Integrated circuit and power supply circuit

Abstract

To provide an integrated circuit capable of improving a total harmonic distortion of an input current of a power factor improvement circuit.SOLUTION: An integrated circuit comprises: a filter to which a rectification voltage from a full wave rectifier circuit for rectifying an AC voltage is applied; an inductor to which a voltage from the filter is applied; and a transistor that controls an inductor current flowing in the inductor, and switches the transistor of the power supply circuit for generating an output voltage of a target level from the AC voltage. The integrated circuit comprises: a first terminal to which a first voltage corresponding to a second current of a sum of a first current flowing in a ground from the filter and the inductor current is applied; and a switching control circuit that turns off the transistor on the basis of the first voltage so that a peak value of the second current becomes a similar figure to the rectification voltage by turning on the transistor when the inductor current becomes smaller than a predetermined value.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to an integrated circuit and a power supply circuit. [Background technology]

[0002] A power factor correction circuit that generates an output voltage of a target level from an AC voltage typically includes an integrated circuit that switches a switching element so as to make the waveform of the peak value of the inductor current similar to the waveform of the full-wave rectified voltage and improve the power factor (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-181342 A Summary of the Invention [Problem to be solved by the invention]

[0004] In some power factor correction circuits, an input filter is provided after the full-wave rectifier circuit. In such cases, a current flows through a capacitor included in the input filter, so the input current to the power factor correction circuit includes a current to the capacitor and an inductor current.

[0005] Therefore, when only the waveform of the peak value of the inductor current is adjusted, the total harmonic distortion (THD) of the input current to the power factor correction circuit may not be improved sufficiently.

[0006] The present invention has been made in consideration of the above-mentioned problems in the conventional art, and an object of the present invention is to provide an integrated circuit capable of improving the total harmonic distortion of the input current of a power factor correction circuit. [Means for solving the problem]

[0007] In order to solve the above problems, a first aspect of an integrated circuit of the present invention is an integrated circuit that switches the transistor of a power supply circuit that generates an output voltage of a target level from the AC voltage, the integrated circuit comprising: a filter to which a rectified voltage from a full-wave rectifier circuit that rectifies an AC voltage is applied, an inductor to which a voltage from the filter is applied, and a transistor that controls an inductor current flowing through the inductor, the integrated circuit comprising: a first terminal to which a first voltage corresponding to a second current that is the sum of a first current flowing from the filter to ground and the inductor current is applied; and a switching control circuit that turns on the transistor when the inductor current becomes smaller than a predetermined value, and turns off the transistor based on the first voltage so that the peak value of the second current is similar to the rectified voltage.

[0008] Also, an aspect of the power supply circuit of the present invention is a power supply circuit that generates an output voltage of a target level from an AC voltage, comprising: a full-wave rectifier circuit that rectifies the AC voltage; a filter to which the rectified voltage is applied; a resistor provided between a low-potential terminal of the full-wave rectifier circuit and ground; an inductor to which a voltage from the filter is applied; a transistor that controls an inductor current flowing through the inductor; and an integrated circuit that switches the transistor, wherein the integrated circuit includes a first terminal to which a first voltage corresponding to a second current that is the sum of a first current flowing from the filter to ground and the inductor current is applied; and a switching control circuit that turns on the transistor when the inductor current becomes smaller than a predetermined value and turns off the transistor based on the first voltage so that the peak value of the second current has a similar shape to the rectified voltage, and the first terminal is connected to the resistor and the terminal.

[0009] Moreover, a second aspect of the integrated circuit of the present invention is an integrated circuit which includes a filter to which a rectified voltage from a full-wave rectifier circuit which rectifies an AC voltage is applied, an inductor to which a voltage from the filter is applied, a transistor which controls an inductor current flowing through the inductor, and a current detection unit provided between the filter and the full-wave rectifier circuit, and which switches the transistor of a power supply circuit which generates an output voltage of a target level from the AC voltage, and which includes a first terminal to which a first voltage generated in the current detection unit corresponding to a second current which is the sum of a first current flowing from the filter to ground and the inductor current is applied, and a switching control circuit which turns on the transistor when the inductor current becomes smaller than a predetermined value, and turns off the transistor based on a target value corresponding to the output voltage and the first voltage. Effect of the Invention

[0010] According to the present invention, it is possible to provide an integrated circuit capable of improving the total harmonic distortion of the input current of a power factor correction circuit.

[0011] The above summary of the invention does not list all of the necessary features of the present invention. Also, subcombinations of these features may also be inventions. [Brief description of the drawings]

[0012] [Figure 1] 1 is a diagram illustrating an example of the configuration of an AC-DC converter 10a. [Diagram 2] FIG. 1 is a diagram showing an example of the configuration of a general AC-DC converter 500. [Diagram 3] FIG. 4 illustrates an example of the operation of the AC-DC converter 500. [Figure 4] FIG. 4 illustrates an example of the operation of the AC-DC converter 500. [Diagram 5] FIG. 2 is a diagram illustrating an example of the configuration of a power factor correction IC 29a. [Figure 6] 4 is a diagram illustrating the operation of the level shift circuit 60. FIG. [Figure 7]FIG. 2 is a diagram showing an example of the configuration of an inverting amplifier circuit 308. [Figure 8] 3 is a diagram for explaining the operation of a multiplier circuit 307 and an inverting amplifier circuit 308. FIG. [Figure 9] 4 is a diagram for explaining the operation of the power factor correction IC 29a. [Figure 10] 4 is a diagram for explaining the operation of the power factor correction IC 29a. [Figure 11] 1 is a diagram showing a simulation result of a typical AC-DC converter 500. FIG. [Figure 12] FIG. 4 is a diagram showing a simulation result of the AC-DC converter 10a. [Figure 13] FIG. 2 is a diagram illustrating an example of the configuration of a power factor correction IC 29b. [Figure 14] FIG. 2 is a diagram showing an example of the configuration of an AC-DC converter 10b. [Figure 15] FIG. 2 is a diagram illustrating an example of the configuration of a power factor correction IC 29c. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The present invention will be described below through the embodiments of the invention, but the following embodiments do not limit the invention according to the claims. In addition, not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention. In addition, the same or equivalent components, members, etc. shown in each drawing are given the same reference numerals, and duplicated descriptions are omitted as appropriate.

[0014] In this specification, the term "connection" is used, and unless otherwise specified, "connection" means "electrically connected." In this specification, when a voltage or signal has a high logical level, it is referred to as an "H" level, and when a voltage or signal has a low logical level, it is referred to as an "L" level.

[0015] FIG. 1 shows an example of the configuration of the AC-DC converter 10a. The AC-DC converter 10a is a boost chopper type power supply circuit that generates an output voltage Vout at a target level from the AC voltage Vac of the AC power supply 11. The AC-DC converter 10a applies the output voltage Vout to the load 12.

