Patent ID: 7012388

Claim:
A circuit for driving a DC motor, the DC motor having a first magnetic coil and a second magnetic coil, wherein the first magnetic coil has a first terminal and a second terminal, the second magnetic coil has a third terminal and a fourth terminal, and a high reference potential is applied to the first and third terminals, said circuit comprises: a first semiconductor switch having a first control terminal, a first output terminal connected to said second terminal of the first magnetic coil, and a second output terminal, wherein said first semiconductor switch is a first bipolar junction transistor, said first control terminal, said first output terminal, and said second output terminal are the base terminal, the collector terminal, and the emitter terminal of said first bipolar junction transistor, respectively; a second semiconductor switch having a second control terminal, a third output terminal connected to said fourth terminal of the second magnetic coil, and a fourth output terminal, wherein said second semiconductor switch is a second bipolar junction transistor, and said second control terminal, said third output terminal, and said fourth output terminal are the base terminal, the collector terminal, and the emitter terminal of said second bipolar junction transistor, respectively; and a constant current source providing an essentially constant current, said constant current source having a fifth terminal and a sixth terminal, said fifth terminal being connected to said second output terminal of said first semiconductor switch and to said fourth output terminal of said second semiconductor switch, a low reference potential being applied to said sixth terminal, said constant current source comprising a third bipolar junction transistor having a third control terminal, wherein said constant current source comprises a third bipolar junction transistor having a third control terminal, and said third control terminal receives a third control voltage signal, which makes said third bipolar junction transistor operate in the active regions; wherein during operation, said first control terminal of said first semiconductor switch receives a first control voltage signal, said second control terminal of said second semiconductor switch receives a second control voltage signal, and said first control voltage signal and said second control voltage signal do not simultaneously turn on said first semiconductor switch and said semiconductor switch, respectively; and wherein, when said first control voltage turns on said first bipolar junction transistor, said first bipolar junction transistor is in the saturation region, and when said second control voltage signal turns on said second bipolar junction transistor, said second bipolar junction transistor is also in the saturation region, and the collector current of each of said first and second bipolar junction transistors in the saturation region is essentially equal to the value of said constant current.