Full-wave rectifier circuit and power supply circuit

Abstract

This provides a full-wave rectifier circuit that can carry input current even when the AC voltage is in a low phase. [Solution] The full-wave rectifier circuit comprises first and second input lines to which an AC voltage is applied, an output line to which a full-wave rectified voltage is output, and a ground line to which the circuit is grounded, and further comprises: a first diode whose anode is connected to the first input line and whose cathode is connected to the output line; a second diode whose anode is connected to the ground line and whose cathode is connected to the first input line; a third diode whose anode is connected to the second input line and whose cathode is connected to the output line; a fourth diode whose anode is connected to the ground line and whose cathode is connected to the second input line; and first to fourth capacitors connected in parallel to each of the first to fourth diodes.

Description

Technical Field

[0001] The present invention relates to a full-wave rectifier circuit and a power supply circuit.

Background Art

[0002] For example, some full-wave rectifier circuits form a diode bridge using four diodes (for example, Patent Documents 1 to 3).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, a full-wave rectifier circuit is often used in a general power factor correction circuit to generate a full-wave rectified voltage from an AC voltage. However, when the AC voltage has a low phase angle, the diodes of the full-wave rectifier circuit turn off, so that no input current flows through the full-wave rectifier circuit, and the input current may be distorted.

[0005] The present invention has been made in view of the above conventional problems, and an object thereof is to provide a full-wave rectifier circuit that can pass an input current even when the AC voltage has a low phase angle.

Means for Solving the Problems

[0006] The full-wave rectifier circuit of the present invention, which solves the aforementioned problems, is a full-wave rectifier circuit comprising first and second input lines to which an AC voltage is applied, an output line that outputs a full-wave rectified voltage, and a ground line that is grounded, the full-wave rectifier circuit comprising: a first diode whose anode is connected to the first input line and whose cathode is connected to the output line; a second diode whose anode is connected to the ground line and whose cathode is connected to the first input line; a third diode whose anode is connected to the second input line and whose cathode is connected to the output line; a fourth diode whose anode is connected to the ground line and whose cathode is connected to the second input line; and first to fourth capacitors connected in parallel to each of the first to fourth diodes.

[0007] The power supply circuit of the present invention, which solves the aforementioned problems, is a power supply circuit that generates an output voltage of a target level from an AC voltage, and comprises: a full-wave rectifier circuit to which the AC voltage is applied and which outputs a full-wave rectified voltage; an inductor to which the full-wave rectified voltage is applied; a transistor that controls the inductor current flowing through the inductor; and a switching control circuit that controls the switching of the transistor, wherein the full-wave rectifier circuit includes first and second input lines to which the AC voltage is applied; an output line that outputs the full-wave rectified voltage for power factor correction; a ground line that is grounded; a first diode whose anode is connected to the first input line and whose cathode is connected to the output line; a second diode whose anode is connected to the ground line and whose cathode is connected to the first input line; a third diode whose anode is connected to the second input line and whose cathode is connected to the output line; a fourth diode whose anode is connected to the ground line and whose cathode is connected to the second input line; and first to fourth capacitors connected in parallel to each of the first to fourth diodes. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a full-wave rectifier circuit that can carry input current even when the AC voltage has a low phase angle. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows an example of a typical AC-DC converter 10. [Figure 2] This figure shows an example of the configuration of the power factor correction IC23. [Figure 3] This figure shows an example of the operation of the power factor correction IC23. [Figure 4] This figure shows an example of the operation of the power factor correction IC23. [Figure 5] This figure shows the relationship between the input current Iin, the inductor current IL, and the discharge current Ic of the capacitor 21. [Figure 6A] This figure shows an example of the current flowing through the full-wave rectifier circuit 20a. [Figure 6B] This figure shows an example of the current flowing through the full-wave rectifier circuit 20a. [Figure 6C] This figure shows an example of the current flowing through the full-wave rectifier circuit 20a. [Figure 6D] This figure shows an example of the current flowing through the full-wave rectifier circuit 20a. [Figure 7A] This figure shows an example of the current flowing through the full-wave rectifier circuit 20a. [Figure 7B] This figure shows an example of the current flowing through the full-wave rectifier circuit 20a. [Figure 7C] This figure shows an example of the current flowing through the full-wave rectifier circuit 20a. [Figure 7D] This figure shows an example of the current flowing through the full-wave rectifier circuit 20a. [Figure 8] This figure shows an example of an AC-DC converter 12. [Figure 9] This figure shows the relationship between the input current Iin, the inductor current IL, and the discharge currents of capacitors C1 to C4. [Figure 10A] This figure shows an example of the current flowing through the full-wave rectifier circuit 20b. [Figure 10B] This figure shows an example of the current flowing through the full-wave rectifier circuit 20b. [Figure 10C] This figure shows an example of the current flowing through the full-wave rectifier circuit 20b. [Figure 10D] It is a diagram showing an example of the current flowing through the full-wave rectifier circuit 20b. [Figure 11A] It is a diagram showing an example of the current flowing through the full-wave rectifier circuit 20b. [Figure 11B] It is a diagram showing an example of the current flowing through the full-wave rectifier circuit 20b. [Figure 11C] It is a diagram showing an example of the current flowing through the full-wave rectifier circuit 20b. [Figure 11D] It is a diagram showing an example of the current flowing through the full-wave rectifier circuit 20b. [Figure 12] It is a diagram for explaining the capacitance values of the capacitors C1 to C4.

