Control ICs and switching power supply circuits

Abstract

We provide a control IC that can control the ON / OFF of the power factor correction function of a power factor correction IC. [Solution] A switching power supply circuit (101) includes a rectifier circuit (DB1), a DC / DC converter, a power factor correction IC (11) configured to have a power factor correction function, and a control IC (21). The control IC includes a first terminal (T25) and a second terminal (T29) configured to receive a feedback voltage based on a DC output voltage output from the DC / DC converter. The control IC is configured to control a switching element included in the DC / DC converter in accordance with the feedback voltage. The control IC is configured to output a voltage for controlling ON / OFF of the power factor correction function from the second terminal.

Description

[Technical Field]

[0001] This disclosure relates to a control IC (Integrated Circuit) and a switching power supply circuit. [Background technology]

[0002] A power factor correction circuit monitors the AC input voltage and AC input current of a power supply device that performs AC (Alternate Current) / DC (Direct Current) conversion, and roughly matches their phases to bring the power factor close to 1 (i.e., 100%) (see, for example, Patent Document 1).

[0003] In applications requiring low standby power, such as AC adapters, in the power range of around 100 W, a two-stage configuration comprising a power factor correction IC and a control IC configured to control the switching elements included in the DC / DC converter is mainstream (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-99142

[0005] [overview] However, if power factor correction is performed when it is not necessary, the power factor correction will result in wasted electricity.

[0006] The control IC disclosed in this specification is configured to be a component of a switching power supply circuit including: a rectifier circuit configured to generate a DC input voltage from an AC input voltage; a DC / DC converter including a transformer and a first switching element configured to be connected in series with a primary winding of the transformer, and configured to generate a DC output voltage from the DC input voltage supplied to the primary circuit while electrically isolating the primary circuit from a secondary circuit; and a power factor correction IC including an inductor disposed between the rectifier circuit and the DC / DC converter and a second switching element configured to control a current flowing through the inductor, and configured to have a power factor correction function that suppresses a difference in phase between the AC input voltage and the AC input current supplied to the rectifier circuit. The control IC has a first terminal configured to receive a feedback voltage based on the DC output voltage and a second terminal. The control IC is configured to control the first switching element in response to the feedback voltage. The control IC is configured to output a voltage from the second terminal for controlling ON / OFF of the power factor correction function.

[0007] The switching power supply circuit disclosed in this specification includes a control IC having the above configuration. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing the configuration of a switching power supply circuit according to a first embodiment. [Figure 2] FIG. 2 is a perspective view of the power factor correction IC and the control IC. [Figure 3] FIG. 3 is a diagram showing a schematic configuration of a power factor correction IC. [Figure 4] FIG. 4 is a diagram showing the configuration of a control circuit provided in the control IC according to the first embodiment. [Figure 5] FIG. 5 is a diagram showing the configuration of a voltage generating circuit provided in the control IC according to the first embodiment. [Figure 6]FIG. 6 is a diagram showing the relationship between the effective value of the AC input voltage and the output power when the power factor correction function of the power factor correction IC switches from OFF to ON in the first embodiment. [Figure 7] FIG. 7 is a diagram showing the configuration of a switching power supply circuit according to the second embodiment. [Figure 8] FIG. 8 is a diagram showing a first configuration example of a voltage generating circuit provided in a control IC according to the second embodiment. [Figure 9] FIG. 9 is a diagram showing the relationship between the effective value of the AC input voltage and the output power when the power factor correction function of the power factor correction IC switches from OFF to ON in the second embodiment. [Figure 10] FIG. 10 is a diagram showing a second configuration example of the voltage generating circuit provided in the control IC according to the second embodiment.

[0009] [Detailed explanation]

[0010] First Embodiment FIG. 1 is a diagram illustrating a configuration of a switching power supply circuit 101 according to a first embodiment. FIG. 2 is a perspective view illustrating the appearance of a power factor correction IC 11 and a control IC 21. The power factor correction IC 11 and the control IC 21 are electronic components formed by encapsulating semiconductor chips in housings (packages) made of resin. The housing of the power factor correction IC 11 has a plurality of exposed external terminals, including terminals T11 to T14 shown in FIG. 1. The power factor correction IC 11 may have external terminals other than the terminals T11 to T14 shown in FIG. 1. The housing of the control IC 21 has a plurality of exposed external terminals, including terminals T21 to T29 shown in FIG. 1. The control IC 21 may have external terminals other than the terminals T21 to T29 shown in FIG. 1. Note that the number of external terminals of each of the power factor correction IC 11 and the control IC 21 and the appearances of each of the power factor correction IC 11 and the control IC 21 shown in FIG. 2 are merely examples.

