High-frequency current source for an active EMI filter, active EMI filter and use of an active EMI filter
A high-frequency current source with a symmetric bipolar output stage piloted by an active bias network with an extended temperature range. The source is configured to provide a high impedance at 1 MHz and above. The invention includes such active EMI filters with such a high-frequency current source, for example in the current-sense current-inject feedback configuration.
1. A high-frequency current source for an active EMI filter comprising a output provided by an output network with two bipolar transistor in a symmetric common-emitter configuration connected between a upper supply rail with a first potential and a lower supply rail with a second potential, an active bias network determining the operating point of the two bipolar transistors, an analogue control network receiving the output and producing a DC correction signal that is fed to an error input of the active bias network to stabilize a DC value of the output, and a HF input controlling a high-frequency output current, wherein the analogue control network is configured to maintain the DC value of the output in a predetermined interval in the middle of a potential difference between the first and the second potential, wherein the analogue control network comprises a gain stage and an integrator stage in a low-pass filter configuration, and the active bias network comprises a voltage reference providing a constant voltage and a temperature-sensitive element introducing a temperature-dependent change in the base voltages of the transistors in the output network such that the DC value of the output is stabilized.
2. The high-frequency current source of claim 1 , having a unipolar power supply.
3. The high-frequency current source of claim 1 , having an output impedance of at least 1 kohm at 30 MHZ, an output capability of at least 1 A peak-to-peak and a temperature operating range extending at least between −40° C. and 125° C.
4. An active EMI filter comprising the high-frequency current source of claim 1 .
5. The active EMI filter of claim 4 , comprising a sense unit configured to sense a noise signal circulating in a power line from a noise source to a load, control the high-frequency current source according to the noise signal, inject the high-frequency output current of the high-frequency current source into the power line through a current-inject unit.
6. The active EMI filter of claim 4 , wherein the noise signal is common-mode.
7. The active EMI filter of claim 4 , wherein the sense unit is a current transformer coupling to a noise current on the power line.
8. Use of the active EMI filter of claim 4 on the power bus of an electric or hybrid vehicle.