Power converter and current detection circuit

Abstract

The present invention relates to a power converter (1) having a coil, comprising a sensing coil (Ld) which is magnetically coupled to the coil, a sensing resistor (Rd) and a sensing capacitor (Cd) which are connected in series with each other and in parallel with the sensing coil (Ld), and a detection circuit (4) which detects a current flowing in the coil based on a voltage across the sensing capacitor (Cd).

Description

Title of the invention: Power converter and current detection circuit Technological background

[0001] The present invention relates to a technique for detecting the current flowing in a coil provided in a power converter.

[0002] There is a current detection circuit in which a coil provided in a power converter is connected in parallel to a detection resistor and a detection capacitor connected in series with each other, and a detection circuit is connected across both terminals of the detection capacitor. The detection circuit detects a current flowing in the coil based on a drop voltage of a direct current (DC) resistance component of the coil, which is obtained by a voltage across the detection capacitor, and corrects the detected current based on the error between the voltage across the detection capacitor and the drop voltage. Japanese Patent Application Publication No. 2000-193687 is prior art related to the current detection circuit described above.

[0003] However, in the current detection circuit described above, the detection capacitor is directly connected to the coil. Therefore, when the current flowing in the coil is detected based on the drop voltage of the DC resistance component of the coil, it is necessary to shift a reference potential of the detection circuit based on the voltage across the detection capacitor or to shift the voltage across the detection capacitor based on the reference potential of the detection circuit. Therefore, manufacturing costs may increase, as may the cost of adding a function of shifting the reference potential of the detection circuit or the voltage across the detection capacitor to the detection circuit.In addition, since the dropout voltage is a relatively small value, the dropout voltage is easily affected by the quantization error in the detection circuit when an analog value is converted to a digital value in the dropout voltage. This may reduce the current detection accuracy.

[0004] The present invention aims in part to eliminate the manufacturing costs of a power converter while improving the accuracy of detecting a current flowing in a coil provided in the power converter. Summary

[0005] According to one aspect of the present invention, a power converter having a coil has a sensing coil that is coupled magnetically to the coil, a sense resistor and a sense capacitor that are connected in series with each other and in parallel with the sense coil, and a sense circuit that senses a current flowing in the coil based on a voltage across the sense capacitor.

[0006] According to another aspect of the present invention, a current detection circuit for detecting a current flowing in a coil provided in a power converter comprises a detection coil which is magnetically coupled to the coil, a detection resistor and a detection capacitor which are connected in series with each other and in parallel with the detection coil, and a detection circuit which detects a current flowing in the coil based on a voltage across the detection capacitor.

[0007] In other words, the invention relates to a power converter comprising a coil, comprising: a pickup coil that is magnetically coupled to the coil; a sense resistor and a sense capacitor which are connected in series with each other and in parallel with the sense coil; and a detection circuit that detects a current flowing in the coil based on a voltage across the detection capacitor.

[0008] According to one embodiment, the coil is a smoothing coil which makes it possible to smooth the current flowing in the power converter.

[0009] According to one embodiment: the smoothing coil has a core, and The pickup coil is formed by winding around the core.

[0010] According to one embodiment, the core has a spacing.

[0011] According to one embodiment, in the case where the number of turns of the coil represents NI and the number of turns of the detection coil represents N2, N2 / N1 is less than or equal to 10.

[0012] According to one embodiment, the power converter further comprises two offset resistors which are connected between a constant voltage source and a reference potential of the detection circuit in series with each other, characterized in that the two offset resistors shift the voltage across the sense capacitor by a difference between an electrical potential at a node between the two offset resistors and the reference potential of the sense circuit.

[0013] According to one embodiment: the smoothing coil is disposed on at least one of the major surfaces of a printed circuit board on which the power converter is mounted, and the detection coil is arranged relative to the smoothing coil in the thickness direction of the printed circuit board.

[0014] According to one embodiment: the printed circuit board is a multi-layer printed circuit board, and The detection coil is arranged on an inner layer of the printed circuit board in a wiring pattern.

[0015] Another aspect relates to a current detection circuit for detecting a current flowing in a coil provided in a power converter, the current detection circuit comprising: a pickup coil that is magnetically coupled to the coil; a sense resistor and a sense capacitor which are connected in series with each other and in parallel with the sense coil; and a detection circuit that detects a current flowing in the coil based on a voltage across the detection capacitor.

[0016] Other aspects and advantages of the invention will emerge from the following description, as well as the accompanying drawings which illustrate by way of example the principles of the invention. Brief description of the drawings

[0017] The invention, as well as its objects and advantages, may be better understood by referring to the following description of the embodiments and to the accompanying drawings in which:

[0018] [Fig-1] [Fig.l] is a diagram illustrating an example of a converter of power according to an embodiment;

[0019] [Fig.2A] [Fig.2A] is a view illustrating an example of a smoothing coil, a core, and a detection coil;

[0020] [Fig.2B] [Fig.2B] is a view illustrating an example of a smoothing coil, a core, and a detection coil;

[0021] [Fig.2C] [Fig.2C] is a view illustrating an example of a smoothing coil, a core, and a detection coil;

[0022] [Fig.2D] [Fig.2D] is a view illustrating an example of a smoothing coil, a core, and a detection coil;

[0023] [Fig.3] [Fig.3] is a diagram illustrating a first modification of the power converter according to the embodiment;

[0024] [Fig.4] [Fig.4] is a diagram illustrating a second modification of the power converter according to the embodiment;

[0025] [Fig.5] [Fig.5] is a diagram illustrating a third modification of the power converter according to the embodiment;

[0026] [Fig.6] [Fig.6] is a diagram illustrating a fourth modification of the power converter according to the embodiment;

[0027] [Fig.7] [Fig.7] is a diagram illustrating a fifth modification of the power converter according to the embodiment; and

[0028] [Fig.8] [Fig.8] is a diagram illustrating a sixth modification of the power converter according to the embodiment. Detailed description of the embodiments

[0029] One embodiment will be described in detail in the following with reference to the drawings.

