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ericgibbs said:hi hardcore.
Can you please post a circuit showing how the components are connected, its not possible to work out the circuit from your text description and mark in the voltage points you are trying to determine.
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?
audioguru said:I started to update your schematic to see how you are going to make hysteresis work backwards (impossible), but then I stopped because YOU should update your schematic so we can see what you are talking about.
so it is impossible to reverse the inputs for the Vsense and the Vref, because of the vref caused by hysterysis, ok... if we still use the +feedback for the Vref, and the Vsense is at the -feedback, if we have the Vref at ON condition which is the 3% of the Icharge, 0.028V, does the comparator turns ON if we will charge a 3V? given that the Vdrop is only 1.2V which is greater than the Vref at ON condition, and therefore the comparator will never turn ON at Vref of 0.028V
If you use a current-limiting resistor instead of a regulated current then the charging will take forever to reach a full charge. It will take a long time and the battery will never be completely fully charged because it is too simple.
I don't know how much is the internal resistance of a Li-Ion battery cell that causes its voltage to rise a corresponding amount immediately when it is connected to a charger. If the battery voltage is 4.1V and you try to charge it then the charger might shut off immediately.
The comparator's inputs don't work if they are within about 2V from the positive supply (input common mode voltage) so don't connect an input to the positive supply. The pushbutton should directly turn on the relay to start the charger. But then if somebody holds down the pushbutton when the battery is fully charged it will become over-charged and might catch on fire.to clarify this, once the pushbutton is pushed, or we used a SPST switch, it should be turn OFF immediately and the Relay is still ON, because on the moment of turning on the relay through a switch, a Vdrop is already sensed and will trigger the Relay permanently even the switch for turning the relay on forcedly is disconnected?
audioguru said:I see your revised schematic now. Its hysteresis is wrong. Hysteresis is positive feedback. Yours is negative feedback.
hardcore misery said:question: mr.AG, does the Vref is set at the -feedback through R1 and R2?It is not feedback. It is the reference voltage for the comparator. Select R1 and R2 to make 28.5mV plus and minus a little hysteresis.
Without my added resistor then the value of the R7 hysteresis resistor will be so low that it will overload the comparator's output.i'm just confused because i'm trying to compare this schematic to the attached one, why did you add another resistor at the +feedback, is it to divide the Vdrop from the current sense resistor? where is the Rh now on the circuit?