Switching control circuits, integrated circuits, and power supply circuits

Abstract

This invention provides a switching control circuit that detects the timing at which the inductor current reaches a predetermined value without using an auxiliary coil. [Solution] A switching control circuit that complementarily switches the first and second transistors of a power supply circuit that generates an output voltage of a target level from an AC voltage to an output capacitor, comprising an inductor to which a voltage obtained by rectifying an AC voltage is applied, a first transistor that controls the current flowing through the inductor, and a second transistor between the inductor and an output capacitor, wherein the power supply circuit includes a first resistor located between the inductor, the connection node of the first transistor and the output capacitor, and a detection circuit that detects the voltage of the first resistor, a first drive circuit that drives the first transistor based on the detection result of the detection circuit and the output voltage, and a second drive circuit that drives the second transistor so as to be switched on and off complementary to the first transistor.

Description

Technical Field

[0001] The present invention relates to a switching control circuit, an integrated circuit, and a power supply circuit.

Background Art

[0002] Some power factor correction circuits operate in a critical mode in which a transistor is turned on when an inductor current reaches a predetermined value (for example, zero). Also, there is a case where the fact that the inductor current flowing through a main coil has reached a predetermined value is detected by the voltage of an auxiliary coil using a transformer having the main coil and the auxiliary coil (for example, Patent Documents 1 to 4).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, it can be difficult to detect when the inductor current flowing through the main coil reaches a predetermined value by using the voltage of the auxiliary coil.

[0006] The present invention has been made in view of the above-mentioned conventional problems, and its objective is to provide a switching control circuit that can detect the timing at which the inductor current reaches a predetermined value without using an auxiliary coil. [Means for solving the problem]

[0007] An embodiment of the switching control circuit according to the present invention that solves the aforementioned problems is a switching control circuit that complementarily switches the first and second transistors of a power supply circuit that generates an output voltage of a target level from the AC voltage to the output capacitor, the power supply circuit including a first resistor located between the inductor, the connection node of the first transistor and the output capacitor, the switching control circuit including a detection circuit that detects a voltage generated in the first resistor, a first drive circuit that drives the first transistor based on the detection result of the detection circuit and the output voltage, and a second drive circuit that drives the second transistor so as to be switched on and off complementaryly with respect to the first transistor.

[0008] An embodiment of the power supply circuit according to the present invention that solves the aforementioned problems is a power supply circuit that generates an output voltage of a target level from an AC voltage to an output capacitor, comprising: n inductors (n is an integer of 2 or more) to which a rectified voltage corresponding to the AC voltage is applied; n first transistors that control the inductor current flowing through each of the n inductors; n second transistors located between each of the n inductors and the output capacitor; n first resistors located between each of the n inductors and each of the n first transistors and the output capacitor, which detect the first current flowing through each of the n second transistors; and complementary components for the n first and second transistors. A power supply circuit comprising n switching control circuits that switch the n first transistors in interleaved operation. Each of the n switching control circuits includes a detection circuit that detects the voltage generated across each of the n first resistors, a first drive circuit that drives each of the n first transistors corresponding to each of the n switching control circuits based on the detection result of the detection circuit and the output voltage, and a second drive circuit that drives each of the n second transistors corresponding to each of the n switching control circuits so as to be switched on and off complementary to each of the n first transistors, wherein the n switching control circuits switch the n first transistors in interleaved operation. [Effects of the Invention]

[0009] According to the present invention, a switching control circuit can be provided that can detect the timing at which the inductor current reaches a predetermined value without using an auxiliary coil. [Brief explanation of the drawing]

[0010] [Figure 1] This figure shows an example of the boost chopper section of AC-DC converter 1. [Figure 2] This figure shows an example of voltage Vds and inductor current IL in AC-DC converter 1. [Figure 3]It is a diagram showing an example of the configuration of the AC-DC converter 10. [Figure 4] It is a diagram showing an example of the configuration of the power factor improvement IC 24. [Figure 5] It is a diagram showing an example of the configuration of the power factor improvement IC 24a. [Figure 6] It is a diagram showing an example of the configuration of the power factor improvement IC 24b. [Figure 7] It is a diagram showing an example of the configuration of the AC-DC converter 12. [Figure 8] It is a diagram showing an example of the configuration of a general AC-DC converter 500.