[0030] [Fig. 1] is a diagram illustrating an example of a power converter according to the present embodiment.

[0031] A power converter 1 illustrated in [Fig.l] is an active clamp-on forward converter that converts a DC power output from a power supply B to a specified DC power and supplies the specified DC power to a load.

[0032] The power converter 1 comprises switches Ql, Q2, capacitors Cp, Cs, a transformer T, diodes Dol, Do2, a smoothing coil Lo, a smoothing capacitor Co, a control circuit 2, and a current detection circuit 3. It should be noted that the switches Ql, Q2 are each formed of a metal oxide semiconductor field effect transistor (MOSFET) for example. A drain terminal of the switch Ql is connected to one terminal of the capacitor Cp, to a source terminal of the switch Q2 and to one terminal of a primary coil Lpl of the transformer T. A source terminal of the switch Ql is connected to the other terminal of the capacitor Cp and to a negative terminal of the power supply B. A drain terminal of the switch Q2 is connected to a positive terminal of the power supply B and to the other terminal of the primary coil Lpl through the capacitor Cs.One cathode terminal of diode Dol is connected to one cathode terminal of diode Do2. The cathode terminal of diode Dol is also connected to one terminal of smoothing capacitor Co and to one terminal of the load through smoothing coil Lo. One anode terminal of diode Dol is connected to one terminal of a secondary coil Lp2 of transformer T. One anode terminal of diode Do2 is connected to the other terminal of secondary coil Lp2, to the other terminal of smoothing capacitor Co and to the other terminal of the load.

[0033] For example, the control circuit 2 is formed of a central processing unit (CPU), a multi-core CPU or a programmable device such as a field programmable gate array (FPGA) or a programmable logic device (PLD).

[0034] When the power converter 1 converts the DC power output of the power supply B into the specified DC power and supplies the specified DC power to the load, the switches Q1, Q2 are turned on and off alternately. and repeatedly by the control circuit 2, so that a voltage across the smoothing capacitor Co reaches a target voltage and a current detected by the current detection circuit 3 reaches a target current.

[0035] First, when the switch Q1 is turned on (when the switch Q1 is in the on state and the switch Q2 is in the off state), a current flows from the power supply B to the primary coil Lpl, and a current flows from the secondary coil Lp2 to the load through the diode Dol and the smoothing coil Lo.

[0036] Then, when the switch Q1 is off (when the switches Ql, Q2 are in the off state (dead time)), a current flows from the primary coil Lpl to the capacitor Cp to charge the capacitor Cp. When the voltage across the capacitor Cp reaches the total voltage of a voltage of the power supply B and a voltage across the capacitor Cs, a current flows from the primary coil Lpl to the capacitor Cs through a body diode of the switch Q2 to charge the capacitor Cs. On one side of the load, the current flows continuously from the diode Dol to the load through the smoothing coil Lo. It should be noted that the energy stored in the primary coil Lpl is reduced by the charging of the capacitors Cp, Cs, so that the transformer T in the state of magnetic saturation is gradually demagnetized.Furthermore, when switch Ql is off, the voltage across capacitor Cp is 0 [V], which reduces switching losses.

[0037] Then, when the switch Q2 is turned on (when the switch Q1 is in the off state and the switch Q2 is in the on state), a current flows from the primary coil Lpl to the capacitor Cs through the switch Q2 to charge the capacitor Cs. In addition, on the load side, a current flows from the diode Do2 to the load through the smoothing coil Lo. It should be noted that the energy stored in the primary coil Lpl is further reduced by the charging of the capacitor Cs, so that the transformer T in the magnetic saturation state is gradually demagnetized. In addition, when the switch Q2 is turned on, a current flows through the body diode of the switch Q2, which reduces the switching losses. Then, when the switch Q2 is in the on state, the direction of the current is reversed and the capacitor Cs is discharged.

[0038] Then, when the switch Q2 is off (when the switches Ql, Q2 are in the off state (dead time)), a current flows from the capacitor Cp to the power supply B through the primary coil Lpl, i.e., the capacitor Cp is discharged. After the capacitor Cp is discharged, a current flows from the body diode of the switch Ql to the power supply B through the primary coil Lpl. In addition, on the load side, the current flows continuously from the diode Do2 to the load through the smoothing coil Lo.

[0039] After that, the switches Q1, Q2 are alternately and repeatedly turned on and off. It should be noted that when the switch Q1 is turned on, current flows through the body diode of the switch Q1, which reduces switching losses.

[0040] The current detection circuit 3 comprises a detection coil Ld, a detection resistor Rd, a detection capacitor Cd and a detection circuit 4. The current detection circuit 3 detects a current (alternating current) flowing in the smoothing coil Lo.

[0041] The sensing coil Ld is wound around a core Cre of the smoothing coil Lo, and the sensing coil Ld is thus magnetically coupled to the smoothing coil Lo. It should be noted that in the case where the number of turns of the smoothing coil Lo is represented by NI and the number of turns of the sensing coil Ld is represented by N2, the turns ratio N2 / N1 is preferably greater than or equal to 0.3 and less than or equal to 10. Furthermore, the turns ratio N2 / N1 is more preferably greater than or equal to 1 and less than or equal to 10. Hereinafter, the turns ratio N2 / N1 is also referred to as the turns ratio n.Thus, the voltage across the detection capacitor Cd increases by setting a turns ratio n to a relatively large value, so that the voltage across the detection capacitor Cd is not easily affected by the quantization error in the detection circuit 4 when an analog value is converted into a digital value in the voltage across the detection capacitor Cd. This can improve the current detection accuracy.

[0042] The sensing resistor Rd and the sensing capacitor Cd are connected in series with each other and are connected in parallel to the sensing coil Ld. That is, one terminal of the sensing capacitor Cd is connected to one terminal of the sensing coil Ld through the sensing resistor Rd, and the other terminal of the sensing capacitor Cd is connected to the other terminal of the sensing coil Ld and to a reference potential of the sensing circuit 4 (e.g., a ground of the power converter 1).

