What does the circuit of Fig. 20-8 do?
This circuit compares two voltages of opposite polarity to determine which is greater. If the magnitude of v_1 is greater than the magnitude of v_2 , the noninverting input is positive, the comparator output is positive, and the green LED is on. On the other hand, if the magnitude of v_1 is less than the magnitude of v_2, the noninverting input is negative, the comparator output is negative, and the red LED is on. If a 741C op amp is used, the LEDs at the output do not need currentlimiting resistors because the maximum output current will be approximately 25 mA. D_1 and D_2 are input clamping diodes.