Embodiments for Carrying Out the Invention

[0011] From the descriptions in this specification and the accompanying drawings, at least the following matters become clear. Hereinafter, the same or equivalent components, members, etc. shown in each drawing are denoted by the same reference numerals, and duplicate explanations may be omitted as appropriate.

[0012] ==When detecting the inductor current IL using an auxiliary coil== FIG. 1 is a diagram showing an example of the boost chopper part of the AC-DC converter 1, and FIG. 2 is a diagram showing an example of the voltage Vds and the inductor current IL in the AC-DC converter 1. The AC-DC converter 1 is assumed to be a power factor improvement circuit operating in the "critical mode". Here, the "critical mode" is a mode in which switching is turned on after the inductor current IL becomes zero.

[0013] The boost chopper is composed of the main coil L1 of the transformer T including the main coil L1 and the auxiliary coil L2, the NMOS transistor Q1, and the diode D1. The auxiliary coil L2 is provided to detect that the inductor current IL flowing through the main coil L1 has reached a predetermined value (for example, zero amperes).

[0014] Hereinafter, with reference to FIG. 2, the path through which the inductor current IL flows will be described. First, at time t0 in FIG. 2, when the NMOS transistor Q1 is turned on, as shown by the dashed line in FIG. 1, the inductor current IL flows to the ground through the main coil L1 and the NMOS transistor Q1. At this time, the drain-source voltage Vds of the NMOS transistor Q1 becomes the ground voltage.

[0015] Next, at time t1, when the NMOS transistor Q1 is turned off, as shown by the dotted line in FIG. 1, the inductor current IL flows through the diode D1 to the capacitor Cd and gradually decreases. At this time, the voltage Vds becomes the output voltage Vout because the diode D1 is turned on. Then, the parasitic capacitor Coss of the NMOS transistor Q1 is charged with the output voltage Vout.

[0016] Then, at time t2 when the inductor current IL reaches a predetermined value, the diode D1 turns off. When the diode D1 turns off, the voltage Vds is no longer maintained at the output voltage Vout. Also, the voltage Vds (i.e., the output voltage Vout) maintained in the parasitic capacitor Coss is higher than the rectified voltage Vrec. Therefore, as shown by the double-dotted line in FIG. 1, the parasitic capacitor Coss and the main coil L1 start a resonance operation, and the inductor current IL flows from the parasitic capacitor Coss through the main coil L1 to the input side. At this time, since the parasitic capacitor Coss is discharged, the voltage Vds decreases.

[0017] After that, at time t3, when the parasitic capacitor Coss is discharged to a certain extent (for example, the voltage Vds decreases by 2×(Vout - Vrec) from the output voltage Vout), the inductor current IL reaches a predetermined value again, and at this time, the NMOS transistor Q1 is turned on again. Thereafter, the same operation is repeated.

[0018] Also, the auxiliary coil L2 detects the time point (for example, time t2´) when the voltage level of the voltage Vds becomes lower than the voltage level of the output voltage Vout, and detects that the inductor current IL has reached a predetermined value.

[0019] However, the rectified voltage Vrec changes significantly depending on the input phase, and accordingly, the range of change in the voltage Vds (i.e., 2 × (Vout - Vrec)) also changes. Therefore, precisely determining when the inductor current IL has reached a predetermined value by comparing it with a constant voltage level was difficult by adjusting the design values ​​of the transformer T and the AC-DC converter 1 alone.

[0020] Therefore, in the embodiment described below, we will describe an AC-DC converter 10 that can detect when the inductor current IL has reached a predetermined value without using a transformer T (i.e., an auxiliary coil L2).

[0021] =====Execution===== Figure 3 shows an example of the configuration of an AC-DC converter 10, which is one embodiment of the present invention. The AC-DC converter 10 is a boost chopper type power supply circuit that generates an output voltage Vout of a target level from the AC voltage Vac of the commercial power supply. The AC-DC converter 10 supplies power to the load 11 by applying the output voltage Vout. As will be described in detail later, the AC-DC converter 10 includes an NMOS transistor 23 (described later) and an NMOS transistor 25 for synchronous rectification, and operates as a power factor correction circuit operating in critical mode.

