audioguru said:
Your comparator is used to turn off the charging when the charging current drops to 3% of the battery's rating. Therefore the charger is off when a battery is connected to it.
You don't need to detect a Vref as high as 0.4V.
1) Will you use a 10.5V supply feeding a current regulator and a 4.2V voltage regulator in series? How much current?
2) What is the value of your current sense resistor? 1 ohm will limit the current for most of the charging time. 0.47 ohms will be better.
3) Will you use a pushbutton to start the charging?
sorry mr.audioguru for being confused on this circuit... if we put hysterysis on the comparator, there will be two Voltage References to be set on this circuit, the Vref during OFF condition, and the Vref during ON condition of the compatator...
for us to charge batteries, for example, a 3.7V battery is to be charge, so to be able to charge the battery, the circuit should satisfy the Vref at OFF condition, right sir? if we need to charge a 3.7V battery, we need a Vref at OFF condition to be set on 0.4V (caused by 4.2V - 3.8V = 0.4V at 1ohm), if we charge a 4V battery(the vdrop is 0.2V which is less than 0.4V, therefore the comparator is OFF) to clarify AG, Vref are set on the -Feedback while the Vsense is at the +feedback...
and for us to charge the battery, we need the pushbutton you have suggested AG,
question: the pushbutton is connected between the 9.4V and the +feedback, if the pushbutton is pushed, the 9.4V gets into +feedback then it closes the RELAY (Vref = 0.4V) does the comparator senses the Vdrop after the pushbutton is released? if so, then the circuit will now then charge the low voltage battery..
what if we will not use a current regulator? does it take time to fully charge a nearly fully charged battery?(ex.4.1V) if not, if we lower down the 1ohm resistor to 0.5 or 0.45V, does it make faster?
please analyse also the Vref of the circuit mr.AG, the Vref at ON state is less than the Vref at OFF state( but looking at the formulas, and after experimentation on getting the necessary input resistors, Vref at ON is always greater than or equal to Vref at OFF state, in example, Vref(ON)=0.028V and Vref(OFF)=0.4V)