Low Supply Rail Detection


Posted on Feb 6, 2014

Here`s a simple low supply rail detection circuit that costs peanuts and takes just 20 minutes or so to make. Its power consumption is quite low, so it could easily be built into battery-powered devices. Instead of using an op amp, the circuit is built around three low-cost transistors (Q1-Q3). Diodes D1-D3 form a 1. 8V voltage reference (Vref) for


Low Supply Rail Detection
Click here to download the full size of the above Circuit.

the emitter of Q1. If the voltage across the voltage divider formed by R1 and VR1 is less than this, Q1 turns on and supplies Q2 with base bias current. This turns on Q3 in proportion to this bias current which then drives LED1. The brightness of the LED gives an indication of the severity of the low voltage condition. The brighter the LED, the lower the supply voltage. Trimpot VR1 is adjusted so that LED1 just comes on at the desired low-voltage point. The current consumption is typically less than 2mA when LED1 is off. Finally, the value shown for RLED is suitable for 6-12V operation. For other voltages, RLED can be calculated using the formula RLED = (Vcc 1. 8)/0. 01 (this equates to a current of about 10mA).




Leave Comment

characters left:

Related Circuits

  • New Circuits

    .

     


    Popular Circuits

    Clock using a Hard Drive
    board anticipation equivalent diagram
    Camera Switch Circuit using 4017
    Simple Light Sensor Alarm circuit with NE555
    Two-Position Dimmer
    random motor circuit
    ISL6323 Hybrid SVI/PVI Monolithic Dual PWM Hybrid Controller Powering AMD SVI Split-Plane and VI Uniplane Processors
    Using AC for LED Christmas Lights
    FM Crystal Controlled Transmitter DPT
    Robots Bandpass Filter Calculator
    Factory secondary low-voltage distribution electrical panel wiring diagram
    5V TOP414G 2A isolated switching power supply circuit



    Top