Power transfer over an isolated capacitive barrier with controlled current
Capacitively isolated current-loaded or current-driven charge pump circuits and related methods transfer electrical energy from a primary side to a secondary side over a capacitive isolation boundary, using a controlled current source to charge isolation capacitors with constant current, as opposed to current impulses, while maintaining output voltage within tolerance. The charge pump circuits provide DC-to-DC converters that can be used in isolated power supplies, particularly in low-power applications and in such devices as sensor transmitters that have separate electrical ground planes. The devices and methods transfer electrical energy over an isolated capacitive barrier in a manner that is efficient, inexpensive, and reduces electromagnetic interference (EMI).
1. A sensor transmitter comprising:
a primary side bridge coupled between a power input and a first ground terminal, the primary side bridge having first switching terminals;
a secondary side bridge coupled between a power output and a second ground terminal, the secondary side bridge having second switching terminals, the secondary side bridge configured to be capacitively coupled to the primary side bridge via the first switching terminals and the second switching terminals; and
an analog front end having a sensor interface, a power terminal, and a reference terminal, the power terminal coupled to the power output, and the reference terminal coupled to the second ground, terminal.
2. The sensor transmitter of claim 1 , further comprising a first capacitor coupled between a first one of the first switching terminals and a first one of the second switching terminals, and a second capacitor coupled between a second one of the first switching terminals and a second one of the second switching terminals.
3. The sensor transmitter of claim 1 , wherein the power terminal is a first power teiminal, the reference terminal is a first reference terminal, the primary side bridge has a second power terminal and a second reference terminal, the second reference terminal coupled to the first ground terminal; and
wherein the sensor transmitter further comprises a current source coupled between the power input and the second power terminal.
4. The sensor transmitter of claim 3 , further comprising control circuitry having control outputs coupled to the current source and to the primary side bridge, the control circuitry configured to control the current source and the primary side bridge to set a voltage between the second power terminal and the second reference terminal based on a target voltage.
5. The sensor transmitter of claim 3 , further comprising control circuitry having control outputs coupled to the current source and to the primary side bridge, the control circuitry configured to control the current source and the primary side bridge to transmit a first current via one of the first switching terminals in a first half of a switching cycle and to receive a second current via the one of the first switching terminals in a second half of the switching cycle, in which the first and second currents are in a form of a square wave in the switching cycle.
6. The sensor transmitter of claim 3 , wherein the current source is a first current source, and the sensor transmitter further comprises a second current source coupled between the second reference terminal and the first ground terminal, the first and second current sources are configured to conduct a same amount of current.
7. The sensor transmitter of claim 1 , wherein the power terminal is a first power terminal, the reference terminal is a first reference terminal, the secondary side bridge has a second power terminal and a second reference terminal, the second reference terminal coupled to the second ground terminal; and
wherein the sensor transmitter includes a current source coupled between the second power terminal and the power output.
8. The sensor transmitter of claim 7 , further comprising control circuitry having control outputs coupled to the current source and to the primary side bridge, the control circuitry configured to control the current source and the secondary side bridge to set a voltage between the second power terminal and the second reference terminal based on a target voltage.
9. The sensor transmitter of claim 7 , further comprising control circuitry having control outputs coupled to the current source and to the primary side bridge, the control circuitry configured to control the current source and the secondary side bridge to receive a first current via one of the second switching terminals in a first half of a switching cycle and to transmit a second current via the one of the second switching terminals in a second half of the switching cycle, in which the first and second currents are in a form of a square wave in the switching cycle.
10. The sensor transmitter of claim 7 , further comprising a capacitor coupled between the second power terminal and the second ground terminal.
11. The sensor transmitter of claim 10 , wherein the capacitor is a first capacitor, and the sensor transmitter further comprises a second capacitor coupled between the power output and the second ground terminal.
12. The sensor transmitter of claim 11 , wherein a capacitance of the first capacitor is between one hundredth and one tenth of a capacitance of the second capacitor.
13. The sensor transmitter of claim 2 , wherein each of the first and second capacitors is a Y-rated capacitor.
14. The sensor transmitter of claim 1 , further comprising a fieldbus interface circuitry coupled to the power input, the fieldbus interface circuitry including the primary side bridge.
15. The sensor transmitter of claim 1 , wherein the analog front end includes an analog to digital converter (ADC) having an analog input coupled to the sensor interface.
16. The sensor transmitter of claim 1 , wherein the analog front end includes a sensor having a sensor output coupled to the sensor interface.
17. A system comprising:
a primary side bridge coupled between a power input and a first ground terminal, the primary side bridge having first switching terminals; and
a secondary side bridge coupled between a power output and a second ground terminal, the secondary side bridge having second switching tenninals, the secondary side bridge configured to be capacitively coupled to the primary side bridge via the first switching terminals and the second switching terminals.
18. The system of claim 17 , further comprising an analog front end having a sensor interface, a power terminal, and a reference terminal, the power terminal coupled to the power output, and the reference terminal coupled to the second ground terminal.
19. The system of claim 17 , further comprising a first capacitor coupled between a first one of the first switching terminals and a first one of the second switching terminals, and a second capacitor coupled between a second one of the first switching terminals and a second one of the second switching terminals.
20. The system of claim 17 , wherein the primary side bridge has a power terminal and a reference terminal, the reference terminal coupled to the first ground terminal; and
wherein the system further comprises a current source coupled between the power input and the power terminal.
21. The system of claim 17 , wherein the secondary side bridge has a power terminal and a second reference terminal, the second reference terminal coupled to the second ground terminal; and
wherein the system further comprises a current source coupled between the power terminal and the power output.