Embodiments for Carrying Out the Invention

[0010] From the description in this specification and the accompanying drawings, at least the following matters become clear. In the following, the same or equivalent components, members, etc. shown in each drawing are denoted by the same reference numerals, and redundant descriptions may be omitted as appropriate.

[0011] =====This Embodiment===== FIG. 1 is a diagram showing an example of the configuration of a general AC-DC converter 10. The AC-DC converter 10 is a boost chopper type power supply circuit that generates an output voltage Vout at a target level from the AC voltage Vac of a commercial power supply.

[0012] The load 11 is, for example, a DC-DC converter or an electronic device operating with a DC voltage.

[0013] ===Outline of the General AC-DC Converter 10=== The AC-DC converter 10 includes a full-wave rectifier circuit 20a, capacitors C0, 21, 26, 33, 34, a transformer 22, a power factor correction IC 23, an NMOS transistor 24, a diode 25, and resistors 30 to 32.

[0014] Capacitor C0 is placed between the first input line L0 and the second input line L1 to suppress noise generated in the input current Iin.

[0015] The full-wave rectifier circuit 20a full-wave rectifies a predetermined AC voltage Vac input from the first input line L0 and the second input line L1, and applies the full-wave rectified voltage Vrec from the output line L2 to the capacitor 21 and the main coil La of the transformer 22. The full-wave rectifier circuit 20a also has a ground line L3. Here, the AC voltage Vac is, for example, a voltage with a range of 100 to 240V and a frequency of 50 to 60Hz.

[0016] Furthermore, although the full-wave rectified voltage Vrec is applied directly to the main coil La, it may also be applied via an element such as a resistor (not shown).

[0017] Capacitor 21 is an element that absorbs the ripple component of the inductor current IL of the main coil La and prevents it from flowing out to the power supply side. When the NMOS transistor 24 is turned on, a full-wave rectified voltage Vrec is applied across the main coil La. On the other hand, when the NMOS transistor 24 is turned off, the main coil La supplies current to capacitor 26 via diode 25. Then, in addition to the ripple current mentioned above, current flows through capacitor 21 due to the application of the full-wave rectified voltage Vrec. This is in accordance with the capacitor's characteristics, which are determined by dVrec / dt, the derivative of the full-wave rectified voltage Vrec with respect to time. As will be described in detail later, when the full-wave rectified voltage Vrec rises and dVrec / dt > 0, capacitor 21 is charged, and when the full-wave rectified voltage Vrec falls and dVrec / dt < 0, capacitor 21 is discharged.

[0018] Furthermore, the main coil La, together with the NMOS transistor 24, diode 25, and capacitor 26, constitutes a boost chopper circuit. Therefore, the charging voltage of capacitor 26 becomes the DC output voltage Vout. The output voltage Vout is, for example, 390V.

[0019] The transformer 22 includes a main coil La and an auxiliary coil Lb that is magnetically coupled to the main coil La. In this embodiment, the auxiliary coil Lb is wound such that the voltage generated in the auxiliary coil Lb has the opposite polarity to the voltage generated in the main coil La. The voltage Vzcd generated in the auxiliary coil Lb is then applied to terminal ZCD of the power factor correction IC 23.

[0020] The power factor correction IC23 is an integrated circuit that controls the switching of the NMOS transistor 24 so that the output voltage Vout level reaches a target level (e.g., 390V) while improving the power factor of the AC-DC converter 10. Specifically, the power factor correction IC23 drives the NMOS transistor 24 based on the inductor current IL flowing through the main coil La and the output voltage Vout.

[0021] Details of the power factor correction IC23 will be described later, but the power factor correction IC23 is equipped with terminals ZCD, FB, COMP, and OUT. In addition to the four terminals ZCD, FB, COMP, and OUT mentioned above, the power factor correction IC23 is also equipped with other terminals, but these are omitted here for convenience.

[0022] The NMOS transistor 24 is a transistor for controlling the power supplied by the AC-DC converter 10 to the load 11. In this embodiment, the NMOS transistor 24 is a MOS (Metal Oxide Semiconductor) transistor, but it is not limited to this. The NMOS transistor 24 may be any transistor capable of controlling power, such as a bipolar transistor. The gate electrode of the NMOS transistor 24 is connected to terminal OUT so as to be driven by the voltage Vdr from terminal OUT.

[0023] Resistors 30 and 31 form a voltage divider circuit that divides the output voltage Vout, generating the feedback voltage Vfb used when switching the NMOS transistor 24. The feedback voltage Vfb generated at the node to which resistors 30 and 31 are connected is applied to terminal FB.

[0024] The resistor 32 and capacitors 33 and 34 are phase compensation elements for the stable operation of the AC-DC converter 10, which includes a power factor correction IC 23 that provides feedback control of the NMOS transistor 24. The resistor 32 and capacitor 33 are connected in series between terminal COMP and ground, and capacitor 34 is connected in parallel with them.

