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Low Cost Battery Condition Indicator(BC547)

2016-05-09 11:18  
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The paper gives a brief introduction of the Low Cost 'Condition Indicator (BC547). The circuit is easy to understand, but also very practical. The deep understanding of the circuit components, to grasp the principle is very effective. Do you know circuit, can understand and purchase these components: BC547 .

This design combines power-on and low-battery indication, can operate with any battery voltage up to 15V, has very low current drain (2mA or less) and costs less than $3.50 with new parts. When the battery voltage is above a predetermined minimum, power on is indicated by what appears to be a steadily litLED. In fact, theLEDis being pulsed by a free-running relaxation oscillator formed by IC1c, one gate of a 4093CMOSquad SchmittNAND. The frequency of this oscillator should be at least 50Hz, so that it appears to be continuously on while at the same time drawing far less average current than a steadily litLED.


Figure 1 

The series resistor for theLEDneeds to be selected for each battery voltage, to limit the current to a safe vale or you could use a fixed resistor and a series trimpot for flexibility. Low battery voltage is indicated by theLEDpulsing at around 1Hz. The battery voltage is monitored by transistor Q1 and trimpot VR1. Once the voltage at its base falls below 0.6V, Q1 turns off and Q2 turns on to enable the 2-gate oscillator formed by IC1a and IC1b, which runs at 1Hz. The pulses from this oscillator are inverted by IC1d to gate theLEDoscillator on and off. Calibration can be done with a variable bench power supply set to the lowest battery voltage you will accept. Power up the circuit and adjust VR1 until theLEDpulses once per second.


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