Rectifier bridge for telephone loop current - has two cross-coupled pairs of transistors each with two complementary transistors

摘要

The rectifier bridge produces a dc voltage proportional to the loop current in telephone equipment and does so with low voltage loss (compared to prior art bridges with diodes). The bridge consists of two pairs of transistors: each pair comprises an npn transistor and a pnp transistor coupled with their base/emitter junctions in parallel. The two emitters of each pair are coupled to one ac input and the collectors of the npn transistors in both pairs are connected to one dc output and the collectors of the pnp transistors to the other dc output. The two bases in one pair are connected via a resistor to the two bases in the other pair.