Switching control circuit, power factor correction circuit

Abstract

To provide a switching control circuit that can improve a power factor.SOLUTION: A switching control circuit is a switching control circuit that, based on an inductor current flowing in an inductor to which a rectification voltage from a rectification circuit for rectifying an AC voltage is applied and an output voltage generated from the AC voltage, controls switching of a transistor for controlling the inductor current. The switching control circuit comprises: a target value output circuit that outputs a target value of a peak value of the inductor current to make the waveform of the peak value similar to the waveform of the rectification voltage; and a driving signal output circuit that outputs a driving signal for turning on the transistor when the inductor current becomes smaller than a predetermined value and turning off the transistor when the peak value of the inductor current reaches the target value.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a switching control circuit and a power factor correction circuit. [Background technology]

[0002] Generally, there is a switching control circuit that improves the power factor by making the waveform of an AC voltage similar to the waveform of an input current (for example, Patent Documents 1 to 5). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2010-104218 A [Patent Document 2] JP 2020-014325 A [Patent Document 3] JP 2018-064410 A [Patent Document 4] JP 2017-085865 A [Patent Document 5] JP 2012-222864 A Summary of the Invention [Problem to be solved by the invention]

[0004] By the way, some switching control circuits control transistors so that the on-time is constant, and operate the power supply circuit in critical mode. When using such a switching control circuit, the power factor may deteriorate due to the effects of diodes and inductors in the power supply circuit.

[0005] The present invention has been made in consideration of the above-mentioned problems in the conventional technology, and an object of the present invention is to provide a switching control circuit capable of improving the power factor. [Means for solving the problem]

[0006] A first aspect of the switching control circuit of the present invention that solves the above-mentioned problems is a switching control circuit that controls switching of a transistor that controls an inductor current based on an inductor current flowing through an inductor to which a rectified voltage from a rectifier circuit that rectifies an AC voltage is applied and an output voltage generated from the AC voltage, and includes a target value output circuit that outputs a target value for the peak value of the inductor current so that the waveform of the peak value of the inductor current is similar to the waveform of the rectified voltage, and a drive signal output circuit that outputs a drive signal that turns on the transistor when the inductor current becomes smaller than a predetermined value and turns off the transistor when the peak value of the inductor current reaches the target value.

[0007] The power factor correction circuit of the present invention that solves the above-mentioned problems is a power factor correction circuit that generates an output voltage from an AC voltage, and includes a rectifier circuit that rectifies the AC voltage, an inductor to which the rectified voltage from the rectifier circuit is applied, a transistor that controls an inductor current flowing through the inductor, and a switching control circuit that controls switching of the transistor based on the inductor current and the output voltage, and the switching control circuit includes a target value output circuit that outputs a target value for the peak value of the inductor current so that the waveform of the peak value of the inductor current is similar to the waveform of the rectified voltage, and a drive signal output circuit that outputs a drive signal that turns on the transistor when the inductor current becomes smaller than a predetermined value and turns off the transistor when the peak value of the inductor current becomes the target value.

[0008] A second aspect of the switching control circuit of the present invention that solves the above-mentioned problems is a switching control circuit that controls switching of a transistor that controls an inductor current, based on an inductor current flowing through an inductor to which a rectified voltage from a rectifier circuit that rectifies an AC voltage is applied, and an output voltage generated from the AC voltage, and includes a target value output circuit that outputs a target value for a peak value of the inductor current, and a drive signal output circuit that outputs a drive signal that turns on the transistor when the inductor current becomes smaller than a predetermined value and turns off the transistor when the peak value of the inductor current reaches the target value, and the target value has the same period and phase as the AC voltage, and has a proportional amplitude. Effect of the Invention

[0009] According to the present invention, it is possible to provide a switching control circuit capable of improving the power factor. [Brief description of the drawings]

[0010] [Figure 1] 1 is a diagram illustrating an example of an AC-DC converter 10. FIG. [Diagram 2] FIG. 2 is a diagram showing the configuration of a power factor correction IC 25a. [Diagram 3] FIG. 4 is a diagram showing a configuration of a switching control circuit 42a. [Figure 4] 11 is a diagram for explaining a method of estimating an estimated value Vr_est. FIG. [Diagram 5] 1 is a diagram for explaining the principle of generation of a ripple component of an output voltage Vout. [Figure 6] 4 is a diagram illustrating the relationship between the output voltage Vout and the pulse width. FIG. [Figure 7] FIG. 4 is a diagram showing a configuration of a switching control circuit 42b. [Figure 8] 4 is a diagram for explaining a method of estimating a rectified voltage Vrec and a method of calculating an inductance value L. FIG. [Figure 9] FIG. 4 is a diagram showing a configuration of a switching control circuit 42c. [Figure 10]FIG. 4 is a diagram showing a configuration of a switching control circuit 42d. [Figure 11] FIG. 2 is a diagram illustrating an example of an AC-DC converter 12. [Figure 12] FIG. 2 is a diagram showing the configuration of a power factor correction IC 25b. [Figure 13] FIG. 4 is a diagram showing a configuration of a switching control circuit 45. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] At least the following points will become apparent from the description of this specification and the accompanying drawings. =====This embodiment===== FIG. 1 is a diagram showing an example of the configuration of an AC-DC converter 10 according to an embodiment of the present invention. The AC-DC converter 10 is a boost chopper type power supply circuit that generates an output voltage Vout at a target level from an AC voltage Vac of a commercial power supply. The AC-DC converter 10 applies the output voltage Vout to a load 11 to supply power and causes a current Iload to flow. Although details will be described later, the AC-DC converter 10 operates as a power factor correction circuit that operates in a critical mode or a discontinuous mode. Here, the "critical mode" is a mode in which switching is turned on when an inductor current IL, which will be described later, becomes zero. The "discontinuous mode" is a mode in which the inductor current IL flows intermittently, that is, an intermittent mode in which there is a period in which the inductor current IL becomes zero every time within a switching period.