[0043] The detection circuit 4 detects the current flowing through the smoothing coil Lo based on the voltage across the detection capacitor Cd (a difference between an electric potential across that terminal of the detection capacitor Cd and the reference potential of the detection circuit 4).

[0044] For example, a voltage across the smoothing coil Lo is represented by VL, the current flowing through the smoothing coil Lo is represented by iL, an inductance of the smoothing coil Lo is represented by L, the voltage across the detection capacitor Cd is represented by Vc, a capacitance of the detection capacitor Cd is represented by C, a voltage across the detection resistor Rd is Vr, a resistance of the sense resistor Rd is represented by R, a current flowing through the sense capacitor Cd and the sense resistor Rd is represented by is, a ratio of the number of turns of the sense coil Ld to the number of turns of the smoothing coil Lo is represented by n, and a Laplace Operator is represented by s. In this case, the voltage VLd across the sense coil Ld is expressed by the following equation: VLd = Vc + Vr where VLd = nx VL = sxnx Lx iL is satisfied, Vc = is / (sx C) is satisfied, and Vr = R x is is satisfied. Therefore, the equation described above is expressed by the following equation: sxnx L x iL = is / (sx C) + R x is

[0045] When this equation is solved for the current is, the current is is expressed by the following equation: is = (sxnx L) / (l / (sx C) + R) x iL

[0046] Thus, the voltage Vr is expressed by the following equation: Vr = Rxis = Rx(sxnx L) / (l / (sx C) + R) x iL

[0047] Therefore, the voltage Vc of the detection capacitor Cd is expressed by the following Equation 1. Vc = VLd - Vr = sxnxLxiL-Rx(sxnx L) / (l / (sx C) + R) x iL = (sxnx L x iL) / (l + sx C x R) (Equation 1)

[0048] Here, a cutoff frequency fc in a filter circuit formed by the sense resistor Rd and the sense capacitor Cd is expressed by the following equation: fc =1 / (2jt x R x C). When the resistance R of the sense resistor Rd and the capacitance C of the sense capacitor Cd are set so that the cutoff frequency fc is sufficiently lower than a switching frequency of the power converter 1, the condition that sx C x R » 1 is satisfied. The "1" in the denominator of Equation 1 above can then be ignored, so that Equation 1 is transformed into the following Equation 2. Vc = (nx L x iL) / (C x R) (Equation 2)

[0049] That is, in the detection circuit 4, the current iL flowing in the smoothing coil Lo is obtained by substituting the voltage Vc across the detection capacitor Cd into Equation 2 described above. It should be noted that the turns ratio n, the inductance L, the capacitance C and the resistance R are each a predetermined value.

[0050] Thus, according to the power converter 1 in the embodiment, since the detection coil Ld is magnetically coupled to the smoothing coil Lo, the smoothing coil Lo and the detection capacitor Cd are electrically separated. (isolated) from each other. This allows the reference potential of the detection capacitor Cd to be set as desired, independently of the smoothing coil Lo. Therefore, when the other terminal (reference potential) of the detection capacitor Cd is connected to the reference potential of the detection circuit 4, the current iL flowing in the smoothing coil Lo is detected based on the voltage Vc across the detection capacitor Cd without shifting the reference voltage of the detection circuit 4 or the voltage across the detection capacitor Cd. Therefore, the power converter 1 does not need to have a function to shift the reference potential of the detection circuit 4 or the voltage across the detection capacitor Cd, so as to avoid increasing the manufacturing costs of the power converter 1.In addition, the current iL flowing in the smoothing coil Lo does not need to be corrected after being detected, which can avoid the increase in the detection time of the current iL.

[0051] The current detection circuit 3 may be formed so as to detect a current flowing through the primary coil Lpl or the secondary coil Lp2 having a core. When the current detection circuit 3 detects the current flowing through the primary coil Lpl or the secondary coil Lp2, the detection coil Ld is formed by winding around the core of the primary coil Lpl or the secondary coil Lp2. In addition, when the detection circuit 4 detects the current flowing through the primary coil Lpl or the secondary coil Lp2 based on the voltage across the detection capacitor Cd, in Equation 2 described above, the turns ratio n represents a ratio of the number of turns of the detection coil Ld to the number of turns of the primary coil Lpl or the secondary coil Lp2, and the inductance L represents an inductance of the primary coil Lpl or the secondary coil Lp2.

[0052] Here, [Fig.2A] to 2D each illustrate an example of the smoothing coil Lo, the sensing coil Ld, and the core Cre. [Fig.2A] is a perspective view illustrating a multilayer printed circuit board (PCB) Sb on which the power converter 1 is mounted, the smoothing coil Lo, and the core Cre. [Fig.2B] is a sectional view illustrating the multilayer PCB Sb, the smoothing coil Lo, and the sensing coil Ld. [Fig.2C] illustrates an example of the core Cre, and [Fig.2D] illustrates another example of the core Cre.

[0053] The smoothing coil Lo illustrated in [Fig.2A] and [Fig.2B] is formed of plate-shaped conductors L1, L2 which are each C-shaped. The plate-shaped conductor L1 is arranged on one main surface (a surface facing a positive side in a Z direction) of the multilayer PCB Sb, and the plate-shaped conductor L2 is arranged on the other main surface (a surface facing a negative side in the Z direction) of the multilayer PCB Sb. For example, one terminal of the plate-shaped conductor L1 is connected to a wiring pattern on the first main surface of the multilayer PCB Sb by soldering, and the other terminal of the plate-shaped conductor L1 is connected to one terminal of the plate-shaped conductor L2 via a conductor in the multilayer PCB Sb. The other terminal of the plate-shaped conductor L2 is connected to a wiring pattern on the other main surface of the multilayer PCB Sb by soldering. Thus, the plate-shaped conductor L1 and the plate-shaped conductor L2 are connected in series with each other and form the two-turn smoothing coil Lo. It should be noted that the smoothing coil Lo can be formed only of the plate-shaped conductor L1 or only of the plate-shaped conductor L2. That is, the smoothing coil Lo is arranged on at least one of the main surfaces of the multilayer PCB Sb on which the power converter 1 is mounted.