[0011] The switching power supply circuit 101 according to the first embodiment is connected to an AC power supply PS1 and a load LD1.

[0012] The switching power supply circuit 101 according to the first embodiment includes a diode bridge DB1, a DC / DC converter, an inductor L3, and a power factor correction IC11.

[0013] The diode bridge DB1 is a rectifier circuit configured to generate a DC input voltage V2 from an AC input voltage V1.

[0014] The DC / DC converter includes a switching element Q1 (see FIG. 4) configured to be connected in series to a transformer TR1 and a primary winding L5 of the transformer TR1, and is configured to generate a DC output voltage V3 from a DC input voltage V2 supplied to the primary circuit system and supply the output voltage V3 to a load LD1 of the secondary circuit system while electrically isolating the primary circuit system from the secondary circuit system. In addition to the primary winding L5, the transformer TR1 also includes a secondary winding L6 and an auxiliary winding L7.

[0015] The inductor L3 is disposed between the diode bridge DB1 and the DC / DC converter.

[0016] The power factor correction IC11 includes a switching element Q1 (see FIG. 4) configured to control the current flowing through the inductor L3, and is configured to have a power factor correction function that suppresses the difference between the phase of the AC input voltage V2 and the phase of the AC input current supplied to the diode bridge DB1.

[0017] The switching power supply circuit 101 according to the first embodiment further includes a control IC 21. The control IC 21 is configured to control a switching element Q1 (see FIG. 4) in accordance with a feedback voltage VFB based on a DC output voltage V3. The control IC 21 incorporates the switching element Q1 (see FIG. 4) of a DC / DC converter.

[0018] The switching power supply circuit 101 according to the first embodiment further includes a fuse F1, capacitors C1 to C10, inductors L1, L2, and L4, resistors R1 to R10, diodes D1 to D7, a phototransistor P1, a photodiode P2, and a shunt regulator S1.

[0019] The filter circuit is made up of the capacitor C1, the inductor L1, and the inductor L2. The inductor L4 is magnetically coupled to the inductor L3. The phototransistor P1 and the photodiode P2 make up a photocoupler.

[0020] Figure 3 shows a schematic configuration of the power factor correction IC 11. The power factor correction IC 11 comprises terminals T12 to T17, a switching element Q2 which is an NMOS (N-type metal-oxide-semiconductor) field-effect transistor, and a logic circuit LG1. The drain of the switching element Q2 is connected to terminal T12. The source of the switching element Q2 is connected to terminal T13. Note that the switching element Q2 may be a switching element other than an NMOS field-effect transistor.

[0021] If the voltage VPFC applied to terminal T14 is at a LOW level, the power factor correction function is turned OFF, and the switching element Q2 is turned OFF.

[0022] When the voltage VPFC applied to terminal T14 is at a HIGH level, logic circuit LG1 turns on the power factor correction function and controls the switching element Q2 ON / OFF according to the voltages applied to terminals T15 to T17. A signal (voltage) indicating whether the primary current Ip is an overcurrent is applied to terminal T15. A voltage divider of the DC input voltage V2 is applied to terminal T16. A signal (voltage) for detecting the zero point of the inductor current IL flowing through inductor L3 is applied to terminal T17. When the voltage VPFC applied to terminal T14 is at a HIGH level, logic circuit LG1 first switches the switching element Q2 from OFF to ON. This increases the inductor current IL. Next, logic circuit LG1 compares the voltage applied to terminal T15 and the voltage applied to terminal T16, and when the voltage applied to terminal T15 is greater, it switches the switching element Q2 from ON to OFF. During the period when the switching element Q2 is OFF, the inductor current IL decreases until it becomes 0[A]. The logic circuit LG1 detects the zero point of the inductor current IL based on the voltage applied to the terminal T17, and when the logic circuit LG1 detects the zero point of the inductor current IL, it switches the switching element Q2 from OFF to ON.