[0022] As will be explained in more detail later, the dashed line in Figure 3 shows the path of the inductor current IL when NMOS transistor 23 is ON (i.e., NMOS transistor 25 is OFF), and the dashed line shows the path of the inductor current IL when NMOS transistor 23 is OFF (i.e., NMOS transistor 25 is ON).

[0023] The AC-DC converter 10 consists of a full-wave rectifier circuit 20, capacitors 21, 27, 32, inductor 22, NMOS transistors 23, 25, power factor correction IC 24, resistors 26, 28, 29, 33, power supply 30, and diode 31.

[0024] The full-wave rectifier circuit 20 full-wave rectifies a predetermined AC voltage Vac that is input to it and applies the input voltage Vrec to the capacitor 21 and the inductor 22. The AC voltage Vac is, for example, a voltage with an effective value of 140 to 240V and a frequency of 50 to 60Hz. In this embodiment, voltage is basically a potential difference with respect to a reference point (GND in Figure 3), but the AC voltage Vac represents the terminal voltage. The input current Iac is the current from the commercial power supply.

[0025] Capacitor 21 smooths the input voltage Vrec, and capacitor 27, together with inductor 22 and NMOS transistors 23 and 25, constitutes a boost chopper circuit. Therefore, the charging voltage of capacitor 27 becomes the DC output voltage Vout. Note that capacitor 27 corresponds to the "output capacitor".

[0026] Furthermore, when the inductor current IL flows in the direction of the arrow shown in Figure 3, it is said that the inductor current IL flows in the positive direction, and when the inductor current IL flows in the opposite direction to the arrow, it is said that the inductor current IL flows in the negative direction.

[0027] The NMOS transistor 23 is a switching element that controls the inductor current IL flowing through the inductor 22 and controls the power supplied to the load 11 of the AC-DC converter 10. In this embodiment, the NMOS transistor 23 is an N-type MOS (Metal Oxide Semiconductor) transistor, but it may also be a bipolar transistor, IGBT, or the like.

[0028] Furthermore, the gate electrode of the NMOS transistor 23 is connected to terminal OUT1 of the power factor correction IC 24. The NMOS transistor 23 also has a parasitic diode Dp1. If a bipolar transistor is used instead of the NMOS transistor 23, a diode equivalent to the parasitic diode Dp1 is provided in parallel. The NMOS transistor 23 corresponds to the "first transistor".

[0029] The power factor correction IC 24 is an integrated circuit that complementarily switches the NMOS transistor 23 and the NMOS transistor 25 for synchronous rectification so that the output voltage Vout level becomes a target level (e.g., 400V) while improving the power factor of the AC-DC converter 10. Specifically, the power factor correction IC 24 drives the NMOS transistor 23 based on the inductor current IL and the output voltage Vout. Details of the power factor correction IC 24 will be described later, but the power factor correction IC 24 is provided with terminals CSH, CSL, FB, OUT1, OUT2, VB, VCC, and VS. In this embodiment, terminals other than CSH etc. of the power factor correction IC 24 are omitted for convenience. The power factor correction IC 24 corresponds to the "switching control circuit".

[0030] The NMOS transistor 25 is a synchronous rectification transistor, switched complementary to the NMOS transistor 23, and is located between the inductor 22 and the capacitor 27. The gate electrode of the NMOS transistor 25 is connected to terminal OUT2 of the power factor correction IC 24. As will be described in detail later, the NMOS transistor 25 is turned on when the NMOS transistor 23 is turned off in order to allow the inductor current IL from the inductor 22 to flow to the capacitor 27. The NMOS transistor 25 also has a parasitic diode Dp2. Furthermore, the NMOS transistor 25 corresponds to the "second transistor".

