LED drive circuit for SCR dimming

A LED drive circuit for SCR dimming comprising:

• an external controller configured to convert AC voltage from a power network to AC voltage with a lacked phase by phase controlling the voltage through a thyristor;
• and
• a LED driver comprising:
• a bridge rectifier configured to shape the AC voltage with the lacked phase output into a unidirectional pulse DC voltage, and deliver the pulse DC voltage to a main circuit;
• a current controlling circuit which comprises a current detecting signal outputted from the main circuit and a controlling signal output from the phase angle detecting circuit, and wherein the current controlling circuit outputs a current reference signal to the main circuit to control and adjust the current;
• a main circuit configured to receive the pulse DC voltage signal output from bridge rectifier and a current reference signal output from a current detecting circuit, and after being modulated by a pulse width modulation circuit further configured to convert its voltage and output DC voltage to a LED load and a current detecting signal to a current controlling circuit;
• and
• a phase angle detecting circuit configured to shape the AC voltage signal output with the lacked phase from the external controller into a saw-tooth wave pulse signal, whose peak value changes according to a variation of thyristor trigger phase angle wherein the saw-tooth voltage signal is converted to a level signal, which changes in proportion to a peak variation of the saw-tooth wave pulse signal, and then outputs the level signal to the current controlling circuit as the output controlling signal from the phase angle detecting circuit.