Rectifying circuit

Abstract

To provide a rectifying circuit in which radiation noise characteristics are improved only by parasitic capacitance of a diode.SOLUTION: One ends of input LC series circuits 2 (1) and 2 (2) are connected to AC input terminals Ta1 and Ta2, respectively. A diode series circuit 3 is connected between the other ends, the diode series circuit 3 being formed by connecting two modules 5 in series, the module 5 being a set of two diodes 4 whose cathodes are connected in common. One end of choke coils Lc1 to Lc5 is connected to each node of the diode series circuit 3. A smoothing capacitor Co is connected between DC output terminals Tdp and Tdm. The choke coils Lc1 to Lc5 whose one end is connected to an anode of the diode 4 are connected to the DC output terminal Tdm, and those whose the other end is connected to a cathode are connected to the DC output terminal Tdp.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a circuit that performs rectification in the high frequency band. [Background technology]

[0002] For example, Patent Document 1 and Non-Patent Document 2 disclose class E rectifier circuits used in applications such as capacitively coupled wireless power transmission in the MHz band. In these class E rectifier circuits, a capacitor C is connected in parallel to a diode, and the diode operates in class E mode, i.e., soft switching is performed at zero voltage, enabling low-noise, highly efficient operation. Non-Patent Document 2, for example, describes the parallel-connected capacitor C as a constant constituted by the parasitic capacitance of the diode or the composite capacitance with a discrete element. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2015 / 087396 [Non-patent literature]

[0004] [Non-Patent Document 1] 2018 IEEE Wireless Power Transfer Conference (WPTC), Montreal, QC, Canada, 3-7 June 2018; pp. 1-4,Fig.2 Summary of the Invention [Problem to be solved by the invention]

[0005] Figure 3 shows the configuration of a conventional class E rectifier circuit. In conventional rectifier circuits, if the capacitance connected in parallel to the diode is insufficient using only the diode's parasitic capacitance Cp1, a discrete element Cp2 is added. Figure 4 shows the relationship between the required parallel capacitance C and the load resistance RL. The required parallel capacitance C increases as the resistance value of the load resistance RL decreases. For most commercially available diodes, the parasitic capacitance Cp1 becomes 100 pF or less when a voltage of several hundred volts is applied during rectification operation, so it is thought that an additional discrete element Cp2 will often be required.

[0006] On the other hand, commercially available diode modules that are easy to use are those that consist of two diodes with a common anode connection in one module, as shown in Figure 3. If we imagine that a discrete capacitor Cp2 is connected outside the package to the lead terminals of this diode module, as shown in the figure, parasitic inductances Lp1, Lp2, and Lp3 of about several nH due to wire bonding and leads will be present between the diode junction capacitance Cp1 and capacitor Cp2. Therefore, when the diodes switch, resonance will occur in the circuit formed by the capacitances Cp1 and Cp2 and the inductances Lp1 to Lp3.

[0007] As a result, compared to a configuration in which the parallel capacitance C is only the parasitic capacitance Cp1 of the diode, harmonics are superimposed on the diode terminal voltage Vka, resulting in a deterioration of the radiation noise characteristics, as shown in Figure 5. If the radiation noise characteristics deteriorate in frequency bands where the standards are strict, there is a risk that the standards will not be met.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a rectifier circuit that has good radiation noise characteristics even with only the parasitic capacitance of the diode. [Means for solving the problem]

[0009] According to the rectifier circuit of claim 1, one end of each of two input LC series circuits (2(1), 2(2)) is connected to each of two AC input terminals (Ta1, Ta2). A diode series circuit (3) is connected between the other ends of the two input LC series circuits, and the diode series circuit (3) is made up of two or more sets (5) of two diodes (4) connected in series, each set having a common cathode. One end of each of five or more choke coils (Lc) is connected to each node in the diode series circuit. A smoothing capacitor (Co) is connected between the DC output terminals (Tdp, Tdm). The other end of each of the choke coils, one connected to the anode of the diode, is connected to the negative side of the DC output terminal, and the other connected to the cathode of the diode, is connected to the positive side of the DC output terminal.

[0010] With this configuration, when rectification is performed, the current flowing through the diode series circuit reaches the DC output terminal via each diode in each set that has the same connection direction. In other words, the parasitic capacitance of the diodes is in parallel for each set of diodes connected in series. Therefore, compared to adding discrete elements to obtain the required capacitance, there is no effect from the parasitic inductance of the added elements. In addition, a choke coil is always placed in the loop that includes the parasitic capacitance and parasitic inductance of the diode, so resonance can be suppressed by the impedance of the choke coil. These effects generally prevent deterioration of noise characteristics. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram illustrating a configuration of a rectifier circuit according to an embodiment. [Figure 2] FIG. 10 is a diagram showing the results of simulating the waveforms of the voltages between the terminals of each diode for the configurations of the prior art and this embodiment. [Figure 3] Diagram showing the configuration of a conventional rectifier circuit [Figure 4] A diagram showing the relationship between the load resistance RL and the parallel capacitance C required for the rectifier circuit [Figure 5]1 shows the voltage waveforms of the diodes and their frequency components for a configuration in which a parallel capacitance is externally connected to the diode module and a configuration in which a parallel capacitance is not externally connected. DETAILED DESCRIPTION OF THE INVENTION

[0012] An embodiment will be described below. As shown in Fig. 1, one end of input LC series circuits 2(1) and 2(2), each consisting of a coil Lf and a capacitor Cf, is connected to AC input terminals Ta1 and Ta2 of a rectifier circuit 1 of this embodiment. A diode series circuit 3 is connected between the other ends of the input LC series circuits 2(1) and 2(2). The diode series circuit 3 has four diodes 4(1) to 4(4). The diodes 4(1) and 4(2) and the diodes 4(3) and 4(4) are paired with their cathodes connected in common.

