Switch control circuit and switch control method

Abstract

The switch control circuit of the present invention switches a transistor that controls the inductor current based on an inductor current flowing through an inductor to which an input voltage is applied and an output voltage generated according to the input voltage, and includes: a first error voltage output circuit that outputs a first error voltage corresponding to an error between a level of the output voltage and a first level based on a feedback voltage corresponding to the output voltage and a reference voltage when a first signal indicating that the switch control circuit is used for a non-insulated first power supply circuit is input; a second error voltage output circuit that outputs a second error voltage based on an error signal corresponding to an error between a level of the output voltage and a second level when a second signal indicating that the switch control circuit is used for an insulated second power supply circuit is input; and a drive circuit that switches the transistor based on the inductor current and the first error voltage when the switch control circuit is used for the first power supply circuit, and switches the transistor based on the inductor current and the second error voltage when the switch control circuit is used for the second power supply circuit.

Description

Technical Field

[0001] The invention relates to a switch control circuit and a switch control method. Background Art

[0002] A conventional power supply circuit detects the level of an output voltage and generates an output voltage of a target level according to an input voltage (for example, Patent Document 1).

[0003] (For example, Patent Document 1).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2014-82924 Summary of the invention

[0007] Technical problem to be solved by the invention

[0008] However, the power supply circuit includes a non-insulated power supply circuit in which the input side and the output side are not insulated, and an insulated power supply circuit in which the input side and the output side are insulated. In the non-insulated power supply circuit, the output voltage can be detected by a voltage dividing resistor or the like, while in the insulated power supply circuit, in order to detect the output voltage, for example, a shunt regulator or an optical coupler is required.

[0009] Therefore, the elements and structures for detecting the output voltage differ depending on whether the power supply circuit is a non-insulated type or an isolated type. Therefore, it is difficult to use a control circuit for controlling the power supply circuit in common in both the non-insulated type power supply circuit and the isolated type power supply circuit.

[0010] The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a switch control circuit that can be used in a non-insulated power supply circuit and an isolated power supply circuit.

[0011] Technical means for solving technical problems

[0012] A first mode of the present invention for solving the above-mentioned problem is a switch control circuit for switching a transistor for controlling the inductor current based on an inductor current flowing through an inductor to which an input voltage is applied and an output voltage generated according to the input voltage, wherein the switch control circuit includes: a first error voltage output circuit for outputting a first error voltage corresponding to an error between a level of the output voltage and a first level based on a feedback voltage corresponding to the output voltage and a reference voltage when a first signal indicating that the switch control circuit is used for a non-insulated first power supply circuit is input; a second error voltage output circuit for outputting a second error voltage based on an error signal corresponding to an error between a level of the output voltage and a second level when a second signal indicating that the switch control circuit is used for an isolated second power supply circuit is input; and a drive circuit for switching the transistor based on the inductor current and the first error voltage when the switch control circuit is used for the first power supply circuit, and for switching the transistor based on the inductor current and the second error voltage when the switch control circuit is used for the second power supply circuit.

[0013] A second embodiment of the present invention is a switching control circuit that controls an inductor current based on an inductor current flowing through an inductor to which an input voltage is applied, and an output voltage generated according to the input voltage. The switching control circuit is characterized in that the switching control circuit is an integrated circuit and includes: a first terminal to which a feedback voltage corresponding to the output voltage is applied when the switching control circuit is used for a non-isolated first power supply circuit, and a voltage of a specified level is applied when the switching control circuit is used for an isolated second power supply circuit; and a determination circuit that determines whether the switching control circuit is used for the first power supply circuit or the second power supply circuit based on the voltage of the first terminal.

[0014] A third aspect of the present invention is a switching control method, which switches a transistor that controls the inductor current based on an inductor current flowing through an inductor to which an input voltage is applied and an output voltage generated according to the input voltage, wherein the switching control method is characterized in that when a first signal indicating that the switching control circuit is used for a non-isolated first power supply circuit is input, a first error voltage corresponding to an error between a level of the output voltage and a first level is output based on a feedback voltage corresponding to the output voltage and a reference voltage, and when a second signal indicating that the switching control circuit is used for an isolated second power supply circuit is input, a second error voltage is output based on an error signal corresponding to an error between a level of the output voltage and a second level, and when the switching control circuit is used for the first power supply circuit, the transistor is switched based on the inductor current and the first error voltage, and when the switching control circuit is used for the second power supply circuit, the transistor is switched based on the inductor current and the second error voltage.

[0015] Effects of the Invention

[0016] According to the present invention, it is possible to provide a switch control circuit that can be used in a non-insulated power supply circuit and an isolated power supply circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a diagram showing an example of the switch control IC 10 .

[0018] Figure 2 is a diagram showing an example of the determination circuit 33 .

[0019] Figure 3 1 is a diagram showing an example of a non-insulated power supply circuit 20 .

[0020] Figure 4 It is a diagram for explaining the operation of the power supply circuit 20 at the time of startup.

[0021] Figure 5 1 is a diagram showing a partial configuration of the switch control IC 10 .

[0022] Figure 6 It is a diagram for explaining the operation of the power supply circuit 20 .

[0023] Figure 7 2 is a diagram showing an example of an insulating power supply circuit 21 .

[0024] Figure 8 It is a diagram for explaining the operation of the power supply circuit 21 at the time of startup.

[0025] Fig. 91 is a diagram showing a partial configuration of the switch control IC 10 .

[0026] Fig.10 It is a diagram for explaining the operation of the power supply circuit 21 .

[0027] Fig.11 is a diagram showing an example of the switch control IC 12 .

[0028] Fig.12 is a diagram showing an example of the voltage output circuit 602a.