[0031] Resistor 26 is located between the connection node of inductor 22 and NMOS transistor 23 and the source electrode of NMOS transistor 25. Resistor 26 also detects the inductor current IL flowing through NMOS transistor 25. The voltage VcsH generated across resistor 26 is applied to terminal CSH of power factor correction IC 24. The current flowing through NMOS transistor 25 corresponds to the "first current," and resistor 26 corresponds to the "first resistance."

[0032] Furthermore, in this embodiment, the resistor 26 is positioned between the connection node of the inductor 22 and the NMOS transistor 23 and the source electrode of the NMOS transistor 25. However, the resistor 26 may also be positioned between the drain electrode of the NMOS transistor 25 and the high-potential side of the capacitor 27.

[0033] Furthermore, resistor 26 may be used to detect the inductor current IL flowing through the NMOS transistor 25 and to detect when an overcurrent flows through the NMOS transistor 25. Resistor 26 may also be used for other protection operations. Additionally, if resistor 26 is used for overcurrent detection or protection, the transmission circuit 104 described later may switch the NMOS transistor 23 on or off based on the voltage across resistor 26.

[0034] Resistors 28 and 29 form a voltage divider circuit that divides the output voltage Vout, generating the feedback voltage Vfb used when switching the NMOS transistor 23. The feedback voltage Vfb generated at the node to which resistors 28 and 29 are connected is applied to terminal FB.

[0035] The power supply 30, together with the diode 31 and capacitor 32, forms a bootstrap circuit and supplies the power supply voltage Vb to terminal VB of the power factor correction IC 24. The power supply 30 also supplies the power supply voltage Vcc to terminal VCC of the power factor correction IC 24.

[0036] Diode 31 has an anode connected to the power supply 30 and a cathode connected to the capacitor 32. When the NMOS transistor 23 is turned on, and the voltage Vs at the connection node of the inductor 22 and the NMOS transistor 23 becomes the ground voltage, it charges the capacitor 32 with the power supply voltage Vcc. The voltage Vs is also applied to the terminal VS of the power factor correction IC 24.

[0037] Capacitor 32 is charged by the current from diode 31 with voltage Vs as the reference, and the power supply voltage Vb is applied to it, supplying the power supply voltage Vb to terminal VB of power factor correction IC 24.

[0038] Resistor 33 is located between the NMOS transistor 23 and ground, and detects the current flowing through the NMOS transistor 23. The voltage VcsL generated across resistor 33 is applied to terminal CSL of the power factor correction IC 24. The current flowing through the NMOS transistor 23 corresponds to the "second current," and resistor 33 corresponds to the "second resistance."

[0039] Furthermore, resistor 33 may be used to detect the inductor current IL flowing through the NMOS transistor 23, and also to detect when an overcurrent flows through the NMOS transistor 23. Resistor 33 may also be used for other protection operations. Additionally, if resistor 33 is used for overcurrent detection or protection operations, the control circuit 103, described later, may turn the NMOS transistor 23 on or off based on the voltage across resistor 33.

[0040] ==Configuration of Power Factor Correction IC24== Figure 4 shows an example of the configuration of the power factor correction IC 24. The power factor correction IC 24 complementaryly switches NMOS transistors 23 and 25. The power factor correction IC 24 also includes a detection circuit 100, drive circuits 101 and 102, a control circuit 103, a transmission circuit 104, and a comparator 105.

[0041] The detection circuit 100 detects the voltage across the resistor 26 and, based on the voltage across the resistor 26, detects that the inductor current IL has reached a predetermined value (for example, zero amperes). Specifically, as shown in Figure 5, the detection circuit 100 may also be a comparator 100a that compares the voltage across the resistor 26 with a reference voltage Vref1a that indicates that the inductor current IL flowing through the NMOS transistor 25 is at a predetermined value.

[0042] Furthermore, when using comparator 100a, in order to determine whether the inductor current IL is an overcurrent, comparator 100b is provided that compares a reference voltage Vref1b, which indicates that the inductor current is an overcurrent, with the voltage generated across resistor 26. Note that reference voltages Vref1a and Vref1b are different from each other.