[0023] Fig. 4 is a diagram showing the configuration of a control circuit provided in the control IC 21. The control circuit shown in Fig. 4 includes a comparator 1, a flip-flop 2, a ZT comparator 3, a one-shot circuit 4, a driver 5, a pull-up resistor R11, and voltage-dividing resistors R12 and R13.

[0024] A terminal T25, to which a feedback voltage VFB based on the DC output voltage V3 is applied, is pulled up by a pull-up resistor R11. The feedback voltage VFB is divided by voltage-dividing resistors R12 and R13 and converted into a feedback voltage VF. A constant voltage VREG generated inside the control IC 21 is applied to a first terminal of the pull-up resistor R11.

[0025] The sense resistor RS converts the source current of the switching element Q1, which is an NMOS field-effect transistor, into a detection voltage VCS. Note that the switching element Q1 may be a switching element other than an NMOS field-effect transistor. The detection voltage VCS is supplied to the non-inverting input terminal (+) of the comparator 1. The feedback voltage VF is supplied to the first inverting input terminal (-) of the comparator 1. The reference voltage VREF for overcurrent protection is supplied to the second inverting input terminal (-) of the comparator 1.

[0026] The comparator 1 outputs a reset signal RST to the reset terminal (R) of the flip-flop 2.

[0027] A ZT voltage VZT, which is a divided voltage of the voltage generated in the auxiliary winding L7, is supplied to the terminal T26.

[0028] A ZT voltage VZT is applied to the non-inverting input terminal (+) of the ZT comparator 3. A threshold voltage VZT1 for zero current detection is supplied to the inverting input terminal (-) of the ZT comparator 3. A one-shot circuit 4 outputs a set signal ST based on the output of the ZT comparator 3. The set signal ST is supplied to the set terminal (S) of the flip-flop 2.

[0029] The driver 5 drives (switches) the switching element Q1 on and off based on the Q signal SQ output from the output terminal (Q) of the flip-flop 2.

[0030] Here, we will explain the quasi-resonant control (QR control) performed by the control circuit shown in Fig. 4. First, when the one-shot circuit 4 outputs a set signal ST that has switched to a high level, the flip-flop 2 is set and the driver 5 turns on the switching element Q1. Turning on is a change from an off state to an on state.

[0031] As a result, a primary current Ip begins to flow through the switching element Q1, and the detection voltage VCS begins to rise. The primary current Ip is the current flowing through the primary winding L5 (see Figure 1). When the primary current Ip increases and the detection voltage VCS rises above the lower of the feedback voltage VF and the reference voltage VREF, the reset signal RST rises to a high level. This resets the flip-flop 2, and the driver 5 turns off the switching element Q1. Turning off is the switching from the ON state to the OFF state.

[0032] When the switching element Q1 is turned off, the primary current Ip stops flowing, and the secondary current Is begins to flow. The secondary current Is is the current flowing through the secondary winding L6 (see Figure 1). When the switching element Q1 is off, the power stored in the primary winding L6 is supplied to the capacitor C9. When this supply ends, the secondary current Is stops flowing, and the drain voltage of the switching element Q1 decreases. As a result, the ZT voltage VZT also decreases. When the ZT voltage VZT falls below the threshold voltage VZT1, the one-shot circuit 4 outputs a set signal ST, which is a high-level pulse for a certain period of time, based on the output from the comparator 3. This sets the flip-flop 2, and the switching element Q1 is turned on.

[0033] Thus, in the QR control using the control circuit shown in Figure 4, the drain voltage of the switching element Q1 is indirectly monitored by the ZT voltage VZT, and the switching element Q1 is turned on when the voltage bottom of the resonant oscillation of the drain voltage that occurs after the energy stored in the transformer TR1 has finished being supplied to the secondary side is detected.

[0034] Figure 5 shows the configuration of the voltage generation circuit provided in the control IC 21. The voltage generation circuit shown in Figure 5 generates a voltage VPFC for ON / OFF control of the power factor correction function of the power factor correction IC 11. The voltage VPFC is output to the outside of the control IC 21 from terminal T29 (see Figure 1). Therefore, the control IC 21 can ON / OFF control of the power factor correction function of the power factor correction IC 11.

