basic UPS power supply

Discussion in 'The Projects Forum' started by, Jul 8, 2008.


    Thread Starter New Member

    May 9, 2008
    i'm a +2 student n i need ur help in doin my project work,...
    i have selected UPS and the circuit diagram along wid the link is given in a trouble as i need to modify the circuit to get a regulated supply of 15 V...its given in the site that connectin two 12 V batteris in series and using a 7815 would solve the problem......
    but is it enough ??? dat the only change i hav 2 make in the circuit...???
    wat r the major problems dat i may face?....precautions???
    plzz help me out as dis is my 1st venture.....

    amrutha g kartha .


    This circuit can be adapted for other regulated and unregulated voltages by using different regulators and batteries. For a 15 Volt regulated supply use two 12 Volt batteries in series and a 7815 regulator. There is a lot of flexibility in this circuit.
    TR1 has a primary matched to the local electrical supply which is 240 Volts in the UK. The secondary winding should be rated at least 12 Volts at 2 amp, but can be higher, for example 15 Volts. FS1 is a slow blow type and protects against short circuits on the output, or indeed a faulty cell in a rechargeable battery. LED 1 will light ONLY when the electricity supply is present, with a power failure the LED will go out and output voltage is maintained by the battery.
  2. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
    The only problem with using a linear regulator such as a 7815 to drop 24V to 15V is that over 40% of the power delivered will be lost as heat which for a battery supplied circuit is probably unacceptable.

    Consider replacing the 7815 with a switching regulator which will have an efficiency nearer to 90% and won't produce anything like the same amount of heat.

    There are a bewildering array of them here:,C1,C1003,C1042&gclid=CN7smoWHsZQCFRSA1QodV0KltQ
  3. SgtWookie


    Jul 17, 2007
    In addition to changing over to a switching regulator, the charging circuit to the battery is not regulated. This will lead to overcharging and short battery life.

    R1 is limiting the current to the battery. If the battery is discharged and the mains power comes on, R1 will be dissipating a great deal of power and the charging cycle will not be efficient.