Supply Voltage Indicator


Posted on Feb 6, 2014

This simple and slightly odd circuit can clearly show the level of the supply voltage (in a larger device): as long as the indicator has good 12 volts at its input, LED1 gives steady, uninterrupted (for the naked eye) yellow light. If the input voltage falls below 11 V, LED1 will start to blink and the blinking will just get slower and slower if t


Supply Voltage Indicator
Click here to download the full size of the above Circuit.

he voltage drops further - giving very clear and intuitive representation of the supplys status. The blinking will stop and LED1 will finally go out at a little below 9 volts. On the other hand, if the input voltage rises to 13 V, LED2 will start to glow, getting at almost full power at 14 V. The characteristic voltages can be adjusted primarily by adjusting the values of R1 and R4. The base-emitter diode of T2 basically just stands in for a zener diode. The emitter-collector path of T1 is inversely polarized and if the input voltage is high enough - T1 will cause oscillations and the frequency will be proportional to the input voltage. The relaxation oscillator ceases cycling when the input voltage gets so low that it no longer can cause breakdown along the emitter-collector path. Not all small NPN transistors show this kind of behavior when inversely polarized in a similar manner, but many do. BC337-40 can start oscillations at a relatively low voltage, other types generally require a volt or two more. If experimenting, be careful not to punch a hole through the device under test: they oscillate at 9-12 V or not at all.




Leave Comment

characters left:

Related Circuits

  • New Circuits

    .

     


    Popular Circuits

    25 Watt amplifier
    Thermocouple-multiplex-system
    Automatic battery charger circuit using lm301-2
    simple circuit mini bicycle bel
    100w inverter circuit
    2 channel audio mixer circuit using transistors
    Bicycle Speedometer With Hub Dynamo
    Puxing 777 Radio Headset Schematic
    200 Watt High Quality Audio Amplifier
    Current negative feedback electronic frequency power amplifier circuit
    A six thyristor AC switch circuits



    Top