Abstract: Preventing the phase reversal of bipolar and JFET operational amplifiers under high noise conditions is a significant problem for their application in power electronics,industrial control,and automobile electronics.Based on the mechanism of the phase reversal phenomenon,a novel protection circuit without the shortcomings of the current techniques is proposed in this paper.The circuit is simple and composed of only three bipolar transistors.When the input signals are in the proper input common-mode voltage range,the protection circuit has no noticeable effect on the parameters of the operational amplifier,such as differential gain,settling time,and static power consumption.Theoretical analysis and simulation results show that not only the phase reversal,but also the concomitant over-current is prevented effectively.

Key words: operational amplifier, phase reversal, over-current limit