[0054] In addition, the detection coil Ld shown in [Fig.2B] is an accumulated coil formed of a wiring pattern and arranged on an inner layer of the multilayer PCB Sb, such that the detection coil Ld faces the smoothing coil Lo in the thickness direction (Z direction) of the multilayer PCB Sb. In [Fig.2B], the detection coil Ld is formed of the wiring pattern that spirally rotates four times; however, the number of turns is not limited to four. It should be noted that the detection coil Ld may be arranged on at least one of the main surfaces of the multilayer PCB Sb. That is, the detection coil Ld is arranged relatively (or with respect to) the smoothing coil Lo in the thickness direction of the multilayer PCB Sb. Furthermore, the Ld sensing coil is not limited to a configuration in which the Ld sensing coil is arranged on the first inner layer of the Sb multilayer PCB.The sensing coil Ld may be formed by connecting winding patterns in series with respect to each other, which are each formed on a corresponding plurality of inner layers. In addition, the sensing coil Ld may be formed of a conductive wire or the like, and the sensing coil is not limited to the wiring pattern. The PCB on which the power converter 1 is mounted does not need to be formed of the multi-layer PCB.

[0055] The core Cre shown in [Fig.2A] is formed of an E-shaped magnetic body Crel and an I-shaped magnetic body Cre2. Three through holes H1 to H3 are arranged in a Y direction in the multilayer PCB Sb. The through hole H2 is arranged inside the smoothing coil Lo, and the through holes H1, H3 are arranged outside the smoothing coil Lo. Three projections of the magnetic body Crel are each inserted into the corresponding through holes H1 to H3 and connected to the magnetic body Cre2 to form the core Cre.

[0056] It should be noted that, as illustrated in [Fig.2C], in the core Cre, when the magnetic body Crel and the magnetic body Cre2 are connected to each other, at at least one of the three projections of the magnetic body Crel can be shortened so that a distal end of the projection does not contact the magnetic body Cre2, which forms a gap AG.

[0057] Alternatively, as illustrated in [Fig.2D], in the core Cre, the gap AG may be formed by connecting the three projections of the magnetic body Crel to the magnetic body Cre2 through a spacer S.

[0058] It is also possible to have no spacing in the Cre core.

[0059] The present invention is not limited to the above embodiment, and may be improved or modified within the scope of the present invention.

[0060] The power converter 1 of the embodiment is not limited to the active clamp direct converter and may be another converter.<Première modification>

[0061] [Fig. 3] is a diagram illustrating a first modification of the power converter 1 according to the embodiment. In [Fig. 3], the same components as those illustrated in [Fig. 1] have the same reference numbers and may not be repeated.

[0062] The power converter 1 illustrated in [Fig.3] is a non-isolated step-down converter which converts a DC power output of the power supply B into a specified DC power and supplies the specified DC power to the load.

[0063] That is, the power converter 1 shown in [Fig. 3] comprises the switch Ql, the diode Do2, the smoothing coil Lo, the smoothing capacitor Co, the control circuit 2 and the current detection circuit 3. The drain terminal of the switch Ql is connected to the positive terminal of the power supply B. The source terminal of the switch Ql is connected to the cathode terminal of diode Do2 and to the first terminal of smoothing capacitor Co and to the first terminal of the load through the smoothing coil Lo. The anode terminal of the diode Do2 is connected to the negative terminal of the power supply B, to the other terminal of the smoothing capacitor Co and to the other terminal of the load. It should be noted that the configuration and operation of the current detection circuit 3 shown in [Fig. 3] are the same as those of the current detection circuit 3 shown in [Fig.l], and the description of the configuration and operation will therefore be omitted. Moreover, a voltage across the load is lower than a voltage of the power supply B, and thus, even when the load is formed from a battery, current does not flow from the load to the power supply B through the body diode of the switch QL.

[0064] When the power converter 1 converts the DC power output of the power supply B into the specified DC power and supplies the specified DC power specified to the load, switch Q1 is repeatedly turned on and off by the control circuit 2 shown in [Fig.3] so that a voltage across the smoothing capacitor Co reaches a target voltage and a current detected by the current detection circuit 3 reaches a target current. When switch Q1 is turned on, a current flows from the power supply B to the load through switch Q1 and the smoothing coil Lo. In addition, when switch Q1 is turned off, current flows continuously from the diode Do2 to the load through the smoothing coil Lo.

[0065] Still in the power converter 1 shown in [Fig. 3], when the detection circuit 4 detects the current flowing through the smoothing coil Lo, the power converter 1 does not need to have the function to shift a reference potential of the detection circuit 4 or the voltage across the detection capacitor Cd, so as to avoid the increase in manufacturing costs of the power converter 1. In addition, still in the power converter 1 shown in [Fig. 3], the voltage across the detection capacitor Cd increases as the turns ratio n increases, so that the voltage across the detection capacitor Cd is not easily affected by the quantization error in the detection circuit 4 when an analog value is converted into a digital value in the voltage across the detection capacitor Cd. This can improve the current detection accuracy.Still in the power converter 1 shown in [Fig.3], the current iL flowing in the smoothing coil Lo does not need to be corrected after being detected, which avoids the increase in the detection time of the current iL. <Deuxième modifie ation>

[0066] [Fig.4] is a diagram illustrating a second modification of the power converter 1 according to the embodiment. In [Fig.4], the same components as those illustrated in [Fig.l] have the same reference numbers and may not be repeated.

[0067] The power converter 1 illustrated in [Fig.4] is an isolated forward converter which converts a DC power output of the power supply B into a specified DC power and supplies the specified DC power to the load.

[0068] That is, the power converter 1 shown in [Fig.4] comprises the switch Ql, the transformer T, the diodes Dol, Do2, the smoothing coil Lo, the smoothing capacitor Co, the control circuit 2 and the current detection circuit 3. The drain terminal of the switch Ql is connected to the positive terminal of the power supply B through the primary coil Lpl of the transformer T, and the source terminal of the switch Ql is connected to the negative terminal of the power supply B. It should be noted that the circuit configuration for the reset of transformer T is omitted in the isolated forward converter shown in [Fig.4]. In addition, the configuration and operation of the current detection circuit 3 shown in [Fig.4] are the same as those of the current detection circuit 3 shown in [Fig.l], and therefore the description of the configuration and operation will be omitted.