[0016] Here, the AC power supply 11 is a commercial AC power supply for applying the AC voltage Vac to the AC-DC converter 10a. The AC voltage Vac is, for example, a voltage of 100 to 277 V and a frequency of 50 to 60 Hz. Also, the load 12 is, for example, an electronic device that operates with a DC-DC converter or a DC voltage.

[0017] <<Configuration of AC-DC Converter 10a>> The AC-DC converter 10a includes an inductor 21, capacitors 22, 28, 46, 47, a full-wave rectifier circuit 23, an input filter 24, a transformer 25, resistors 26, 41 to 45, diodes 27, 50, 51, a power factor correction IC 29a, and a MOS transistor 40.

[0018] ==Input to the Full-Wave Rectifier Circuit 23== The inductor 21 and the capacitor 22 remove noise from the voltage Vac and the current supplied from the AC power supply 11 to the full-wave rectifier circuit 23. From the AC power supply 11 through the inductor 21 and the capacitor 22, a voltage with noise removed from the voltage Vac and an input current Iin are supplied to the full-wave rectifier circuit 23.

[0019] ==Configuration from the Full-Wave Rectifier Circuit 23 to the Load 12== The full-wave rectifier circuit 23 full-wave rectifies the predetermined AC voltage Vac with noise removed and applied to the terminals T0 and T1, and applies it as a rectified voltage Vrec0 from the high-potential terminal T2 to the input filter 24 via the line LN1. On the other hand, the full-wave rectifier circuit 23 has a ground line LN2 connected to the low-potential terminal T3 via a resistor 42 (described later). Note that the full-wave rectifier circuit 23 is a general diode bridge circuit composed of four diodes.

[0020] The input filter 24 is configured as a differential mode filter, that is, a π-type filter made up of capacitors 30 and 32 and an inductor 31, and smoothes and removes noise from the rectified voltage Vrec0 applied by the full-wave rectifier circuit 23. The rectified voltage Vrec0 that has been filtered and has had noise removed by the input filter 24 is applied to the main coil L1 of the transformer 25.

[0021] The current flowing from input filter 24 to ground, i.e., to ground line LN2, is referred to as current If. Also, although an example in which a differential mode filter is used for input filter 24 has been described, for example, rectified voltage Vrec0 may be smoothed using only capacitor 30.

[0022] The transformer 25 includes a main coil L1 and an auxiliary coil L2 magnetically coupled to the main coil L1. In this embodiment, the auxiliary coil L2 is wound so that the polarity of the voltage generated in the auxiliary coil L2 is opposite to that of the voltage generated in the main coil L1.

[0023] The auxiliary coil L2 is connected to a terminal ZCD of a power factor correction IC 29a (described later) via a resistor 26. A current corresponding to the inductor current IL flowing through the main coil L1 flows through the auxiliary coil L2, and therefore a voltage Vzcd corresponding to the inductor current IL is applied to the terminal ZCD.

[0024] The main coil L1 of the transformer 25 constitutes a boost chopper circuit together with a MOS transistor 40 (described later), a diode 27, and a capacitor 28. As a result, the charging voltage of the capacitor 28 is boosted to a DC output voltage Vout and supplied to the load 12.

[0025] The power factor correction IC 29a is an integrated circuit that controls the switching of the MOS transistor 40 so that the level of the output voltage Vout becomes a target level (e.g., 400 V) while correcting the power factor of the AC-DC converter 10a. The power factor correction IC 29a drives the MOS transistor 40 based on the current If flowing from the input filter 24 to the ground line LN2, the inductor current IL flowing through the main coil L1, and the output voltage Vout.

[0026] The power factor correction IC 29a includes terminals CS, CS2, COMP, FB, OUT, ZCD, and VH. Note that the power factor correction IC 29a has terminals other than the terminals CS, CS2, COMP, FB, OUT, ZCD, and VH (for example, a power terminal, a GND terminal, etc.), but these other terminals are omitted in the figure.

[0027] The MOS transistor 40 is a power transistor for controlling the power to the load 12 of the AC-DC converter 10a. Specifically, the MOS transistor 40 controls the inductor current IL flowing through the main coil L1 of the transformer 25.

[0028] The MOS transistor 40 in this embodiment is an N-type MOS (Metal Oxide Semiconductor) transistor, but is not limited to this. That is, the MOS transistor 40 may be any transistor that can control power, for example, a bipolar transistor. Here, the gate electrode of the MOS transistor 40 is connected to the terminal OUT of the power factor correction IC 29a.

[0029] A voltage Vdr is applied from a power factor correction IC 29a to a gate electrode of the MOS transistor 40. The power factor correction IC 29a controls the power to the load 12 by controlling the timing at which the voltage level of the voltage Vdr is changed.

[0030] The resistor 41 generates a voltage Vcs according to the drain-source current of the MOS transistor 40. Since the drain-source current of the MOS transistor 40 changes according to the inductor current IL, the inductor current IL can be detected by detecting the voltage Vcs generated across the resistor 41. One end of the resistor 41 is connected to the source electrode of the MOS transistor 40, and the other end is connected to the ground line LN2 and is grounded. The voltage Vcs generated across the resistor 41 is applied to a terminal CS. The terminal CS corresponds to a "second terminal."

[0031] The resistor 42 is a resistor for detecting a current It (It=If+IL) corresponding to the sum of the current If and the inductor current IL. The resistor 42 is provided between the terminal T3 of the full-wave rectifier circuit 23 and the ground line LN2, and a voltage Vcs2 generated across the resistor 42 is applied to the terminal CS2 of the power factor correction IC 29a.

[0032] Since terminal CS2 is connected to terminal T3 of full-wave rectifier circuit 23 and resistor 42, voltage Vcs2 becomes a negative voltage according to the sum of current If and inductor current IL. Terminal CS2 corresponds to the "first terminal", current If corresponds to the "first current", current It corresponds to the "second current", and voltage Vcs2 corresponds to the "first voltage". Resistor 42 corresponds to the "current detection unit".

[0033] The resistors 43 and 44 form a voltage divider circuit that generates, in response to the output voltage Vout, a feedback voltage Vfb used to switch the MOS transistor 40. The voltage divider circuit applies the divided voltage Vfb as a feedback voltage to the terminal FB of the power factor correction IC 29a.

[0034] The resistor 45 and the capacitors 46 and 47 are elements for phase compensation used in feedback control. The resistor 45 and the capacitor 46 are connected in series between the terminal COMP and the ground. The capacitor 47 is connected in parallel to the resistor 45 and the capacitor 46.

