converter

With the micro-usb connector and a breadboard, you have to connect the buck converter, the Polyswitch, the 1N5817 diode and a 1000 ohm resistor.

You connect a voltmeter to the resistor.

Then you turn the buck converter screw to obtain 2.6V.

Step 3: Turn on a Green LED When the Supercapacitor Is Charged to 2.5V

The TL431 device is a three-terminal adjustable shunt regulator. The output voltage can be set to any value between Vref ( 2.5 V) and 36 V.

So it's easy to turn on a LED on 2.5V with a TL431...

Step 4: Breadboard and Perfboard Supercapacitor Flashlight

When the switch is engaged, the supercapacitor feeds a small boost converter which boosts the voltage to 3.3V to power a LED through a 11.4 ohm resistor.

If you need more information, you can read the original description (in french) of this supercapacitor flashlight here :


Enjoy !



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    Awesome project !
    How long time it takes to recharge the capacitor and how long it lasts ?


    Schematic, breadboard and perfboard are different - which is the right one and how does it connect up on the perfboard?

    Have you got a link to the regulators and their datasheets - full output from 500mV sounds a little too good to be true, but I'd like to have a look at them, to see if they'd fit some of my future projects.

    Going for a CC solution should yield you a much better efficiency - as is, it's not much above 25% (no matter the efficiency of the 2 switch mode converters).

    Regards :)


    Breadboard and perfboard have the same schematic.

    You can actually find the Buck converter here :


    You can find the Boost converter module here :


    This converter module use a BL8530 :


    BL8530 need 800mV to start, but when it's started, it can work as low voltage as 300mV.

    If you can provide links to interesting components, I'm interested.

    Any ideas to improve the flashlight are welcome.


    The schematic show the charging part. After, there's only the button, the boost converter, a 11.4 resistor and the White LED...

    There's no difference with breadboard and perfboard.

    Thank you very much for the links :) I'¨ll have to study them in detail as soon as time allows.

    If I find a current-mode module, I'll drop you a link - in my mind I was just contemplating making the circuit from the ground up, but I think I've seen small current mode switch modules. You might be able to get 3..4 times the run time (based on the energy the cap can hold) - I'd probably charge it through some tabs on the housing (rather than fiddle with Micro-USB) and use a linear charger/supply - shouldn't take long to recharge... Almost Tap 'N' Go :)

    Nice to see some French work btw. I'm aware that a load of electronics is going on in your country... But unfortunately I only took (slightly less than) a year of French back in the mist of time, so it's not all that easy to enjoy.


    Thank you for the message.

    I wanted to make a small flashlight and I didn't find a very small current mode switch module. I will apreciate your link.

    I have chosen Micro-USB because I wanted a solution to charge the flashlight with a thing that all people have : a smartphone charger.

    Yes, I am French and I hope I do not make too many mistakes in writing English. We are often very bad at foreign languages...

    A good read, if you're planning to build from scratch (at some point in the future perhaps):


    And the MCP1624


    • Low Start-up Voltage: 0.65V
    • Operating Input Voltage: 0.35V to 5.5V
    • Adjustable Output Voltage Range: 2.0V to 5.5V

    Seems quite handy for your purpose.

    Your English is OK! I was referring to the general population - I've spend "fun" time shopping the shadier parts of Paris - I didn't know how to say "No! I don't wan't a huge switchblade and a pair of brass knuckles, just an F'in plain small pocket knife" in French to an old guy without hurting his pride (it was fine stuff he was piling up on the desk after all).

    Why go through all this bucking and boosting when you can get plenty of 5.5 volt super capacitors at Ali Express?

    There were many comments to complete and enhance the response to this question. So here's a summary of those comments to make it more readable for those interested :

    Normal supercapacitors have a voltage between 2.5V and 2.85V. The 5.5V supercapacitors are composed of two 2.75V supercapacitors in series.

    This flashlight shows a possible technique to recharge a single 2.7V supercapacitor from a 5V voltage source and then shows how to use the supercapacitor to power a 3.1V to 3.4V LED.

    So here I have used a buck converter to lower the voltage on charge and a boost converter to increase the voltage to turn on the LED.

    This is technically interesting, but it is true that this is not the simplest and not the most logical. For a next version of flashlight, I will use a 5.5V supercapacitor. So I will not need to use a buck converter. To power the LED, I will use a buck-boost converter to fully exploit the energy of the supercapacitor (lowering the voltage when it is above 3.3V and increasing the voltage when it drops below 3.3V).

    Here I used a 30F supercapacitor. For the next flashlight, I will take the equivalent of a 40F supercapacitor but in 5.5V.

    When you put two supercapacitors in series, the rule is :

    1/Ctot = 1/C1 + 1/C2

    The equivalent of a 40F 2.75V supercapacitor at 5.5V is the connection of two supercapacitors 20F 2.75V in series.

    1/Ctot = 1/20 + 1/20

    1/Ctot = 1/10

    Ctot = 10

    I will use a 10F 5.5V supercapacitor.

    The energy stored in a capacitor can be expressed as : W = 1/2 CV^2

    W = energy stored (Joules)

    C = capacitance (Farad)

    V = potential difference (Voltage)

    For a 40F 2.75V supercapacitor, the energy stored is:

    W = 1/2 x 40 x 2.75^2 = 151.25 Joules

    For a 10F 5.5V supercapacitor, the energy stored is :

    W = 1/2 x 10 x 5.5^2 = 151.25 Joules

    A 40F 2.75V supercapacitor have the same amount of energy as a 10F 5.5V supercapacitor. In fact, two parallel 20F 2.7V supercapacitors (= 1 SC 40F 2.75V) have the same amount of energy as two supercapacitors in series (= 1 SC 10F 5.5V).

    I hope I have summarized the discussion as it should.

    Thanks to pmshah, Lovot, przemek, GianlucaG1 and david.colclazier.