[0069] When the power converter 1 converts the DC power output of the power supply B into the specified DC power and supplies the specified DC power to the load, the switch Q1 is repeatedly turned on and off by the control circuit 2 shown in [Fig.4] so that a voltage across the smoothing capacitor Co reaches a target voltage and a current detected by the current detection circuit 3 reaches a target current. When the switch Q1 is turned on, a current flows from the power supply B to the primary coil Lpl, and a current flows from the secondary coil Lp2 of the transformer T to the load through the diode Dol and the smoothing coil Lo. Then, when the switch Q1 is turned off, the current continuously flows from the diode Do2 to the load through the smoothing coil Lo.

[0070] Still in the power converter 1 shown in [Fig.4], when the detection circuit 4 detects the current flowing through the smoothing coil Lo, the power converter 1 does not need to have the function to shift a reference potential of the detection circuit 4 or the voltage across the detection capacitor Cd, so as to avoid the increase in manufacturing costs of the power converter 1. In addition, still in the power converter 1 shown in [Fig.4], the voltage across the detection capacitor Cd increases as the turns ratio n increases, so that the voltage across the detection capacitor Cd is not easily affected by the quantization error in the detection circuit 4 when an analog value is converted into a digital value in the voltage across the detection capacitor Cd. This can improve the current detection accuracy.Still in the power converter 1 shown in [Fig.4], the current iL flowing in the smoothing coil Lo does not need to be corrected after being detected, which avoids the increase in the detection time of the current iL. cThird modification> .

[0071] [Fig. 5] is a diagram illustrating a third modification of the power converter 1 according to the embodiment. In [Fig. 5], the same components as those illustrated in [Fig. 1] have the same reference numbers and may not be repeated.

[0072] The power converter 1 illustrated in [Fig.5] is an isolated push-pull converter which converts a DC power output of the power supply B into a specified DC power and supplies the specified DC power to the load.

[0073] That is, the power converter 1 shown in [Fig.5] comprises the switches Ql, Q2, the transformer T, the diodes Dol, Do2, the smoothing coil Lo, the smoothing capacitor Co, the control circuit 2 and the current detection circuit 3. The source terminal of the switch Ql is connected to the negative terminal of the power supply B, and the drain terminal of the switch Ql is connected to the first terminal of the primary coil Lpl of the transformer T. The source terminal of the switch Q2 is connected to the negative terminal of the power supply B, and the drain terminal of the switch Q2 is connected to the other terminal of the primary coil Lpl of the transformer T. The positive terminal of the power supply B is connected to a center tap of the primary coil Lpl. The cathode terminal of the diode Dol is connected to the cathode terminal of the diode Do2.The cathode terminal of diode Dol is also connected to the first terminal of smoothing capacitor Co and the first terminal of the load through smoothing coil Lo. The anode terminal of diode Dol is connected to the first terminal of secondary coil Lp2 of transformer T. The anode terminal of diode Do2 is connected to the other terminal of secondary coil Lp2. A center tap of secondary coil Lp2 is connected to the other terminal of smoothing capacitor Co and the other terminal of the load. It should be noted that the configuration and operation of current detection circuit 3 shown in [Fig.5] are the same as those of current detection circuit 3 shown in [Fig.l], and therefore the description of the configuration and operation will be omitted.

[0074] When the power converter 1 converts the DC power output of the power supply B into the specified DC power and supplies the specified DC power to the load, the switches Ql, Q2 are alternately and repeatedly turned on and off by the control circuit 2, shown in [Fig.5] so that a voltage across the smoothing capacitor Co reaches a target voltage and a current detected by the current detection circuit 3 reaches a target current. When the switch Q2 is off and the switch Ql is on, a current flows from the power supply B to the primary coil Lpl through the center tap of the primary coil Lpl, and a current flows from the secondary coil Lp2 to the load through the diode Dol and the smoothing coil Lo.When switch Ql is off and switch Q2 is on, a current flows from power supply B to primary coil Lpl through the center tap of primary coil Lpl, and a current flows from secondary coil Lp2 to the load through diode Do2 and smoothing coil Lo.

[0075] Still in the power converter 1 shown in [Fig.5], when the detection circuit 4 detects the current flowing through the smoothing coil Lo, the power converter 1 does not need to have the function to shift a reference potential of the detection circuit 4 or the voltage across the detection capacitor Cd, so as to avoid the increase in manufacturing costs of the power converter 1. In addition, still in the power converter 1 shown in [Fig.5], the voltage across the detection capacitor Cd increases as the turns ratio n increases, so that the voltage across the detection capacitor Cd is not easily affected by the quantization error in the detection circuit 4 when an analog value is converted into a digital value in the voltage across the detection capacitor Cd. This can improve the current detection accuracy.Still in the power converter 1 shown in [Fig.5], the current iL flowing in the smoothing coil Lo does not need to be corrected after being detected, which avoids the increase in the detection time of the current iL.<Quatrième modification> .

[0076] [Fig. 6] is a diagram illustrating a fourth modification of the power converter 1 according to the embodiment. In [Fig. 6], the same components as those illustrated in [Fig. 1] have the same reference numbers and may not be repeated.

[0077] The power converter 1 illustrated in [Fig.6] is an isolated half-bridge converter which converts a DC power output of the power supply B into a specified DC power and supplies the specified DC power to the load.

