A buck converter includes a first transistor, a second transistor, a filter circuit, a capacitor and a switch. The first transistor has a drain for receiving a first DC voltage, a gate for receiving a first control signal, and a source coupled to a node. The second transistor has a drain coupled to the node, a gate for receiving a second control signal, and a source coupled to a constant voltage. The filter circuit is electrically coupled to the node for outputting a second DC voltage. The switch has a first terminal electrically coupled to the gate of the second transistor via the capacitor, a second terminal electrically coupled to the source of the second transistor, and a control terminal for receiving the first control signal. The switch has a faster switching speed than the first transistor.