[0012] The AC-DC converter 10 includes a full-wave rectifier circuit 20, capacitors 21 and 27, an inductor 22, an NMOS transistor 23, resistors 24, 28, and 29, a power factor correction IC 25, and a diode .

[0013] The full-wave rectifier circuit 20 full-wave rectifies a predetermined input AC voltage Vac, and applies the result as an input voltage Vrec to the capacitor 21 and the inductor 22. The AC voltage Vac has an effective value of 140 to 240 V and a frequency of 50 to 60 Hz, for example. In the following description of the present embodiment, the voltage is basically a potential difference with respect to a reference point (GND in FIG. 1), but the AC voltage Vac refers to the voltage between terminals.

[0014] The capacitor 21 smoothes the input voltage Vrec, and the capacitor 27, together with the inductor 22, the NMOS transistor 23, and the diode 26, constitute a boost chopper circuit. Therefore, the charging voltage of the capacitor 27 becomes the DC output voltage Vout. The current flowing through the diode 26 is the current Id, and the current flowing through the capacitor 27 is the charging current Ic.

[0015] The NMOS transistor 23 is a switching element for controlling the power 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 may be, for example, a bipolar transistor. A gate electrode of the NMOS transistor 23 is connected to a terminal OUT of the power factor correction IC 25.

[0016] The resistor 24 is a resistor for detecting the inductor current IL flowing through the inductor 22 when the NMOS transistor 23 is turned on. One end of the resistor 24 is connected to the source electrode of the NMOS transistor 23 and the other end is connected to the terminal CS of the power factor correction IC 25.

[0017] The power factor correction IC 25 is an integrated circuit that controls switching of the NMOS transistor 23 so that the level of the output voltage Vout becomes a target level (e.g., 400 V) while improving the power factor of the AC-DC converter 10. Specifically, the power factor correction IC 25 drives the NMOS transistor 23 based on the inductor current IL and the output voltage Vout. The power factor correction IC 25 is provided with terminals CS, FB, and OUT, which will be described in detail later. In this embodiment, terminals other than the terminal CS of the power factor correction IC 25 are omitted for convenience.

[0018] The resistors 28 and 29 form a voltage divider circuit that divides the output voltage Vout and generates a feedback voltage Vfb used when switching the NMOS transistor 23. The feedback voltage Vfb generated at the node to which the resistors 28 and 29 are connected is applied to the terminal FB.

[0019] <<<About the Power Factor Correction IC25>>> == Configuration of power factor correction IC25a == 2 is a diagram showing a configuration of a power factor correction IC 25a which is one embodiment of the power factor correction IC 25. The power factor correction IC 25a includes analog-to-digital converters (ADCs) 40 and 41, a switching control circuit 42, and a buffer circuit 43.

[0020] The AD converter 40 converts the feedback voltage Vfb into a digital value, and the AD converter 41 converts the voltage indicating the inductor current IL, which is detected by the resistor 24 and has its polarity inverted by a level shift circuit (not shown), into a digital value. In this embodiment, the feedback voltage Vfb converted into a digital value is referred to as the feedback voltage Vfb for convenience. Similarly, the signal indicating the inductor current IL converted into a digital value and processed in the switching control circuit 42 is also referred to as the inductor current IL for convenience.

[0021] The switching control circuit 42 outputs a drive signal Sdrv based on the feedback voltage Vfb and the inductor current IL.

[0022] The buffer circuit 43 amplifies the drive signal Sdrv and outputs a voltage Vdr for driving the NMOS transistor 23 .

[0023] ==Switching control circuit 42a== 3 is a diagram showing a configuration of a switching control circuit 42a which is one embodiment of the switching control circuit 42. The switching control circuit 42a outputs a drive signal Sdrv based on a feedback voltage Vfb and an inductor current IL.

[0024] The switching control circuit 42a includes a target value output circuit 50a, a drive signal output circuit 51a, a low-pass filter (LPF) 52, and a multiplier 53.

[0025] The target value output circuit 50a outputs a target value ILtarget for making the waveform of the peak value of the inductor current IL similar to the waveform of the rectified voltage Vrec.

[0026] Specifically, the target value output circuit 50a outputs a low target value ILtarget when the feedback voltage Vfb rises and becomes higher than the reference voltage VREF0 that is the reference for the target level of the output voltage Vout. On the other hand, the target value output circuit 50a outputs a high target value ILtarget when the feedback voltage Vfb falls and becomes lower than the reference voltage VREF0.

[0027] The target value output circuit 50 a includes a subtractor 60 , a voltage regulator (AVR) 61 , and a multiplier 62 .

[0028] The subtractor 60 subtracts the feedback voltage Vfb from the reference voltage VREF0 to calculate an error E1 between the reference voltage VREF0 and the feedback voltage Vfb.