[0035] The voltage generating circuit shown in FIG. 5 includes a comparator 6. The comparator 6 is configured to determine whether to turn on or off the power factor correction function of the power factor correction IC 11 depending on the result of comparison between the feedback voltage VF and the threshold voltage VTH. The feedback voltage VF is supplied to a non-inverting input terminal (+) of the comparator 6. The threshold voltage VTH is supplied to an inverting input terminal (-) of the comparator 6. Note that, unlike this embodiment, the comparator 6 may be configured to compare the feedback voltage VFB with the threshold voltage VTH.

[0036] If the feedback voltage VF is greater than the threshold voltage VTH, the voltage VPFC goes to a HIGH level. If the feedback voltage VF is not greater than the threshold voltage VTH, the voltage VPFC goes to a LOW level.

[0037] Terminal T29 of control IC21 is connected to terminal T14 (see Figure 1) of power factor correction IC11. When power factor correction IC11 receives a high-level voltage VPFC, it turns on its power factor correction function. When power factor correction IC11 receives a low-level voltage VPFC, it turns off its power factor correction function. As a result, the power factor correction function of power factor correction IC11 is turned off during light loads when power factor correction is not necessary, and the switching power supply circuit 101 can reduce power consumption during light loads.

[0038] Here, when the power factor correction function of the power factor correction IC 11 is OFF, the value of the DC input voltage V2 becomes the peak value (amplitude value) of the AC input voltage V1. Therefore, when the power factor correction function of the power factor correction IC 11 is OFF, the value of the DC input voltage V2 changes significantly depending on the AC input voltage V1.

[0039] The output power POUT of the switching power supply circuit 101 is expressed by the following formula, where Lp is the primary inductance. 2 is the primary side peak current. Fsw is the switching frequency of the switching element Q1. POUT=(1 / 2)×Lp×Ippk 2 ×Fsw

[0040] The feedback voltage VFB is expressed by the following formula: Rs is the resistance value of the sense resistor G is the ratio of the feedback voltage VF to the feedback voltage VFB, which is determined by the resistance values ​​of the voltage dividing resistors R12 and R13. VFB=Rs×Ippk / G

[0041] In the switching power supply circuit 101, the control circuit shown in Figure 4 performs QR control, so the switching frequency Fsw of the switching element Q1 changes depending on the RMS value of the AC input voltage V1. More specifically, the larger the RMS value of the AC input voltage V1, the higher the switching frequency Fsw of the switching element Q1. Therefore, as shown in Figure 6, the output power POUT when the power factor correction function of the power factor correction IC 11 switches from OFF to ON changes significantly depending on the RMS value of the AC input voltage V1. In other words, depending on the RMS value of the AC input voltage V1, the switching power supply circuit 101 may switch the power factor correction function of the power factor correction IC 11 from OFF to ON even when power factor correction is not necessary, or it may not switch from OFF to ON even when power factor correction is necessary.

[0042] Second Embodiment 7 is a diagram showing the configuration of a switching power supply circuit 102 according to the second embodiment. The switching power supply circuit 102 according to the second embodiment is configured to be able to suppress the output power POUT from changing in accordance with the effective value of the AC input voltage V1 when the power factor correction function of the power factor correction IC 11 is switched from OFF to ON.

[0043] The switching power supply circuit 102 according to the second embodiment differs from the switching power supply circuit 101 according to the first embodiment in that it includes a control IC 22 instead of the control IC 21, but is otherwise basically the same as the switching power supply circuit 101 according to the first embodiment. The appearance of the control IC 22 is the same as the appearance of the control IC 21.

[0044] The control circuit IC22 includes the control circuit shown in FIG. 4, similar to the control circuit IC21.

[0045] FIG. 8 is a diagram showing a first configuration example of a voltage generation circuit provided in the control IC 22. The voltage generation circuit shown in FIG. 8 generates a voltage VPFC for controlling ON / OFF of the power factor correction function of the power factor correction IC 11. The voltage generation circuit shown in FIG. 8 includes a comparator 6, similar to the voltage generation circuit shown in FIG. 5. The comparator 6 is configured to determine whether to turn ON or OFF the power factor correction function of the power factor correction IC 11 depending on the result of comparison between the feedback voltage VF and the threshold voltage VTH. The feedback voltage VF is supplied to a non-inverting input terminal (+) of the comparator 6. The threshold voltage VTH is supplied to an inverting input terminal (-) of the comparator 6. Note that, unlike this embodiment, the comparator 6 may be configured to compare the feedback voltage VFB with the threshold voltage VTH.

