Abstract: An HVAC switching circuit may comprise a current source circuit charging a capacitor used to power an HVAC DC power relay coil. The power relay coil terminal is connected to an activation control circuit which comprises at least one of (1) each of (a) a threshold circuit which activates a first transistor to energize the power relay coil when the voltage across the threshold circuit reaches a first threshold value and (b) a regenerative feedback circuit configured to lower the first threshold value to a second threshold voltage, and (2) a voltage divider connected between a first terminal on the power relay coil and the negative DC supply, and a programmable shunt regulator, configured as a level triggered switch, programmed by the voltage divider and connected between the second power relay coil terminal and the negative DC supply.

Abstract: An HVAC switching circuit may comprise a current source circuit charging a capacitor used to power an HVAC DC power relay coil. The power relay coil terminal is connected to an activation control circuit which comprises at least one of (1) each of (a) a threshold circuit which activates a first transistor to energize the power relay coil when the voltage across the threshold circuit reaches a first threshold value and (b) a regenerative feedback circuit configured to lower the first threshold value to a second threshold voltage, and (2) a voltage divider connected between a first terminal on the power relay coil and the negative DC supply, and a programmable shunt regulator, configured as a level triggered switch, programmed by the voltage divider and connected between the second power relay coil terminal and the negative DC supply.

Abstract: An HVAC switching circuit may comprise a current source circuit charging a capacitor used to power an HVAC DC power relay coil. The power relay coil terminal is connected to an activation control circuit which comprises at least one of (1) each of (a) a threshold circuit which activates a first transistor to energize the power relay coil when the voltage across the threshold circuit reaches a first threshold value and (b) a regenerative feedback circuit configured to lower the first threshold value to a second threshold voltage, and (2) a voltage divider connected between a first terminal on the power relay coil and the negative DC supply, and a programmable shunt regulator, configured as a level triggered switch, programmed by the voltage divider and connected between the second power relay coil terminal and the negative DC supply.

Abstract: An HVAC switching circuit may comprise a current source circuit charging a capacitor used to power an HVAC DC power relay coil. The power relay coil terminal is connected to an activation control circuit which comprises at least one of (1) each of (a) a threshold circuit which activates a first transistor to energize the power relay coil when the voltage across the threshold circuit reaches a first threshold value and (b) a regenerative feedback circuit configured to lower the first threshold value to a second threshold voltage, and (2) a voltage divider connected between a first terminal on the power relay coil and the negative DC supply, and a programmable shunt regulator, configured as a level triggered switch, programmed by the voltage divider and connected between the second power relay coil terminal and the negative DC supply.