[0029] The voltage regulator 61 outputs a command voltage VA for matching the level of the feedback voltage Vfb with the level of the reference voltage VREF0 in accordance with the error E1. The subtractor 60 and the voltage regulator 61 correspond to a so-called error amplifier circuit that amplifies and integrates the error E1, for example.

[0030] Multiplier 62 multiplies an estimate value Vr_est of rectified voltage Vrec from multiplier 53 (described later) by a command voltage VA, and outputs the multiplication result as a target value ILtarget of inductor current IL. That is, multiplier 62 multiplies the command voltage VA, which varies based on fluctuations in output voltage Vout, by a component of the estimate value Vr_est, and outputs the target value ILtarget.

[0031] As a result, the target value output circuit 50a controls the inductor current IL by lowering or increasing the target value ILtarget of the inductor current IL in order to maintain the output voltage Vout at a target level as the output voltage Vout increases or decreases.

[0032] As a result, the waveform of the average value ILmean of the inductor current IL becomes similar to the waveform of the rectified voltage Vrec, and the switching control circuit 42 improves the power factor. That is, the waveform of the input current Iac also becomes similar to the waveform of the AC voltage Vac, and the power factor of the AC-DC converter 10 is improved. The target value output circuit 50a outputs a reference voltage indicating the target value ILtarget as the target value ILtarget. Therefore, the target value ILtarget is in phase with the rectified voltage Vrec, has the same period, and has a proportional amplitude.

[0033] The drive signal output circuit 51a is a circuit that outputs a drive signal Sdrv that turns on and off the NMOS transistor 23 based on the inductor current IL. Specifically, the drive signal output circuit 51a outputs the drive signal Sdrv that turns on the NMOS transistor 23 when the inductor current IL becomes smaller than a predetermined value, and turns off the NMOS transistor 23 when the peak value of the inductor current IL becomes a target value ILtarget.

[0034] The drive signal output circuit 51a includes comparators (CMP) 70 and 72, and an SR flip-flop 71.

[0035] The comparator 70 detects when the inductor current IL becomes smaller than a predetermined value. Specifically, when the inductor current IL becomes a predetermined value (e.g., approximately zero), the comparator 70 outputs a high-level (hereinafter referred to as "H" level) signal S0. On the other hand, when the inductor current IL does not become the predetermined value, the comparator 70 outputs a low-level (hereinafter referred to as "L" level) signal S0. Note that "when the inductor current IL becomes a predetermined value" also includes "after the inductor current IL becomes a predetermined value."

[0036] The SR flip-flop 71 outputs the drive signal Sdrv based on the signals S0 and S1 from the comparators 70 and 72. Specifically, the SR flip-flop 71 outputs the drive signal Sdrv at an "H" level when the comparator 70 outputs the signal S0 at an "H" level, and outputs the drive signal Sdrv at an "L" level when the comparator 72, which will be described later, outputs the signal S1 at an "H" level.

[0037] On the other hand, when the comparators 70 and 72 both output the signals S0 and S1 at the “L” level, the SR flip-flop 71 does not transition the logical level of the drive signal Sdrv. When the drive signal Sdrv is at the “H” level, the NMOS transistor 23 is turned on, and when the drive signal Sdrv is at the “L” level, the NMOS transistor 23 is turned off.

[0038] The comparator 72 detects when the peak value of the inductor current IL reaches the target value ILtarget. Specifically, when the peak value of the inductor current IL reaches the target value ILtarget, the comparator 72 outputs a signal S1 at an "H" level. On the other hand, when the peak value of the inductor current IL is smaller than the target value ILtarget, the comparator 72 outputs a signal S1 at an "L" level.

[0039] For this reason, the drive signal output circuit 51a outputs the drive signal Sdrv so that the AC-DC converter 10 operates in the critical mode.

[0040] Based on a signal S2 having a logical level opposite to that of the drive signal Sdrv, the low pass filter (LPF) 52 integrates the drive signal Sdrv during the period in which the NMOS transistor 23 is turned off, and outputs an off voltage Voff. In this embodiment, an estimated value Vr_est from a multiplier 53 (described later) is input to the multiplier 62, but the off voltage Voff from the LPF 52 may be input to the multiplier 62. In other words, the off voltage Voff can also be used as an estimated value of the rectified voltage Vrec.

[0041] Multiplier 53 multiplies off-voltage Voff by feedback voltage Vfb, and outputs estimated value Vr_est with ripple components of off-voltage Voff removed. The reason why multiplier 53 can remove ripple components of off-voltage Voff will be described later. LPF 52 corresponds to an "estimation circuit" or an "integration circuit", and multiplier 53 corresponds to an "removal circuit".

[0042] <<<How to estimate the estimated value Vr_est>>> 4 is a diagram for explaining a method for estimating the estimated value Vr_est. Here, the inductor current IL is indicated by a solid line, the target value ILtarget is indicated by a dashed line, and the average value ILmean of the inductor current IL is indicated by a two-dot chain line. Moreover, the signal S2 has a logical level opposite to that of the drive signal Sdrv, and is a signal output from the inverted output of the SR flip-flop 71.

[0043] Therefore, the period during which the signal S2 is at the "L" level is the on-period Ton during which the NMOS transistor 23 is on, and the period during which the signal S2 is at the "H" level is the off-period Toff during which the NMOS transistor 23 is off.

