Hi Swagatam. I know it was asked before, but still, if you can help me out, I'd really appreciate it. I'd like a circuit/ic for purely low voltage cut off. I have a 8-pack of AA (NiMH LSD) batteries, which should never discharge below 7.2V. I'm using these with a (car) 12V to 5V USB charger, which I'd like to use on the go. The setup of simply using a transistor and a variable resistor in conjunction with a TIP122 transistor for handling larger currents, resulted in draining the battery further than the absolute minimum of 7.2V. I'd like this to use this with no relays (as they use too much power). I'm looking at 0.5-1.5A on the primary side (batteries) and 1-2.5A on the secondary 5V side. For charging both the phone and the tablet. I just hate it, when a circuit like this is used in a 1$ devices. I don't want to buy of the shelf products. Thank you really much! -David
As mentioned earlier, the possible oscillation at the thresholds can be prevented by adding some hysteresis to the above design, it may be done by the following two methods, the second option appears to be more logical and clean.
Note: Please add a 3V zener diode in series with pin#6 of the opamp, (anode to pin#6) to counter offset problem.
Feedback from Mr. Robert
voltage from pin#6 of the opamp which is not allowing the transistor to
switch OFF....connect a 1K resistor across the base and emitter of the
TIP127, or you can also try a 3V zener in series with the base of the
transistor, the anode will go towards the base and the cathode towards