[0035] The anodes of the diodes 50 and 51 are connected to the inputs of the full-wave rectifier circuit 23, and the cathodes of the diodes 50 and 51 are connected to each other. A rectified voltage Vrec1 is generated at the cathodes of the diodes 50 and 51, and the rectified voltage Vrec1 is applied to the terminal VH of the power factor correction IC 29a.

[0036] Although details of the power factor correction IC 29a will be described later, the power factor correction IC 29a turns on the MOS transistor 40 when the inductor current IL flowing through the main coil L1 of the transformer 25 becomes a predetermined value (e.g., almost zero; hereinafter, "almost zero" will be referred to as "zero"), and the power factor correction IC 29a turns off the MOS transistor 40 when the current It corresponding to the sum of the current If and the inductor current IL reaches a target value determined based on the voltage Vrec1 and the voltage Vfb (more specifically, the voltage Vcomp of the terminal COMP corresponding to the voltage Vfb).

[0037] In this way, the power factor correction IC 29a can match the phase of the current It, which corresponds to the sum of the current If and the inductor current IL, with the phase of the AC voltage, thereby improving the power factor. Note that the current It is almost equal to the input current Iin, although there is a loss in the AC-DC converter 10a.

[0038] <<Configuration of a typical AC-DC converter 500>> The AC-DC converter 10a has been described above, which has the resistor 42 provided between the terminal T3 of the full-wave rectifier circuit 23 and the ground line LN2 in order to detect the current If and the inductor current IL. Below, a general AC-DC converter 500 using a power factor improvement IC 100 that turns off the MOS transistor 40 based on the inductor current IL and the output voltage Vout will be described.

[0039] 2 is a diagram showing an example of the configuration of an AC-DC converter 500. The AC-DC converter 500 differs from the AC-DC converter 10a in that the power factor correction IC 29a and the resistor 42 are removed and a power factor correction IC 100 and a resistor 101 are added.

[0040] The power factor correction IC 100 is an integrated circuit that operates based on the voltage Vcs2 generated across a resistor 101 provided between the input filter 24 and the ground line LN2. Details of the power factor correction IC 29a will be described later, but in the same way as the power factor correction IC 29a, it improves the power factor as follows.

[0041] The power factor correction IC 100 turns on the MOS transistor 40 when the inductor current IL flowing through the main coil L1 of the transformer 25 becomes zero. Then, the power factor correction IC 100 turns off the MOS transistor 40 when the inductor current IL reaches a target value determined based on the voltage Vrec1 and the feedback voltage Vfb (more specifically, the voltage Vcomp of the terminal COMP corresponding to the voltage Vfb). The power factor correction IC 100 determines the timing to turn off the MOS transistor 40 based on the voltage Vcs2 generated across the resistor 101 by the inductor current IL.

[0042] <<<Outline of operation of a typical AC-DC converter 500>>> FIG. 3 is a diagram showing the relationship between the inductor current IL and the voltage Vdr when the rectified voltage Vrec0 is high.

[0043] At time t0, the inductor current IL flowing through the coil L1 becomes zero.

[0044] At time t1 when a delay period tch has elapsed from time t0, the power factor correction IC 100 applies, to the MOS transistor 40, a voltage Vdr that turns on the MOS transistor 40. When the MOS transistor 40 turns on, the inductor current IL increases.

[0045] At time t2 when the inductor current IL reaches the target value, the power factor improvement IC 100 applies, to the MOS transistor 40, a voltage Vdr that turns off the MOS transistor 40. When the MOS transistor 40 turns off, the inductor current IL decreases.

[0046] At time t3, the inductor current IL becomes zero, and the same operation is repeated thereafter.

[0047] Here, when the MOS transistor 40 turns off and the inductor current IL becomes zero, the charging voltage Vr of the capacitors 30 and 32 included in the input filter 24 is sufficiently high, so the voltage on the input filter 24 side of the coil L1 becomes lower than the charging voltage Vr. Therefore, the current If that charges the capacitors 30 and 32 does not flow from the coil L1. Therefore, resonance occurs between the output capacitance Coss of the MOS transistor 40 and the coil L1.

[0048] That is, when the rectified voltage Vrec0 is high, a resonant current flows between the coil L1 and the output capacitance Coss, and no current flows in the negative direction from the coil L1 to the capacitors 30 and 32 other than the resonant current.

[0049] Therefore, if the power factor improvement IC 100 turns on the MOS transistor 40 with a delay of the delay period tch after the inductor current IL becomes zero, the MOS transistor 40 can be turned on in a state where the voltage of the drain electrode of the MOS transistor 40 is reduced. This suppresses the switching loss of the MOS transistor 40. The delay period tch is half the resonant period.

[0050] On the other hand, when the rectified voltage Vrec0 is low, the AC-DC converter 500 cannot operate as described with reference to Fig. 3. Such a case will be described below with reference to Fig. 4.

[0051] FIG. 4 is a diagram showing the relationship between the inductor current IL and the voltage Vdr when the rectified voltage Vrec0 is low.

[0052] At time t10, the inductor current IL flowing through the coil L1 becomes zero. After the inductor current IL becomes zero, a resonant operation starts between the coil L1 and the output capacitance Coss. When the rectified voltage Vrec0 is low and the charging voltage Vr charged in the capacitors 30 and 32 of the input filter 24 is low, the voltage on the input filter 24 side of the coil L1 becomes higher than the charging voltage Vr, and the inductor current IL flows in the negative direction from the coil L1 to the capacitors 30 and 32. Then, the inductor current IL charges the capacitors 30 and 32.

[0053] At time t11, when the delay time tch has elapsed since time t10, the power factor correction IC 100 applies, to the MOS transistor 40, the voltage Vdr that turns on the MOS transistor 40. However, until the voltage on the input filter 24 side of the coil L1 becomes equal to the charging voltage Vr, the inductor current IL flows in the negative direction through the parasitic diode Dp, the coil L1, and the capacitors 30 and 32 in that order.

[0054] In this case, although the MOS transistor 40 is turned on, the positive inductor current IL does not flow through the coil L1 from the coil L1 to the MOS transistor 40. After that, when the voltage on the input filter 24 side of the coil L1 becomes equal to the charging voltage Vr, the negative inductor current IL stops flowing and the inductor current IL starts flowing in the positive direction.

[0055] At time t12 when the inductor current IL reaches the target value, the power factor improvement IC 100 applies, to the MOS transistor 40, a voltage Vdr that turns off the MOS transistor 40. When the MOS transistor 40 turns off, the inductor current IL decreases.

[0056] At time t13, the inductor current IL becomes zero, and thereafter, the same operation is repeated.