[0029] Fig.13 is a diagram showing an example of the configuration of the power supply circuit 22 .

[0030] Fig.14 2 is a diagram showing an example of a waveform at the time of startup of the power supply circuit 22 .

[0031] Fig.15 is a diagram showing an example of the structure of the voltage output circuit 602 b.

[0032] Fig.16 is a diagram showing an example of the structure of the voltage output circuit 602c.

[0033] Fig.17 is a diagram showing an example of the switch control IC 13 .

[0034] Fig.18 is a diagram showing an example of the switch control IC 14 .

[0035] Fig.19 is a diagram showing an example of the switch control IC 15 .

[0036] Fig. 20 is a diagram showing an example of the switch control IC 16 .

[0037] Fig.21 is a diagram showing an example of the switch control IC 17 .

[0038] Fig. 22 is a diagram showing an example of the masking circuit 660 .

[0039] Fig.23 It is a diagram for explaining the operation of the power supply circuit 20 .

[0040] Fig.24 It is a diagram for explaining the operation of the power supply circuit 22 . DETAILED DESCRIPTION

[0041] Cross-reference to related applications

[0042] This application claims priority based on Japanese Patent Application No. 2019-079860 filed on April 19, 2019, and cites the contents thereof.

[0043] At least the following matters are clear from the description of this specification and the drawings.

[0044] ======Present Implementation Method======

[0045] <<<Structure of switch control IC 10>>>

[0046] Figure 1 1 is a diagram showing the structure of a switch control IC 10 as one embodiment of the present invention. The switch control IC 10 (switch control circuit) is an integrated circuit that determines whether the switch control IC 10 is used for a non-insulated power supply circuit or an isolated power supply circuit, and controls the operation of the power supply circuit according to the determination result. Specifically, when the switch control IC 10 is used for a non-insulated switching power supply circuit, it operates based on a feedback voltage corresponding to the output voltage. On the other hand, when the switch control IC 10 is used for an isolated switching power supply circuit, it operates based on a current representing an error from a target level of the output voltage.

[0047] The switch control IC 10 has terminals VCC, ZCD, A, B, and OUT. In addition, the switch control IC 10 is provided with, for example, a GND terminal to which a ground voltage is applied or other terminals, but these are omitted here for the sake of convenience.

[0048] The terminal VCC is a terminal to which a power supply voltage Vcc for operating the switch control IC 10 is applied.

[0049] The terminal ZCD is a terminal for detecting an inductor current of a power supply circuit using the switching control IC 10 .

[0050] Terminal A (first terminal) is a terminal to which a voltage is applied for determining whether a power supply circuit using the switch control IC 10 is a non-insulated type or an isolated type. In addition, when the switch control IC 10 is used for a non-insulated type power supply circuit, a feedback voltage corresponding to the output voltage of the power supply circuit is applied to terminal A. In addition, the voltage of terminal A is set to voltage Va.

[0051] Terminal B (second terminal) is a terminal to which a phase compensation element is connected when the switch control IC 10 is used in a non-insulated power supply circuit, and a phototransistor is connected when the switch control IC 10 is used in an isolated power supply circuit. In addition, although the details will be described later, the current flowing through the phototransistor is equivalent to an error signal indicating the error from the target level of the output voltage. In addition, the voltage of terminal B is set to voltage Vb.

[0052] The terminal OUT is a terminal to which a drive signal Vdr for controlling switching of the switching element is applied.

[0053] The switch control IC 10 includes a power supply circuit 30 , voltage detection circuits 31 , 32 , a determination circuit 33 , comparators 40 , 45 , a pulse circuit 41 , an oscillation circuit 42 , an error amplifier circuit 43 , an error voltage output circuit 44 , and a drive circuit 46 .

[0054] The power supply circuit 30 is a circuit (for example, a series regulator) that generates a power supply voltage Vdd for operating the internal circuit of the switching control IC 10 based on the power supply voltage Vcc applied from the outside of the switching control IC 10. In addition, among the circuits included in the switching control IC 10, the circuit that provides the power supply voltage Vdd is a circuit other than the power supply circuit 30 and the buffer circuit 71 (described later) of the drive circuit 46. In the present embodiment, the buffer circuit 71 of the drive circuit 46 operates based on the power supply voltage Vcc.

[0055] The voltage detection circuit 31 is a circuit for detecting whether the level of the power supply voltage Vdd reaches the prescribed level X. In addition, the "prescribed level X" is a level indicating that the power supply voltage Vdd rises. When the target level of the power supply voltage Vdd is 5V, the "prescribed level X" is, for example, 4.5V. In addition, if the level of the power supply voltage Vdd rises and reaches the prescribed level X, the voltage detection circuit 31 changes the level of the signal UVLO from a high level (hereinafter referred to as "H" level) to a low level (hereinafter referred to as "L" level). In addition, in the present embodiment, the level of the power supply voltage Vcc when the level of the power supply voltage Vdd reaches the prescribed level X is set to the "prescribed level Vt1".

[0056] The voltage detection circuit 32 is a circuit that detects whether the level of the power supply voltage Vcc reaches the "predetermined level Vt2" that starts the operation of the internal circuit of the switch control IC 10. If the level of the power supply voltage Vcc rises and reaches the predetermined level Vt2, the voltage detection circuit 32 changes the level of the signal ENB from the "H" level to the "L" level. In addition, in the present embodiment, the above-mentioned level Vt1 is lower than the predetermined level Vt2. Therefore, if the power supply voltage Vcc starts to rise from zero, the voltage detection circuit 31 first changes the signal UVLO to the "L" level, and thereafter, the voltage detection circuit 32 changes the signal ENB to the "L" level. In addition, although in Figure 1 Although omitted in the figure, in the present embodiment, the signals UVLO and ENB are input to each circuit of the switching control IC 10 .

