Patent ID: 8901836

Claim:
A dimming controlling circuit for LED, comprising: a switch configured to connect a main circuit and a power grid; a switch-on duration controlling circuit configured to output a switch-on duration controlling signal according to action times of the switch; a switch-off controlling circuit configured to compare a voltage of the switch-on duration controlling signal and a voltage of a signal from a terminal of a switch transistor in the main circuit to obtain a comparison result and to output a switch-off controlling signal according to the comparison result; a switch-on controlling circuit configured to generate a switch-on controlling signal after a first preset duration since receiving the switch-off controlling signal; and a logic unit configured to output a switch transistor controlling signal according to the switch-off controlling signal and the switch-on controlling signal, wherein the switch-on duration controlling circuit comprises: a power generating circuit configured to generate a first voltage according to an input voltage; a detecting circuit configured to detect the input voltage, to output an invalid shift controlling signal when determining the input voltage reaches a first threshold voltage and to output a valid shift controlling signal when determining the input voltage descends below a second threshold voltage and above the third threshold voltage; a shift register configured to output a shift result according to the invalid or valid shift controlling signal; a resetting circuit configured to reset the shift register to zero; a decoding circuit configured to decode according to the shift result to obtain a decoding result; and a selecting circuit configured to select a voltage corresponding to the switch-on duration controlling signal according to the decoding result.