Two-wire industrial process field device power supply circuitry

A method of providing power to a field device for use in monitoring or controlling an industrial process, the method comprising:

• coupling first and second loop terminals of the field device to a two-wire process control loop;
• powering device circuitry of the field device with power received from the two-wire process control loop, the device circuitry configured to monitor a process variable sensor or control a control device;
• regulating a loop current through the two-wire process control loop using a current regulator of the field device connected in series with the two-wire process control loop, the first and second loop terminals, and the device circuitry;
• regulating a first voltage across the device circuitry using a first shunt voltage regulator of the field device connected in series with the two-wire process control loop and the current regulator, and in parallel with the device circuitry to wholly power the device circuitry, the first shunt voltage regulator receiving a voltage control input from the device circuitry which controls the first voltage;
• powering supplemental circuitry connected in series with the first shunt voltage regulator and the second loop terminal with power received from the two-wire process control loop shunted through the first shunt voltage regulator;
• and
• regulating a second voltage across the supplemental circuitry using a second shunt voltage regulator of the field device connected in series with the first shunt voltage regulator and the second loop terminal, and in parallel with the supplemental circuitry thereby powering the supplemental circuitry separately from the power provided to the device circuitry by the first shunt regulator.