[0057] The determination circuit 33 is a circuit that determines, based on the voltage Va of the terminal A, whether the switch control IC 10 is used for a non-insulated power supply circuit or an isolated power supply circuit. Figure 2 is a diagram showing an example of the configuration of the determination circuit 33 . The determination circuit 33 includes a comparator 50 and a D flip-flop 51 .

[0058] The comparator 50 compares the reference voltage Vref1 for distinguishing the non-insulated power supply circuit and the insulated power supply circuit with the voltage Va. Here, when the switch control IC10 is used for the non-insulated power supply circuit, the feedback voltage Vfb corresponding to the output voltage is applied to the terminal A. On the other hand, when the switch control IC10 is used for the insulated power supply circuit, the switch control IC10 operates without using the voltage Va of the terminal A. Therefore, the level of the voltage Va of the insulated power supply circuit is set to be outside the range of the voltage Va of the non-insulated power supply circuit (the voltage range in which the feedback voltage Vfb changes), thereby distinguishing the two.

[0059] For example, in a non-insulated power supply circuit, when the feedback voltage Vfb varies within a range of, for example, 0 to 3 V, the voltage Va of the isolated power supply circuit is set to a specified level other than 0 to 3 V (for example, 5.4 V), thereby enabling the two to be distinguished based on the voltage of the terminal Va.

[0060] In this embodiment, in a non-insulated power supply circuit, in order to distinguish the voltage range of the feedback voltage Vfb (for example, 0 to 3V) and the voltage Va (for example, 5.4V) of the isolated power supply circuit, a reference voltage Vref1 (for example, 4V) is used, which is higher than the voltage range of the feedback voltage Vfb and lower than the voltage Va of the isolated power supply circuit.

[0061] Therefore, the comparator 50 can determine whether the power supply circuit using the switch control IC 10 is of a non-insulated type or an isolated type by comparing the reference voltage Vref1 with the voltage Va.

[0062] The D flip-flop 51 is a circuit that holds the comparison result of the comparator 50 when the switch control IC 10 is started. In the D flip-flop 51, the signal UVLO is input to the R input, and the signal ENB is input to the CK input. Therefore, if the power supply voltage Vcc rises and the voltage detection circuit 31 changes the signal UVLO to the "L" level, the reset of the D flip-flop 51 is released. Thereafter, if the power supply voltage Vcc further rises and the voltage detection circuit 32 changes the signal ENB to the "L" level, the comparison result of the comparator 50 input to the D input is held. Then, the comparison result held by the D flip-flop 51 is output from the Q output as the signal S1.

[0063] In addition, in this embodiment, if it is determined that the switch control IC10 is used for a non-insulated power supply circuit, an "L" level signal S1 (first signal) is output; if it is determined that the switch control IC10 is used for an isolated power supply circuit, an "H" level signal S1 (second signal) is output.

[0064] The comparator 40 is a so-called zero current detection circuit, and detects whether the inductor current IL (described later) of the power supply circuit becomes zero based on the voltage Vzcd of the terminal ZCD. Here, "zero" means, for example, that the inductor current IL is a current value (for example, 0.1 mA) at which the inductor current IL is approximately zero. Therefore, the comparator 40 compares the voltage Vzcd with a reference voltage Vref2 corresponding to a current of, for example, 0.1 mA, to detect that the inductor current IL is zero. In addition, if the comparator 40 detects that the inductor current IL is zero, the signal Vc2 changes to the "L" level.

[0065] When it is detected that the inductance IL is zero and the signal Vc2 changes to the “L” level, the pulse circuit 41 outputs the pulse signal Vp of the “H” level.

[0066] Every time the pulse signal Vp at the “H” level is input, the oscillation circuit 42 outputs a ramp wave Vr whose amplitude gradually increases.

[0067] When it is determined that the switch control IC 10 is used for a non-insulated power supply circuit, the error amplifier circuit 43 (first error voltage output circuit) outputs an error voltage Ve1 for making the output voltage of the power supply circuit a target level. Specifically, if the signal S1 of the "L" level is input, the error amplifier circuit 43 amplifies the error between the voltage Va and the prescribed reference voltage Vref3 and outputs the error voltage Ve1 (first error voltage).

[0068] Furthermore, when the signal S1 of the "H" level is input, the error amplifier circuit 43 stops outputting the error voltage Ve1. In addition, the reference voltage Vref3 is a voltage determined based on the target level of the output voltage Vout1 of the non-insulated power supply circuit. In addition, the error voltage Ve1 is stopped, for example, by the output of the error amplifier circuit 43 becoming a high impedance state.

[0069] The error amplifier circuit 44 (second error voltage output circuit) is a circuit that outputs an error voltage Ve2 for making the output voltage of the power supply circuit a target level when it is determined that the switch control IC 10 is used for an isolated power supply circuit, and includes a resistor 60 and a switch 61. In addition, although the details will be described later, when the switch control IC 10 is used for an isolated power supply circuit, a phototransistor is connected to the terminal B, and the phototransistor generates a current corresponding to the error between the target levels of the output voltage.

[0070] A switch 61 is provided between a resistor 60 to which a power supply voltage Vdd is applied at one end and the terminal B. The switch 61 connected in series to the resistor 60 is turned on when an "H" level signal S1 is input, and is turned off when an "L" level signal S1 is input.