[0046] If the feedback voltage VF is greater than the threshold voltage VTH, the voltage VPFC goes to a HIGH level. If the feedback voltage VF is not greater than the threshold voltage VTH, the voltage VPFC goes to a LOW level.

[0047] The voltage generation circuit shown in Figure 8 includes a suppression circuit 7A, which is configured to suppress fluctuations in the output power POUT when the power factor correction function of the power factor correction IC 11 switches from OFF to ON.

[0048] The suppression circuit 7A is configured to change the value of the threshold voltage VTH according to the peak value (amplitude) of the AC input voltage V1 when the power factor correction function of the power factor correction IC 11 is turned OFF.

[0049] The suppression circuit 7A comprises voltage divider resistors R21 and R22, comparators COMP1 to COMP6, flip-flops FF1 to FF6, flip-flops FF11 to FF16, switches SW1 to SW6, and voltage divider resistors R23 to R30.

[0050] Reference voltages VREF1 to VREF6 having different values ​​are supplied to the non-inverting input terminals (-) of the comparators COMP1 to COMP6. The magnitude relationship of the reference voltages VREF1 to VREF6 is reference voltage VREF1<reference voltage VREF2<reference voltage VREF3<reference voltage VREF4<reference voltage VREF5<reference voltage VREF6.

[0051] The switches SW1 to SW6 are switches for selecting a resistor to be short-circuited to ground from among the voltage-dividing resistors R25 to R30. As the peak value (amplitude) of the AC input voltage V1 increases, the switches SW1 to SW6 are sequentially turned ON, and the value of the threshold voltage VTH decreases. Therefore, as shown in FIG. 9, the output power POUT when the power factor correction function of the power factor correction IC11 switches from OFF to ON is approximately constant regardless of the effective value of the AC input voltage V1. In other words, the switching power supply circuit 102 can prevent the power factor correction function of the power factor correction IC11 from switching from OFF to ON even when power factor correction is not required, or from not switching from OFF to ON even when power factor correction is required. Note that in FIG. 9, for comparison, the relationship between the effective value of the AC input voltage V2 and the output power POUT when the power factor correction function of the power factor correction IC11 switches from OFF to ON in the first embodiment is shown by a dotted line.

[0052] The frequency of the reset signal supplied to each reset input terminal of the flip-flops FF1 to FF6 and the frequency of the clock signal supplied to each clock input terminal of the flip-flops FF11 to FF16 are set to be lower than 50 Hz so that the peak value (amplitude) of the 50 Hz or 60 Hz AC input voltage V1 (commercial AC voltage in Japan) can be detected by the comparators COMP1 to COMP6, the flip-flops FF1 to FF6, and the flip-flops FF11 to FF16.

[0053] The suppression circuit 7A is configured to fix the value of the threshold voltage VTH regardless of the peak value (amplitude) of the AC input voltage V1 when the power factor correction function of the power factor correction IC 11 is turned ON. Specifically, when the power factor correction function of the power factor correction IC 11 is turned ON, the flip-flops FF11 to FF16 are reset by the reset signal EN supplied to the reset input terminals of each flip-flop FF11 to FF16, and all switches SW1 to SW6 are turned OFF. This is because when the power factor correction function of the power factor correction IC 11 is turned ON, the DC input voltage V2 becomes constant regardless of the peak value (amplitude) of the AC input voltage V1, and there is no need to change the value of the threshold voltage VTH.

[0054] Figure 10 shows a second example configuration of the voltage generation circuit provided in the control IC 22. The voltage generation circuit shown in Figure 10 differs from the voltage generation circuit shown in Figure 8 in that it includes a suppression circuit 7B instead of a suppression circuit 7A, but is otherwise basically the same as the voltage generation circuit shown in Figure 8.

[0055] The suppression circuit 7A is configured to change the value of the threshold voltage VTH according to the switching frequency Fsw of the switching element Q1 when the power factor correction function of the power factor correction IC 11 is turned OFF.

[0056] The suppression circuit 7B is configured by removing the voltage divider resistors R21 and R22 from the suppression circuit 7A and adding a constant current source 8, a capacitor 9, and a discharge switch 10. The capacitor 9 is charged by the constant current output from the constant current source 8. The capacitor 9 also discharges when the discharge switch 10 is ON. The discharge switch 10 is controlled ON / OFF by a signal Ssw that is synchronized with the control signal supplied to the control terminal (gate) of the switching element Q1. The smaller the switching frequency Fsw of the switching element Q1, the larger the peak value of the charging voltage of the capacitor 9.

