4 6V Uninterruptible Power Supply (UPS) Circuit

This is a simple 6V UPS circuit that you can use to device that plays a critical function and needs not be interrupted .This UPS is much cheaper compared to the 12V version since it uses only transistor and no IC.

UPS schematic

Part List:
R1, R3 - 560 ohms 1/4W
R2 - 1 kilo ohms 1/4W
D1 - 1N4736A or any 6.8V zener diode
D2 - 1N4001 or similar diode
LED - red LED or any low power LED ( see Led info to know more)
C1 - 47uF electrolytic capacitor rated 16V
Q1 - 2N3440 or similar NPN transistor
BAT - 6V battery (Lead Acid or chargeable)
DC IN - see AC-DC converter below

2N3440 pinout

DC IN:

AC-DC converter schematic

Part List:
Transformer - Primary (220V or 110V)' Secondary (9V-0V-9V) rated 10VA
D - 1N4001 or similar rectifier diode
C - 470uF electrolytic capacitor rated 16V