[0044] First, the on-period Ton and the off-period Toff will be described. When the inductor current IL reaches a predetermined value, the SR flip-flop 71 outputs a drive signal Sdrv of "H" level, and the on-period Ton begins. Then, when the inductor current IL reaches a target value ILtarget, the SR flip-flop 71 outputs a drive signal Sdrv of "L" level, and the off-period Toff begins. After that, when the inductor current IL reaches a predetermined value, the SR flip-flop 71 outputs a signal drive signal Sdrv of "H" level, and the on-period Ton begins again. Thereafter, this operation continues.

[0045] At this time, if the inductance value of the inductor 22 is L, the following relationship holds between the target value ILtarget, the inductance value L, the rectified voltage Vrec, the on-period Ton, the off-period Toff, and the output voltage Vout.

[0046] ILtarget=Vrec / L×Ton=(Vout-Vrec) / L×Toff ···(1) From equation (1), the on-period Ton and the switching period obtained by adding the on-period Ton and the off-period Toff are expressed by the following equation.

[0047] Ton=(Vout-Vrec) / Vrec×Toff...(2) Ton+Toff=Vout / Vrec×Toff (3) Therefore, from equations (2) and (3), the off-duty α expressed by Toff / (Ton+Toff) is expressed by the following equation.

[0048] α = Vrec / Vout (4) Moreover, since α<1 and the rectified voltage Vrec is smaller than the output voltage Vout in the AC-DC converter 10, the formula (4) always holds in this embodiment.

[0049] Furthermore, equation (4) indicates that, assuming that the output voltage Vout is constant, the off-duty α has an AC component of the rectified voltage Vrec. Therefore, if the off-duty α can be calculated, the estimated value Vr_est of the rectified voltage Vrec can be estimated.

[0050] Further, the off-duty α is obtained as an off-voltage Voff obtained by smoothing or integrating the signal S2 by the LPF 52, and the off-voltage Voff is an estimated value of the rectified voltage Vrec. However, since the output voltage Vout has a ripple component based on the AC component of the AC voltage Vac as described later, the off-voltage Voff also contains a ripple component.

[0051] Therefore, the multiplier 53 multiplies the feedback voltage Vfb, which has a ripple component of the output voltage Vout, by the off-voltage Voff to remove the ripple component of the off-voltage Voff, and outputs the result as the estimated value Vr_est. The target value output circuit 50a then outputs the target value ILtarget based on the estimated value Vr_est from which the ripple component has been removed.

[0052] <<<Ripple component of output voltage Vout>>> 5 is a diagram for explaining the principle of generation of the ripple component of the output voltage Vout. In addition, in Vac / Iac, the solid line indicates the AC voltage Vac, and the dashed line indicates the input current Iac.

[0053] First, if the amplitude of the AC voltage Vac is V and the amplitude of the input current Iac is I, the AC voltage Vac, the input current Iac, and the input power Pac can be expressed as follows:

[0054] Vac = Vsinθ (5) Iac = I sinθ (6) Pac=Vac×Iac=VIsin 2 θ =VI / 2-VI / 2×cos2θ (7) If the current flowing through the diode 26 of the AC-DC converter 10 is represented as a current Id, the current Id can be expressed as follows using the output voltage Vout.

[0055] Id=Pac / Vout =VI / 2 / Vout-VI / 2 / Vout×cos2θ (8) Here, if the first term in equation (8) is the DC component, that is, the load current Iload, the charging current Ic can be expressed as follows:

[0056] Ic=-VI / 2 / Vout×cos2θ (9) The ripple component ΔVout of the output voltage Vout is obtained by integrating the current Ic and dividing it by the capacitance value C of the capacitor 27, and is expressed as follows:

[0057] ΔVout=-VI / 4 / Vout / C×sin2θ (10) Therefore, the ripple component ΔVout fluctuates at a frequency twice that of the AC voltage Vac, and the amplitude of the ripple component ΔVout is inversely proportional to the capacitance value C.

[0058] <<<Relationship between output voltage Vout and pulse width>>> Fig. 6 is a diagram for explaining the relationship between the output voltage Vout and the pulse width. The relationship between the AC voltage Vac, the input current Iac, and the output voltage Vout is the same as in Fig. 5. The voltage at the connection point between the inductor 22 and the NMOS transistor 23 is taken as voltage Vsw. When the NMOS transistor 23 is on, the voltage Vsw becomes the ground voltage, and when the NMOS transistor 23 is off, the voltage Vsw becomes a voltage according to the output voltage Vout.

[0059] Moreover, from the formula (1), the target value ILtarget is expressed as follows:

[0060] ILtarget=(Vout-Vrec) / L×Toff (11) By modifying the equation (11), the off period Toff is expressed as follows:

[0061] Toff=ILtarget×L / (Vout-Vrec) ···(12) Here, in a certain switching period, if the target value ILtarget and the rectified voltage Vrec are set to predetermined values, according to equation (12), the higher the output voltage Vout, the shorter the off period Toff becomes. Therefore, when the ripple component ΔVout of the output voltage Vout is taken into consideration, the pulse width of the voltage Vsw changes as shown in FIG.

[0062] In addition, when the inductor current IL is within a certain range defined by the target value ILtarget, the rectified voltage Vrec is approximately equal to the average value of the voltage Vsw. This is because, when the rectified voltage Vrec is higher than the average value of the voltage Vsw, the inductor current IL increases without limit, and when it is smaller, the inductor current IL stops flowing.