[0043] Furthermore, the detection circuit 100 may also include an analog-to-digital converter (ADC) 100c that converts the voltage across the resistor 26 into a digital value, and a digital comparator (CMP) 100d, as shown in Figure 6. In this case, the transmission circuit 104, described later, may transmit a signal (e.g., signal SDET) to a circuit that operates at the power supply voltage Vcc (e.g., the control circuit 103, described later) based on the comparison result of the comparator 100d.

[0044] On the other hand, the transmission circuit 104, described later, transmits the digital value to the control circuit 103, described later, and the control circuit 103 may include a digital comparator 100d that compares the digital value with a threshold. The control circuit 103 may then output a signal (e.g., signal S1) to a circuit that operates at the power supply voltage Vcc (e.g., the drive circuit 101, described later) based on the comparison result of the comparator 100d.

[0045] The comparator 100d compares the digital value with a first threshold Th1 for detecting when the inductor current IL reaches a predetermined value, and a second threshold Th2 for detecting when the inductor current IL becomes an overcurrent. The first threshold Th1 and the second threshold Th2 are different thresholds. In this example, one comparator 100d compares the digital value with the first threshold Th1 and the second threshold Th2, but two comparators may be used, each comparing the digital value with the first threshold Th1 and the second threshold Th2, respectively.

[0046] The drive circuit 101 drives the NMOS transistor 23 based on the detection result of the detection circuit 100 and the output voltage Vout. The drive circuit 101 corresponds to the "first drive circuit".

[0047] The drive circuit 101 switches the NMOS transistor 23 based on the signal S1 from the control circuit 103, which will be described later. Specifically, the drive circuit 101 turns the NMOS transistor 23 on and off based on the detection result of the detection circuit 100, the output voltage Vout, and the detection result of the comparator 105, which will be described later. That is, when the drive circuit 101 detects that the inductor current IL has reached a predetermined value, it turns on the NMOS transistor 23, and when a period corresponding to the output voltage Vout has elapsed, it turns off the NMOS transistor 23.

[0048] The drive circuit 102 drives the NMOS transistor 25 so that it is switched on and off in a complementary manner to the NMOS transistor 23. The drive circuit 102 switches the NMOS transistor 25 based on the signal S2 from the transmission circuit 104, which will be described later. Note that the drive circuit 102 corresponds to the "second drive circuit".

[0049] The control circuit 103 outputs a signal S1 for controlling the NMOS transistor 23 based on the comparison result between the signal SDET from the transmission circuit 104 (described later), the output voltage Vout, and the comparator 105 (described later). The control circuit 103 also outputs a signal SIN to the transmission circuit 104 (described later) for controlling the NMOS transistor 25.

[0050] Furthermore, when the comparator 105 (described later) detects that the inductor current IL flowing through the NMOS transistor 23 is an overcurrent, the control circuit 103 outputs a signal S1 to the drive circuit 101 to turn off the NMOS transistor 23. Signal S1 corresponds to the "first signal," and signal SIN corresponds to the "second signal."

[0051] The transmission circuit 104 transmits the signal SIN to the drive circuit 102 and switches the NMOS transistor 25 via the drive circuit 102. Specifically, the transmission circuit 104 transmits the detection result of the detection circuit 100 to the control circuit 103 and transmits the signal S2 based on the signal SIN to the drive circuit 102. Also, if the detection circuit 100 is composed of a comparator 100a, the transmission circuit 104 transmits the comparison result of the comparator 100a to the control circuit 103.

[0052] The drive circuit 101 then drives the NMOS transistor 23 based on the signal S1. The drive circuit 102 also drives the NMOS transistor 25 based on the signal SIN.

[0053] Furthermore, the transmission circuit 104 internally provides an interface between a circuit operating at the power supply voltage Vb (e.g., detection circuit 100) and a circuit operating at the power supply voltage Vcc (e.g., control circuit 103). In this case, the transmission circuit 104 level-shifts a pulsed signal based on the detection result of the detection circuit 100 of the power supply voltage Vb to the power supply voltage Vcc. Also, to indicate the timing when the inductor current IL reaches a predetermined value, it is unnecessary to transmit, for example, an analog quantity proportional to the current value of the inductor current IL, and a pulsed signal is sufficient.