[0057] <Other> The above-described embodiments should be considered to be illustrative in all respects and not restrictive. The technical scope of the present disclosure is indicated by the claims, not by the description of the above-described embodiments, and should be understood to include all modifications that fall within the meaning and scope equivalent to the claims.

[0058] For example, in the first and second embodiments described above, the switching element Q1 is built into the control IC 21 or the control IC 22, but the switching element Q1 may be provided outside the control IC 21 or the control IC 22.

[0059] For example, in the second embodiment described above, when the power factor correction function of the power factor correction IC 11 is turned off, the value of the threshold voltage VTH is changed according to the peak value (amplitude) of the AC input voltage V1 or the switching frequency Fsw of the switching element Q1, but instead of the value of the threshold voltage VTH, the ratio of the feedback voltage VF to the feedback voltage VFB or the resistance value of the sense resistor RS may be changed.

[0060] <Additional Notes> A supplementary note will be provided for the present disclosure, the specific configuration examples of which have been shown in the embodiments described above.

[0061] The control ICs (21, 22) of the present disclosure include a rectifier circuit (DB1) configured to generate a DC input voltage from an AC input voltage, a DC / DC converter including a transformer (TR1) and a first switching element (Q1) configured to be connected in series to a primary winding of the transformer, and configured to generate a DC output voltage from the DC input voltage supplied to the primary circuit system and supply the DC output voltage to a load (LD1) of the secondary circuit system while electrically isolating the primary circuit system from a secondary circuit system, an inductor (L3) arranged between the rectifier circuit and the DC / DC converter, and a second switch (L4) configured to control a current flowing through the inductor. a power factor correction IC (11) configured to have a power factor correction function that includes a switching element (Q2) and that suppresses a difference between the phase of the AC input voltage and the phase of the AC input current supplied to the rectifier circuit, the control IC having a first terminal (T25) and a second terminal (T29) configured to receive a feedback voltage based on the DC output voltage, and configured to control the first switching element in response to the feedback voltage, and configured to output a voltage for ON / OFF control of the power factor correction function from the second terminal (first configuration).

[0062] The control IC of the first configuration outputs, from the second terminal, a voltage for controlling the ON / OFF of the power factor correction function of the power factor correction IC, and therefore can control the ON / OFF of the power factor correction function of the power factor correction IC.

[0063] In the control IC of the first configuration described above, the first switching element may be incorporated (second configuration).

[0064] The control IC of the first or second configuration may be configured (third configuration) to determine whether to turn on or off the power factor correction function depending on the result of comparing the voltage based on the feedback voltage with a threshold voltage.

[0065] In the control IC of the third configuration described above, there may also be a configuration (fourth configuration) that includes suppression circuits (7A, 7B) configured to suppress fluctuations in the DC output power supplied to the load when the power factor correction function switches from OFF to ON.

[0066] In the control IC of the fourth configuration described above, the suppression circuit may be configured to change the threshold voltage according to the amplitude of the AC input voltage when the power factor correction function is turned OFF (fifth configuration).

[0067] In the control IC of the fourth configuration described above, the suppression circuit may be configured to change the threshold voltage according to the switching frequency of the first switching element when the power factor correction function is turned OFF (sixth configuration).

[0068] In the control IC of the fourth configuration, the suppression circuit may be configured to control the first switching element in accordance with the voltage division of the feedback voltage, and the suppression circuit may be configured to change the voltage division ratio to the feedback voltage in accordance with the amplitude of the AC input voltage when the power factor correction function is turned off (seventh configuration).

[0069] In the control IC of the fourth configuration, the first switching element may be controlled in accordance with the voltage division of the feedback voltage, and the suppression circuit may be configured to change the ratio of the voltage division to the feedback voltage in accordance with the switching frequency of the first switching element when the power factor correction function is turned OFF (eighth configuration).

[0070] The control IC of the fourth configuration may further include a sense resistor (RS) configured to convert the current flowing through the first switching element into a voltage, and the suppression circuit may be configured to change the resistance value of the sense resistor in accordance with the amplitude of the AC input voltage when the power factor correction function is turned off (ninth configuration).