[0025] ===Configuration of Power Factor Correction IC23=== Figure 2 shows an example of the configuration of the power factor correction IC 23. The power factor correction IC 23 drives the NMOS transistor 24 based on the inductor current IL and the feedback voltage Vfb. The power factor correction IC 23 is composed of comparator circuits 100, 106, a delay circuit 101, an SR flip-flop 102, a buffer 103, an error voltage output circuit 104, and an oscillator circuit 105.

[0026] The comparator circuit 100 detects when the inductor current IL becomes zero based on the voltage Vzcd at terminal ZCD. Specifically, the comparator circuit 100 compares the voltage Vzcd with the reference voltage Vref0, and when the voltage Vzcd becomes lower than the reference voltage Vref0, it outputs a high-level (hereinafter referred to as "H" level) signal Vdet, indicating that the inductor current IL has become zero. On the other hand, when the voltage Vzcd becomes higher than the reference voltage Vref0, the comparator circuit 100 outputs a low-level (hereinafter referred to as "L" level) signal Vdet.

[0027] The delay circuit 101 outputs a pulse signal Sset to turn on the NMOS transistor 24 after a predetermined period td has elapsed since the inductor current IL became zero. Specifically, the delay circuit 101 outputs a "H" level pulse signal Sset after a predetermined period td has elapsed since the rising edge of the signal Vdet from the comparator circuit 100. On the other hand, the delay circuit 101 does not output a pulse signal Sset if the comparator circuit 100 outputs a "L" level signal Vdet.

[0028] The SR flip-flop 102 outputs a drive signal Vq1 for switching the NMOS transistor 24. Specifically, when the delay circuit 101 outputs a high-level pulse signal Sset, the SR flip-flop 102 outputs a high-level drive signal Vq1 to turn on the NMOS transistor 24. On the other hand, when the comparator circuit 106 (described later) outputs a high-level signal Sreset, the SR flip-flop 102 outputs a low-level drive signal Vq1 to turn off the NMOS transistor 24.

[0029] Buffer 103 switches the NMOS transistor 24 based on the drive signal Vq1. Specifically, when SR flip-flop 102 outputs a high-level signal Vq1, buffer 103 outputs a voltage Vdr that turns on the NMOS transistor 24. On the other hand, when SR flip-flop 102 outputs a low-level signal Vq1, buffer 103 outputs a voltage Vdr that turns off the NMOS transistor 24.

[0030] The error voltage output circuit 104 generates an error current Ierr according to the error between a reference voltage Vref1 corresponding to the output voltage Vout at the target level and the feedback voltage Vfb, charges capacitors 33 and 34 via terminal COMP, and generates a voltage Vcomp.

[0031] The oscillator circuit (OSC) 105 generates the oscillation voltage Vramp required to turn off the NMOS transistor 24. Specifically, when the inductor current IL becomes zero and a high-level drive signal Vq1 is input, the oscillator circuit 105 outputs an oscillation voltage Vramp whose amplitude gradually increases with a predetermined slope.

[0032] The comparator circuit 106 compares the voltage Vcomp with the oscillation voltage Vramp to determine the timing for turning off the NMOS transistor 24. Specifically, the voltage Vcomp is applied to the inverting input line of the comparator circuit 106, and the oscillation voltage Vramp is applied to the non-inverting input line of the comparator circuit 106. Therefore, the comparator circuit 106 outputs a "L" level signal Sreset when the level of the oscillation voltage Vramp is lower than the level of the voltage Vcomp, and outputs a "H" level signal Sreset when the level of the oscillation voltage Vramp is higher than the level of the voltage Vcomp.

[0033] ===Operation of Power Factor Correction IC23=== Figure 3 shows an example of the operation of the power factor correction IC23.

[0034] At time t0, when the power factor correction IC 23 outputs a voltage Vdr that turns on the NMOS transistor 24, the NMOS transistor 24 turns on. When the NMOS transistor 24 turns on, the oscillator circuit 105 starts outputting an oscillation voltage Vramp having a predetermined slope.

[0035] At time t1, when the oscillation voltage Vramp becomes higher than the voltage Vcomp, the comparator circuit 106 outputs a high-level signal Sreset. Then, the SR flip-flop 102 outputs a low-level signal Vq1, and the buffer 103 outputs a voltage Vdr that turns off the NMOS transistor 24.

[0036] At time t2, when the inductor current IL becomes zero, the comparator circuit 100 outputs a signal Vdet at the "H" level.

[0037] At time t3, after a predetermined period td has elapsed from time t2, the delay circuit 101 outputs a pulse signal Sset at the "H" level. When the delay circuit 101 outputs the pulse signal Sset at the "H" level, the SR flip-flop 102 outputs a drive signal Vq1 at the "H" level, and the buffer 103 outputs a voltage Vdr that turns on the NMOS transistor 24. The NMOS transistor 24 is then turned on. The same operation is repeated thereafter.

[0038] Here, when the AC-DC converter 10 generates an output voltage Vout of the desired level from a predetermined AC voltage Vac, the capacitance of the capacitor 26 is sufficiently large, and the feedback voltage Vfb remains almost constant for a period of about one cycle of Vac. As a result, the on-period of the NMOS transistor 24 (for example, the period from time t0 to t1) also remains almost constant.