[0013] It is assumed that the pair of two diodes 4 described above uses commercially available molded-packaged three-terminal diode modules 5(1) and 5(2), such as the SCS240KE2 from Rohm. Hereinafter, these will be referred to simply as "module 5." The terminals of module 5(1) are designated T1 to T3, and the terminals of module 5(2) are designated T4 to T6. The diode series circuit 3 is configured by connecting two modules 5(1) and 5(2) in series by connecting terminals T3 and T4. Therefore, the diode series circuit 3 has five terminals. The capacitance Cp1 and inductances Lp1 to Lp3 indicated by dashed lines inside module 5 are the parasitic capacitance of diode 4 and the parasitic inductance of the wiring and leads within module 5.

[0014] One ends of choke coils Lc1 to Lc5 are connected to the five terminals of the diode series circuit 3 outside the module 5. The other ends of the choke coils Lc2 and Lc4 are connected to a positive side DC output terminal Tdp of the rectifier circuit 1, and the other ends of the choke coils Lc1, Lc3, and Lc5 are connected to the negative side DC output terminal Tdm of the rectifier circuit 1. A smoothing capacitor Co is connected between the DC output terminals Tdp and Tdm, and a resistive element RL is also connected as a load.

[0015] With this configuration, even when the resistance value of the load resistor RL is low and the required parallel capacitance is relatively large, the required capacitance can be obtained by connecting the parasitic capacitance Cp1 of the diode 4 in parallel without increasing unnecessary inductance, compared to when an external capacitor is attached to the module 5. The configuration of this embodiment corresponds to the case where the required parallel connection capacitance is approximately twice the parasitic capacitance Cp1. Note that the inductance of the choke coil Lc is preferably 5 μH or more.

[0016] 2 shows the results of simulating the waveforms of the voltages across the terminals of each diode for a configuration in which a capacitor is externally attached to the diode module (prior art) and the configuration of this embodiment (the present invention). In the configuration of the prior art, resonance occurs in the voltages Vd1_1 and Vd1_2 across the terminals of each diode. In contrast, in the configuration of this embodiment, the waveforms of the voltages Vd2_1 and Vd2_3 across the terminals of diodes in the same direction overlap with the waveforms of the voltages Vd2_2 and Vd2_4 across the terminals, but it can be seen that resonance is suppressed.

[0017] The FFT analysis results compare the inter-terminal voltage Vd1_1 of the configuration of the conventional technology with the inter-terminal voltage Vd2_1 of the configuration of this embodiment. The inter-terminal voltage Vd2_1 has a generally lower voltage level in the frequency band that actually matters.

[0018] As described above, according to this embodiment, in the class E rectifier circuit 1, one end of each of the input LC series circuits 2(1), 2(2) is connected to each of the AC input terminals Ta1, Ta2, and the other ...

[0019] With this configuration, when the rectifier circuit 1 performs rectification, the current flowing through the diode series circuit 3 reaches the DC output terminal Tdm via each diode 4, which has the same connection direction in each set. In other words, the parasitic capacitance Cp of each set of diodes 4 connected in series is paralleled. Therefore, compared to adding discrete elements to obtain the required capacitance, there is no effect from the parasitic inductance of the added elements. Furthermore, since the choke coil Lc is always placed in the loop including the parasitic capacitance Cp and parasitic inductance Lp of the diode 4, resonance can be suppressed by the impedance of the choke coil Lc. These effects generally prevent deterioration of noise characteristics.

[0020] (Other embodiments) The number of diode modules 5 connected in series may be three or more depending on the required parallel capacitance, and the number of choke coils Lc may be increased by two accordingly. The diode module 5 is not limited to SCS240KE2. Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and equivalent modifications. In addition, various combinations and forms, including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure. [Explanation of symbols]

[0021] In the drawing, 1 is a rectifier circuit, 2 is an input LC series circuit, 3 is a diode series circuit, 4 is a diode, 5 is a diode module, Lf is a coil, Cf is a capacitor, Lc is a choke coil, and Co is a smoothing capacitor.

Claims

[Claim 1] an input LC series circuit (2(1), 2(2)) of a coil (Lf) and a capacitor (Cf), one end of which is connected to each of two AC input terminals (Ta1, Ta2); A diode series circuit (3) is connected between the other ends of the two input LC series circuits, and is formed by connecting two or more sets (5) of two diodes (4) in series, each set having a common cathode; Five or more choke coils (Lc), one end of which is connected to each node in the diode series circuit; a smoothing capacitor (Co) connected between the DC output terminals (Tdp, Tdm); The other end of the choke coil, one end of which is connected to the anode of the diode, is connected to the negative side of the DC output terminal, A rectifier circuit, one end of which is connected to the cathode of the diode, is connected to the positive side of the DC output terminal.

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