Smart solid state relay

A solid state relay comprising:

• a power MOSFET for switching current to a load, the MOSFET including a source, a gate and a drain;
• the gate comprising an active low gate for controlling source to drain current through the power MOSFET, the power MOSFET being isolated from ground potential except through the gate when the solid state relay is connected between a positive battery voltage and a load;
• and
• a circuit for applying a gate input to shut off source to drain current when a voltage drop between the MOSFET source and drain exceeds a reference voltage;
• wherein the circuit and the active low gate are configured to float in the absence of an active low input to the gate, and are not tied to ground, to prevent leakage when the power MOSFET is commanded to a nonconducting state OFF state by removal of an low gate input.

A solid state Form A relay including a first relay terminal (30) connectable to a high battery voltage potential, a second relay terminal (87) connectable to the high side of a load, and a third relay terminal (86) comprising a signal input terminal, the solid state Form A relay including circuitry comprising:

• a power MOSFET having a source connected to the first relay terminal (30) and a drain connected to the second relay terminal (87);
• the power MOSFET including a gate connected to the third relay terminal (86), the power MOSFET being turned to an On state by an active low input applied to the third relay terminal (86);
• a pull up resistor connected between the first and third relay terminal (30 and 86);
• a voltage sensing circuit comprising means for sensing source-drain voltage drop when the power MOSFET is in an ON state, the voltage sensing circuit being connected to the gate so that when the source-drain voltage drop exceeds a reference level, the power MOSFET is turned to an OFF state;
• and
• the solid state Form A relay circuitry floating relative to ground potential when the active low input is removed from the third terminal (86) so that leakage current between a high battery voltage potential and a ground voltage potential is eliminated when the power MOSFET and the solid state form A relay are commanded to an OFF state by the absence of an active low input at the third relay terminal (86).

25 A solid state relay including a first relay terminal (30) connectable to a high battery voltage potential, a second relay terminal (87) connectable to the high side of a load, a third relay terminal (86) comprising a signal input terminal, and a fourth relay terminal (87a) comprising a voltage sense pin, the solid state relay including circuitry comprising:

• a power MOSFET having a source connected to the first relay terminal (30) and a drain connected to the second relay terminal (87) and the fourth relay terminal (87a);
• the power MOSFET including a gate connected to the third relay terminal (86), the power MOSFET being turned to an On state by an active low input applied to the third relay terminal (86);
• a pull up resistor connected between the first and third relay terminal (30 and 86);
• a voltage sensing circuit comprising means for sensing source-drain voltage drop when the power MOSFET is in an ON state, the voltage sensing circuit being connected to the gate so that when the source-drain voltage drop exceeds a reference level, the power MOSFET is turned to an OFF state;
• the fourth relay terminal (87a) being connected to the voltage sensing circuit so that upon disconnection of the fourth relay terminal (87a) from a voltage at the second relay terminal, the power MOSFET is turned to the OFF state;
• and
• the solid state relay circuitry floating relative to ground potential when the active low input is removed from the third terminal (86) so that leakage current between a high battery voltage potential and a ground voltage potential is eliminated when the power MOSFET and the solid state relay are commanded to an OFF state by the absence of an active low input at the third relay terminal (86).