[0054] The detection circuit 100, the drive circuit 102, and the transmission circuit 104 operate at the power supply voltage Vb. Furthermore, the detection circuit 100 and the drive circuit 102 operate with voltage Vs as a reference.

[0055] The comparator 105 detects the inductor current IL flowing through the NMOS transistor 23 based on the voltage generated across the resistor 33. Specifically, the comparator 105 detects that the inductor current IL flowing through the NMOS transistor 23 is an overcurrent when the voltage generated across the resistor 33 exceeds the reference voltage Vref0 which indicates an overcurrent. The comparator 105 corresponds to the "first comparator".

[0056] ==Path of inductor current IL== Returning to Figure 3, we will explain the path of the inductor current IL when NMOS transistors 23 and 25 are switched on and off. The dashed line shown in Figure 3 represents the path of the inductor current IL when NMOS transistor 23 is on (i.e., NMOS transistor 25 is off), and the dashed line represents the path of the inductor current IL when NMOS transistor 23 is off (i.e., NMOS transistor 25 is on).

[0057] First, when the NMOS transistor 23 is turned on, the inductor current IL flows in the following order: full-wave rectifier circuit 20, inductor 22, NMOS transistor 23, and resistor 33. Therefore, resistor 33 can detect the inductor current IL flowing through the NMOS transistor 23.

[0058] Next, when the NMOS transistor 23 is off, the inductor current IL flows in the following order: full-wave rectifier circuit 20, inductor 22, resistor 26, NMOS transistor 25, and capacitor 27. Therefore, resistor 26 can detect the inductor current IL flowing through the NMOS transistor 25.

[0059] Furthermore, when NMOS transistor 23 is turned on and then turned off, the inductor current IL peaks and then decreases to a predetermined value. Subsequently, when NMOS transistor 25 is turned on, the voltage level of the output voltage Vout is higher than the voltage level of the rectified voltage Vrec, so the inductor current IL tends to flow in the negative direction. Therefore, by detecting the voltage generated across resistor 26, it is possible to detect that the inductor current IL has reached a predetermined value.

[0060] This makes it possible to provide a switching control circuit that can detect the timing at which the inductor current reaches a predetermined value without using an auxiliary coil.

[0061] ===Unique Text=== Figure 7 shows an example of the configuration of the AC-DC converter 12. The AC-DC converter 12 is shown as an example of an interleaved configuration using n (n is an integer of 2 or more) power factor correction ICs 24. The configuration of the peripheral circuits of the power factor correction ICs 24 is the same as in the case of the AC-DC converter 10 in Figure 1, so the explanation is omitted. Each of the n power factor correction ICs 24 switches each of the n NMOS transistors 23 corresponding to the n power factor correction ICs 24 to perform interleaved operation. Each of the n power factor correction ICs 24 also drives each of the n NMOS transistors 25 corresponding to the n power factor correction ICs 24.

[0062] ==Path of inductor current IL in interleaved configuration== Using Figure 7, we will explain the path of the inductor current IL when NMOS transistors 23 and 25 are switched on and off. First, we will explain the paths of the inductor currents IL1 and IL2 when NMOS transistors 23 and 25 are switched on and off in a typical AC-DC converter 500 shown in Figure 8. Figure 8 shows the interleaved configuration when n is 2.

[0063] In Figure 8, each power factor correction IC501 is equipped with a resistor 34 to detect when the inductor currents IL1 and IL2 have reached predetermined values.

[0064] In Figure 8, the dashed line shows the path of the inductor current IL when NMOS transistor 23 is ON (i.e., NMOS transistor 25 is OFF), and the dashed line shows the path of the inductor current IL when NMOS transistor 23 is OFF (i.e., NMOS transistor 25 is ON). The same applies to Figure 7.

[0065] The path of the inductor current when the NMOS transistor 23 is turned on or off is the same as explained using Figure 3, so the explanation is omitted. Also, for example, during the period when the first NMOS transistor 23 and the second NMOS transistor 23 shown in Figure 8 are off, the sum of the currents IL1 and IL2 flowing through the inductor 22 flows to ground via the capacitor 27. The sum of the inductor currents IL1 and IL2 that flowed towards ground is divided due to the difference in impedance of the respective ground lines, each of which is provided with a resistor 34.