[0063] That is, in this embodiment, considering that the inductor current IL flows while being limited by the target value ILtarget, it can be said that the rectified voltage Vrec is approximately equal to the average value of the voltage Vsw. Also, the rectified voltage Vrec, i.e., the average value of the voltage Vsw, is proportional to the product of the pulse width of the voltage Vsw and the output voltage Vout.

[0064] The pulse width of the voltage Vsw is the same as the pulse width of the signal S2 from the SR flip-flop 71. As described above, the off-voltage Voff from the LPF 52 that smoothes or integrates the signal S2 becomes higher when the ripple component ΔVout of the output voltage Vout becomes negative, and conversely, becomes lower when the ripple component ΔVout of the output voltage Vout becomes positive.

[0065] Therefore, the estimated value Vr_est obtained by multiplying the feedback voltage Vfb corresponding to the output voltage Vout by the off-voltage Voff by the multiplier 53 is a voltage from which the ripple component ΔVout of the output voltage Vout has been removed.

[0066] ==Switching control circuit 42b== Fig. 7 is a diagram showing a configuration of a switching control circuit 42b which is one embodiment of the switching control circuit 42. Note that in Fig. 7, the same reference symbols as in Fig. 3 are given to the same objects as in Fig. 3. Therefore, detailed descriptions of the same objects will be omitted.

[0067] The switching control circuit 42b turns on the NMOS transistor 23 to reduce the switching loss of the NMOS transistor 23 by utilizing the pseudo-resonance that occurs between the inductor 22 and the parasitic capacitance after the NMOS transistor 23 is turned off. Specifically, when a predetermined period of time has elapsed after the inductor current IL reaches a predetermined value and the voltage Vsw, which is the drain-source voltage of the NMOS transistor 23, drops due to the pseudo-resonance, the switching control circuit 42b turns on the NMOS transistor 23.

[0068] The switching control circuit 42b includes a target value output circuit 50a, a drive signal output circuit 51b, and an estimation circuit .

[0069] The drive signal output circuit 51b includes comparators (CMP) 70 and 72, an SR flip-flop 71, and a delay circuit 73.

[0070] When the inductor current IL becomes smaller than a predetermined value and a predetermined period has elapsed, the delay circuit 73 turns on the NMOS transistor 23. Specifically, after the SR flip-flop 71 outputs an “H” level signal S3 to turn on the NMOS transistor 23, the delay circuit 73 outputs an “H” level drive signal Sdrv to turn on the NMOS transistor 23 after the predetermined period has elapsed.

[0071] The estimation circuit 54 estimates an estimate value Vr_est of the rectified voltage Vref based on the signal from the drive signal output circuit 51b, the inductor current IL, and the feedback voltage Vfb. Specifically, the estimation circuit 54 calculates the on-period Ton and the falling period Tf, and estimates the estimate value Vr_est together with the inductor current IL and the feedback voltage Vfb. The estimation circuit 54 includes counters 80 and 81 and a calculator 82.

[0072] The counter 80 calculates the period during which the drive signal Sdrv output from the delay circuit 73 is at the "H" level as the ON period Ton.

[0073] The counter 81 calculates, based on the signals S0 and S2, the period from when the inductor current IL reaches the target value ILtarget to when it reaches a predetermined value, as a falling period Tf.

[0074] The calculator 82 estimates the estimated value Vr_est based on the on-period Ton, the falling period Tf, the inductor current IL, and the feedback voltage Vfb. The method by which the calculator 82 estimates the estimated value Vr_est will be described later. The on-period Ton corresponds to the "first period", and the falling period Tf corresponds to the "second period".

[0075] <<<How to estimate the estimated value Vr_est>>> FIG. 8 is a diagram for explaining a method of estimating the voltage Vrec and a method of calculating the inductance value L. In FIG.

[0076] As can be seen from Fig. 8, in the case of the switching control circuit 42b, the AC-DC converter 10 operates as if in a discontinuous mode, and there is a period in which the inductor current IL temporarily becomes almost zero. Therefore, the formula (4) described in Fig. 4 does not hold. However, if the falling period Tf is used instead of the off period Toff, the relationship of the formula (1) becomes as follows.

[0077] ILtarget=Vrec / L×Ton=(Vout-Vrec) / L×Tf (13) From equation (13), the on-period Ton and the cycle obtained by adding the on-period Ton and the falling period Tf are expressed as follows.

[0078] Ton=(Vout-Vrec) / Vrec×Tf ···(14) Ton+Tf=Vout / Vrec×Tf (15) Therefore, the rectified voltage Vrec is expressed as follows:

[0079] Vrec=Vout×Tf / (Ton+Tf) ···(16) However, the falling period Tf is small when the target value ILtarget is small, so it is difficult to calculate the falling period Tf with high accuracy.

[0080] On the other hand, when the inductance value L of the inductor 22 is used, the rectified voltage Vrec is expressed as follows:

[0081] Vrec=L×ILtarget / Ton...(17) In this case, the inductance value L is expressed as follows:

[0082] L=Vout / ILtarget×Ton×Tf / (Ton+Tf) ···(18) Therefore, when the change in inductance value L can be almost ignored, the falling period Tf, which becomes relatively large when the target value ILtarget is large, is calculated and the inductance value L is calculated from equation (18). Furthermore, by using the calculated inductance value L in equation (17), the rectified voltage Vrec can be estimated without calculating the falling period Tf, which is difficult to calculate accurately.

