US Patent 9820344 Led thyristor switched constant current driver

A circuit for controlling power to a load from a rectified AC supply is disclosed. The load like an LED or another type is driven by a power device such as a MOSFET or a transistor. The power device is biased from a resistive string which also includes a thyristor switch in series combination. At a specific trigger or conduction angle of the thyristor switch the proper bias for the power device is obtained to enable the load current to remains fairly constant with AC supply voltage fluctuations or loading. Furthermore the trigger circuit of the thyristor switch is properly configured in order for the load current to stay constant or even change with ambient temperature variations as well.