[0039] Furthermore, when the NMOS transistor 24 is turned on, if the level of the voltage Vrec obtained by rectifying the AC voltage Vac increases, the current value of the inductor current IL also increases. As a result, as shown in Figure 4, the waveform of the peak value of the inductor current IL is similar in shape to that of the voltage Vrec. Therefore, since the input current Iin is the average value of the inductor current IL, it is similar in shape to that of the voltage Vrec, and the power factor of the AC-DC converter 10 approaches 1.

[0040] Furthermore, if the peak value level of the inductor current IL when the NMOS transistor 24 is turned off is high, the time it takes for the inductor current IL to become zero when the NMOS transistor 24 is turned off becomes longer. Therefore, when the voltage Vrec level is low, the switching frequency of the NMOS transistor 24 becomes high, and when the voltage Vrec level is high, the switching frequency of the NMOS transistor 24 becomes low. In other words, when the phase angle of the AC voltage Vac is low, the switching frequency of the NMOS transistor 24 becomes high, and when the phase angle of the AC voltage Vac is high, the switching frequency of the NMOS transistor 24 becomes low.

[0041] Furthermore, a "high phase angle" of an AC voltage Vac means that the angle is in the range of, for example, 90 ± 10 + 180n degrees, i.e., (80 to 100) + 180n degrees. On the other hand, a "low phase angle" means that the angle is in the range of, for example, 0 ± 10 + 180n degrees, i.e., (-10 to +10) + 180n degrees. Here, n is an integer.

[0042] ===Configuration of a typical full-wave rectifier circuit 20a=== As described above, the full-wave rectifier circuit 20a receives the AC voltage Vac applied to the first input line L0 and the second input line L1, performs full-wave rectification of the AC voltage Vac, and outputs the full-wave rectified voltage Vrec from the output line L2. The ground line L3 of the full-wave rectifier circuit 20a is grounded. Here, "grounding" means connecting to the circuit's reference potential, i.e., GND, and does not necessarily mean connecting to the earth potential. The same applies to the following explanation.

[0043] As shown in Figure 1, the full-wave rectifier circuit 20a includes diode D1 having an anode connected to the first input line L0 and a cathode connected to the output line L2, diode D2 having an anode connected to the ground line L3 and a cathode connected to the first input line L0, diode D3 having an anode connected to the second input line L1 and a cathode connected to the output line L2, and diode D4 having an anode connected to the ground line L3 and a cathode connected to the second input line L1. Note that diodes D1 to D4 used in the full-wave rectifier circuit 20a are low-speed diodes intended for rectifying commercial frequency components.

[0044] ===Operation of a typical full-wave rectifier circuit 20a and capacitor 21=== Figure 5 shows the relationship between the input current Iin, the inductor current IL, and the discharge current Ic of capacitor 21. The thin solid line represents the input current Iin, the dotted line represents the inductor current IL, and the thick solid line represents the discharge current Ic of capacitor 21. While the actual waveform of the inductor current IL is the triangular wave shown in Figure 4, here we show the average value for each pulse period, excluding the switching ripple current component. Furthermore, this waveform is a full-wave rectified waveform similar to the voltage Vrec, but for comparison with the input current Iin, the waveform with polarity determined according to the positive or negative AC input voltage, i.e., the dropped waveform as seen from the input side of the AC voltage Vac, is shown. Hereafter, the term "inductor current IL" refers to this equivalent waveform. Similarly, the discharge current Ic also includes a switching component, but in the following explanation, the low-frequency component excluding the switching ripple will be referred to as the discharge current Ic. Also, Figure 5 shows the waveform for one period of the AC voltage Vac, and the discharge current Ic of capacitor 21 is depicted with the case where current flows in the discharge direction as positive. Furthermore, in Figures 6A to 6D and 7A to 7D, the inductor current IL flowing through the main coil La is shown by a solid line, and the current Ic flowing through capacitor 21 is shown by a dashed line. The dashed arrows indicate the positive or negative polarity of the AC voltage Vac; when the arrow points upward, the AC voltage Vac is positive, and when the arrow points downward, the AC voltage Vac is negative. Also, α represents dVrec / dt.

[0045] Between 20 milliseconds and 25 milliseconds, when the AC voltage Vac increases as a positive voltage, α > 0. When the AC voltage Vac becomes higher than the charging voltage Vc of capacitor 21, diode D1 turns on, and consequently D4 also turns on. Diode D3 turns off because a reverse voltage is applied, and consequently diode D2 also turns off. Also, since α > 0, capacitor 21 is charged, and the inductor current IL and current Ic flow as shown in Figure 6A. That is, the inductor current IL flows to the main coil La through the ON diode D1 and returns to the commercial power supply through the ON diode D4. Also, current Ic charges capacitor 21 through diode D1 and returns to the commercial power supply through diode D4. Therefore, the input current Iin is the sum of the inductor current IL and current Ic. In Figure 5, the case where current flows through capacitor 21 in the discharge direction is depicted as positive. Therefore, in this case, the current Ic is negative, and the input current Iin is the sum of the inductor current IL and the absolute value of the current Ic. The ringing of the input current Iin and current Ic between time 20 milliseconds and time 22 milliseconds will be described later.

