![]() ![]() The set circuit is now ready to be attached with the battery in question, whenever the battery voltage reaches the 11.4V mark, the LED would light up, providing the required low battery information. The 100K variable resistor is adjusted such that the LED indicator just turns on when the battery voltage (Vin) falls to the required level e.g. The key components are the 100K variable resistor, the LM741 Op-Amp, and a 5.6 Volt Zener Diode. Now the preset may be glued by some permanent adhesive for preventing the setting from getting disturbed. Pictured above is a circuit diagram for this 12 Volt battery monitor. Next, the preset should be adjusted such that the LED just lights up. Suppose, the specified lower threshold is 11.4V for a 12V battery, the applied sample voltage can be fixed at 11.4V and applied to the circuit. The above setting can be done manually by applying a sample voltage to the circuit imitating the lower threshold level. The battery voltage is allowed to reach pin#2 of the IC via the preset, which must be manually set such that voltage at pin#2 just falls below the 1/3rd of the zener voltage when the battery voltage reaches the specified lower threshold. Therefore in the proposed design the supply pin of the IC is fixed at some reference level using a zener diode. The LEDs will light up when the voltage goes below 9V, since this is a simple circuit, it will light up even on temporary dip in voltage such as when firing the. The above fact also indicates that pin#2 responds with reference to the supply voltage applied at pin#8 of the IC, which implies this voltage at pin#8 should be clamped to some constant level. ![]() We all know regarding the basic characteristic of the IC 555 when it's being used in the comparator mode: if pin#2 is subjected to a potential lower than 1/3rd of the Vcc, the output pin#3 goes high. The circuit functioning may be understood with the following points: This is a very simple 9V low battery indicator circuit which has 2 LEDs, one green which will light up when the battery voltage is higher than 6.9 volts and one red LED which will light up when the battery voltage is bellow 6.9 volts. An over discharge could mean a permanent damage to the battery.Ī novel little low battery indicator circuit can be learned here, which incorporates just a single IC555 and a few resistors, it's a simple "plug and watch" kind of circuit. It’s very simple.Many electronic circuits such as emergency lights, battery chargers, UPS systems, flashlights etc essentially require a low battery indication feature in order to avoid over discharge of the involved battery. Give it a try on the breadboard and feed various voltages via your power supply. When voltage is too low the zener is no longer reverse biased, turning off the transistor and current flows through the red led. When the voltage is above 7.6v, current flows through the zener to the base of the npn turning it on preventing the red led to turn on. Attach the collector to a 1k resistor which will go to the positive rail and to an led which will go to the negative rail. Attach the base of the npn transistor just below the zener. We have now fixed the reference voltage for the Opamp’s U1:A to U1:D for 100 to 25 charge indication. Repeating the above procedure gives 3.9V for 50 to U1:C and 3.6V for 25 to U1:D. From the positive rail, add a 1k resistor followed by a 5.6v zener followed by a 1 k resistor to ground. 4.2V is the reference voltage to the Opamp U1:B which is for 75 of battery charge indication. ![]() When it is to low, the zener prevents the flow of current to the led and it is off. If the voltage is higher then about 7.6v the green stays lit due to the zener being reverse biased. ![]() Here is how the circuit goes.įrom the positive rail, attach a zener followed by a 1k resistor followed bya green led to ground. In my case I used a 5.6v zener and a 2v led giving me 7.6v. The zener breakdown voltage together with the forward voltage of the led you use will determine at what voltage it will switch. Introduction: 9v Battery Status Indicator Circuit I used Green and Red led as green Led lights up when the voltage is upper than 6.9v and Red led lights up. While opamps as comparator are a better option zeners are OK to use as well. ![]()
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