[0071] Therefore, when the signal S1 of the "H" level is input and the switch is turned on, the current of the phototransistor (described later) flows through the resistor 60. Then, the error voltage Ve2 (second error voltage) corresponding to the error between the target levels of the output voltage is output from the resistor 60. On the other hand, when the signal S1 of the "L" level is input and the switch is turned off, the output of the error voltage Ve2 is stopped.

[0072] Thus, the error amplifier circuit 43 outputs the error voltage Ve1 when the signal S1 at the "L" level is input, and the error voltage output circuit 44 outputs the error voltage Ve2 when the signal S1 at the "H" level is input. Therefore, in the present embodiment, only one of the error amplifier circuit 43 and the error voltage output circuit 44 operates to output a voltage corresponding to the error of the output voltage. In addition, the voltage applied to the terminal B is the voltage Vb, so when the signal S1 is at the "L" level, the voltage Vb becomes the error voltage Ve1, and when the signal S1 is at the "H" level, the voltage Vb becomes the error voltage Ve2.

[0073] The comparator 45 compares the voltage Vb of the terminal B with the magnitude of the ramp wave Vr, and outputs a signal Vc3 as a comparison result. Here, the voltage Vb is applied to the inverting input terminal of the comparator 45, and the ramp wave Vr is applied to the non-inverting input terminal of the comparator 45. Therefore, when the level of the ramp wave Vr is lower than the level of the voltage Vb, the signal Vc3 becomes an "L" level, and when the level of the ramp wave Vr becomes higher than the level of the voltage Vb, the signal Vc3 becomes an "H" level.

[0074] When the pulse signal Vp is output, the drive circuit 46 turns on the switch element “described later”, and turns off the switch element when the comparison result of the comparator 45 , that is, the signal Vc3 becomes “H” level. The drive circuit 46 includes an SR flip-flop 70 and a buffer circuit 71 .

[0075] The pulse signal Vp is input to the S input of the SR flip-flop 76, and the signal Vc3 is input to the R input. Therefore, when the pulse signal Vp becomes "H" level, the Q output of the SR flip-flop 70 becomes "H" level. On the other hand, when the signal Vc3 becomes "H" level, the Q output becomes "L" level.

[0076] The buffer circuit 71 outputs a drive signal Vdr for driving the switch element based on the Q output of the SR flip-flop 70. Specifically, the buffer circuit 71 outputs an "H" level drive signal Vdr when the Q output becomes an "H" level, and outputs an "L" level drive signal Vdr when the Q output becomes an "L" level.

[0077] <<<An example of a non-insulated power supply circuit>>>

[0078] Figure 3 1 is a diagram showing an example of the structure of a non-insulated power supply circuit 20. The power supply circuit 20 (first power supply circuit) is a step-up chopper type AC-DC converter that generates an output voltage Vout1 of a target level V1 (for example, 400 V) at a load 11 based on an AC voltage Vac of a commercial power supply. In addition, the load 11 is, for example, an electronic device such as a DC-DC converter or a microcomputer.

[0079] The power supply circuit 20 includes a switching control IC 10 , a full-wave rectifier circuit 100 , capacitors 101 , 102 , 106 , 132 , and 133 , a transformer 103 , resistors 104 , 120 , 121 , 122 , and 131 , diodes 105 and 107 , and an NMOS transistor 108 .

[0080] Switch control IC10 is Figure 1 The control IC described in improves the power factor of the power supply circuit 20 and controls the switching of the NMOS transistor 108 so that the level of the output voltage Vout1 reaches the target level V1 (first level).

[0081] The full-wave rectifier circuit 100 performs full-wave rectification on the applied predetermined AC voltage Vac and outputs the resultant voltage to the capacitor 101 as the voltage Vrec1. The AC voltage Vac is, for example, 100 to 240 V and has a frequency of 50 to 60 Hz.

[0082] The capacitor 101 smoothes the voltage Vrec1, and thus the smoothed voltage Vrec1 is applied to the primary coil L1 of the transformer 103. The voltage applied to the primary coil L1 (inductor) corresponds to the input voltage.

[0083] The transformer 103 includes a main coil L1 and an auxiliary coil L2 magnetically coupled to the main coil L1. In this embodiment, the auxiliary coil L2 is wound so that the polarity of the voltage generated by the auxiliary coil L2 is opposite to the polarity of the voltage generated by the main coil L1.

[0084] Since the resistor 104 is provided between one end of the auxiliary coil L2 and the terminal ZCD, the voltage Vz1 generated in the auxiliary coil L2 is applied to the terminal ZCD as the voltage Vzcd.

[0085] Since a diode 105 and a capacitor 106 are provided between one end of the auxiliary coil L2 and the ground, the capacitor 106 is charged by the voltage Vz1. In this embodiment, a charging voltage Vx1 of the capacitor 106 is provided as a power supply voltage Vcc of the switch control IC 10.

[0086] The capacitor 102 forms a step-up chopper circuit together with the main coil L1, the diode 107, and the NMOS transistor 108. Therefore, the charging voltage of the capacitor 102 becomes a DC output voltage Vout1.

[0087] The NMOS transistor 108 is a switching element for controlling the power to the load 11. In addition, in the present embodiment, although the NMOS transistor 108 is a MOS (Metal Oxide Semiconductor) transistor, it is not limited to this. As long as it is a transistor capable of controlling power, the NMOS transistor 108 may be, for example, a bipolar transistor.

[0088] The resistors 120 and 121 constitute a voltage dividing circuit that divides the output voltage Vout1, and generates a feedback voltage Vfb used when switching the NMOS transistor 108. In addition, the feedback voltage Vfb generated at the node where the resistors 120 and 121 are connected is applied to the terminal A. Therefore, in the power supply circuit 20, the voltage Va of the terminal A becomes the feedback voltage Vfb.