[0057] For this reason, even if the MOS transistor 40 is turned on, the effective on-period during which the inductor current IL flows in the positive direction is shortened. In this case, the capacitors 30 and 32 are not sufficiently discharged, and the voltage difference between the AC voltage Vac and the charging voltage Vr becomes small, so that the diode included in the full-wave rectifier circuit 23 has difficulty passing a current.

[0058] As a result, when the rectified voltage Vrec0 is low (i.e., the AC voltage Vac is low), the full-wave rectifier circuit 23 may not be able to supply a sufficient current. If the MOS transistor 40 continues to be turned on, the inductor current IL gradually flows in the positive direction, discharging the capacitors 30 and 32. As the charging voltage Vr decreases, the diodes included in the full-wave rectifier circuit 23 are fully turned on and start to supply the necessary current.

[0059] When operating in this manner, the waveform of the input current Iin may not be similar to the waveform of the AC voltage Vac. This phenomenon may occur because the resistor 101 detects only the inductor current IL.

[0060] Furthermore, if the current If is ignored and the MOS transistor 40 is switched only by the inductor current IL, when the rectified voltage Vrec0 is low, the current value of the input current Iin becomes larger than the current value of the inductor current IL by the amount of the charging current If. In this case, the input current Iin becomes distorted with respect to the AC voltage Vac, which deteriorates the power factor and may also cause harmonic distortion.

[0061] Meanwhile, by providing the resistor 42 in the AC-DC converter 10a, it is possible to detect the current It corresponding to the sum of the current If for charging the capacitors 30, 32 of the input filter 24 and the inductor current IL.

[0062] This allows the AC-DC converter 10a to take into consideration even if the rectified voltage Vrec0 is low and a charging current If is generated to the capacitors 30 and 32. When the rectified voltage Vrec0 is high, the charging current If is unlikely to be generated and the current It becomes substantially the inductor current IL, so that distortion of the input current Iin is unlikely to occur.

[0063] In addition, by considering the current If together with the inductor current IL, the distortion of the input current Iin with respect to the AC voltage Vac can be reduced and the total harmonic distortion can be improved, which may improve the power factor of the AC-DC converter 10a. Therefore, the power factor improvement IC 29a capable of improving the total harmonic distortion in this way will be described in detail below.

[0064] == Configuration of power factor correction IC29a == Fig. 5 shows an example of the configuration of the power factor correction IC 29a. The power factor correction IC 29a switches the MOS transistor 40 based on the voltage Vcs2 applied to the terminal CS2 in Fig. 1, the rectified voltage Vrec1 applied to the terminal VH, and the output voltage Vout so that the waveform of the input current Iin becomes similar to the waveform of the AC voltage Vac.

[0065] Here, "similar shapes" refers to the fact that the phases of the waveform of the AC voltage Vac and the waveform of the input current Iin match and that their amplitudes are in a positive proportional relationship, and "so as to have similar shapes" refers to making the power factor approach 1.

[0066] The power factor correction IC 29 a includes a level shift circuit 60 , a switching control circuit 61 a , and a comparator 62 .

[0067] ===Level shift circuit 60=== The level shift circuit 60 shifts the level of the voltage Vcs2, which is a negative voltage, by a predetermined voltage V1 (>0) and outputs a positive voltage Vcs2_shift. Specifically, the level shift circuit 60 is composed of a resistor 200 to which a power supply voltage Vdd is applied, and a resistor 201 provided between the resistor 200 and a terminal CS2, and outputs the voltage Vcs2_shift from the connection point of the resistors 200 and 201.

[0068] The resistance values ​​of the resistors 200 and 201 are determined so as not to affect the detection of the current It by the resistor 42. The voltage Vcs2_shift corresponds to a "second voltage."

[0069] FIG. 6 is a diagram showing the relationship between the voltage Vcs2 (dotted line) and the level-shifted voltage Vcs2_shift (solid line).

[0070] For example, in the period before time t20, when the current flowing through the resistor 42 in Fig. 1 is "0", the voltage Vcs2 is also "0 V". As a result, the voltage Vcs2_shift becomes the voltage V1.

[0071] Then, when the MOS transistor 40 is turned on at time t20, for example, the inductor current IL increases, and the voltage Vcs2 drops from "0 V." Therefore, the voltage Vcs2_shift obtained by level-shifting the voltage Vcs2 also drops from the voltage V1.

[0072] Furthermore, when the MOS transistor 40 is turned off at time t21, for example, the inductor current IL becomes small, and the voltage Vcs2 becomes large, for example, becoming "0 V" at time t22. Therefore, the voltage Vcs2_shift also becomes the voltage V1 at time t22.

[0073] In this manner, in this embodiment, for example, when the inductor current IL is "0", the voltage Vcs2_shift becomes the voltage V1, and when the inductor current IL increases, the voltage Vcs2_shift decreases from the voltage V1.

[0074] ===Switching control circuit 61a=== 5 switches the MOS transistor 40 based on the inductor current IL and the output voltage Vout. Specifically, the switching control circuit 61a turns on the MOS transistor 40 when the inductor current IL becomes smaller than zero.

[0075] On the other hand, the switching control circuit 61a turns off the MOS transistor 40 based on the voltage Vcs2 so that the waveform of the peak value of the current It, which corresponds to the sum of the current If and the inductor current IL, becomes similar to the waveform of the rectified voltage Vrec1.

[0076] The switching control circuit 61a includes a hysteresis comparator 300, a delay circuit 301, OR circuits 302 and 310, a restart timer 303, an SR flip-flop 304, a voltage divider circuit 305, an error amplifier circuit 306, a multiplier circuit 307, an inverting amplifier circuit 308, a comparator 309, and a buffer 311.

[0077] The hysteresis comparator 300 detects whether the inductor current IL has become zero based on the voltage Vzcd applied to the terminal ZCD. Since the auxiliary coil L2 is electromagnetically coupled to the main coil L1, the voltage Vzcd applied to the terminal ZCD corresponds to the inductor current IL flowing through the main coil.

[0078] Specifically, the hysteresis comparator 300 has thresholds Vthl and Vthh, and compares the voltage Vzcd with the threshold Vthl when the inductor current IL indicates zero and with the threshold Vthh when the inductor current IL indicates an increase.

[0079] When the inductor current IL decreases to zero, the hysteresis comparator 300 outputs an “H” level signal Vz to the delay circuit 301. On the other hand, when the inductor current IL increases and the voltage Vzcd exceeds the threshold Vthh, the hysteresis comparator 300 outputs an “L” level signal Vz to the delay circuit 301.

[0080] Moreover, the threshold value Vthl is a lower threshold value of the hysteresis comparator 300 according to the reference voltage Vref0 applied to the hysteresis comparator 300. Similarly, the threshold value Vthh is a higher threshold value of the hysteresis comparator 300 according to the reference voltage Vref0.

