Method and circuit for galvanically isolated transmission of a signal
View Patent ↗A method for galvanically isolated transmission of a signal, especially a switching signal for controlling at least one switching means includes using a transformer. The primary side of a transformer is fed with a pulse-width modulated voltage in which different duty factors are indicative of different signal states. The voltage obtained on the secondary side is converted by an electronic circuit into at least one signal voltage which is dependent on the duty factor and whose magnitude represents a signal state.
1. A circuit comprising a transformer configured to galvanically isolate signals and to have a pulse-width modulated voltage applied to a primary side thereof, a secondary side of the transformer being connected to a second circuit comprising:
a first series connection including a first and a second rectified diode, a first central potential of the first series connection being connected to a first end of a secondary coil of the transformer;
a second series connection including a first and a second capacitor, a second central potential of the second series connection being connected to a second end of the secondary coil of the transformer, the second series connection being connected in parallel with the first series connection; and
a load including a comparator connected in parallel with the first and second series connections, wherein a first input signal of the comparator is derived from the second central potential, the first input signal derived from the second central potential being dependent on the pulse-width modulated voltage.
2. The circuit as recited in claim 1 further comprising an element connected in series with a primary coil of the transformer, the element being configured to suppress DC components through the primary coil.
3. The circuit as recited in claim 2 wherein the element includes a third capacitor.
4. The circuit as recited in claim 1 wherein the load includes at least one resistive load.
5. The circuit as recited in claim 4 wherein the resistive load includes a series connection of at least two ohmic resistors.
6. The circuit as recited in claim 5 wherein the comparator is configured to have a second input signal thereof derived from a voltage tap at the series connection of the at least two ohmic resistors.
7. The circuit as recited in claim 1 further comprising at least one fourth capacitor connected in parallel with the first series connection, a capacitance of the fourth capacitor being larger than a respective capacitance of the first capacitor and of the second capacitor.
8. The circuit as recited in claim 7 wherein the capacitance of the fourth capacitor is at least 5 times larger than the respective capacitance of the first capacitor and of the second capacitor.
9. The circuit as recited in claim 8 wherein the capacitance of the fourth capacitor is 40 to 60 times larger than the respective capacitance of the first capacitor and of the second capacitor.
10. The circuit as recited in claim 7 wherein at least one of a supply voltage of the comparator and a reference voltage for a second input signal of the comparator is derived from a voltage across the at least one fourth capacitor.
11. The circuit as recited in claim 1 further comprising at least one switching device, and wherein the output signal of the comparator is applied to a control input of the at least one switching device.
12. The circuit as recited in claim 11 wherein the control input includes a gate of a field effect transistor.
13. The circuit as recited in claim 12 wherein the field-effect transistor is a MOSFET.
14. The circuit as recited in claim 1 wherein the load includes a component, a second output signal of the component being inverted relative to a first output signal of the comparator.
15. The circuit as recited in claim 14 wherein the component includes a second comparator having second inputs driven inversely relative to first inputs of the first comparator.