[0089] The resistor 122 functions as a startup resistor when the power supply circuit 20 is started. The resistor 131, the capacitor 132, and the capacitor 133 are phase compensation elements for stabilizing the feedback loop of the power supply circuit 20, and are provided between the terminal B and the ground.

[0090] ==Operation of non-insulated power supply circuit==

[0091] Figure 4 2 is a diagram for explaining the operation at the time of startup of the power supply circuit 20. Here, the power supply voltage Vcc becomes the voltage Vx1, and the voltage Va becomes the feedback voltage Vfb.

[0092] First, when the AC voltage Vac is supplied to the power supply circuit 20 at time t0, the voltage Vrec1 full-wave rectified by the full-wave rectifier circuit 100 is applied to the capacitor 106 via the start-up resistor 122. As a result, the charging voltage Vx1 of the capacitor 106 increases, and the power supply voltage Vcc (= Vx1) at the terminal VCC also increases.

[0093] In addition, if the voltage Vrec1 increases, the capacitor 102 is charged via the diode 107, so the output voltage Vout1 increases. As a result, the feedback voltage Vfb that divides the output voltage Vout1 also increases. In addition, at this time, the output voltage Vout1 will not become higher than the effective value of the AC voltage Vac. Therefore, the feedback voltage Vfb will not become higher than the value obtained by dividing the effective value of the AC voltage Vac by the resistors 120 and 121. That is, before the switch control IC 10 starts the switch control, the range of the feedback voltage Vfb change is from zero to the voltage value obtained by dividing the effective value of the AC voltage Vac by the resistors 120 and 121.

[0094] Then, when the power supply voltage Vcc (= Vx1 ) rises and reaches a predetermined level Vt1 at time t1 , the voltage detection circuit 31 changes the signal UVLO to the “L” level. As a result, the reset of the D flip-flop 51 is released.

[0095] Furthermore, when the power supply voltage Vcc (= Vx1 ) further rises and reaches a predetermined level Vt2 at time t2 , the voltage detection circuit 32 changes the signal ENB to the “L” level.

[0096] Here, the voltage Vref1 of the comparator 50 of the determination circuit 33 is set to be higher than the value obtained by dividing the effective value of the AC voltage Vac by the resistors 120 and 121. Therefore, at time t2, the D flip-flop 51 holds the comparison result of the "L" level from the comparator 50, and thus the level of the signal S1 is maintained at the "L" level.

[0097] As a result, Figure 1 In the switch control IC10, in the error amplifier circuit 43 and the error voltage output circuit 44, as shown in FIG. Figure 5 As shown, only the error amplifier circuit 43 operates. Figure 5 In the figure, the error voltage output circuit 44 is omitted for ease of understanding.

[0098] Furthermore, if the signal ENB changes to the "L" level at time t2, the operation of each circuit of the switch control IC 10 including the error amplifier circuit 43 starts. As a result, the error amplifier circuit 43 outputs an error voltage Ve1 corresponding to the error between the voltage Va (= Vfb) and the reference voltage Vref3, and the error voltage Ve1 rises. In addition, although the details will be described later, in the power supply circuit 20, the error amplifier circuit 43 operates so that the level of the feedback voltage Vfb coincides with the level of the reference voltage Vref3. Therefore, after time t2, the voltage Va (= Vfb) rises and becomes the reference voltage Vref3.

[0099] Figure 6 1 is a diagram for explaining the operation after the power supply circuit 20 is started. The power supply circuit 20 is started at, for example, a time t2 when the signal ENB changes to the "L" level and the operation of each circuit of the switch control IC 10 starts.

[0100] First, when the pulse signal Vp is output at time t10, the drive signal Vdr1 changes to "H" level, and the NMOS transistor 108 is turned on. As a result, the inductor current IL1 increases. In addition, when the pulse signal Vp is output, the amplitude of the ramp wave Vr from the oscillation circuit 42 increases.

[0101] Then, when the amplitude level of ramp wave Vr becomes higher than the level of voltage Vb (= Ve1) at time t11, comparator 45 changes signal Vc3 to "H" level. As a result, SR flip-flop 70 is reset and signal Vdr1 also becomes "L" level.

[0102] When the signal Vdr1 becomes "L" level, the NMOS transistor 108 is turned off, so the inductor current IL gradually decreases. In addition, when the NMOS transistor 108 is turned off, the voltage on the input side (voltage Vrec1 side) of the main coil L1 becomes lower than the output side (output voltage Vout1 side) of the main coil L1, so the voltage Vz1 at the other end of the auxiliary coil L2 whose one end is grounded becomes positive. As a result, the voltage Vzcd (= Vz1) becomes higher than the reference voltage Vref2, so the signal Vc2 from the comparator 40 becomes "H" level.

[0103] Then, when the inductor current IL1 becomes substantially zero at time t12, the voltage Vz1 of the auxiliary coil L2 magnetically coupled to the main coil L1 drops sharply. As a result, at time t13, the voltage Vz1 becomes lower than the reference voltage Vref2, and the signal Vc2 from the comparator 40 becomes "L" level.

[0104] When the signal Vc2 from the comparator 40 changes to the "L" level, the pulse signal Vp is output, so that the NMOS transistor 108 is turned on. Then, after the time t13, the operation from the time t10 to the time t13 is repeated.