[0078] That is, the power converter 1 shown in [Fig.6] comprises the switches Ql, Q2, a capacitor Cr, the transformer T, the diodes Dol, Do2, the smoothing coil Lo, the smoothing capacitor Co, the control circuit 2 and the current detection circuit 3. The drain terminal of the switch Ql is connected to the positive terminal of the power supply B, and the source terminal of the switch Ql is connected to the drain terminal of the switch Q2 and to the first terminal of the primary coil Lpl of the transformer T. The source terminal of the switch Q2 is connected to the other terminal of the primary coil Lpl through the capacitor Cr and to the negative terminal of the power supply B. The cathode terminal of the diode Dol is connected to the cathode terminal of the diode Do2.The cathode terminal of diode Dol is also connected to the first terminal of smoothing capacitor Co and to the first terminal of the load through smoothing coil Lo. The anode terminal of diode Dol is connected to the first terminal of secondary coil Lp2 of transformer T. The anode terminal of diode Do2 is connected to the other terminal of secondary coil Lp2. The center tap of secondary coil Lp2 is connected to . the other terminal of the smoothing capacitor Co and to the other terminal of the load. It should be noted that the configuration and operation of the current detection circuit 3 shown in [Fig.6] are the same as those of the current detection circuit 3 shown in [Fig.l], and therefore the description of the configuration and operation will be omitted.

[0079] In addition, when the power converter 1 converts the DC power output of the power supply B into the specified DC power and supplies the specified DC power to the load, the switches Q1, Q2 are alternately and repeatedly turned on and off by the control circuit 2, shown in [Fig.6] so that a voltage across the smoothing capacitor Co reaches a target voltage and a current detected by the current detection circuit 3 reaches a target current.

[0080] First, when the switch Ql is turned on (when the switch Ql is in the on state and the switch Q2 is in the off state), a current flows from the power supply B to the primary coil Lpl through the switch Ql, and a current flows from the secondary coil Lp2 to the load through the diode Dol and the smoothing coil Lo.

[0081] Then, when the switch Ql is off (when the switches Ql, Q2 are in the off state (dead time)), a current flows from the other terminal of the primary coil Lpl to the first terminal of the primary coil Lpl through the capacitor Cr and the body diode of the switch Q2, and the current flows continuously from the secondary coil Lp2 to the load through the diode Dol and the smoothing coil Lo.

[0082] Then, when the switch Q2 is turned on (when the switch Q1 is in the off state and the switch Q2 is in the on state), a current flows from the one terminal of the capacitor Cr to the other terminal of the capacitor Cr through the primary coil Lpl and the switch Q2, and a current flows from the secondary coil Lp2 to the load through the diode Do2 and the smoothing coil Lo. It should be noted that, when the switch Q2 is turned on, the current flows through the body diode of the switch Q2, which reduces the switching losses.

[0083] Then, when the switch Q2 is off (when the switches Ql, Q2 are in the off state (dead time)), a current flows from the negative terminal of the power supply B to the positive terminal of the power supply B through the capacitor Cr, the primary coil Lpl and the body diode of the switch Ql, and the current flows continuously from the secondary coil Lp2 to the load through the diode Do2 and the smoothing coil Lo.

[0084] After that, the switches Ql, Q2 are alternately and repeatedly turned on and off. It should be noted that when the switch Ql is turned on, current flows through the body diode of the switch Ql, which reduces switching losses.

[0085] Still in the power converter 1 shown in [Fig.6], when the detection circuit 4 detects the current flowing through the smoothing coil Lo, the power converter 1 does not need to have the function to shift a reference potential of the detection circuit 4 or the voltage across the detection capacitor Cd, so as to avoid the increase in manufacturing costs of the power converter 1. In addition, still in the power converter 1 shown in [Fig.6], the voltage across the detection capacitor Cd increases as the turns ratio n increases, so that the voltage across the detection capacitor Cd is not easily affected by the quantization error in the detection circuit 4 when an analog value is converted into a digital value in the voltage across the detection capacitor Cd. This can improve the current detection accuracy.Still in the power converter 1 shown in [Fig.6], the current iL flowing in the smoothing coil Lo does not need to be corrected after being detected, which avoids the increase in the detection time of the current iL.<Cinquième modifie ation> .

[0086] [Fig.7] is a diagram illustrating a fifth modification of the converter of power 1 according to the embodiment. It should be noted that in [Fig.7], the same components as those illustrated in [Fig.l] have the same reference numbers and may not be repeated.

[0087] The power converter 1 illustrated in [Fig.7] is an isolated full-bridge converter which converts a DC power output of the power supply B into a specified DC power and supplies the specified DC power to the load.

[0088] That is, the power converter 1 shown in [Fig.7] comprises the switches Ql, Q2, switches Q3, Q4, the transformer T, the diodes Dol, Do2, the smoothing coil Lo, the smoothing capacitor Co, the control circuit 2 and the current detection circuit 3. It should be noted that the switches Q3, Q4 are each formed of a MOSFET, for example. The drain terminal of the switch Ql is connected to the positive terminal of the power supply B and to a drain terminal of the switch Q3. The source terminal of the switch Ql is connected to the first terminal of the primary coil Lpl of the transformer T and to the drain terminal of the switch Q2. The source terminal of the switch Q2 is connected to the negative terminal of the power supply B and to a source terminal of the switch Q4. One source terminal of switch Q3 is connected to the other terminal of primary coil Lpl and one drain terminal of switch Q4.The cathode terminal of diode Dol is connected to the cathode terminal of diode Do2. The cathode terminal of diode Dol is also connected to the first terminal of smoothing capacitor Co and to the first terminal of the load through the inductor. smoothing Lo. The anode terminal of diode Dol is connected to the first terminal of secondary coil Lp2 of transformer T. The anode terminal of diode Do2 is connected to the other terminal of secondary coil Lp2. The center tap of secondary coil Lp2 is connected to the other terminal of smoothing capacitor Co and the other terminal of the load. It should be noted that the configuration and operation of current detection circuit 3 shown in [Fig.7] are the same as those of current detection circuit 3 shown in [Fig.l], and therefore the description of the configuration and operation will be omitted.

