View Full Version : little help needed for lm7805 ic supply

01-25-2010, 08:19 PM
hey guyz, i have almost constructed my robot schematic but got stucked up as inspite of getting more than 8v in lm 7805 ic input terminals i am getting an output as low as 1.5v by which my M.C.U.(at89s52 here) is not working... is this problem due to a capacitor needed between output and ground of 7805 ic (as i have not used it thinking that i am using cells of 9v dc ) ....plz tell immediately...

01-25-2010, 09:01 PM
Measure voltage when load is connected , i believe 9v battery is not supporting the load. Looks like simple problem of under powered circuit.

01-25-2010, 09:04 PM
pin connections ok?pin1 input(8to 18v dc unregulated)pin2 ground,pin3 out. dc input sufficient?any shortcircuits?last but not least input must be at least three volt greater than required output ,here input minimum=output(5v)+3=8v.if every thing ok try another 7805,

01-25-2010, 09:05 PM
so shall i use more batteries to my robot or go for trying capacitors

01-25-2010, 09:07 PM
i have not used capacitors 0.1 uf and 10 uf so what shud i do??

01-25-2010, 09:12 PM
no shorting no open circuit but problem is only wid 7805...one more thing i am using 4 motors dc giving a seperate battery for it connected via a single l293d ic (both motors connected in parallel with l293d output pins) ....

01-26-2010, 10:17 PM
hey, as Vikas said, i think its only because of low power at input. If you are using 9v (generally used in remots of toy cars), please don't use then those does not work with robotics .. as you will be using motors (inductive load) they need more current and your 9v battery can not supply . Change the battery and try it .

01-26-2010, 10:54 PM
shall i go for ni cad batteries...thnx for the reply

01-27-2010, 06:29 PM
if your robot is not autonomous then use lead acid.They are cheap & powerful.

01-27-2010, 06:30 PM
if your robot is not autonomous then use lead acid.They are cheap & powerful. If going for ni-cd please buy branded & orignal & not used.

01-28-2010, 09:04 PM
i have bought li-ion battery 7.4 volt rechargeable really very good and light...will it be able to run four motors and a microcontroller and a l293d

02-02-2010, 10:56 PM
no reply given please tell immediately

02-03-2010, 04:05 AM
It should work , But do you have a Lith Ion charger ... They are dangerous batteries to work without proper charger.

02-03-2010, 10:40 AM
yes i have its charger...i want to run the 4 motors from a single li-ion battery of 7.4v and 2000mah