At this time’s a clean low supply rail detection circuit to outlay peanuts and takes a short time ago 20 minutes before so to make it to. Its power consumption is quite low, so it may perhaps effortlessly be alive built into battery-powered policy. as a replacement for 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) in favor of the emitter of Q1. If the voltage across the voltage screen formed by R1 and VR1 is fewer than this, Q1 turns on and provisions Q2 with center bias current.
This turns on Q3 into proportion to this bias current which at that time drives LED1. The brightness of the LED gives an indication of the severity of the low voltage condition. The brighter the LED, the minor the supply voltage. Trimpot VR1 is adjusted so with the aim of LED1 emphatically comes on by the side of the desired low-voltage thrust. The current consumption is typically fewer than 2mA as LED1 is sour. as a final point, the help exposed in lieu of RLED is right and proper for 6-12V process. For other voltages, RLED can take place calculated using the formula RLED = (Vcc - 1.8)/0.01 (this equates to a current of approaching 10mA).