[0105] ==Feedback Control and Power Factor Improvement==

[0106] Here, in the power supply circuit 20, if the output voltage Vout1 starts to increase from the target level V1 (for example, 400V), the feedback voltage Vfb increases. As a result, the error voltage Ve1 decreases, and the period during which the NMOS transistor 108 is turned on becomes shorter, so the output voltage Vout1 decreases. On the other hand, if the output voltage Vout1 starts to decrease from the target level V1, the feedback voltage Vfb decreases. As a result, the error voltage Ve1 increases, and the period during which the NMOS transistor 108 is turned on becomes longer, so the output voltage Vout1 increases. Thus, feedback control is performed in the power supply circuit 20 so that the output voltage Vout1 reaches the target level V1.

[0107] Therefore, when the power supply circuit 20 generates the output voltage Vout1 of the target level V1 according to the predetermined AC voltage Vac and supplies power to a constant load, the feedback voltage Vfb is constant. As a result, the error voltage Ve1 output from the error amplifier circuit 43 is also constant, and thus the period during which the NMOS transistor 108 is turned on (for example, the period from time t10 to time t11) is also constant.

[0108] When the NMOS transistor 108 is turned on, the level of the voltage Vrec1 obtained by rectifying the AC voltage Vac becomes higher, and the current value of the inductor current IL1 also becomes larger. As a result, the waveform of the peak value of the inductor current IL1 becomes the same as the waveform of the voltage Vrec1, and the power factor is improved. Therefore, the power supply circuit 20 operates as a PFC (Power Factor Correction) circuit. As a result, the switch control IC 10 can make the non-insulated power supply circuit 20 perform the desired operation.

[0109] <<<An example of an isolated power supply circuit>>>

[0110] Figure 7 1 is a diagram showing an example of the structure of the insulating power supply circuit 21. The power supply circuit 21 (second power supply circuit) is a flyback AC-DC converter that generates an output voltage Vout2 of a target level V2 (eg, 15V) at a load 11 based on an AC voltage Vac of a commercial power supply.

[0111] The power supply circuit 21 includes a full-wave rectification circuit 300 , capacitors 301 and 306 , a transformer 302 , an NMOS transistor 303 , a control block 304 , a diode 305 , a constant voltage circuit 307 , and a light emitting diode 308 .

[0112] The full-wave rectifying circuit 300 performs full-wave rectification on the applied predetermined AC voltage Vac, and outputs the resultant voltage to the capacitor 301 as the voltage Vrec2 .

[0113] The capacitor 301 filters the voltage Vrec2 , and thus the filtered voltage Vrec2 is applied to the transformer 302 .

[0114] The transformer 302 includes a primary coil L10 (inductor), a secondary coil L11, and an auxiliary coil L12, and the primary coil L10, the secondary coil L11, and the auxiliary coil L12 are insulated from each other. In the transformer 302, a voltage is generated in the secondary coil L11 on the secondary side according to a change in the voltage across the primary coil L10 on the primary side, and a voltage is generated in the auxiliary coil L12 on the primary side according to a change in the voltage of the secondary coil L10.

[0115] In addition, one end of the primary coil L10 is connected to the drain of the NMOS transistor 303, so when the switching of the NMOS transistor 303 starts, the voltage of each of the secondary coil L211 and the auxiliary coil L12 changes. In addition, the primary coil L10 and the secondary coil L11 are electromagnetically coupled with opposite polarities, and the secondary coil L11 and the auxiliary coil L12 are electromagnetically coupled with the same polarity.

[0116] The control block 304 is a circuit block for controlling the switching of the NMOS transistor 303 , and its details will be described later.

[0117] The diode 305 rectifies the voltage of the secondary coil L11, and the capacitor 306 filters the rectified voltage. As a result, a filtered output voltage Vout2 is generated in the capacitor 306. The output voltage Vout2 becomes a DC voltage (for example, 15V) of a target level V2 (second level).

[0118] The constant voltage circuit 307 is a circuit for generating a constant DC voltage, and is configured using, for example, a shunt regulator.

[0119] The light emitting diode 308 is an element that emits light having an intensity corresponding to the difference between the output voltage Vout2 and the output of the constant voltage circuit 307, and constitutes a photocoupler together with a phototransistor 530 described later. In this embodiment, when the level of the output voltage Vout2 becomes higher, the intensity of the light from the light emitting diode 308 becomes stronger.

[0120] <<<Control block 304>>>

[0121] The control block 304 includes a control IC 10 , a capacitor 500 , diodes 501 , 510 , resistors 502 , 511 , 520 , a Zener diode 521 , and a phototransistor 530 .

[0122] The switch control circuit IC10 is used to control Figure 1 The NMOS transistor 303 is a switch integrated circuit illustrated in FIG.

[0123] The other end of the capacitor 500, one end of which is grounded, the cathode of the diode 501, and the cathode of the diode 510 are connected to the terminal VCC. Therefore, the capacitor 500 is charged by the current from the diode 501 and the current from the diode 510. The charging voltage Vx2 of the capacitor 500 becomes the power supply voltage Vcc for operating the switch control IC 10. In addition, the current from the diode 510 is generated after the switch control IC 10 is started, so the switch control IC 10 is started based on the charging voltage Vx2 generated by the current from the diode 501.

[0124] A resistor 511 is connected between the terminal ZCD and the auxiliary coil L12. Therefore, the voltage Vz2 generated in the auxiliary coil L12 is applied to the terminal ZCD as the voltage Vzcd. In addition, as described above, the auxiliary coil L12 generates a voltage with a polarity opposite to that of the primary coil L10. Therefore, when the inductor current IL2 flowing through the primary coil L10 decreases, the auxiliary coil L12 generates a positive voltage Vz2, and when the inductor current L2 flowing through the primary coil L10 increases, the auxiliary coil L12 generates a negative voltage Vz2.

