Dimming circuit

A dimming circuit for controlling the brightness of a light emitting diode, comprising:

• a power conversion unit having an input end, an output end, an inductor and a switch, the power conversion unit configured to receive an input voltage from the input end, and convert the input voltage into an output voltage output from the output end by operation of the switch;
• an input voltage sampling circuit configured to generate an input voltage sampling signal by detecting the input voltage;
• an output voltage sampling circuit configured to generate an output voltage sampling signal by detecting the output voltage;
• a current sampling circuit configured to generate a current sampling signal by detecting a current flowing through the switch;
• a dimming signal sampling circuit configured to receive a dimming signal to calculate and generate a dimming current signal;
• a driving circuit connected to the switch for driving the switch to turn on or turn off;
• and
• a control unit configured to receive the input voltage sampling signal, the output voltage sampling signal, the current sampling signal and the dimming current signal, and output a control signal to the driving circuit to control the switch;
• wherein,
• the control unit compares the dimming current signal with a first current threshold and a second current threshold,
• when the dimming current signal is higher than or equal to the first current threshold, the control unit controls the switch such that the power conversion unit operates in a continuous conduction mode or a boundary conduction mode;
• when the dimming current signal is lower than the first current threshold, the control unit controls the switch such that the power conversion unit operates in a discontinuous conduction mode;
• and
• in the discontinuous conduction mode, when the dimming current signal is lower than the second current threshold, the control unit controls the switch such that the power conversion unit operates in a chopping control mode.