[0046] Between 25 milliseconds and 29 milliseconds, when the AC voltage Vac decreases as a positive voltage, α < 0. In this case, since the inductor current IL is greater than the current Ic, diode D1 turns on, and consequently D4 also turns on. Diode D3 turns off because a reverse voltage is applied, and consequently diode D2 also turns off. Also, since α < 0, capacitor 21 is discharged, and the inductor current IL and current Ic flow as shown in Figure 6B. That is, the inductor current IL flows to the main coil La through the ON diode D1 and returns to the commercial power supply through the ON diode D4. Also, current Ic returns to the commercial power supply through diode D1 and flows from the commercial power supply through diode D4.

[0047] Between 29 milliseconds and 30.5 milliseconds, when the AC voltage Vac > 0 but is close to zero volts, the inductor current IL becomes small. On the other hand, since the rate of change of a sine wave is maximum when its value is zero, the discharge current of capacitor 21 increases and at some point becomes equal to the inductor current IL. Beyond this point, the current flowing in from the diode bridge, i.e. (inductor current IL - discharge current Ic of capacitor 21), tries to become negative, but since diodes do not conduct current of the opposite polarity, as a result, the charging voltage Vc of capacitor 21 becomes higher than the AC voltage Vac. As shown in Figure 6C, diodes D1 to D4 are turned off, and capacitor 21 is disconnected from the AC input. In this case, the inductor current IL and the current Ic are equal. After passing 30 milliseconds, the sign of the AC voltage Vac changes. Similarly, when the AC voltage Vac < 0 but is close to zero volts, diodes D1 to D4 are turned off, as shown in Figure 6D.

[0048] Between 30.5 milliseconds and 32 milliseconds, as the AC voltage Vac increases as a negative voltage, α > 0. When the absolute voltage level of the AC voltage Vac becomes higher than the charging voltage Vc of capacitor 21, diodes D2 and D3 turn on as shown in Figure 7A, and capacitor 21 is charged. At this timing, that is, when the AC voltage Vac increases from near zero volts as a negative voltage, α is almost at its maximum, and the current Ic flowing through capacitor 21 is at its maximum. Therefore, because the current Ic changes in a step-like manner due to the conduction of the diodes, the inductance component of the AC power supply circuit (not shown) and capacitors C0 and C21 undergo LC resonance, and the input current Iin also rings. Similarly, between 20 milliseconds and 22 milliseconds, when the AC voltage Vac increases from near zero volts as a positive voltage, α is almost at its maximum, and ringing occurs in both the current Ic and the input current Iin.

[0049] Furthermore, between 30 milliseconds and 35 milliseconds, when the AC voltage Vac becomes a large negative voltage, α > 0. In this case, since the absolute voltage level of the AC voltage Vac is higher than the voltage level of the charging voltage Vc of capacitor 21, diode D3 turns on, and consequently D2 also turns on, diode D1 turns off because a reverse voltage is applied, and consequently diode D4 also turns off. Also, since α > 0, capacitor 21 is charged, and the inductor current IL and current Ic flow as shown in Figure 7A. That is, the inductor current IL flows to the main coil La through the ON diode D3 and returns to the commercial power supply through the ON diode D2. Also, current Ic charges capacitor 21 through diode D3 and returns to the commercial power supply through diode D2. Therefore, the input current Iin is the sum of the inductor current IL and current Ic. Note that in Figure 5, the case where current flows in the discharge direction through capacitor 21 is depicted as positive. Therefore, in this case, the current Ic is negative, and the input current Iin is the sum of the absolute value of the inductor current IL and the absolute value of the current Ic.

[0050] Between 35 milliseconds and 39 milliseconds, the AC voltage Vac becomes a negative voltage, and α < 0. In this case, the inductor current IL is greater than the current Ic, so diode D3 turns on, and consequently D2 also turns on. Diode D1 turns off because a reverse voltage is applied, and consequently diode D4 also turns off. Also, since α < 0, capacitor 21 is discharged, and the inductor current IL and current Ic flow as shown in Figure 7B. That is, the inductor current IL flows to the main coil La through the ON diode D3 and returns to the commercial power supply through the ON diode D2. Also, current Ic returns to the commercial power supply through diode D3 and flows from the commercial power supply through diode D2.

[0051] Between 39 milliseconds and 40 milliseconds, the sign of the AC voltage Vac changes. When the AC voltage Vac is < 0 but close to zero volts, the charging voltage Vc of capacitor 21 becomes higher than the AC voltage Vac, and diodes D1 to D4 turn off, as shown in Figure 7C. In this case, the inductor current IL and the current Ic match, and no current flows through the full-wave rectifier circuit 20a. Similarly, when the AC voltage Vac is > 0 but close to zero volts beyond 40 milliseconds, diodes D1 to D4 turn off, as shown in Figure 7D.

[0052] Therefore, in a typical full-wave rectifier circuit 20a, for example, when diodes D1 to D4 are turned off between 29 milliseconds and 30 milliseconds, the input current Iin becomes zero during that time, causing distortion in the input current Iin and leading to a deterioration of the power factor.

[0053] ===Overview of AC-DC Converter 12=== The AC-DC converter 12 consists of a full-wave rectifier circuit 20b, capacitors C0, 21, 26, 33, 34, a transformer 22, a power factor correction IC 23, an NMOS transistor 24, a diode 25, and resistors 30-32. The main coil La of the transformer 22 corresponds to an "inductor," and the power factor correction IC 23 corresponds to a "switching control circuit."