[0083] ==Switching control circuit 42c== Fig. 9 is a diagram showing a configuration of a switching control circuit 42c which is one embodiment of the switching control circuit 42. Note that in Fig. 9, the same reference symbols as in Fig. 3 are assigned to the same objects as in Fig. 3. Therefore, detailed descriptions of the same objects will be omitted.

[0084] The switching control circuit 42c is an embodiment in which the multiplier 53 of the switching control circuit 42a is replaced with an adder 55. As is clear from the description of FIG. 6, the output voltage Vout and the off-voltage Voff change in opposite directions. Therefore, the estimated value Vr_est obtained by adding the feedback voltage Vfb and the off-voltage Voff by the adder 55 does not include the ripple component ΔVout of the output voltage Vout. Therefore, the adder 55 adds the on-voltage Von, which is the output of the LPF 52, to the output voltage Vout to remove the ripple component ΔVout of the output voltage Vout. The adder 55 corresponds to the "removal circuit."

[0085] ==Switching control circuit 42d== Fig. 10 is a diagram showing the configuration of a switching control circuit 42d which is one embodiment of the switching control circuit 42. Note that in Fig. 10, the same reference symbols as in Fig. 3 are given to the same objects as in Fig. 3. Therefore, detailed descriptions of the same objects will be omitted.

[0086] The switching control circuit 42d differs from the switching control circuit 42a in that it outputs an off-voltage Voff using an LPF 56 and a subtractor 57. Specifically, the LPF 56 smoothes or integrates the drive signal Sdrv to output an on-voltage Von, and the subtractor 57 subtracts the on-voltage Von from an internal power supply Vdd (which becomes the power supply voltage of the switching control circuit 42d) from a power supply circuit (not shown) to output an off-voltage Voff. The LPF 56 and the subtractor 57 correspond to an "estimation circuit" or an "integration circuit."

[0087] === Variations === <<<AC-DCコンバータ12> >> Fig. 11 is a diagram showing an example of the configuration of an AC-DC converter 12 according to an embodiment of the present invention. In Fig. 11, the same reference symbols as in Fig. 1 are assigned to the same objects as in Fig. 1. Therefore, detailed descriptions of the same objects will be omitted.

[0088] The AC-DC converter 12 has resistors 30 and 31 that configure a voltage divider circuit that divides the rectified voltage Vrec and outputs the divided voltage as a voltage Vr. The power factor correction IC 25b further includes a terminal A to which the voltage Vr is applied.

[0089] == Configuration of power factor correction IC25b == Fig. 12 is a diagram showing the configuration of a power factor correction IC 25b which is one embodiment of the power factor correction IC 25. In Fig. 12, the same reference symbols as in Fig. 2 are assigned to the same objects as in Fig. 2. Therefore, detailed descriptions of the same objects will be omitted.

[0090] The power factor improvement IC 25b includes AD converters (ADC: Analog-to-Digital Converters) 40, 41, and 44, a switching control circuit 45, and a buffer circuit 43. The AD converter 44 converts the voltage Vr into a digital value. The switching control circuit 45 outputs a drive signal Sdrv based on the feedback voltage Vfb, the inductor current IL, and the voltage Vr.

[0091] ==Switching control circuit 45== Fig. 13 is a diagram showing a configuration of a switching control circuit 45. In Fig. 13, the same reference symbols as in Fig. 3 are given to the same objects as in Fig. 3. Therefore, detailed descriptions of the same objects will be omitted.

[0092] The switching control circuit 45 differs from the switching control circuit 42a in that the target value output circuit 50b outputs the target value ILtarget based on the voltage Vr, not on the estimated value Vr_est.

[0093] ===Summary=== The AC-DC converters 10 and 12 of this embodiment have been described above. The switching control circuits 42 and 45 include target value output circuits 50a and 50b and a drive signal output circuit 51a. The target value output circuits 50a and 50b output a target value ILtarget based on the output voltage Vout and the estimated value Vr_est or the voltage Vr. The drive signal output circuit 51a outputs a drive signal that turns on the NMOS transistor 23 when the inductor current IL becomes smaller than a predetermined value, and turns off the NMOS transistor 23 when the peak value of the inductor current IL becomes the target value ILtarget. As a result, the switching control circuits 42 and 45 do not control the NMOS transistor 23 with a constant on-time, but determine the target value ILtarget according to the output voltage Vout and determine the on-time according to the target value ILtarget. As a result, the switching control circuits 42 and 45 can improve the power factor without being affected by the diodes or inductors of the AC-DC converters 10 and 12. Therefore, a switching control circuit that improves the power factor can be provided.

[0094] Moreover, the switching control circuits 42a and the like further include an estimation circuit that estimates the estimated value Vr_est based on the drive signal Sdrv. This allows the switching control circuits 42a and the like to improve the power factor without using a voltage divider circuit for obtaining the divided voltage Vr of the rectified voltage Vrec. Furthermore, by not using a voltage divider circuit, a steady current does not flow through the voltage divider circuit during standby or the like. This reduces the power loss of the AC-DC converter 10 during standby.

[0095] Furthermore, the switching control circuit 42a and the like include an LPF 52 that outputs an off-voltage Voff as an estimation circuit. This makes it possible to obtain the off-voltage Voff, which is an estimate of the rectified voltage Vrec, with a simple circuit.