[0081] The delay circuit (DELAY) 301 outputs a pulse signal Vd that turns on the MOS transistor 40 after a delay period tch has elapsed after the inductor current IL becomes zero. Specifically, the delay circuit 301 outputs an “H” level pulse signal Vd after a delay period tch has elapsed, which is a half-cycle of the resonance period when the coil L1 and the output capacitance Coss resonate after the inductor current IL becomes zero.

[0082] The OR circuit 302 calculates the logical sum of the pulse signal Vd from the delay circuit 301 and the pulse signal Vtim from the restart timer 303 (described later). Therefore, when the pulse signal Vd from the delay circuit 301 or the pulse signal Vtim from the restart timer 303 is input, the OR circuit 302 outputs an on signal Sset of an “H” level.

[0083] When the MOS transistor 40 is not turned on for a predetermined period, the restart timer (TIM) 303 outputs a pulse signal Vtim to turn on the MOS transistor 40. Specifically, the restart timer 303 outputs the pulse signal Vtim when the drive signal Vq1 that drives the MOS transistor 40 does not become "H" level for a predetermined period.

[0084] On the other hand, if the drive signal Vq1 becomes "H" level during the predetermined period, the restart timer 303 resets the time measurement for the predetermined period and restarts the time measurement. Therefore, if the drive signal Vq1 becomes "H" level during the predetermined period, the restart timer 303 stops outputting the pulse signal Vtim.

[0085] ==SR Flip-Flop 304== The SR flip-flop 304 changes the Q output based on the on signal Sset and the off signal Sreset (described later), and outputs it as the drive signal Vq1. Specifically, when the OR circuit 302 outputs the on signal Sset of the “H” level, the SR flip-flop 304 outputs the drive signal Vq1 of the “H” level.

[0086] On the other hand, when the OR circuit 310 (described later) outputs a signal Sreset of "H" level, the SR flip-flop 304 outputs a drive signal Vq1 of "L" level. Note that the SR flip-flop 304 is a reset-priority flip-flop. Also, the SR flip-flop 304 corresponds to a "drive signal output circuit."

[0087] The voltage divider circuit (RDIV) 305 divides the voltage Vh (equal to the rectified voltage Vrec1 in FIG. 1) from the terminal VH to generate a voltage Vh_div.

[0088] The error amplifier circuit 306 is a transconductance amplifier, and when the output voltage Vout becomes higher than a target level, it discharges the capacitors 46 and 47 in FIG. 1 so that the on-period of the MOS transistor 40 becomes shorter.

[0089] Specifically, when the feedback voltage Vfb corresponding to the output voltage Vout is lower than the reference voltage Vref1, the error amplifier circuit 306 charges the capacitors 46, 47 with the current Ierr. On the other hand, when the feedback voltage Vfb is higher than the reference voltage Vref1, the error amplifier circuit 306 discharges the capacitors 46, 47 with the current Ierr. The voltage Vcomp of the terminal COMP corresponds to the "third voltage corresponding to the output voltage."

[0090] ==Multiplication circuit 307== The multiplication circuit (MUL) 307 outputs a voltage Vm indicating a target value of the peak value of the current It corresponding to the sum of the current If and the inductor current IL based on the voltage Vh_div and the voltage Vcomp. Specifically, the multiplication circuit 307 multiplies the voltage Vh_div by the voltage Vcomp and outputs the voltage Vm. The voltage Vcomp corresponds to a "third voltage corresponding to the output voltage", the voltage Vh_div corresponds to a "fourth voltage", and the voltage Vm corresponds to a "fifth voltage indicating the target value".

[0091] Here, the multiplication circuit 307 multiplies the voltage Vh_div by the voltage Vcomp, which indicates whether the output voltage Vout is higher or lower than the target level, to determine the peak value of the current It. The voltage Vh_div is used to reflect the waveform of the rectified voltage Vrec1 in the waveform of the peak value, and the voltage Vcomp is used to determine the amplitude of the waveform of the peak value. This allows the power factor correction IC 29a to make the waveform of the peak value of the current It similar to the waveform of the rectified voltage Vrec0 while maintaining the output voltage Vout at the target level.

[0092] ==Inverting amplifier circuit 308== The inverting amplifier circuit (INV) 308 inverts the voltage Vm, amplifies it with a predetermined gain, and outputs it as a voltage Vm_inv. Specifically, the inverting amplifier circuit 308 includes an operational amplifier 400 and resistors 401 and 402, and is configured as shown in FIG.

[0093] The relationship between the voltage Vm, the voltage Vm_inv, and the reference voltage Vref3 is expressed by the following formula. Vref3=(R1 / (R1+R2))×(Vm_inv-Vm)+Vm...Equation (1) Here, R1 is the resistance value of resistor 401, and R2 is the resistance value of resistor 402.

[0094] Transforming equation (1) gives the following equation: Vm_inv=-(R2 / R1)×Vm+(1+R2 / R1)Vref3...Equation (2)

[0095] Furthermore, the resistance values ​​R1, R2 and the reference voltage Vref3 are determined so that (1+R2 / R1)Vref3 is equal to the voltage V1 (that is, the voltage Vcs2_shift output by the level shift circuit 60 when the voltage Vcs2 is 0V).

[0096] In this way, by determining the resistance values ​​R1, R2 and the reference voltage Vref3, the comparator 309 (described later) can almost correctly compare the voltage Vm_inv with the voltage Vcs2_shift. Note that the inverting amplifier circuit 308 corresponds to an "inverting circuit", and the voltage Vm_inv corresponds to a "sixth voltage" and a "seventh voltage".

[0097] The multiplication circuit 307 and the inverting amplifier circuit 308 operate as shown in Fig. 8 as the phase angle of the AC voltage Vac changes from 0 degrees to 360 degrees. Specifically, when the phase angle of the AC voltage Vac is 0 degrees, the voltage Vh_div is 0V, and the multiplication circuit 307 outputs a voltage Vm of 0V. Then, the inverting amplifier circuit 308 outputs the voltage V1 as the voltage Vm_inv, as shown in equation (2). Note that in Fig. 8, the voltage Vcomp is assumed to be constant.

[0098] Furthermore, when the phase angle of the AC voltage Vac is near 90 degrees, the voltage Vh_div becomes a voltage corresponding to the maximum level of the AC voltage Vac, and the multiplier circuit 307 outputs the maximum voltage Vm. Then, the inverting amplifier circuit 308 outputs the voltage Vm_inv that is the lowest voltage from the voltage V1. Thereafter, the multiplier circuit 307 and the inverting amplifier circuit 308 operate in the same manner when the phase angle of the AC voltage Vac changes from 180 degrees to 360 degrees.

