Load open circuit indication circuit

It can be used to indicate open circuit or burnout of loads (such as lamps, electric heaters,
contactor coils, etc.). The selection of the resistor Rz should ensure that the voltage drop UR
    on it is not greater than the forward voltage drop of the light-emitting diode VL, which is calculated according to the following formula:     %z-[, blue (n)     R2-. In the formula, UF- light-emitting diode forward voltage drop (usually 1.7-2V), V;     IF- light-emitting diode operating current (usually about 10mA), A.   U.R. Generally, 3~4V is acceptable.