[0066] Therefore, if the AC-DC converter 500 is configured to perform interleaved operation, it is not possible to detect that the inductor currents IL1 and IL2 have reached predetermined values ​​simply based on the current flowing through resistor 34.

[0067] Furthermore, in the power factor correction IC 501 shown in Figure 8, when the NMOS transistor 23 is off, the NMOS transistor 25 is on. Therefore, even if the inductor current IL decreases to a predetermined value, the voltage Vds shown in Figure 2 does not decrease. Consequently, even if an auxiliary coil is provided for the inductor 22, it is not possible to detect that the inductor current IL has reached a predetermined value.

[0068] On the other hand, as shown in Figure 7, if the resistor 26 is provided, for example, between the connection node of the inductor 22 and the NMOS transistor 23 and the NMOS transistor 25, then the inductor currents IL1 to ILn before they merge at the capacitor 27 can be detected.

[0069] This makes it possible to provide a switching control circuit that can detect the timing at which the inductor current reaches a predetermined value without using an auxiliary coil, even in a circuit configuration that performs interleaved operation while synchronous rectification using an NMOS transistor 25.

[0070] ===Summary=== The AC-DC converter 10 of this embodiment has been described above. The power factor correction IC 24 includes a detection circuit 100 and drive circuits 101 and 102. This makes it possible to provide a switching control circuit that can detect the timing at which the inductor current reaches a predetermined value without using an auxiliary coil.

[0071] Furthermore, the resistor 26 is located between the connection node of the inductor 22 and the NMOS transistor 23 and the NMOS transistor 25. This allows the voltage generated across the resistor 26 to be detected with respect to the voltage Vs, thus enabling more accurate detection of when the inductor current IL has reached a predetermined value.

[0072] Furthermore, the power factor correction IC24 includes a control circuit 103 and a transmission circuit 104. This allows signals to be transmitted between a circuit that operates with the power supply voltage Vb, with voltage Vs as the reference (e.g., detection circuit 100), and a circuit that operates with the power supply voltage Vcc, with ground as the reference (e.g., drive circuit 101).

[0073] Furthermore, the detection circuit 100 is a comparator 100a. This makes it easier to detect when the inductor current IL has reached a predetermined value than when using the analog-to-digital conversion circuit 100c. On the other hand, when the analog-to-digital conversion circuit 100c is provided, it is possible to use the information on the current value of the inductor current IL to perform more advanced control, such as suppressing input current distortion.

[0074] Furthermore, the AC-DC converter 10 includes a resistor 33, and the power factor correction IC 24 includes a comparator 105. This allows detection of whether the inductor current IL flowing through the NMOS transistor 23 has become an overcurrent.

[0075] Furthermore, the AC-DC converter 10 includes a diode 31 and a capacitor 32. This allows the power supply voltage Vb to be generated by utilizing the fact that the voltage level of voltage Vs fluctuates between the output voltage Vout and ground.

[0076] Furthermore, the AC-DC converter 12 operates in an interleaved manner using multiple power factor correction ICs 24. In addition, by using resistors 26, even when interleaved operation is performed, the inductor currents IL1 to ILn flowing through each of the NMOS transistors 25 can be detected separately, and it is possible to detect when each of the inductor currents IL1 to ILn reaches a predetermined value.

[0077] Furthermore, the AC-DC converter 12 includes a resistor 33, and the power factor correction IC 24 includes a comparator 105. This allows detection of whether or not each of the inductor currents IL1 to ILn flowing through each of the NMOS transistors 23 has become overcurrent.