[0099] ==Comparator 309== 5 determines the timing to turn off the MOS transistor 40. Specifically, the comparator 309 outputs an “H” level signal Scmp when the level of the voltage Vcs2_shift becomes the level of the voltage Vm_inv. This means that the current It has reached the target value, and the switching control circuit 61a turns off the MOS transistor 40 when the voltage Vcs2_shift becomes the voltage Vm_inv indicating the target value of the peak value of the current It.

[0100] On the other hand, when the level of the voltage Vcs2_shift is higher than the level of the voltage Vm_inv, the comparator 309 outputs a signal Scmp at an “L” level. The comparator 309 corresponds to a “first comparison circuit” and a “second comparison circuit”.

[0101] The OR circuit 310 calculates the logical sum of the signal Scmp from the comparator 309 and the signal Socp from a comparator 62 (described later).

[0102] When the drive signal Vq1 of the "H" level is input, the buffer 311 applies the voltage Vdr to the MOS transistor 40 to turn on the MOS transistor 40, and when the drive signal Vq1 of the "L" level is input, the buffer 311 applies the voltage Vdr to the MOS transistor 40 to turn off the MOS transistor 40. In this way, the buffer 311 drives the MOS transistor 40, which has a large gate capacitance, etc.

[0103] ==Comparator 62== The comparator 62 detects whether or not the inductor current IL flowing through the MOS transistor 40 has exceeded a predetermined current. Specifically, the comparator 62 compares the voltage Vcs generated by the inductor current IL flowing through the resistor 41 with a reference voltage Vref2.

[0104] Furthermore, when the voltage Vcs is higher than the reference voltage Vref2, the comparator 62 outputs a signal Socp of "H" level to the switching control circuit 61a to turn off the MOS transistor 40. On the other hand, when the voltage Vcs is lower than the reference voltage Vref2, the comparator 62 outputs a signal Socp of "L" level. The comparator 62 corresponds to an "overcurrent protection circuit."

[0105] <<<Operation of power factor correction IC29a>>> Fig. 9 is a diagram showing an example of the operation of the power factor correction IC 29a. The power factor correction IC 29a turns on the MOS transistor 40 based on the inductor current IL, and turns off the MOS transistor 40 based on the current It. However, in Fig. 9, the current It flowing from the ground line LN2 to the terminal T3 of the full-wave rectifier circuit 23 in the resistor 42 in Fig. 1 is assumed to be a positive current, and when the inductor current IL is zero, the current If is also zero.

[0106] At time t30, the inductor current IL becomes zero, and the hysteresis comparator 300 outputs a signal Vz (not shown) of an "H" level.

[0107] At time t31 when the delay period tch has elapsed from time t30, the delay circuit 301 outputs the pulse signal Vd, and the power factor correction IC 29a applies, to the MOS transistor 40, the voltage Vdr that turns on the MOS transistor 40. Thereafter, the current It increases.

[0108] At time t32 when the voltage Vcs2_shift becomes the voltage Vm_inv, the comparator 309 outputs the signal Scmp of the “H” level. Then, the power factor correction IC 29a applies the voltage Vdr that turns off the MOS transistor 40 to the MOS transistor 40. After that, the current It decreases.

[0109] At time t33 when the inductor current IL becomes zero, the hysteresis comparator 300 outputs a signal Vz of an “H” level. After that, the same operation is repeated.

[0110] The operation of the power factor correction IC 29a has been described above. In this way, the power factor correction IC 29a operates, so that the waveform of the current value Iave, which is the average value of the current It, becomes similar to the waveform of the rectified voltage Vrec1. In other words, the waveform of the input current Iin also becomes similar to the waveform of the AC voltage Vac.

[0111] Fig. 10 is a diagram showing the relationship between the current value Iave and the rectified voltage Vrec1. When the power factor correction IC 29a operates as described with reference to Fig. 9, the peak value of the voltage Vcs2_shift, i.e., the peak value of the current It, coincides with the voltage Vm_inv indicating the AC component of the rectified voltage Vrec1.

[0112] As a result, the waveform of the current value Iave becomes similar to the waveform of the rectified voltage Vrec1, improving the power factor. In addition, since control also takes into account the current If, distortion of the input current Iin is suppressed and harmonic distortion is also improved.

[0113] <<<Comparison of simulation results>>> FIG. 11 is a diagram showing a simulation result for a general AC-DC converter 500, and FIG. 12 is a diagram showing a simulation result for AC-DC converter 10a.

[0114] In FIG. 11, in a period a shown in the figure, when the current It (shown as the voltage value generated in the resistor 42) is compared with the inductor current IL, the current It is relatively larger.

[0115] On the other hand, when comparing the current It and the inductor current IL during the period b shown in FIG. 11, there is not much difference between the two.

[0116] In addition, in Fig. 12, when comparing the current It (shown as the voltage value generated in the resistor 42) and the inductor current IL during the period a shown in the figure, there is not much difference between them, unlike the case of Fig. 11. The same is true for the period b.

[0117] Also, focusing on the input current Iin and comparing the period a in Figures 11 and 12, the amount of sudden increase in the input current Iin in Figure 12 is smaller than the amount of sudden increase in the input current Iin in Figure 11. Therefore, by the power factor improvement IC 29a controlling the AC-DC converter 10a, the distortion of the input current Iin is reduced, and as a result, the harmonic distortion is also improved.

[0118] === Variations === === Configuration of power factor correction IC29b === The power factor correction IC 29a has been described above. Fig. 13 is a diagram showing an example of the configuration of a power factor correction IC 29b, which is a modified example of the power factor correction IC 29a. The power factor correction IC 29b includes a level shift circuit 60, a switching control circuit 61b, a comparator 62, and an inverting amplifier circuit 63.

[0119] In the power factor improvement IC 29b, an inverting amplifier circuit (INV) 63 inverts the voltage Vcs2_shift from the level shift circuit 60 and applies it to the non-inverting input of the comparator 312 as a voltage Vcs2_inv.

[0120] Moreover, the voltage Vm from the multiplication circuit 307 is applied to the inverting input of the comparator 312. Then, when the level of the voltage Vcs2_inv becomes the level of the voltage Vm, the comparator 312 outputs a signal Scmp of the “H” level. The comparator 312 corresponds to a “first comparison circuit.”

[0121] ===Configuration of AC-DC Converter 10b=== 14 is a diagram showing an example of the configuration of an AC-DC converter 10b. In the AC-DC converter 10b, a current detection transformer (CT) 52 for detecting a current It is provided instead of the resistor 42 in the AC-DC converter 10a. In addition, the power factor correction IC 29a is replaced with a power factor correction IC 29c that receives a voltage Vcs2 from the current detection transformer 52.