[0089] When the power converter 1 converts the DC power output of the power supply B into the specified DC power and supplies the specified DC power to the load, the switches Q1, Q4 are turned on and the switches Q2, Q3 are turned off, and then the switches Q1, Q4 are turned off and the switches Q2, Q3 are turned on, by the control circuit 2 shown in [Fig.7]. This switching operation is repeated so that a voltage across the smoothing capacitor Co reaches a target voltage and a current detected by the current detection circuit 3 reaches a target current.When the switches Ql, Q4 are turned on (when the switches Ql, Q4 are in the on state and the switches Q2, Q3 are in the off state), a current flows from the positive terminal of the power supply B to the negative terminal of the power supply B through the switch Ql, the primary coil Lpl and the switch Q4, and a current flows from the secondary coil Lp2 to the load through the diode Dol and the smoothing coil Lo. When the switches Q2, Q3 are turned on (when the switches Ql, Q4 are in the off state and the switches Q2, Q3 are in the on state), a current flows from the positive terminal of the power supply B to the negative terminal of the power supply B through the switch Q3, the primary coil Lpl and the switch Q2, and a current flows from the secondary coil Lp2 to the load through the diode Do2 and the smoothing coil Lo.

[0090] Still in the power converter 1 shown in [Fig.7], when the detection circuit 4 detects the current flowing through the smoothing coil Lo, the power converter 1 does not need to have the function to shift a reference potential of the detection circuit 4 or the voltage across the detection capacitor Cd, so as to avoid the increase in manufacturing costs of the power converter 1. In addition, still in the power converter 1 shown in [Fig.7], the voltage across the detection capacitor Cd increases as the turns ratio n increases, so that the voltage across the detection capacitor Cd is not easily affected by the quantization error in the detection circuit 4 when an analog value is converted into a digital value in the voltage across the detection capacitor Cd. This can improve the current detection accuracy. Also in the power converter 1 shown in [Fig.7], the current iL flowing in the smoothing coil Lo does not need to be corrected after being detected, which can avoid the increase in the detection time of the current iL. <Sixième modification>

[0091] [Fig.8] is a diagram illustrating a sixth modification of the power converter 1 according to the embodiment. It should be noted that in [Fig.8], the same components as those illustrated in [Fig.l] have the same reference numbers and may not be repeated.

[0092] The power converter 1 illustrated in [Fig.8] is an active clamp forward converter which converts a DC power output of a high voltage battery BH into a specified DC voltage and supplies the specified DC voltage to a low voltage battery BL.

[0093] That is, the power converter 1 shown in [Fig.8] comprises relays Rel, Re2, a smoothing capacitor Cb, switches Ql, Q2, capacitor Cs, transformer T, switches Q5, Q6, smoothing coil Lo, smoothing capacitor Co, control circuit 2 and current detection circuit 3. It should be noted that switches Q5, Q6 are each formed of a MOSFET for example. The drain terminal of switch Ql is connected to the source terminal of switch Q2 and the first terminal of the primary coil Lpl of transformer T, and the source terminal of switch Ql is connected to a negative terminal of high-voltage battery BH via relay Rel and to a terminal of smoothing capacitor Cb. The drain terminal of switch Q2 is connected to a positive terminal of high-voltage battery BH through capacitor Cs and relay Re2.The drain terminal of switch Q2 is also connected to the other terminal of primary coil Lpl and to the other terminal of smoothing capacitor Cb through capacitor Cs. One drain terminal of switch Q5 is connected to one drain terminal of switch Q6. The drain terminal of switch Q5 is also connected to the first terminal of smoothing capacitor Co and to a positive terminal of low voltage battery BL through smoothing coil Lo. One source terminal of switch Q5 is connected to the first terminal of secondary coil Lp2 of transformer T, to the other terminal of smoothing capacitor Co and to a negative terminal of low voltage battery BL. One source terminal of switch Q6 is connected to the other terminal of secondary coil Lp2.

[0094] The current detection circuit 3 illustrated in [Fig.8] comprises the detection coil Ld, the detection resistor Rd, the detection capacitor Cd, the detection circuit 4 and the offset resistors RI, R2.

[0095] The detection coil Ld is wound around the core Cre of the smoothing coil Lo.

[0096] The sense resistor Rd and the sense capacitor Cd are connected in series with each other and are connected in parallel to the sense coil Ld.

[0097] The offset resistors RI, R2 are connected between a constant voltage power supply Pvc and a reference potential of the detection circuit 4 in series with each other. A node between the offset resistors RI, R2 is connected to a node between the detection coil Ld and the detection capacitor Cd. Thus, the total voltage of a voltage across the detection capacitor Cd and a voltage across the offset resistor R2 is input to the detection circuit 4. That is, through the offset resistors RI, R2, the voltage across the detection capacitor Cd is shifted by a difference between an electric potential at the node between the offset resistors RI, R2 and the reference potential of the detection circuit 4, and once shifted, the voltage of the detection capacitor Cd is input to the detection circuit 4.The detection circuit 4 substitutes the voltage Vc across the detection capacitor Cd, which has been shifted in the above-described equation 2 to obtain the current iL flowing in the smoothing coil Lo. Therefore, while the current flowing in the forward direction through the smoothing coil Lo is detected based on a voltage higher than the electric potential at the node between the shift resistors RI, R2, of the voltage input to the detection circuit 4, the current flowing in the reverse direction in the smoothing coil Lo is detected based on a voltage lower than the electric potential at the node between the shift resistors RI, R2, of the voltage input to the detection circuit 4.

[0098] In the power converter 1 shown in [Fig.8], the electric potential at the smoothing capacitor Cb is zero before the power converter 1 is started. Before a normal operation in which the DC power output by the high-voltage battery BH is converted into specified DC power and the specified DC power is supplied to the low-voltage battery BL, the relays Rel, Re2 are set to an electrically disconnected state by the control circuit 2, and the smoothing capacitor Cb is charged in advance by power supplied from the low-voltage battery BL. After that, the relays Rel, Re2 are set to an electrically connected state by the control circuit 2 and power is supplied from the high-voltage battery BH to the low-voltage battery BL.With this operation, when the relays Rel, Re2 change from the electrically disconnected state to the electrically connected state, a relatively large inrush current is prevented from flowing from the high voltage battery BH to the smoothing capacitor Cb.

