Circuit error

Discussion in 'General Electronics Chat' started by vinukc, Jul 14, 2012.

  1. vinukc

    Thread Starter New Member

    Jul 2, 2011
    Hi all,
    I am stuck with this circuit. (plz look the image). The author of this circuit says that when charging a battery, the green led glows and when battery gets the full charge (about 13.5v) the charging will stop and red LED starts to glow. But in my case this red LED glows always. (even my battery has only 12.5v). Then i replace the battery with an empty one.(almost 2.2v dead battery). And now the result is the same. Then i crosschecked the circuit and i couldn't find any error in my soldering or any other parts. the components connected in the right way. So please help me to correct this. Is there any chance to conduct the transistor all time regardless the base voltage. I mean does the transistor got damaged ?.
  2. crutschow


    Mar 14, 2008
    Check the polarity of the zener ZD.
    Also measure the voltage across it with a low battery.
  3. Dodgydave

    Distinguished Member

    Jun 22, 2012
    Put the red led in series with the collector instead of the emitter, and try that, looks like the circuit turns on the transistor as the batt volts rises, and that reduces the lm317 output by shorting out the vr1/r1.

    failing that see if there are any better circuits here.
    Last edited: Jul 14, 2012