CURRENT DETECTING CIRCUIT

PURPOSE:To detect a bi-directional current by a few circuit elements, by constituting a bi-directional current mirror circuit of a PNP current mirror and an NPN current mirror, and using the current mirror circuit for dropping the voltage. CONSTITUTION:When supplying an AC signal to a load 5 from an AC signal source 1, a switch 4 is turned on. In this case, voltage V1 and voltage V1-ILR3 are generated in the signal source 1 side and the switch 4 side, respectively. It is simplified to R32=R33 (33). A period in which a load current IL flows toward the switch 4 from the AC signal source 1 is the time when diodes 34, 38 and a transistor (TR) 36 is on, positive voltage of VA=R3.R40/R31+R32 is generated in a terminal 401, and in a period in which the load current IL flows toward the AC signal source 1 from the switch 4, negative voltage of the same value as the previous one is generated, and voltage being proportional to the load current IL is applied to the input terminal of a detector 11. Accordingly, when a resistance value is set under some specified condition, the load current IL can be detected extending over the whole range of a DC voltage source V6 (6) and an AC voltage sourve V1 (1).