BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a power supply having a power factor correction configuration according to the prior art;
FIG. 2 shows the waveforms in the power factor correction converter 102 of FIG. 1;
FIG. 3 shows the characteristic curve for the rms value of the ripple current in the output capacitive unit versus the rms value of the input voltage when the power factor correction converter 102 of FIG. 1 operates in the critical continuous conduction mode with an output power of 90 W;
FIG. 4 shows the circuitry of a power supply according to a first embodiment of the present invention;
FIG. 5 shows the characteristic curve of the rms value of the ripple current under different inductance of the resonant inductor and different capacitance of the resonant capacitor;
FIGS. 6(A) and 6(B) shows the simulation results according to the present invention;
FIGS. 7(A) and 7(B) shows the experimental results according to the present invention;
FIG. 8 shows the circuitry of a power supply according to a second embodiment of the present invention;
FIG. 9 shows the circuitry of a power supply according to a third embodiment of the present invention; and
FIG. 10 shows the circuitry of a power supply according to a fourth embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Several preferred embodiment embodying the features and advantages of the present invention will be expounded in following paragraphs of descriptions. It is to be realized that the present invention is allowed to have various modification in different respects, none of which departs from the scope of the present invention, and the description herein and the drawings are to be taken as illustrative in nature, but not to be taken as limitative.
A first embodiment of the present invention is shown in FIG. 4. FIG. 4 shows the circuitry of a power supply 400 having a power factor correction (PFC) converter 402 and a DC-DC converter 404. The PFC converter 402 includes a bridge rectifier 410, a boost inductor L41, a transistor switch S41, and a diode D41. The bridge rectifier 410 is configured to rectify an input AC voltage Vin into a full-wave rectified DC voltage having a predetermined voltage level. The boost inductor L41 is connected to an output terminal of the bridge rectifier 410, and configured to receive currents from the bridge rectifier 410 and transfer the stored energy to an output capacitive unit Cb with capacitive impedance through the diode D41 according to the on/off operations of the transistor switch S41. The transistor switch S41 is driven by a PFC control signal Vg. With the on/off operations of the transistor switch S41, the boost inductor L41 may charge the output capacitive unit Cb with the energy stored therein, and thereby generating an intermediate DC voltage across the output capacitive unit Cb. The DC-DC converter 404 is connected to the PFC converter 402 through the output capacitive unit Cb, and configured to convert the intermediate DC voltage into an output DC voltage having a desired voltage level for use by a load (not shown).
In FIG. 4, a resonant network 412 formed by an inductive filtering unit Lr having inductive impedance and a capacitive filtering unit Cr having capacitive impedance acts as a ripple attenuator for reducing the ripple current flowing in the output capacitive unit Cb. The resonant network 412 is placed between the PFC converter 402 and the DC-DC converter 404 and connected to the output capacitive unit Cb. The resonant network 412 is a filter device in which the capacitive filtering unit Cr is a high-frequency capacitor having a smaller equivalent series resistance (ESR). The capacitive filtering unit Cr is connected between the PFC converter 402 and the output capacitive unit Cb and connected in parallel with the output capacitive unit Cb, and the inductive filtering unit Lr is connected between the capacitive filtering unit Cr and the output capacitive unit Cb. The resonant network 412 is configured to allow the low-frequency ripple current to flow in the output capacitive unit Cb and suppress the high-frequency ripple current flowing in the output capacitive unit Cb.
The operation of the circuitry shown in FIG. 4 is illustrated as follows. When the transistor switch S41 is turned on, the boost inductor L41 receives an AC current from the bridge rectifier 410 and thus stores energy therein. When transistor switch S41 is turned off, the boost inductor L41 releases the stored energy by an inductor current iL, in which a portion of the inductor current iL is provided to the back-end DC-DC converter 404 and a portion of the inductor current iL is provided to flow in the resonant network 412 and the output capacitive unit Cb. Due to the low equivalent impedance of the capacitive filtering unit Cr, among the portion of the iL flowing in the resonant network 412 and Cb, the majority flows in the capacitive filtering unit Cr. Also, due to the high equivalent impedance of the circuit branch formed by the inductive filtering unit Lr and the output capacitive unit Cb, the minority flows in the filtering unit Lr and the output capacitive unit Cb. Thus, the ripple current flowing in the output capacitive unit Cb is reduced, and also the high-frequency voltage ripple generated across the output capacitive unit Cb is reduced as well.
If it is desired to achieve an efficient performance on ripple attenuation, the parameters of the resonant network 412 have to be appropriately selected. FIG. 5 shows the characteristic curve of the rms value of the ripple current compiled under different inductance L1 of the resonant inductor Lr and different capacitance C1 of the resonant capacitor Cr. It can be seen from FIG. 5 that if the value of the inductance L1 and the setting of the capacitance C1 are both relatively large (located at the points within the enclosed region A), which makes the resonant frequency
of the resonant network 412 will be lower than the minimum switching frequency, thus the rms value of the ripple current flowing in the output capacitive unit Cb will be lower than that flowing in the output capacitive unit Cb when the inductance L1 is zero (located at the points within the enclosed region B). When the setting of the inductance L1 and the setting of the capacitance C1 are located at the points within the enclosed region C, the rms value of the ripple current flowing in the output capacitive unit Cb will be very large. FIGS. 6(A) and 6(B) are the simulation results obtained on the condition that the parameters of the resonant network are appropriately selected (located at region A) and those are not appropriately selected (located near to region C and away from region A), respectively. As shown in FIGS. 6(A) and 6(B), the waveform of the ripple current iCb flowing in the output capacitive unit Cb and the waveform of the current iD flowing in the diode D41 are depicted.