[0054] ===Configuration of Full-Wave Rectifier Circuit 20b=== In the full-wave rectifier circuit 20b, similar to the full-wave rectifier circuit 20a, an AC voltage Vac is applied to the first input line L0 and the second input line L1, the AC voltage Vac is full-wave rectified, and the full-wave rectified voltage Vrec is output from the output line L2. In addition, the ground line L3 of the full-wave rectifier circuit 20b is grounded.

[0055] As shown in Figure 8, the full-wave rectifier circuit 20b includes a diode D1 having an anode connected to the first input line L0 and a cathode connected to the output line L2, a diode D2 having an anode connected to the ground line L3 and a cathode connected to the first input line L0, a diode D3 having an anode connected to the second input line L1 and a cathode connected to the output line L2, a diode D4 having an anode connected to the ground line L3 and a cathode connected to the second input line L1, and capacitors C1 to C4 connected in parallel to diodes D1 to D4. Note that each of diodes D1 to D4 corresponds to the "first to fourth diodes," and each of capacitors C1 to C4 corresponds to the "first to fourth capacitors."

[0056] ===Operation of full-wave rectifier circuit 20b and capacitors C1~C4=== Figure 9 shows the relationship between the input current Iin, the inductor current IL, the discharge currents Ic23 through capacitors C2 and C3, and the discharge currents Ic14 through capacitors C1 and C4. The thin solid line represents the input current Iin, the thin dotted line represents the inductor current IL, the thick solid line represents the discharge currents Ic23 through capacitors C2 and C3, and the thick dotted line represents the discharge currents Ic14 through capacitors C1 and C4. Figure 9 also shows the waveform for one cycle of the AC voltage Vac, with the discharge currents Ic23 and Ic14 drawn with the case where current flows in the discharge direction being considered positive. Furthermore, in Figures 10A to 10D and 11A to 11D, the inductor current IL flowing through the main coil La is shown with a solid line, and the currents Ic23 and Ic14 flowing through capacitors C1 to C4 are shown with dashed lines. Similar to Figure 5, the inductor current IL is calculated by removing the switching ripple component and determining the polarity according to the voltage polarity of the AC power supply. Similarly, the discharge currents Ic23 and Ic14 also exclude switching ripple. The dashed arrows indicate the positive and negative polarity of the AC voltage Vac; an upward arrow indicates a positive voltage Vac, and a downward arrow indicates a negative voltage Vac. α represents dVrec / dt. Current Ic23 is the current flowing through capacitors C2 and C3, and current Ic14 is the current flowing through capacitors C1 and C4. The charging voltages of capacitors C1 to C4 are denoted as voltages Vc1, Vc2, Vc3, and Vc4, respectively.

[0057] Between 20 milliseconds and 25 milliseconds, when the AC voltage Vac increases as a positive voltage, α > 0. When the AC voltage Vac becomes higher than the charging voltage Vc3 of capacitor C3, diode D1 turns on, and consequently D4 also turns on. Diode D2 turns off because a reverse voltage is applied, and consequently diode D3 also turns off. Also, since α > 0, capacitors C2 and C3 are charged, and the inductor current IL and current Ic23 flow as shown in Figure 10A. That is, the inductor current IL flows to the main coil La through the ON diode D1 and returns to the commercial power supply through the ON diode D4. Also, current Ic23 charges capacitor C3 through diode D1 and returns to the commercial power supply without going through the diode. Also, current Ic23 charges capacitor C2 without going through the diode and returns to the commercial power supply through diode D4. Therefore, the input current Iin is the sum of the inductor current IL and current Ic23. Note that in Figure 9, the case where current flows in the discharge direction through capacitors C1 to C4 is depicted as positive. Therefore, in this case, the current Ic23 is negative, and the input current Iin is the sum of the inductor current IL and the absolute value of the current Ic23.

[0058] Between 25 milliseconds and 29.5 milliseconds, when the AC voltage Vac decreases as a positive voltage, α < 0. In this case, since the inductor current IL is greater than the current Ic23, diode D1 turns on, and consequently D4 also turns on. Diode D2 turns off because a reverse voltage is applied, and consequently diode D3 also turns off. Also, since α < 0, capacitors C2 and C3 are discharged, and the inductor current IL and current Ic23 flow as shown in Figure 10B. That is, the inductor current IL flows to the main coil La through the ON diode D1 and returns to the commercial power supply through the ON diode D4. Also, current Ic23 flows from the commercial power supply without going through the diodes and returns to the commercial power supply while discharging capacitor C3 through diode D1. Also, current Ic23 flows from the commercial power supply through diode D4 and returns to the commercial power supply without going through the diode while discharging capacitor C2.

[0059] Between 29.5 milliseconds and 30 milliseconds, if the AC voltage Vac > 0 but is close to zero volts, the AC voltage Vac becomes lower than the charging voltage Vc3 of capacitor C3, and diodes D1-D4 turn off. In this case, since the AC voltage Vac is lower than the charging voltages Vc2 and Vc3, as shown in Figure 10C, capacitor C3 discharges to the commercial power supply via capacitor C1. Also, capacitor C2 discharges to the commercial power supply by allowing current to flow through capacitor C4. Inductor current IL also flows through capacitors C1-C4. Thus, despite diodes D1-D4 being off, current flows through the full-wave rectifier circuit 20b. After passing 30 milliseconds, the sign of the AC voltage Vac changes. Similarly, even if the AC voltage Vac < 0 but is close to zero volts, despite diodes D1-D4 being off, current flows through the full-wave rectifier circuit 20b as shown in Figure 10D.

