Converter apparatus using source-activated discharge circuits

A motor drive comprising:

• a rectifier having an input configured to be coupled to an AC power source;
• a DC bus coupled to an output of the rectifier;
• an inverter having an input coupled to the DC bus and an output configured to be coupled to a motor;
• at least one capacitor coupled to the DC bus;
• and
• a normally-on or normally-closed switch and a resistor coupled in series to the DC bus;
• and
• a control circuit coupled to the input of the rectifier and configured to cause the normally-on or normally-closed switch to transition from a non-conducting state to a conducting state responsive to a decrease in an AC voltage at the input of the rectifier to thereby discharge the at least one capacitor through the normally-on or normally-closed switch and the resistor, the control circuit comprising:
• a regulator circuit having an input coupled to the input of the rectifier;
• and
• a DC-DC converter circuit coupled to an output of the regulator circuit and configured to drive a control terminal of the normally-on or normally-closed switch.

An apparatus comprising:

• a normally-on or normally-closed switch and a resistor configured to be coupled in series to a DC bus of a motor drive;
• and
• a control circuit configured to cause the normally-on or normally-closed switch to transition from a non-conducting state to a conducting state responsive to a reduction in an AC voltage at an input of a rectifier coupled to the DC bus to thereby discharge at least one capacitor coupled to the DC bus through the normally-on or normally-closed switch and the resistor;
• the control circuit comprising:
• a regulator circuit having an input coupled to the input of the rectifier;
• and
• a DC-DC converter circuit coupled to an output of the regulator circuit and configured to drive a control terminal of the normally-on or normally-closed switch.