Patent ID: 7053505

Claim:
A noise reducing apparatus that reduces noise propagating to a pair of power lines for power supply, comprising: a leakage current detecting section that detects current induced by an output winding of a transformer having the output winding passing through a magnetic core with the power lines, thereby detecting a leakage current caused by noise flowing into a ground line from the power lines; and a current supplying section that supplies a compensation current for canceling the leakage current to the injection point which is on the ground line closer to an input of the power lines than a leakage current detecting point, wherein the current supplying section uses the leakage current detected by said leakage current detecting section as the compensation current; wherein said current supplying section includes an amplifying circuit that amplifies the leakage current detected by said leakage current detecting section, and said amplifying circuit amplifies current to be supplied to the ground line with an amplitude set to 1, when power is supplied from a predetermined DC power source; and said amplifying circuit includes an NPN transistor, a PNP transistor and a capacitor, a collector of said NPN transistor is connected to a positive pole of the DC power source, an emitter of said PNP transistor is connected to an emitter of said NPN transistor, a collector of said PNP transistor is connected to a negative pole of the DC power source, one end of the outout winding of the transformer is connected to a base of said NPN transistor and a base of said PNP transistor, the other end of the output winding of the transformer is connected to the emitter of said NPN transistor and the emitter of said PNP transistor, and said capacitor is connected between the ground line and the bases of said NPN transistor and said PNP transistor.