[0060] Furthermore, between 30 milliseconds and 35 milliseconds, when the AC voltage Vac becomes a large negative voltage, α > 0. In this case, since the AC voltage Vac is higher than the charging voltage Vc1 of capacitor C1, diode D3 turns on, and consequently D2 also turns on. Diode D1 turns off because a reverse voltage is applied, and consequently diode D4 also turns off. Also, since α > 0, capacitors C1 and C4 are charged, and the inductor current IL and current Ic14 flow as shown in Figure 11A. That is, the inductor current IL flows to the main coil La through the ON diode D3 and returns to the commercial power supply through the ON diode D2. Also, current Ic14 charges capacitor C1 through diode D3 and returns to the commercial power supply. Also, current Ic14 charges capacitor C4 without going through the diode and returns to the commercial power supply through diode D2. Therefore, the input current Iin is the sum of the inductor current IL and current Ic14. Note that in Figure 9, the case where current flows in the discharge direction through capacitors C1 and C4 is depicted as positive. Therefore, in this case, the current Ic14 is negative, and the input current Iin is the sum of the absolute value of the inductor current IL and the absolute value of the current Ic14.

[0061] Between 35 milliseconds and 39.5 milliseconds, when the AC voltage Vac becomes a negative voltage, α < 0. In this case, since the inductor current IL is greater than the current Ic14, diode D3 turns on, and consequently D2 also turns on. Diode D1 turns off because a reverse voltage is applied, and consequently diode D4 also turns off. Also, since α < 0, capacitors C1 and C4 are discharged, and the inductor current IL and current Ic14 flow as shown in Figure 11B. That is, the inductor current IL flows to the main coil La through the ON diode D3 and returns to the commercial power supply through the ON diode D2. Also, current Ic14 returns to the commercial power supply through diode D3 while discharging capacitor C1. Also, current Ic14 flows from the commercial power supply through diode D2 and returns to the commercial power supply while discharging capacitor C4.

[0062] Between 39.5 milliseconds and 40 milliseconds, if the AC voltage Vac is < 0 but close to zero volts, the AC voltage Vac becomes lower than the charging voltage Vc4 of capacitor C4, and diodes D1 to D4 turn off. In this case, because the AC voltage Vac is lower than the charging voltage Vc4, capacitor C4 discharges to the commercial power supply, as shown in Figure 11C. Capacitor C1 also discharges to the commercial power supply via capacitor C3. Inductor current IL flows through capacitors C1 to C4. Thus, despite diodes D1 to D4 being off, current flows through the full-wave rectifier circuit 20b. After passing 40 milliseconds, the sign of the AC voltage Vac changes. Similarly, even if the AC voltage Vac is > 0 but close to zero volts, despite diodes D1 to D4 being off, current flows through the full-wave rectifier circuit 20b, as shown in Figure 11D.

[0063] Therefore, for example, even if diodes D1 to D4 are turned off between 29.5 milliseconds and 30 milliseconds, the input current Iin does not become zero, thus reducing distortion in the input current Iin and leading to improved power factor. This makes it possible to provide a full-wave rectifier circuit that can supply input current even when the AC voltage is at a low phase angle.

[0064] ===Capacitance values ​​of capacitors C1 to C4=== Figure 12 illustrates the capacitance values ​​of capacitors C1 to C4. Figure 12 shows the simulation results for the currents flowing through diodes D1 and D2, the inductor current IL, and the anode-cathode voltage Vak of diodes D1 and D2. The current flowing through diode D1 is shown by a solid line, and the current flowing through diode D2 is shown by a dashed line. Similarly, the voltage Vak across diode D1 is shown by a solid line, and the voltage Vak across diode D2 is shown by a dashed line. Below, we will first focus on the currents flowing through diodes D1 and D2 and the voltage Vak across diodes D1 and D2. The inductor current IL flows throughout the entire simulation period.

[0065] Between 20.3 and 29 milliseconds, diode D1 turns on, and current flows through it. In this case, since diode D1 is on, the voltage Vak across diode D1 is near zero volts. On the other hand, a reverse voltage is applied to diode D2, causing it to turn off, so the voltage Vak across diode D2 becomes a negative voltage corresponding to the AC voltage Vac. Note that the voltages Vak of diodes D1 and D2 are depicted as anode voltages with reference to the cathode.

[0066] Between 29 and 30 milliseconds, diodes D1 and D2 are off, and no current flows through them. However, inductor current IL flows through capacitors C1 to C4. Around 30 milliseconds, the AC voltage Vac changes from positive to negative, and a reverse voltage is applied to diode D1, causing it to turn off. A forward voltage is then applied to diode D2, causing it to turn on. Current then begins to flow through diode D2.

[0067] Between 30 and 40 milliseconds, current flows through diode D2, and the voltage Vak across diode D1 becomes negative.