FIGS. 7(A) and 7(B) are the experimental results in the circumstances that the PFC converter 402 is working in the critical continuous conduction mode with an input voltage around 150V and an output power of 90 W. FIG. 7(A) indicates that the ripple current flowing in the output capacitive unit Cb will be 0.48 A when the capacitance of the output capacitive unit Cb is 36 μF and the inductance of the inductor Lr and the capacitance of the capacitor Cr are respectively 0 μH and 1 μF. FIG. 7(B) indicates that the ripple current flowing in the output capacitive unit Cb will be reduced to 0.27 A when Cb is 36 μF and Lr and Cr are 15 μH and 1 μF, respectively. When the circuit is working in continuous conduction mode or discontinuous conduction mode, the ripple current flowing in the output capacitive unit Cb will be dramatically reduced through the use of the ripple reduction technique of the present invention.
FIG. 8 shows the circuitry of a power supply according to a second embodiment of the present invention. In FIG. 8, the inductive filtering unit (indicated by the inductor Lr shown in the diagram) is connected in series with the output capacitive unit (indicated by the capacitor Cb shown in the diagram). Thus, the resonant network formed by the inductive filtering unit Lr and the capacitive filtering unit Cr not only can reduce the ripple current originated from the front-end PFC converter 402, but also can reduce the ripple current of the back-end DC-DC converter 404.
FIG. 9 shows the circuitry of a power supply according to a third embodiment of the present invention. The circuitry of FIG. 9 is derived by replacing the inductive filtering unit Lr of FIG. 4 with a center-tapped inductive element. Therefore, the inductive filtering unit of FIG. 9 is implemented by tap inductors Lr1 and Lr2, in which the first tap inductor Lr1 is connected between the capacitive filtering unit Cr and the output capacitive unit Cb and the second tap inductor Lr2 is connected in series with the output capacitive unit Cb. The circuitry of FIG. 9 not only combines the advantages offered by the first embodiment and the second embodiment of the present invention, but also allows the location of the tap in the inductors to be optimally allocated according to different parameter settings of the inductor. Another possible circuitry modified from the circuitry of FIG. 8 can be made by replacing the tap inductors with a coupled inductor.
FIG. 10 shows the circuitry of a power supply according to a fourth embodiment of the present invention. The resonant network shown in FIG. 10 is configured to reduce the ripple current originated from the front-end PFC converter 402 and the ripple current originated from the back-end DC-DC converter 404. The resonant network shown in FIG. 10 includes a capacitive filtering unit Cr connected between the DC-DC converter 404 and the output capacitive unit Cb and connected in parallel with the output capacitive unit Cb, a first inductive filtering unit L101 connected between the capacitive filtering unit Cr and the output capacitive unit Cb, and a second inductive filtering unit L102 connected in series with the capacitive filtering unit Cr. With the circuitry of FIG. 10, the circuit branch formed by the first inductive filtering unit L101, the second inductive filtering unit L102, and the capacitive filtering unit Cr constitutes a low-impedance current path for reducing the ripple current of the front-end PFC converter 402 when the resonant frequency fs1 of L101, L102 and Cr is close to the frequency of the harmonic current from the PFC converter stage which is needed to be reduced, wherein
Also, the circuit branch formed by the second inductive filtering unit L102 and the capacitive filtering unit Cr constitutes a low-impedance current path for reducing the ripple current of the back-end DC-DC converter 404 when the resonant frequency fs2 of L102 and Cr is close to the harmonic current frequency from the DC-DC converter stage which is needed to be reduced, wherein
Therefore, the ripple currents flowing in the output capacitive unit Cb can be dramatically reduced.
The front-end converters in the above preferred embodiment are boost PFC circuits, which output high ripple current. In fact, the front-end converter can also supply low ripple current source, such as a buck converter, while the back-end converter pulls pulse ripple current from the front-end converter, such as an asymmetrical half bridge (AHB) converter. The resonant network can also be applied in this kind of structure to reduce the ripple current flowing through the output capacitive unit connected between the front-end and the back-end converter.
In conclusion, the present invention contrives a ripple attenuator being placed between a front-end power converter and a back-end power converter and connected to an output capacitor. The ripple attenuator according to the present invention is configured as a resonant network including inductors and capacitors for filtering the current flowing in the output capacitor, and further reducing the ripple current of the output capacitor. With the ripple reduction technique disclosed herein, the ripple current existed in the power supply can be effectively suppressed without the need of a bulky capacitive element. Therefore, the voltage ripple can be reduced and the reliability of the power supply can be enhanced.
While the present invention has been described in terms of what are presently considered to be the most practical and preferred embodiments, it is to be understood that the present invention need not be restricted to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures. Therefore, the above description and illustration should not be taken as limiting the scope of the present invention which is defined by the appended claims.
Patent Application
20070236968