[0078] 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]

[0079] 10,12,500 AC-DC converter 11 Load 20 Full wave rectifier circuit 21, 27, 32 Capacitors 22 Inductors 23,25 NMOS transistors 24,501 Power Factor Correction IC 26, 28, 29, 33, 34 resistors 30 power supply 31 diodes 100 detection circuit 100a, 100b, 100d, 105 Comparator 101,102 Drive Circuit 103 Control circuit 104 Transmission Circuit

Claims

1. A switching control circuit for a power supply circuit that generates an output voltage of a target level from the AC voltage to the output capacitor, comprising an inductor to which a rectified voltage corresponding to an AC voltage is applied, a first transistor for controlling the inductor current flowing through the inductor, and a second transistor located between the inductor and an output capacitor, wherein the first and second transistors are switched complementaryly. The aforementioned power supply circuit is A first resistor located between the connection node of the inductor and the first transistor and the output capacitor, for detecting the first current flowing through the second transistor, Includes, The aforementioned switching control circuit is A detection circuit for detecting the voltage generated across the first resistor, A first drive circuit drives the first transistor based on the detection result of the detection circuit and the output voltage, A second drive circuit drives the second transistor so that it is switched on and off in a complementary manner to the first transistor, A switching control circuit including a switch.

2. A switching control circuit according to claim 1, The first resistor is Located between the aforementioned connection node and the second transistor, Switching control circuit.

3. A switching control circuit according to claim 1, A control circuit that outputs a first signal for controlling the first transistor and a second signal for controlling the second transistor based on the detection result of the detection circuit and the output voltage, A transmission circuit that transmits the detection result of the detection circuit to the control circuit and transmits the second signal to the second drive circuit, Equipped with, The first drive circuit is, Based on the first signal, the first transistor is driven, The second drive circuit is, Based on the second signal, the second transistor is driven, Switching control circuit.

4. A switching control circuit according to claim 3, The detection circuit is This is a comparator that compares the voltage generated across the first resistor with a reference voltage that indicates the first current is at a predetermined value. The aforementioned transmission circuit is The comparison result of the comparator is transmitted to the control circuit. The first drive circuit is, When it is detected that the first current has reached a predetermined value, the first transistor is turned on, and when a period corresponding to the output voltage has elapsed, the first transistor is turned off. Switching control circuit.

5. A switching control circuit according to claim 4, The aforementioned power supply circuit is A capacitor to which a voltage is applied to operate the second drive circuit and the transmission circuit, The system includes a diode that charges the capacitor during the period when the first transistor is turned on. Switching control circuit.

6. A switching control circuit according to any one of claims 1 to 5, A second resistor for detecting the second current flowing through the first transistor, Equipped with, The aforementioned switching control circuit is A first comparator detects the second current flowing through the first transistor based on the voltage generated across the second resistor. Includes, The first drive circuit is, Based on the detection result of the detection circuit, the output voltage, and the detection result of the first comparator, the first transistor is turned on or off. Switching control circuit.

7. A power supply circuit that generates an output voltage of a desired level from an AC voltage and outputs it to an output capacitor, n inductors (where n is an integer of 2 or more) to which a rectified voltage corresponding to the aforementioned AC voltage is applied, n first transistors control the inductor current flowing through each of the n inductors, n second transistors located between each of the n inductors and the output capacitor, N first resistors are located between each of the n inductors, each of the n first transistors, and the output capacitor, and detect the first current flowing through each of the n second transistors. n switching control circuits that complementarily switch the n first and second transistors, Equipped with, Each of the n switching control circuits is A detection circuit for detecting the voltage generated in each of the n first resistors, A first drive circuit that drives each of the n first transistors corresponding to each of the n switching control circuits based on the detection result of the detection circuit and the output voltage, A second drive circuit that drives each of the n second transistors corresponding to each of the n switching control circuits so that they are switched on and off complementaryly with respect to each of the n first transistors, Includes, The n switching control circuits are, The n first transistors are switched to operate in an interleaved manner. power circuit.

8. The power supply circuit according to claim 7, n second resistors for detecting the second current flowing through each of the n first transistors, Equipped with, Each of the aforementioned switching control circuits is: A first comparator that detects the second current flowing through each of the n first transistors corresponding to each of the n switching control circuits, based on the voltage generated across each of the second resistors corresponding to each of the n first transistors, Includes, The first drive circuit is, Based on the detection result of the detection circuit, the output voltage, and the detection result of the first comparator, each of the n first transistors corresponding to each of the n switching control circuits is turned on or off. power circuit.

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