Apparatus and method for improving electromagnetic compatibility
A method and apparatus for providing improved electromagnetic compatibility between a power source ( 20 ) and a switching element ( 22 ) in a switched mode power supply includes a device ( 24 ) for measuring an electrical variable, for example current, that fluctuates as the switching element ( 22 ) switches power received from the power source ( 20 ). A signal injector ( 28 ) is arranged to generate an electrical signal, for example current, of substantially the same amplitude, but opposite polarity, as the measured current, and to inject it between the power source ( 20 ) and the switching element ( 22 ) so as to tend to minimize fluctuations in the electrical variable.
1. An apparatus for providing improved electromagnetic compatibility between a power source and a switching element that switches power supplied from the power source to provide a required frequency power supply, the power source and the switching element being coupled via a first power line at a supply potential and a second power line at a reference potential, the apparatus comprising a measuring device for coupling to at least one of the power lines between the power source and the switching element to provide a first electrical signal proportional to an electrical variable that fluctuates as the switching element switches power received from the power source, and a signal injector coupled to the measuring device and to at least one of the power lines and responsive to said first electrical signal to provide second electrical signal thereto so as to tend to minimize fluctuations in the electrical variable.
2. An apparatus according to claim 1 , wherein the electrical variable comprises voltage measured across the first and second power lines.
3. An apparatus according to claim 2 , wherein the measuring device comprises a pair of measuring electrodes for coupling between the first and second power lines.
4. An apparatus according to claim 1 , wherein the electrical variable comprises voltage measured across the second power line and a ground reference potential.
5. An apparatus according to claim 4 , wherein the measuring device comprises a pair of measuring electrodes for coupling between the second power line and ground reference potential.
6. An apparatus according to claim 4 , wherein the measuring device and the signal injector comprise an operational amplifier having a pair of inputs for coupling to the second power line and to ground reference potential, respectively, a pair of power inputs for coupling to the first and second power lines, respectively, and an output for coupling to ground reference potential for injecting the electrical signal thereto, thereby drawing power from the power lines in such a manner as to tend to minimize fluctuations in the voltage measured between the second power line and ground reference potential.
7. An apparatus according to claim 1 , wherein the electrical variable comprises current measured through a component in the first power line.
8. An apparatus according to claim 6 , wherein the measuring device comprises a pair of measuring electrodes for coupling to a pair of electrodes of the component provided in the first power line.
9. An apparatus according to claim 1 , wherein the second electrical signal injected into at least one of the power lines comprises voltage.
10. An apparatus according to claim 1 , wherein the second electrical signal injected into at least one of the power lines comprises current.
11. A power supply system comprising a power source, a switching element coupled to the power supply via a first power line at a supply potential and a second power line at a reference potential, and an apparatus according to claim 1 .
12. A power supply system according to claim 10 , further comprising a passive electromagnetic filter provided between the power source and the apparatus.
13. A power supply system according to claim 10 , wherein the switching element forms part of a switched mode power supply device.
14. A power supply system according to claim 10 , further comprising an inductor provided in the first power line.
15. A method for providing improved electromagnetic compatibility between a power source and a switching element that switches power supplied from the power source to provide a required frequency power, the power source and the switching element being coupled via a first power line at a supply potential and a second power line at a reference potential, the method comprising the steps of providing a first electrical signal proportional to an electrical variable that fluctuates as the switching element switches power received from the power source, and in response to said electrical signal, injecting a second electrical signal into at least one of the power lines so as to tend to minimize fluctuations in the electrical variable.
16. A method according to claim 15 , wherein the electrical variable comprises voltage measured across the first and second power lines.
17. A method according to claim 15 , wherein the electrical variable comprises voltage measured across the second power line and a ground reference potential.
18. A method according to claim 15 , wherein the electrical variable comprises current measured through a component in the first power line.
19. A method according to claim 15 , wherein the second electrical signal injected into at least one of the power lines comprises voltage.
20. A method according to claim 15 , wherein the second electrical signal injected into at least one of the power lines comprises current.