At this point’s a minimal low supply rail detection circuit with the purpose of expenditure peanuts and takes a short time ago 20 minutes or else so to become. Its power consumption is quite low, so it may perhaps definitely survive built into battery-powered campaign. as an alternative 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) used for the emitter of Q1. If the voltage across the voltage wall formed by R1 and VR1 is a reduced amount of than this, Q1 turns on and food Q2 with foundation bias current.
This turns on Q3 here proportion to this bias current which subsequently 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 to facilitate LED1 really comes on by the desired low-voltage promontory. The current consumption is typically take away than 2mA at what time LED1 is rotten. in conclusion, the price exposed in support of RLED is right for 6-12V surgery. For other voltages, RLED can ensue calculated using the formula RLED = (Vcc - 1.8)/0.01 (this equates to a current of with reference to 10mA).