Low Power Bypass Circuit for LED Open Circuit and Reverse Polarity Protection

A string of series connected LEDs comprising:

• a plurality of individual LEDs connected one to another in series;
• a low power bypass circuit connected in parallel with each individual LED, said low power bypass circuit including:
• a two-terminal semiconductor diode connected in series with a resistor which two-terminal semiconductor diode and resistor combination becomes conductive upon the failure of an LED or the connection of the string of series-conducted LEDs to a reverse polarity flow of electrical energy;
• said series connected two-terminal semiconductor diode and resistor combination causing a three-terminal gate-controlled semiconductor switching device to become conductive upon the failure of an LED so that electrical energy no longer flows through said series-connected two-terminal semiconductor diode and said resistor combination but through said three-terminal gate-controlled semiconductor switching device;
• said series connected two-terminal semiconductor diode and resistor combination causing said three-terminal gate-controlled semiconductor switching device to become conductive upon the connection of the string of series-connected LEDs to a reverse polarity flow of electrical energy so the electrical energy flows through both said series-connected two-terminal semiconductor diode and resistor combination and said three-terminal gate-controlled semiconductor switching device.

A method for bypassing an open LED in a string of series-connected LEDs and protecting the integrity of the string of series-connected LEDs if improperly connected to a direct current electrical energy power supply, said method comprising:

• causing a two-terminal semiconductor diode in a low power bypass circuit to become conductive when an LED becomes non-conductive;
• causing a three-terminal gate-controlled semiconductor switching device in said low power bypass circuit to become conductive when said two-terminal semiconductor diode becomes conductive;
• causing said two-terminal semiconductor diode to drop out of said low power bypass circuit when said three-terminal gate-controlled semiconductor switching device becomes conductive;
• wherein said three-terminal gate-controlled semiconductor switching device allows the flow of electrical energy therethrough in a first direction in the open LED condition, and
• wherein said three-terminal gate-controlled semiconductor switching device allows the flow of electrical energy therethrough in a second direction in a reverse polarity condition.

A light source for an illuminated sign comprising:

• one or more direct current electrical energy power supplies;
• one or more strings of series-connected LEDs electrically connected to said one or more direct current electrical energy power supplies;
• a low power bypass circuit connected in parallel around each LED, said low power bypass circuit including:
• a two-terminal semiconductor diode connected in series with a resistor, said two-terminal semiconductor diode and resistor combination becoming conductive upon the failure of an LED or the connection of said string of series-connected LEDs improperly connected to said one or more direct current electric energy power supply is a reverse polarity condition;
• said series-connected two-terminal semiconductor diode and resistor combination causing a three-terminal gate-controlled semiconductor switching device to become conductive upon the failure of an LED so that electrical energy no longer flows through said series-connected semiconductor diode and resistor combination but through said three-terminal gate-controlled semiconductor switching device;
• said series connected two-terminal semiconductor diode and resistor combination causing said three-terminal gate-controlled semiconductor switching device to become conductive upon the connection of the said one or more strings of series-connected LEDs to a reverse polarity flow of electrical energy so that electrical energy flows through both said series-connected two-terminal semiconductor diode and resistor combination and said three-terminal gate-controlled semiconductor switching device.