6 12V emergency light using power LED

Another emergency light circuit that is very easy to construct and uses power LED not an array of LEDs unlike the simple led emergency light. The circuit is composed of two parts, the charger and the led driver. When the battery voltage is higher than the voltage of zener diode DZ + 0.7V, the charger automatically turns off (protect the battery from overvoltage).  Transistor Q4, R6, D1, D2 is the led driver circuit (See cheap led driver to know more how this circuit works).
schematic diagram
Part List:
R1 - 560 ohms 1/2W
R2 - 220 ohms 1/4W
R3 - 1 kilo ohms 1/4W
R4 - 10 kilo ohms 1/4W
R5 - 500 ohms 1/4W
R6 - value is dependent on LED power, see notes below
Q1, Q4 - TIP41C, or similar NPN Power Transistor
Q2 - 2N2222, CS9013, or similar NPN transistor
Q3 - CS9012, 2N4403 or similar PNP transistor
Dz - 12V zener diode minimum 1/2W rating
D1, D2 - 1N4001, or similar diode
Bat - 12V lead acid battery
LED - 3W white power LED
DC input - see  AC-DC converter circuit below

DC Input Supply
schematic diagram of AC-DC converter
Part List:
Transformer - 220V to 12V center tap transformer rated 10VA
D - 1N4004 or similar silicon diode
C - 1000uF electrolytic capacitor rated 25V

Value of R6
Resistor R6 will limit or control the current of the LED. The basic idea is we need to know the rated forward current for the LED. After that, we can use the formula below to determine the value of R2.
R2 = 0.8 / Current and power of R2 = Current*Current*R2
Example: 3W LED has the current rating of 530mA
               R2 = 0.8/0.530 = 1.5 ohms
               Power Rating = 0.8*0.8*1.5 = 0.96W or 1W

Parts Diagram and Pinout: click image to enlarge
TIP41C pin
2N2222, CS9013 pin
CS9012, 2N4403 pins
LED pins

Modification below allows you to know if the battery is fully charged. When LED1 is off and circuit is connected to AC, it means the battery is charging . When battery is on, it means the battery is fully charged.
full-charge indicator
Part list Modification: (Other parts same as above)
R3 - 390 ohms 1/4W
Dz - 1N5240B or any 10V zener
LED1 - red LED or any LED with forward voltage around 2V (see LED info to know more)


  1. Hey I just finished making this circuit of yours. Wanted to ask if I can do some kind of mod to indicate the charging or when its finished.


  2. I added some updates above. But its for full charge indicator only.

  3. Can I add Multiple say 4-6 LED for more lights? ANy Changes in the Ckt.

  4. i was trying to calculate the value of R6 using the posted formula. I found some mistakes:
    1- the number 0.8 is used as a voltage in first formula and as amps in another formula, which is incorrect.
    2- R6 is written R2 which confuses the readers.

    Please post more explanations to make sure i am right or wrong.

  5. can i use a 12v 7amp lead battery for this led driver ?