[0068] Next, we will focus on the simulation result in the lower right, which is magnified to show the voltage Vak across diode D1 from 20.2 milliseconds to 20.4 milliseconds, and explain it below. When diode D1 is off, a reverse voltage is applied to diode D1, so diode D1 turns off. In this case, by adjusting the capacitance values ​​of capacitors C1 to C4, even if a voltage showing a ripple component due to the switching frequency of NMOS transistor 24 is generated across capacitors C1 to C4 when the AC voltage Vac is at a low phase angle, it will not change until it is close to the forward voltage. Therefore, diode D1 will not turn on due to the ripple component.

[0069] On the other hand, after the time 20.3 milliseconds when diode D1 turns on, the ripple component is suppressed by capacitors C1 to C4, and the voltage across capacitors C1 to C4 does not become negative due to the ripple component, so diode D1 does not turn off. Also, as mentioned above, diodes D1 to D4 used in the full-wave rectifier circuit 20b are low-speed diodes intended for rectifying the commercial frequency component, so if diodes D1 to D4 repeatedly turn on and off in a short period of time, the reverse recovery loss may become excessive. However, because the ripple component is suppressed by capacitors C1 to C4, the repeated on and off of diodes D1 to D4 is suppressed, and the reverse recovery loss of diodes D1 to D4 is suppressed.

[0070] Thus, each of capacitors C1 to C4 has a capacitance value such that when each of diodes D1 to D4 is turned on based on the AC voltage Vac, the ripple component prevents diodes D1 to D4 from turning off. This suppresses repeated on / off switching of diodes D1 to D4, and reduces the reverse recovery loss of diodes D1 to D4 when the AC voltage Vac is at a low phase angle.

[0071] ===Summary=== The AC-DC converter 12 of this embodiment has been described above. The full-wave rectifier circuit 20b includes diodes D1 to D4 and capacitors C1 to C4 connected in parallel to each of the diodes D1 to D4. The full-wave rectifier circuit 20b allows the input current Iin to flow through capacitors C1 to C4 even when the diodes D1 to D4 are turned off. This makes it possible to provide a full-wave rectifier circuit that can flow the input current even when the AC voltage is at a low phase angle.

[0072] Furthermore, the AC-DC converter 12 includes a full-wave rectifier circuit 20b, a main coil La, an NMOS transistor 24, and a power factor correction IC 23. This provides a full-wave rectifier circuit that can supply input current even when the AC voltage is at a low phase angle.

[0073] Furthermore, capacitors C1 to C4 have capacitance values ​​such that when each of the diodes D1 to D4 switches from off to on, the ripple component caused by the switching frequency of the NMOS transistor 24 prevents each of the on diodes D1 to D4 from switching off. This suppresses the ripple component of the voltage applied to diodes D1 to D4, similar to capacitor 21 in a typical full-wave rectifier circuit 20a, and suppresses reverse recovery losses due to the on / off switching of diodes D1 to D4 when the AC voltage Vac is at a low phase angle.

[0074] The embodiments described above are provided to facilitate understanding of the present invention and are not intended to limit its interpretation. Furthermore, the present invention may be modified or improved without departing from its spirit, and it goes without saying that equivalents thereof are included. [Explanation of symbols]

[0075] 10,12 AC-DC converters 11 Load 20a,20b full wave rectifier circuit 21, 33, 34 Capacitors 22 transformers 23 Power Factor Correction IC 24 NMOS transistors 25 Bypass 26 Capacitors 30-32 resistors 100 comparison circuit 101 Delay Circuit 102 SR Flip-Flop 103 buffer 104 Error Voltage Output Circuit 105 Oscillator Circuit 106 Comparison circuit

Claims

1. A full-wave rectifier circuit comprising first and second input lines to which AC voltages are applied, an output line that outputs a full-wave rectified voltage, and a ground line that is grounded, A first diode having its anode connected to the first input line and its cathode connected to the output line, A second diode, whose anode is connected to the ground line and whose cathode is connected to the first input line, A third diode, whose anode is connected to the second input line and whose cathode is connected to the output line, A fourth diode, the anode of which is connected to the ground line and the cathode of which is connected to the second input line, The first to fourth capacitors are connected in parallel to each of the first to fourth diodes, A full-wave rectifier circuit equipped with [a specific feature / feature].

2. A power supply circuit that generates an output voltage of a target level from an AC voltage, A full-wave rectifier circuit to which the aforementioned AC voltage is applied and which outputs a full-wave rectified voltage, The inductor to which the full-wave rectified voltage is applied, A transistor that controls the inductor current flowing through the aforementioned inductor, A switching control circuit for controlling the switching of the transistor, Equipped with, The full-wave rectifier circuit described above is The first and second input lines to which the AC voltage is applied, An output line that outputs the full-wave rectified voltage in order to improve the power factor, The grounding line to be grounded, A first diode having its anode connected to the first input line and its cathode connected to the output line, A second diode, whose anode is connected to the ground line and whose cathode is connected to the first input line, A third diode, whose anode is connected to the second input line and whose cathode is connected to the output line, A fourth diode, the anode of which is connected to the ground line and the cathode of which is connected to the second input line, The first to fourth capacitors are connected in parallel to each of the first to fourth diodes, A power supply circuit including this.

3. The power supply circuit according to claim 2, Each of the first to fourth capacitors is, When each of the first to fourth diodes is turned on based on the AC voltage, the capacitance value is such that each of the first to fourth diodes does not turn off due to the ripple component caused by the switching frequency of the transistor. power circuit.

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