LED constant-voltage dimming power supply and LED lamp dimming system

The present invention provides an LED constant-voltage dimming power supply and an LED lamp dimming system. The LED constant-voltage dimming power supply is used for changing a duty ratio of an output constant voltage when receiving a control signal of a dimmer, and comprises a constant voltage source, a damping bleeder circuit module connected at an input end of the constant voltage source, a phase detection circuit module electrically connected at an output end of the constant voltage source, a duty ratio control module coupled with the phase detection circuit module, and a switch tube electrically connected with the duty ratio control module. The damping bleeder circuit module is used for maintaining current for normal operation of the dimmer when the dimmer is connected. The phase detection circuit module is used for sampling the output voltage of the constant voltage source and converting a voltage sampling signal into a first duty ratio signal. The duty ratio control module is used for converting the first duty ratio signal to a second duty ratio signal suitable for controlling the switch tube. The switch tube is used for changing a duty ratio of the output constant voltage according to the second duty ratio signal, thereby changing output power.