[0096] Moreover, the switching control circuit 42a etc. includes a multiplier 53 or an adder 55 that removes a ripple component ΔVout included in the off-voltage Voff from the LPF 52. As a result, the estimated value Vr_est from which the influence of the ripple component ΔVout has been removed is output to the target value output circuit 50a etc.

[0097] Moreover, the switching control circuit 42a etc. further includes a multiplier 53 as an elimination circuit for eliminating the ripple component ΔVout of the output voltage Vout. This makes it possible to eliminate the ripple component ΔVout of the output voltage Vout included in the off-voltage Voff.

[0098] Moreover, the switching control circuit 42a etc. further includes an adder 55 as a removal circuit for removing the ripple component ΔVout of the output voltage Vout. This makes it possible to remove the ripple component ΔVout of the output voltage Vout contained in the off-voltage Voff.

[0099] In addition, the switching control circuit 42b further includes a delay circuit that turns on the NMOS transistor 23 when the inductor current IL becomes smaller than a predetermined value and a predetermined period has elapsed. This allows the switching control circuit 42b to reduce the switching loss of the NMOS transistor 23.

[0100] The switching control circuit 42b further includes an estimation circuit that estimates an estimated value Vr_est of the rectified voltage Vrec based on the on-period Ton, the falling period Tf, and the output voltage Vout. This allows the switching control circuit 42b to improve the power factor without using a voltage divider circuit to obtain a divided voltage Vr of the rectified voltage Vrec. Furthermore, by not using a voltage divider circuit, a steady current does not flow through the voltage divider circuit during standby or the like. This reduces the power loss of the AC-DC converter 10 during standby.

[0101] The switching control circuits 42 and 45 include target value output circuits 50a and 50b and a drive signal output circuit 51a. The target value output circuits 50a and 50b output a target value ILtarget based on the output voltage Vout and the estimated value Vr_est or the voltage Vr. The drive signal output circuit 51a outputs a drive signal that turns on the NMOS transistor 23 when the inductor current IL becomes smaller than a predetermined value, and turns off the NMOS transistor 23 when the peak value of the inductor current IL becomes the target value ILtarget. The target value ILtarget has the same period and phase as the AC voltage Vac, and the amplitude is proportional to the AC voltage Vac. Thus, the switching control circuits 42 and 45 do not control the NMOS transistor 23 with a constant on-time, but determine the target value ILtarget according to the output voltage Vout and determine the on-time according to the target value ILtarget. Thus, the switching control circuits 42 and 45 can improve the power factor without being affected by the diodes or inductors of the AC-DC converters 10 and 12.

[0102] Moreover, the switching control circuits 42a and the like further include an estimation circuit that estimates the estimated value Vr_est based on the drive signal Sdrv. This allows the switching control circuits 42a and the like to improve the power factor without using a voltage divider circuit for obtaining the divided voltage Vr of the rectified voltage Vrec. Furthermore, by not using a voltage divider circuit, a steady current does not flow through the voltage divider circuit during standby or the like. This reduces the power loss of the AC-DC converter 10 during standby.

[0103] Furthermore, the switching control circuit 42a and the like include an LPF 52 that outputs an off-voltage Voff as an estimation circuit. This makes it possible to obtain the off-voltage Voff, which is an estimate of the rectified voltage Vrec, with a simple circuit.

[0104] Moreover, the switching control circuit 42a etc. includes a multiplier 53 or an adder 55 that removes a ripple component ΔVout included in the off-voltage Voff from the LPF 52. As a result, the estimated value Vr_est from which the influence of the ripple component ΔVout has been removed is output to the target value output circuit 50a etc.

[0105] Moreover, the switching control circuit 42a etc. further includes a multiplier 53 as an elimination circuit for eliminating the ripple component ΔVout of the output voltage Vout. This makes it possible to eliminate the ripple component ΔVout of the output voltage Vout included in the off-voltage Voff.

[0106] Moreover, the switching control circuit 42a etc. further includes an adder 55 as a removal circuit for removing the ripple component ΔVout of the output voltage Vout. This makes it possible to remove the ripple component ΔVout of the output voltage Vout contained in the off-voltage Voff.

[0107] In addition, the switching control circuit 42b further includes a delay circuit that turns on the NMOS transistor 23 when the inductor current IL becomes smaller than a predetermined value and a predetermined period has elapsed. This allows the switching control circuit 42b to reduce the switching loss of the NMOS transistor 23.

[0108] The switching control circuit 42b further includes an estimation circuit that estimates an estimated value Vr_est of the rectified voltage Vrec based on the on-period Ton, the falling period Tf, and the output voltage Vout. This allows the switching control circuit 42b to improve the power factor without using a voltage divider circuit to obtain a divided voltage Vr of the rectified voltage Vrec. Furthermore, by not using a voltage divider circuit, a steady current does not flow through the voltage divider circuit during standby or the like. This reduces the power loss of the AC-DC converter 10 during standby.