[0125] The other end of the resistor 520 to which the charging voltage Vx2 is applied and the cathode of the Zener diode 521 are connected to the terminal A. Therefore, if the charging voltage Vx2 becomes sufficiently high, the voltage Va applied to the terminal A becomes the breakdown voltage Vz0 (eg, 5.1V) of the Zener diode 521.

[0126] Terminal B is a terminal for generating an error voltage, which indicates the error between the level of the output voltage Vout2 and the target level V2, and a phototransistor 530 is connected to terminal B. The phototransistor 530 allows a bias current Ib of a magnitude corresponding to the intensity of light from the light emitting diode 308 to flow from terminal B to ground. Therefore, the phototransistor 530 operates as a transistor for generating an absorption current. In addition, a capacitor or other element for removing noise may also be provided between terminal B and ground.

[0127] The terminal OUT is connected to the gate of the NMOS transistor 303 , and thus the NMOS transistor 303 performs switching according to the drive signal Vdr2 .

[0128] ==Operation of the Insulated Power Supply Circuit==

[0129] Figure 8 It is a diagram for explaining the operation at the time of starting the power supply circuit 21. Here, the power supply voltage Vcc is the voltage Vx2.

[0130] First, when the AC voltage Vac is supplied to the power supply voltage 21 at time t20 and the voltage Vrec2 is generated, the capacitor 500 is charged via the diode 501. As a result, the charging voltage Vx2 of the capacitor 500 rises, and as a result, the power supply voltage Vcc (= Vx2) at the terminal VCC also rises.

[0131] Furthermore, if the power supply voltage Vcc (= Vx2) increases, the voltage Va also increases, and at time t21, the voltage Va becomes higher than the reference voltage Vref1 of the comparator 50. As a result, the signal Vc1 of the comparator 50 changes to the "H" level. In addition, in this embodiment, the resistance value of the resistor 520 and the breakdown voltage Vz0 of the Zener diode 521 are selected so that when the power supply circuit 21 is started, the voltage Va becomes higher than the reference voltage Vref1.

[0132] Furthermore, if the power supply voltage Vcc further rises and the voltage Va becomes higher than the breakdown voltage Vz0 at time t22, the voltage Va is clamped by the breakdown voltage Vz0. In addition, in the present embodiment, the breakdown voltage Vz0 (e.g., 5.4V) is set to a voltage higher than the reference voltage Vref1, so if the Zener diode 521 is turned on, the voltage Va must become higher than the reference voltage Vref1.

[0133] Then, when the power supply voltage Vcc (= Vx2 ) rises and reaches the predetermined level Vt1 at time t23 , the voltage detection circuit 31 changes the signal UVLO to the “L” level. As a result, the reset of the D flip-flop 51 is released.

[0134] Furthermore, when the power supply voltage Vcc (= Vx2) further rises and reaches the predetermined level Vt2 at time t24, the voltage detection circuit 32 changes the signal ENB to the "L" level. When the signal ENB changes to the "L" level, the D flip-flop 51 holds the "H" level comparison result from the comparator 50, and thus the level of the signal S1 changes to the "H" level.

[0135] As a result, Figure 1 In the switch control IC10, the error amplifier circuit 43 and the error voltage output circuit 44, as shown in FIG. Fig. 9 As shown in FIG. 1 , only the error amplifier circuit 43 operates. In addition, the output of the error amplifier circuit 43 is in a high impedance state, so the output of the error amplifier circuit 43 does not affect the voltage Vb of the terminal B.

[0136] Furthermore, when the signal ENB changes to the "L" level at time t24, the switch 61 of the error voltage output circuit 44 becomes conductive, and therefore the error voltage Ve2 of the resistor 60 becomes Ve2=Vdd-R×Ib. Here, the resistance value of the resistor 60 is set to "R", and the current value of the bias current Ib of the phototransistor 530 is set to "Ib". In addition, the on-resistance value of the switch 61 is sufficiently small, so that the voltage Vb of the terminal B becomes the error voltage Ve2.

[0137] Fig.10 2 is a diagram for explaining the operation after the power supply circuit 21 is activated. The activation timing of the power supply circuit 21 is, for example, the timing when the signal ENB becomes "L" level at time t24 and the operation of each circuit of the switch control IC 10 starts.

[0138] First, when the pulse signal Vp is output at time t30, the drive signal Vdr2 becomes "H" level, and the NMOS transistor 303 is turned on. As a result, the inductor current IL2 increases. In addition, when the pulse signal Vp is output, the amplitude of the ramp wave Vr from the oscillation circuit 42 increases. When the NMOS transistor 303 is turned on, the secondary coil L11 is electromagnetically coupled with the opposite polarity, so the diode 305 is turned off, and energy is accumulated in the transformer 302.

[0139] Then, when the amplitude level of ramp wave Vr becomes higher than the level of voltage Vb (= Ve2) at time t31, comparator 45 changes signal Vc3 to "H" level. As a result, SR flip-flop 70 is reset and signal Vdr also becomes "L" level.

[0140] When the signal Vdr2 becomes L level, the NMOS transistor 303 is turned off. As a result, the inductor current IL2 decreases rapidly, and the voltage Vz2 at the other end of the auxiliary coil L12, one end of which is grounded, becomes positive. In addition, the energy stored in the transformer 302 is output from the secondary coil L11 through the diode 305. As a result, the voltage Vzcd (= Vz2) becomes higher than the reference voltage Vref2, and therefore the signal Vc2 from the comparator 40 becomes "H" level.

[0141] Then, when the inductance current IL3 of the secondary coil L11 becomes substantially zero at time t32, the voltage Vz2 of the auxiliary coil L12 magnetically coupled to the main coil L10 drops sharply. As a result, at time t33, the voltage Vzcd (= Vz2) becomes lower than the reference voltage Vref2, and the signal Vc2 from the comparator 40 becomes "L" level.