[0122] === Configuration of power factor correction IC29c === Fig. 15 is a diagram showing an example of the configuration of a power factor correction IC 29c. The power factor correction IC 29c includes a switching control circuit 61c and a comparator 62. Note that the power factor correction IC 29c in Fig. 15 is illustrated as having a voltage level of the voltage Vcs2 from the current detection transformer 52 adjusted to a voltage level between the power supply voltage Vdd and the ground voltage.

[0123] Therefore, in the power factor correction IC 29c, the level shift circuit 60 included in the power factor correction ICs 29a and 29b and connected to the terminal CS2 is omitted. Also, a comparator 313 is provided in place of the comparators 309 and 312.

[0124] A voltage Vcs2 is applied to a non-inverting input of the comparator 313, and a voltage Vm from the multiplication circuit 307 is applied to an inverting input of the comparator 313. When the level of the voltage Vcs2 reaches the level of the voltage Vm, the comparator 313 outputs an "H" level signal Scmp. The comparator 313 corresponds to a "third comparison circuit."

[0125] ==Summary== The AC-DC converter 10a of this embodiment has been described above. The power factor correction IC 29a includes a terminal CS2 and a switching control circuit 61a. A voltage Vcs2 corresponding to a current It, which is the sum of a current If flowing from the input filter 24 to the ground and an inductor current IL, is applied to the terminal CS2. Therefore, the current If for charging the capacitors 30 and 32 is taken into consideration in controlling the AC-DC converter 10a. This makes it possible to provide an integrated circuit that can improve the total harmonic distortion of the input current of the power factor correction circuit.

[0126] The power factor correction IC 29a also includes a level shift circuit 60, and a resistor 42 that is provided between the terminal T3 of the full-wave rectifier circuit 23 and the ground line LN2 and detects the current It is connected to the terminal CS2. The switching control circuit 61a turns off the MOS transistor 40 based on the voltage Vm, which is a target value of the peak value of the current It and indicates a target value according to the rectified voltage Vrec1 and the output voltage Vout, and the voltage Vcs2_shift. This allows the power factor correction IC 29a to make the waveform of the peak value of the current It similar to the waveform of the rectified voltage Vrec0, thereby improving the distortion of the input current Iin and bringing the power factor closer to 1.

[0127] Furthermore, the switching control circuits 61a and 61b include a multiplication circuit 307, an inverting amplifier circuit 63 or 308, a comparator 309 or 312, and an SR flip-flop 304. This makes it possible to generate the timing for turning off the MOS transistor 40 based on the voltage Vcs2, which is a negative voltage.

[0128] Moreover, the switching control circuit 61a includes a multiplication circuit 307, an inverting amplifier circuit 308, a comparator 309, and an SR flip-flop 304. In this case, the inverting amplifier circuit 308 inverts the voltage Vm from the multiplication circuit 307, and the frequency of the voltage to be inverted becomes lower compared to the case where the voltage Vcs2_shift is inverted. As a result, the inverting amplifier circuit 308 does not invert a high-frequency signal, and therefore the inverting amplifier circuit 308 may have low functionality.

[0129] The power factor correction IC 29a also includes a terminal CS and a comparator 62. As a result, the power factor correction IC 29a has a terminal CS in addition to the terminal CS2, and the terminal CS2 used for switching the MOS transistor 40 in normal operation and the terminal CS for detecting the inductor current IL flowing through the MOS transistor 40 are separately provided.

[0130] The switching control circuit 61c also includes a multiplication circuit 307, a comparator 309, and an SR flip-flop 304. As a result, even if the power factor correction IC 29c uses the current detection transformer 52 instead of the resistor 42, it is possible to make the waveform of the peak value of the current It similar to the waveform of the rectified voltage Vrec0, thereby improving the distortion and total harmonic distortion of the input current Iin and bringing the power factor closer to 1.

[0131] Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It is clear to those skilled in the art that various modifications or improvements can be made to the above embodiments. It is clear from the claims that the technical scope of the present invention may include forms with such modifications or improvements and their equivalents without departing from the spirit of the invention.

[0132] It should be noted that the order of execution of each process, such as operations, procedures, steps, and stages, in the devices, systems, programs, and methods shown in the claims, specifications, and drawings is not specifically stated as "before," "prior to," etc., and may be realized in any order unless the output of a previous process is used in a later process. Even if the operational flow in the claims, specifications, and drawings is explained using "first," "next," etc. for convenience, it does not mean that it is essential to perform the process in this order. [Explanation of symbols]

[0133] 10a, 10b, 500 AC-DC converter 11 AC power supply 12 Load 21 Choke coil 22,28,30,32,46,47 Capacitors 23 Full wave rectifier circuit 24 Input Filter 25 Transformer 26,41~45,101,200,201,401,402 Resistance 27 Diode 29a, 29b, 29c, 100 Power factor correction IC 31 Inductor 40 MOS transistor 50,51 Diode 52 Current detection transformer 60 Level shift circuit 61a, 61b, 61c Switching control circuit 62,309,312,313 Comparator 63 Inverting amplifier circuit 300 Hysteresis Comparator 301 Delay circuit 302,310 OR circuit 303 Restart timer 304 SR Flip-Flop 305 Voltage divider circuit 306 Error Amplifier Circuit 307 Multiplication Circuit 308 Inverting amplifier circuit 311 Buffer 400 Op Amps

Claims

1. An integrated circuit for switching a transistor of a power supply circuit that generates an output voltage of a target level from the AC voltage, the integrated circuit comprising: a filter to which a rectified voltage from a full-wave rectifier circuit that rectifies an AC voltage is applied; an inductor to which a voltage from the filter is applied; and a transistor that controls an inductor current flowing through the inductor, the integrated circuit comprising: a first terminal to which a first voltage corresponding to a second current, which is a sum of a first current flowing from the filter to ground and the inductor current, is applied; a switching control circuit that turns on the transistor when the inductor current becomes smaller than a predetermined value, and turns off the transistor based on the first voltage so that a peak value of the second current has a similar shape to the rectified voltage; 1. An integrated circuit comprising:

2. 2. The integrated circuit of claim 1, a level shift circuit that level-shifts the first voltage and outputs it as a second voltage; Including, a resistor that is provided between a low-potential terminal of the full-wave rectifier circuit and the ground and that detects the second current is connected to the first terminal; The switching control circuit includes: turning off the transistor based on a target value of a peak value of the second current, the target value corresponding to the rectified voltage and the output voltage, and the second voltage; Integrated circuits.