[0099] For example, it is assumed that the direction of current flow from the high-voltage battery BH to the low-voltage battery BL is defined as forward direction, and the direction of current flow from the low-voltage battery BL to the high-voltage battery BH is defined as reverse direction. Furthermore, an input voltage range of the detection circuit 4 for its analog-to-digital conversion is defined as a range of 0 [V] to 5 [V], and the electric potential at the node between the shift resistors RI, R2 is defined as 2.5 [V]. The voltage across the detection capacitor Cd, once shifted, is represented by Vc.

[0100] In this case, the relays Rel, Re2 are first turned off by the control circuit 2, the switch Q1 is constantly turned off, and the switches Q2, Q5, Q6 are repeatedly turned on and off by the control circuit 2, so that the current in the reverse direction detected by the current detection circuit 3 reaches a target value. When the switch Q6 is turned on (when the switches Ql, Q2, Q5 are in the off state and the switch Q6 is in the on state), a current flows from the low-voltage battery BL to the secondary coil Lp2, and a current flows from the primary coil Lpl through the smoothing capacitor Cb. At this time, the direction of the current flowing through the smoothing coil Lo is the reverse direction.When switch Q6 is turned off (when switches Ql, Q6 are in the off state and switches Q2, Q5 are in the on state), transformer T is reset and the current flowing in the reverse direction through the smoothing coil Lo increases. In other words, in this case too, the direction of the current flowing through the smoothing coil Lo is the reverse direction. Therefore, the voltage input to the detection circuit 4 is less than 2.5 [V] and greater than or equal to 0 [V], so that the detection circuit 4 detects the current flowing in the reverse direction through the smoothing coil Lo. This allows the smoothing capacitor Cb to be charged before the relays Rel, Re2 are put in the electrically connected state. It should be noted that switch Ql can be turned on and off in synchronization with switch Q6.

[0101] Then, when the voltage across the smoothing capacitor Cb is greater than or equal to a threshold voltage (for example, a voltage of the high voltage battery BH), the control circuit 2 puts the relays Rel, Re2 in the electrically connected state.

[0102] Then, the switches Q5, Q6 are alternately and repeatedly turned on and off, and the switches Q1, Q2 are alternately and repeatedly turned on and off by the control circuit 2, so that the voltage across the smoothing capacitor Co reaches a target voltage and the current detected in the forward direction by the current detection circuit 3 reaches a target current. When the switches Q1, Q6 are turned on (when the switches Q1, Q6 are in the on state and the switches Q2, Q5 are in the off state), a current flows from the high-voltage battery BH to the primary coil Lpl, and a current flows from the secondary coil Lp2 to the low-voltage battery BL through the switch Q6 and the smoothing coil Lo. When the switch Q2 is turned on (when the switches Ql, Q6 are in the off state and the switches Q2, Q5 are in the on state), a current flows from the primary coil Lpl to the capacitor Cs through the switch Q2, so that the transformer T in the magnetic saturation state is gradually demagnetized. In addition, on one side of the low-voltage battery BL, a current flows from the switch Q5 to the low-voltage battery BL through the smoothing coil Lo. Here, the voltage input to the detection circuit 4 is greater than 2.5 [V] and less than or equal to 5 [V], and the detection circuit 4 detects the forward current flowing in the smoothing coil Lo.

[0103] Still in the power converter 1 shown in [Fig.8], the voltage across the detection capacitor Cd increases as the turns ratio n increases, so that the voltage across the detection capacitor Cd is not easily affected by the quantization error in the detection circuit 4 when an analog value is converted into a digital value in the voltage across the detection capacitor Cd. This can improve the current detection accuracy. Still in the power converter 1 shown in [Fig.8], the current iL flowing in the smoothing coil Lo does not need to be corrected after being detected, thereby avoiding the increase in the detection time of the current iL.

Claims

Claims

1. A power converter (1) having a coil, comprising: a detection coil (Ld) which is magnetically coupled to the coil; a detection resistor (Rd) and a detection capacitor (Cd) which are connected in series with each other and in parallel with the detection coil (Ld); and a detection circuit (4) which detects a current flowing in the coil on the basis of a voltage across the detection capacitor (Cd).

2. Power converter (1) according to claim 1, characterized in that the coil is a smoothing coil (Lo) which makes it possible to smooth the current flowing in the power converter (1).

3. A power converter (1) according to claim 2, characterized in that: the smoothing coil (Lo) has a core (Cre), and the detection coil (Ld) is formed by winding around the core (Cre).

4. Power converter (1) according to claim 3, characterized in that the core has a spacing (AG).

5. Power converter (1) according to claim 1, characterized in that, in the case where the number of turns of the coil represents N1 and the number of turns of the detection coil (Ld) represents N2, N2 / N1 is less than or equal to 10.

6. A power converter (1) according to claim 1, further comprising two offset resistors (RI, R2) which are connected between a constant voltage source (Pvc) and a reference potential of the detection circuit (4) in series with each other, characterized in that the two offset resistors (RI, R2) shift the voltage across the detection capacitor (Cd) by a difference between an electrical potential at a node between the two offset resistors (RI, R2) and the reference potential of the detection circuit (4).

7. Power converter (1) according to claim 2, characterized in that: the smoothing coil (Lo) is arranged on at least one of main surfaces of a printed circuit board on which the power converter (1) is mounted, and the detection coil (Ld) is arranged relative to the smoothing coil (Lo) in the thickness direction of the printed circuit board.

8. A power converter (1) according to claim 7, characterized in that: the printed circuit board is a multi-layer printed circuit board (Sb), and the detection coil (Ld) is arranged on an inner layer of the printed circuit board in a wiring pattern.

9. A current detection circuit (3) for detecting a current flowing in a coil provided in a power converter (1), the current detection circuit (3) comprising: a detection coil (Ld) which is magnetically coupled to the coil; a detection resistor (Rd) and a detection capacitor (Cd) which are connected in series with each other and in parallel with the detection coil (Ld); and a detection circuit (4) which detects a current flowing in the coil on the basis of a voltage across the detection capacitor (Cd).

Images