[0109] The above-mentioned embodiment is for the purpose of facilitating understanding of the present invention, and is not intended to limit the present invention. Furthermore, the present invention can be modified or improved without departing from the spirit of the present invention, and it goes without saying that the present invention includes equivalents thereof. [Explanation of symbols]

[0110] 10,12 AC-DC converter 11 Load 20 Full wave rectifier circuit 21,27 Capacitor 22 Inductor 23 NMOS transistor 24, 28, 29, 30, 31 Resistance 26 Diode 40,41,44 A / D converter 42, 42a, 42b, 42c, 42d, 45 Switching control circuit 43 Buffer Circuit 50a, 50b Target value output circuit 51a, 51b Drive signal output circuit 52,56 Low-pass filter 53,62 Multiplier 54 Estimation circuit 55 Adder 57,60 Subtractor 61 Voltage Regulator 70,72 Comparator 71 SR Flip-Flop 73 Delay Circuit 80,81 Counter 82 Arithmetic unit

Claims

1. A switching control circuit that controls switching of a transistor that controls an inductor current based on an inductor current flowing through an inductor to which a rectified voltage from a rectifier circuit that rectifies an AC voltage is applied, and an output voltage generated from the AC voltage, the switching control circuit comprising: a target value output circuit that outputs a target value of the peak value of the inductor current so that the waveform of the peak value of the inductor current is similar to the waveform of the rectified voltage; a drive signal output circuit that outputs a drive signal that turns on the transistor when the inductor current becomes smaller than a predetermined value and turns off the transistor when the peak value of the inductor current reaches the target value; an estimation circuit that estimates an estimate value of the rectified voltage based on the drive signal; Equipped with The target value output circuit includes: outputting the target value based on the output voltage and the estimated value; Switching control circuit.

2. 2. The switching control circuit of claim 1, The estimation circuit includes: an integration circuit that integrates the drive signal during a period in which the transistor is turned off; Switching control circuit.

3. 3. A switching control circuit according to claim 1, a removal circuit for removing a ripple component of the estimated value based on the output voltage; Switching control circuit.

4. 4. A switching control circuit according to claim 3, The removal circuit includes: a multiplier that multiplies the output of the estimation circuit by the output voltage to remove the ripple component; Switching control circuit.

5. 4. A switching control circuit according to claim 3, The removal circuit includes: an adder that adds the output of the estimation circuit and the output voltage to remove the ripple component; Switching control circuit.

6. 2. The switching control circuit of claim 1, The drive signal output circuit includes: a delay circuit that turns on the transistor when the inductor current becomes smaller than the predetermined value and a predetermined period of time has elapsed; Switching control circuit.

7. 7. A switching control circuit according to claim 6, The estimation circuit includes: the estimated value is estimated based on a first period during which the transistor is turned on, a second period during which the inductor current is smaller than the predetermined value after the transistor is turned off, and the output voltage, the first period being a period that varies according to the drive signal; Switching control circuit.

8. A power factor correction circuit that generates an output voltage from an AC voltage, a rectifier circuit that rectifies the AC voltage; an inductor to which a rectified voltage from the rectifier circuit is applied; a transistor for controlling an inductor current flowing through the inductor; a switching control circuit that controls switching of the transistor based on the inductor current and the output voltage; Equipped with The switching control circuit includes: a target value output circuit that outputs a target value of the peak value of the inductor current so that the waveform of the peak value of the inductor current is similar to the waveform of the rectified voltage; a drive signal output circuit that outputs a drive signal that turns on the transistor when the inductor current becomes smaller than a predetermined value and turns off the transistor when the peak value of the inductor current reaches the target value; an estimation circuit that estimates an estimate value of the rectified voltage based on the drive signal; Including, The target value output circuit includes: outputting the target value based on the output voltage and the estimated value; Power factor correction circuit.

9. 9. The power factor correction circuit according to claim 8, The power factor correction circuit operates in a boundary mode or a discontinuous mode.

10. A switching control circuit that controls switching of a transistor that controls an inductor current based on an inductor current flowing through an inductor to which a rectified voltage from a rectifier circuit that rectifies an AC voltage is applied, and an output voltage generated from the AC voltage, the switching control circuit comprising: a target value output circuit that outputs a target value for the peak value of the inductor current; a drive signal output circuit that outputs a drive signal that turns on the transistor when the inductor current becomes smaller than a predetermined value and turns off the transistor when the peak value of the inductor current reaches the target value; an estimation circuit that estimates an estimate value of the rectified voltage based on the drive signal; Equipped with The target value has the same period and phase as the AC voltage, and the amplitude is proportional to the AC voltage. The target value output circuit includes: outputting the target value based on the output voltage and the estimated value; Switching control circuit.

11. 11. A switching control circuit according to claim 10, The estimation circuit includes: an integration circuit that integrates the drive signal during a period in which the transistor is turned off; Switching control circuit.

12. 12. A switching control circuit according to claim 10 or 11, a removal circuit for removing a ripple component of the estimated value based on the output voltage; Switching control circuit.

13. 13. A switching control circuit according to claim 12, comprising: The removal circuit includes: a multiplier that multiplies the output of the estimation circuit by the output voltage to remove the ripple component; Switching control circuit.

14. 13. A switching control circuit according to claim 12, comprising: The removal circuit includes: an adder that adds the output of the estimation circuit and the output voltage to remove the ripple component; Switching control circuit.

15. 11. A switching control circuit according to claim 10, The drive signal output circuit includes: a delay circuit that turns on the transistor when the inductor current becomes smaller than the predetermined value and a predetermined period of time has elapsed; Switching control circuit.

16. 16. A switching control circuit according to claim 15, comprising: The estimation circuit includes: the estimated value is estimated based on a first period during which the transistor is turned on, a second period during which the inductor current is smaller than the predetermined value after the transistor is turned off, and the output voltage, the first period being a period that varies according to the drive signal; Switching control circuit.

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