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3v Low Battery Voltage Flasher(PN2907)

2016-05-10 23:47  
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This article describes the 3v Low Battery Voltage Flasher (PN2907). The principle is very simple, very practical. The circuit components can help you understand better grasp this principle. For example, in this circuit, you can go to find and buy these components: PN2907.

Many battery powered devices use two AA alkaline cells. Often you will not know when it is time to replace the batteries until the device powered by them actually stops operating. The hobby circuit below can be connected to a 3v battery, to give you some warning when the battery is nearing its end of life.

Figure:1 Circuit diagram

Figure 1 Circuit diagram

It will flash aLEDwhen the battery voltage drops to about 2.4 volts. The electronic circuit draws only 1ua of current in standby mode and jumps to only 20ua when flashing, so it can safely be included without depleting the battery energy. A voltage detector IC from Panasonic (Microchip also makes similar devices) is used to monitor the battery voltage. The device’s open drain output swings low, when the battery voltage is below 2.4 to 2.5 volts. This action turns on the two transistor oscillator circuit, which drives theLEDwith short current pulses lasting only 2ms.



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