3.6 Volt Cell Phone Battery MeterThis is a agnate ambit to the aloft and provides a 4 LED bar blueprint advertence the voltage of a accepted 3.6 volt Lithium – Ion recharable corpuscle buzz battery. The advertence voltage is provided by a TL431 programmable voltage antecedent which is set to 3.9 volts area the TL431 connects to the 1K resistor. The lower advertence for the LED at pin 14 is set with the 5K adjustable resistor.
The programmed voltage of the TL431 is formed out with a voltage affiliate (10K 5.6K). The acclimation terminal or alliance of the two resistors is consistently 2.5 volts. So, if we use a 10K resistor from the acclimation terminal to ground, the resistor accepted will be 2.5/10000 = 250uA. This aforementioned accepted flows through the high resistor (5.6K) and produces a voltage bead of .00025 * 5600 = 1.4 volts. So the blow adapted achievement voltage at the cathode of the TL431 will be 2.5 + 1.4, or 3.9 volts.
Working out the LED voltages, there are three 390 ohm resistors in alternation with addition adjustable (5K) resistor at the bottom. Assuming the basal resistor is set to 2K ohms, the absolute attrition is 390+390+390+2000 = 3170 ohms. So, the resistor accepted is the advertence voltage (3.9) disconnected by the absolute resistance, or about 3.9/ (390 + 390 + 390 + 2000) equals 1.23 mA. This gives us about .00123*2000= 2.46 volts for the basal LED, and about .00123*390 = .48 volts for anniversary footfall aloft the bottom. So, the LEDs should ablaze at accomplish of 2.46, 2.94, 3.42, and 3.9. A absolutely answerable corpuscle buzz array is about 4.2 volts. You can acclimatize the 5.6K resistor to set the top voltage college or lower, and acclimatize the lower 5K resistor to set the basal LED for the everyman voltage. But you do charge a 6 to 12 volt or greater array to ability the circuit.
