DC to DC converter with a single-fault tolerant clamp

A voltage regulated dual-bus architecture, comprising:

• a primary bus for distributing a regulated primary bus voltage;
• a plurality of motor-generator loads that are capable of collectively sinking or sourcing current;
• a secondary bus for distributing a secondary bus voltage to said motor-generator loads;
• a power stage connected between said primary and secondary buses for sourcing current to said motor-generator loads through said secondary bus and establish said secondary bus voltage;
• a bus voltage error amplifier that senses said secondary bus voltage and compares it to a bus setpoint voltage to generate a voltage control signal that controls the amount of source current delivered to said loads to regulate said secondary bus voltage;
• a fault-protection clamp element that is connected to said secondary bus;
• a comparator that switches between enable and disable states when said voltage control signal crosses a threshold to respectively activate and deactivate said fault-protection clamp element when said secondary bus voltage respectively exceeds and is less than said bus setpoint voltage;
• a regulator clamp element having a controllable resistance that is connected in series with said fault-protection clamp element;
• and
• a sink error amplifier that senses the secondary bus voltage, compares it to a clamp setpoint voltage and, when said fault-protection clamp element is activated, sets the regulator clamp element's resistance to sink excess current sourced by the motor-generator loads and clamps said secondary bus voltage at said clamp setpoint voltage.

A voltage regulating system comprising a plurality of voltage converter modules connected in parallel between a primary bus and a secondary bus to selectively source and sink current to and from a plurality of motor-generator loads while regulating the secondary bus voltage V.sub.bus, each said voltage convert module comprising:

• a DC-to-DC converter that sources current to said secondary bus to establish the secondary bus voltage when said motor-generator loads are collectively sinking current, said converter sensing said secondary bus voltage and comparing it to a bus setpoint voltage V.sub.set to generate a voltage control signal that controls the amount of source current thereby regulating said secondary bus voltage;
• a current regulator having a controllable resistance;
• a sink error amplifier that senses the secondary bus voltage, compares it to a clamp setpoint voltage V.sub.clamp that may vary from module-to-module, and, when V.sub.bus >V.sub.clamp, sets the current regulator's resistance to sink excess current sourced by the motor-generator loads and clamp said secondary bus voltage at said clamp setpoint voltage;
• a control circuit that disables the clamp circuit when said DC-to-DC converter is sourcing current to prevent the current regulator from sinking current sourced by the DC-to-DC converter;
• a current sense resistor that senses the amount of current flowing through said clamp circuit;
• and
• a feedback resistor that is connected between said current sense resistor and said sink error amplifier to increase the secondary bus voltage as the current through said current sense resistor increases to further activate other ones of said modules to share the excess current produced by the motor-generator loads.