A power supply device capable of providing a stable power to a control circuit, wherein the control circuit controls a circuit breaker connected to a power system, wherein the power supply device comprises a power circuit for supplying a power to the control circuit, wherein the power circuit includes: a semiconductor switch element having an input terminal connected to a first node to receive a direct current, and an output terminal connected to a reference node, wherein the reference node has a voltage lower than a voltage of the first node; and the power circuit charcterised by comprising a first voltage drop element disposed between the first node and a second node, wherein the second node is connected to a switching terminal of the semiconductor switch element, wherein the power supply device further comprises a rectifying circuit, configured to receive an alternating current from a current transformer, to rectify the alternating current to the direct current, and to supply the rectified direct current to the power circuit, wherein the semiconductor switching element is configured to: when a gate voltage applied to the switching terminal rises, increase a magnitude of a current flowing from the first node to the reference node, and when the gate voltage applied to the switching terminal drops, decrease the magnitude of the current flowing from the first node to the reference node. wherein the power supply device comprises a power circuit for supplying a power to the control circuit, wherein the power circuit includes: a semiconductor switch element having an input terminal connected to a first node to receive a direct current, and an output terminal connected to a reference node, wherein the reference node has a voltage lower than a voltage of the first node; and the power circuit charcterised by comprising a first voltage drop element disposed between the first node and a second node, wherein the second node is connected to a switching terminal of the semiconductor switch element, wherein the power supply device further comprises a rectifying circuit, configured to receive an alternating current from a current transformer, to rectify the alternating current to the direct current, and to supply the rectified direct current to the power circuit, wherein the semiconductor switching element is configured to: when a gate voltage applied to the switching terminal rises, increase a magnitude of a current flowing from the first node to the reference node, and when the gate voltage applied to the switching terminal drops, decrease the magnitude of the current flowing from the first node to the reference node. a semiconductor switch element having an input terminal connected to a first node to receive a direct current, and an output terminal connected to a reference node, wherein the reference node has a voltage lower than a voltage of the first node; and the power circuit charcterised by comprising a first voltage drop element disposed between the first node and a second node, wherein the second node is connected to a switching terminal of the semiconductor switch element, wherein the power supply device further comprises a rectifying circuit, configured to receive an alternating current from a current transformer, to rectify the alternating current to the direct current, and to supply the rectified direct current to the power circuit, wherein the semiconductor switching element is configured to: when a gate voltage applied to the switching terminal rises, increase a magnitude of a current flowing from the first node to the reference node, and when the gate voltage applied to the switching terminal drops, decrease the magnitude of the current flowing from the first node to the reference node. when a gate voltage applied to the switching terminal rises, increase a magnitude of a current flowing from the first node to the reference node, and when the gate voltage applied to the switching terminal drops, decrease the magnitude of the current flowing from the first node to the reference node.