HVAC system with improved control switching

摘要

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.

主权项

1. A heating ventilation and/or air conditioning (HVAC) switching circuit comprising:
a positive direct current (DC) supply and a negative DC supply; a current source circuit comprising a first current source terminal connected to the positive DC supply; a capacitor comprising a first capacitor terminal connected to a second current source terminal of the current source circuit, and a second capacitor terminal connected to the negative DC supply; an HVAC DC power relay comprising a power relay coil with a first power relay coil terminal and a second power relay coil terminal, wherein the first power relay coil terminal is connected to the first capacitor terminal; and an HVAC DC power relay activation control circuit, wherein the HVAC DC power relay activation control circuit 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, the first transistor thereby configured to be activated until the voltage across the threshold circuit falls below a second threshold value lower than the first threshold value; and(2) a voltage divider connected to the first power relay coil terminal 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.