3. 3. An integrated circuit according to claim 2, comprising: The switching control circuit includes: a multiplication circuit that multiplies a third voltage corresponding to the output voltage by a fourth voltage obtained by dividing the rectified voltage, and outputs a fifth voltage indicating the target value; an inverter circuit that inverts either the fifth voltage or the second voltage; a first comparison circuit that compares the other of the fifth voltage and the second voltage with a sixth voltage output by the inversion circuit; a drive signal output circuit that outputs a drive signal for turning on the transistor when the inductor current becomes smaller than the predetermined value, and outputs the drive signal for turning off the transistor when the level of the other voltage becomes the level of the sixth voltage; [0023] An integrated circuit including

4. 3. An integrated circuit according to claim 2, comprising: The switching control circuit includes: a multiplication circuit that multiplies a third voltage corresponding to the output voltage by a fourth voltage obtained by dividing the rectified voltage, and outputs a fifth voltage indicating the target value; an inversion circuit that inverts the fifth voltage; a second comparison circuit that compares a seventh voltage output by the inversion circuit with the second voltage; a drive signal output circuit that outputs a drive signal for turning on the transistor when the inductor current becomes smaller than the predetermined value, and outputs the drive signal for turning off the transistor when the level of the second voltage becomes the level of the seventh voltage; [0023] An integrated circuit including

5. An integrated circuit according to any one of claims 1 to 4, a second terminal to which a voltage corresponding to the inductor current is applied; an overcurrent protection circuit that causes the switching control circuit to turn off the transistor when it detects that the inductor current is greater than a predetermined current based on a voltage at the second terminal; 1. An integrated circuit comprising:

6. 2. The integrated circuit of claim 1, The power supply circuit includes: The full-wave rectifier circuit; a resistor provided between a low-potential terminal of the full-wave rectifier circuit and ground; Equipped with The first terminal is connected to the resistor and the terminal. Integrated circuits.

7. 2. The integrated circuit of claim 1, The switching control circuit includes: a multiplication circuit that multiplies a third voltage corresponding to the output voltage by a fourth voltage obtained by dividing the rectified voltage, and outputs a fifth voltage that indicates a target value for a peak value of the second current; a third comparison circuit that compares the fifth voltage with the first voltage; a drive signal output circuit that outputs a drive signal for turning on the transistor when the inductor current becomes smaller than a predetermined value, and outputs the drive signal for turning off the transistor when the level of the first voltage becomes the level of the fifth voltage; [0023] An integrated circuit including

8. A power supply circuit that generates an output voltage of a target level from an AC voltage, a full-wave rectifier circuit that rectifies the AC voltage; a filter to which the rectified voltage is applied; a resistor provided between a low-potential terminal of the full-wave rectifier circuit and ground; an inductor to which a voltage from the filter is applied; a transistor for controlling an inductor current flowing through the inductor; an integrated circuit for switching the transistor; Equipped with The integrated circuit comprises: a first terminal to which a first voltage corresponding to a second current, which is a sum of a first current flowing from the filter to ground and the inductor current, is applied; a switching control circuit that turns on the transistor when the inductor current becomes smaller than a predetermined value, and turns off the transistor based on the first voltage so that a peak value of the second current has a similar shape to the rectified voltage; Including, The first terminal is connected to the resistor and the terminal. power circuit.

9. An integrated circuit for switching the transistor of a power supply circuit that generates an output voltage of a target level from the AC voltage, the integrated circuit comprising: a filter to which a rectified voltage from a full-wave rectifier circuit that rectifies an AC voltage is applied; an inductor to which a voltage from the filter is applied; a transistor that controls an inductor current flowing through the inductor; and a current detection unit provided between the filter and the full-wave rectifier circuit, a first terminal to which a first voltage generated in the current detection unit corresponding to a second current, which is a sum of a first current flowing from the filter to ground and the inductor current, is applied; a switching control circuit that turns on the transistor when the inductor current becomes smaller than a predetermined value, and turns off the transistor based on a target value corresponding to the output voltage and the first voltage; 1. An integrated circuit comprising:

10. 10. An integrated circuit according to claim 9, comprising: a level shift circuit that level-shifts the first voltage and outputs it as a second voltage; the target value is in accordance with the AC voltage and the output voltage, the switching control circuit turns off the transistor based on the target value and the second voltage. Integrated circuits.

11. 11. An integrated circuit according to claim 10, The switching control circuit includes: a multiplication circuit that multiplies a third voltage corresponding to the output voltage by a fourth voltage obtained by dividing the rectified voltage, and outputs a fifth voltage indicating the target value; an inverter circuit that inverts either the fifth voltage or the second voltage; a first comparison circuit that compares the other of the fifth voltage and the second voltage with a sixth voltage output by the inversion circuit; a drive signal output circuit that outputs a drive signal for turning on the transistor when the inductor current becomes smaller than the predetermined value, and outputs the drive signal for turning off the transistor when the level of the other voltage becomes the level of the sixth voltage; [0023] An integrated circuit including

12. 11. An integrated circuit according to claim 10, The switching control circuit includes: a multiplication circuit that multiplies a third voltage corresponding to the output voltage by a fourth voltage obtained by dividing the rectified voltage, and outputs a fifth voltage indicating the target value; an inversion circuit that inverts the fifth voltage; a second comparison circuit that compares a seventh voltage output by the inversion circuit with the second voltage; a drive signal output circuit that outputs a drive signal for turning on the transistor when the inductor current becomes smaller than the predetermined value, and outputs the drive signal for turning off the transistor when the level of the second voltage becomes the level of the seventh voltage; [0023] An integrated circuit including

13. An integrated circuit according to any one of claims 9 to 12, a second terminal to which a voltage corresponding to the inductor current is applied; an overcurrent protection circuit that causes the switching control circuit to turn off the transistor when it detects that the inductor current is greater than a predetermined current based on a voltage at the second terminal; 1. An integrated circuit comprising:

14. 10. An integrated circuit according to claim 9, comprising: The power supply circuit includes: The full-wave rectifier circuit, Equipped with The current detection unit a resistor provided between a low-potential terminal of the full-wave rectifier circuit and ground; The first terminal is connected to the resistor and the terminal. Integrated circuits.

15. 10. An integrated circuit according to claim 9, comprising: The switching control circuit includes: a multiplication circuit that multiplies a third voltage corresponding to the output voltage by a fourth voltage obtained by dividing the rectified voltage, and outputs a fifth voltage that indicates a target value for a peak value of the second current; a third comparison circuit that compares the fifth voltage with the first voltage; a drive signal output circuit that outputs a drive signal for turning on the transistor when the inductor current becomes smaller than a predetermined value, and outputs the drive signal for turning off the transistor when the level of the first voltage becomes the level of the fifth voltage; [0023] An integrated circuit including

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