Disclosed are dimmable LED driver circuits and methods. A dimmable LED driver can include: an SCR, an electronic transformer, and a rectifier bridge to convert an AC voltage to a DC voltage signal; a power stage circuit that receives the DC voltage signal, and outputs a constant current to drive an LED load, where the power stage circuit includes first and second power stage circuits, the first power stage circuit receiving the DC voltage signal, and generating a first output voltage to the second power stage; and an input current control circuit that receives an input current of the first power stage circuit and the first output voltage, and generates a first control signal to control the input current as a square wave signal during an on time of the SCR, and the input current is substantially zero during an off time of the SCR.