Switching power supply
View Patent ↗In a switching power supply apparatus for performing a switching control of a power MOS transistor that flows current to a coil and converting input voltage into output voltage, even if there occurs offset voltage in a current sensing operational amplifier, source potential of a current sensing MOS transistor is precisely kept at source potential of a low side power MOS transistor. For example, an offset cancel capacitor is arranged at an inverting input terminal of the current sensing operational amplifier, and voltage in the direction to offset the offset voltage occurring in the operational amplifier is charged to this capacitor.
1. A switching power supply apparatus for performing a switching control of a power semiconductor element that flows current to an inductor and converting input voltage into specified output voltage, comprising
a current sensing circuit wherein a feedback loop is structured by use of a single power supply operational amplifier that operates with positive voltage so that voltage of the same potential as that of source voltage or emitter voltage of the power semiconductor element should be applied to a node that connects a current sensing semiconductor element to which the power semiconductor element is connected with drain terminals thereof or collector terminals thereof, and a current sensing resister that is connected to source terminal or emitter terminal of the current sensing semiconductor element, wherein
a first capacitor is arranged at the input terminal at one side of the single power supply operational amplifier, and current sensing signals are output on the basis of signals occurring in the current sensing resister.
2. The switching power supply apparatus according to claim 1 ,
wherein a second capacitor is arranged at the input terminal at the other side of the single power supply operational amplifier.
3. The switching power supply apparatus according to claim 1 ,
wherein offset voltage of the single power supply operational amplifier is sampled in sync with gate drive voltage or base drive voltage of the power semiconductor element.
4. The switching power supply apparatus according to claim 1 ,
wherein offset voltage of the single power supply operational amplifier is sampled in a period of part of ON period of gate drive voltage or base drive voltage of the power semiconductor element.
5. The switching power supply apparatus according to claim 1 ,
wherein the offset voltage of the single power supply operational amplifier always becomes positive or negative.
6. The switching power supply apparatus according to claim 2 ,
wherein signals from the time point before the center timing of ON period of gate drive voltage or base drive voltage of the power semiconductor element to the time point of the center timing thereof are sampled by a third capacitor, and outputs as current sensing signals.
7. The switching power supply apparatus according to claim 1 ,
wherein the terminal at one side of the current sensing resister is connected to the output terminal of the single power supply operational amplifier, and the terminal at the other side thereof is connected to the input terminal at one side of the single power supply operational amplifier and the source terminal or the emitter terminal of the current sensing semiconductor element.
8. The switching power supply apparatus according to claim 1 ,
wherein a plurality of power supplies are operated in parallel with each other.
9. The switching power supply apparatus according to claim 1 ,
wherein means for securing action margins of the single power supply operational amplifier is provided.
10. The switching power supply apparatus according to claim 1 ,
wherein the potential at one end of the current sensing resister cyclically becomes 1 mV or below.