The INA19xA uses a new, unique, internal circuit topology that provides common mode range extending from –16 V to 80 V while operating from a single power supply. The common mode rejection in a classic instrumentation amplifier approach is limited by the requirement for accurate resistor matching. By converting the induced input voltage to a current, the INA19xA provides common mode rejection that is no longer a function of closely matched resistor values, providing the enhanced performance necessary for such a wide common mode range. A simplified diagram (see Figure 7-1) shows the basic circuit function. When the common mode voltage is positive, amplifier A2 is active.

The differential input voltage, V_IN+ – V_IN– applied across R_S, is converted to a current through a 5-kΩ resistor. This current is converted back to a voltage through R_L, and then amplified by the output buffer amplifier. When the common mode voltage is negative, amplifier A1 is active. The differential input voltage, V_IN+ – V_IN– applied across R_S, is converted to a current through a 5-kΩ resistor. This current is sourced from a precision current mirror whose output is directed into R_L, converting the signal back into a voltage and amplified by the output buffer amplifier. Patent-pending circuit architecture ensures smooth device operation, even during the transition period where both amplifiers A1 and A2 are active.

Figure 7-2 Monitor Bipolar Output Power-Supply Current

Figure 7-3 Bidirectional Current Monitoring

Figure 7-4 Inductive Current Monitor Including Flyback

Figure 7-5 INA19xA With Comparator