[0071] The control IC of the fourth configuration may further include a sense resistor (RS) configured to convert the current flowing through the first switching element into a voltage, and the suppression circuit may be configured to change the resistance value of the sense resistor according to the switching frequency of the first switching element when the power factor correction function is turned off (tenth configuration).

[0072] The switching power supply circuits (101, 102) of this disclosure have a configuration (11th configuration) that includes control ICs (21, 22) of any of the first to tenth configurations described above. [Explanation of symbols]

[0073] 1, 6, COMP1 to COMP6 comparators 2. FF1~FF6, FF11~FF16 flip-flops 3 ZT Comparator 4 One-shot circuit 5 Drivers 7A, 7B suppression circuit 8 constant current source 9 Capacitors 10 Discharge switch 11 Power factor correction IC 21, 22 Control IC 101 Switching power supply circuit according to the first embodiment 102 Switching power supply circuit according to the second embodiment C1~C10 capacitors D1~D7 diodes DB1 Diode Bridge F1 Fuse L1~L4 inductors L5 primary winding L6 secondary winding L7 Auxiliary winding LD1 load LG1 Logic Circuit P1 phototransistor P2 photodiode Q1, Q2 switching elements R1~R10 Resistors R11 pull-up resistor R12, R13, R21 to R30: Voltage dividing resistors RS Sense resistor S1 Shunt Regulator T11~T17, T21~T29 terminals TR1 transformer PS1 AC power supply

Claims

1. a rectifier circuit configured to generate a DC input voltage from an AC input voltage; a DC / DC converter including a transformer and a first switching element configured to be connected in series to a primary winding of the transformer, and configured to generate a DC output voltage from the DC input voltage supplied to the primary circuit system and supply the DC output voltage to a load of the secondary circuit system while electrically isolating the primary circuit system from a secondary circuit system; an inductor disposed between the rectifier circuit and the DC / DC converter; a power factor correction IC including a second switching element configured to control a current flowing through the inductor, the power factor correction IC having a power factor correction function of suppressing a difference between the phase of the AC input voltage and the phase of the AC input current supplied to the rectifier circuit; A control IC configured to be a component of a switching power supply circuit comprising: a first terminal configured to receive a feedback voltage based on the DC output voltage; A second terminal; Equipped with configured to control the first switching element in response to the feedback voltage; a control IC configured to output a voltage for controlling ON / OFF of the power factor correction function from the second terminal;

2. The control IC according to claim 1 , wherein the control IC includes the first switching element.

3. The control IC according to claim 1 , configured to determine whether to turn on or off the power factor correction function depending on a result of comparison between the voltage based on the feedback voltage and a threshold voltage.

4. The control IC of claim 3 , further comprising a suppression circuit configured to suppress fluctuations in the DC output power supplied to the load when the power factor correction function switches from OFF to ON.

5. The control IC according to claim 4 , wherein the suppression circuit is configured to change the threshold voltage in accordance with the amplitude of the AC input voltage when the power factor correction function is turned off.

6. The control IC according to claim 4 , wherein the suppression circuit is configured to change the threshold voltage in accordance with a switching frequency of the first switching element when the power factor correction function is turned off.

7. The first switching element is controlled in accordance with a voltage division of the feedback voltage, The control IC according to claim 4 , wherein the suppression circuit is configured to change the voltage division ratio with respect to the feedback voltage in accordance with the amplitude of the AC input voltage when the power factor correction function is turned off.

8. The first switching element is controlled in accordance with a voltage division of the feedback voltage, 5. The control IC according to claim 4, wherein the suppression circuit is configured to change the voltage division ratio with respect to the feedback voltage in accordance with a switching frequency of the first switching element when the power factor correction function is turned off.

9. a sense resistor configured to convert a current flowing through the first switching element into a voltage; The control IC according to claim 4 , wherein the suppression circuit is configured to change a resistance value of the sense resistor in accordance with an amplitude of the AC input voltage when the power factor correction function is turned off.

10. a sense resistor configured to convert a current flowing through the first switching element into a voltage; 5. The control IC according to claim 4, wherein the suppression circuit is configured to change the resistance value of the sense resistor in accordance with the switching frequency of the first switching element when the power factor correction function is turned off.

11. A switching power supply circuit comprising the control IC according to any one of claims 1 to 9.

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