Switching power supply
AssigneePanasonic Corporation
InventorsHideki Nishihara, Akeyuki Komatsu
Life of this patent
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Abstract
An object of the present invention is to provide a switching power supply which can stably determine whether an overcurrent occurs or not on the secondary side. A sample voltage corresponding to a load current value detected by detection resistors R7 and R8 is compared with a reference voltage by an input-side transistor Q4 and an output-side transistor Q3 which compose a first current mirror circuit 14, so that it is possible to determine whether an overcurrent occurs or not. Moreover, a current passing through the output circuit of the transistor Q3 is temperature-compensated by a second current mirror circuit 17 made up of transistors Q6 and Q5.
Claims3
A switch power supply for outputting a secondary-side voltage of a voltage conversion section after rectifying and smoothing the voltage, and controlling switching on a primary side of the voltage conversion section according to a detected load current to perform overcurrent protection;
- the switching power supply comprising:
- a detection resistor for detecting a load current on a secondary side of the voltage conversion section;
- a first current mirror circuit made up of a first transistor of an input side and a second transistor of an output side;
- and
- a second current mirror circuit made up of a third transistor of the input side and a fourth transistor of the output side,
- wherein a detected voltage of the detection resistor is applied between one end of the first transistor and one end of the second transistor,
- the fourth transistor fed with a current set by the third transistor is interposed between the second transistor and a reference potential, and
- switching on the primary side of the voltage conversion section is controlled according to a potential of a junction point of the second transistor and the fourth transistor to perform overcurrent protection.
Dependencies are inferred from the claim text.