[0142] When the signal Vc2 changes to the "L" level, the pulse signal Vp is output, and the NMOS transistor 303 is turned on. Then, after time t33, the operation of time t30 to t33 is repeated. In addition, the timing when the inductor current IL3 becomes substantially zero varies according to the current value of the inductor current IL2. Therefore, the switch control IC10 turns on the NMOS transistor 303 based on the inductor current IL2.

[0143] ==Feedback Control==

[0144] Here, if the load 11 is a light load, the output voltage Vout2 rises from the target level V2. At this time, the current flowing through the shunt regulator (not shown) of the constant voltage circuit 307 increases, so the current of the light emitting diode 308 also increases. The phototransistor 530 increases the bias current Ib according to the degree of amplification of the light from the light emitting diode 308, so the error voltage Ve2 (=Vb) decreases. As a result, the period during which the NMOS transistor 303 is turned on becomes shorter, so the output voltage Vout2 decreases.

[0145] On the other hand, if the output voltage Vout2 starts to decrease from the target level V2, the current of the light emitting diode 308 decreases in the opposite manner to the above case. As a result, the bias current Ib decreases and the error voltage Ve2 (=Vb) increases. Therefore, the period during which the NMOS transistor 303 is turned on becomes longer, and the output voltage Vout2 increases. Thus, feedback control is performed in the power supply circuit 21 so that the output voltage Vout2 reaches the target level V2. Therefore, the switch control IC 10 can make the isolated power supply circuit 21 perform the desired operation.

[0146] ===Switch control IC for soft-starting power supply circuits ===

[0147] <<<Structure of switch control IC12>>>

[0148] Fig.11 1 is a diagram showing an example of a switch control IC 12 that soft-starts a power supply circuit when an isolated power supply circuit is started. Here, "soft start" means suppressing a large current from flowing through a switched transistor when the power supply circuit is started. In addition, in the present embodiment, "starting the switch control IC" means, for example, that a signal ENB of the switch control IC becomes "L" level, and the operation of each circuit of the switch control IC 10 starts.

[0149] The switch control IC12 is the following circuit: Figure 1The switch control IC 10 of the embodiment is provided with an on-timer 600, an OR gate circuit 601, and a voltage output circuit 602, and includes a comparator 603 instead of the comparator 45. In addition, in the embodiment, common circuits and components are given common reference numerals, and for the sake of convenience, for example, description of a part of the circuits or components (for example, the terminal VCC, the power supply circuit 30, the voltage detection circuits 31, 32) is omitted. Therefore, here, the description is mainly made with respect to the circuits not included in the switch control IC 10.

[0150] The on-timer 600 outputs a pulse signal Vp2 for turning on the switching transistor when the power supply circuit is started or when the AC voltage Vac is cut off and the pulse signal Vp1 from the pulse circuit 41 is not output. Specifically, when the pulse signal Vp1 is not output for a predetermined period, the on-timer 600 outputs a pulse signal Vp2 of the "H" level in each predetermined period.

[0151] When either of the pulse signals Vp1 and Vp2 changes to the "H" level, the OR circuit 601 outputs a pulse signal Vp3 for turning on the switching transistor.

[0152] When the signal S1 of the “H” level indicating that the switch control IC 12 is determined to be used for an isolated power supply circuit is input, the voltage output circuit 602 outputs the voltage Vo whose level gradually increases. Fig.12 7 is a diagram showing an example of a voltage output circuit 602a as an embodiment of the voltage output circuit 602. The voltage output circuit 602a is configured to include a clock generation circuit 700 and a charge pump 701. The voltage Vo output by the voltage output circuit 602 corresponds to the "first voltage".

[0153] The clock generation circuit 700 outputs a clock signal CLK of a predetermined frequency, and the charge pump 701 generates a voltage Vo based on the clock signal CLK when the signal S1 at the "H" level is input. Specifically, the charge pump 701 gradually increases the voltage Vo from 0V to a predetermined voltage (for example, the power supply voltage Vdd) when the signal S1 becomes at the "H" level.

[0154] The comparator 603 is a so-called three-input comparator, and outputs a comparison result between a lower voltage of any one of the voltages applied to the two inverting inputs and a voltage applied to the non-inverting input. Therefore, the comparator 603 compares the lower voltage of the voltages Vb and Vo with the magnitude of the ramp wave Vr, and outputs a signal Vc4 as a comparison result. In addition, although the details will be described later, for example, the phototransistor 530 and the capacitor 531 are connected to the terminal B generating the voltage Vb.

[0155] Although the details will be described later, the voltage output circuit 602 operates only when the switch control IC 12 is used as an isolated power supply circuit. Therefore, for example, the phototransistor 530 and the capacitor 531 are connected to the terminal B generating the voltage Vb.

[0156] Fig.13 1 is a diagram showing an example of a structure in which the switch control IC 12 is used for an isolated power supply circuit 22. Similar to the power supply circuit 21, the power supply circuit 22 is a flyback AC-DC converter that generates an output voltage Vout2 of a target level V2 (e.g., 15V) at the load 11 based on the AC voltage Vac of the commercial power supply. The power supply circuit 22 is configured to include, in addition to the elements included in the power supply circuit 21, a capacitor 531 connected to the terminal B of the switch control IC 12, a diode 550 for recirculating the current of the primary coil L10, a capacitor 551, and a resistor 552.

[0157] The capacitor 531 is used when the switching control IC 12 performs a soft start operation and removes noise generated at the terminal B.

[0158] The diode 550 refluxes the current of the primary coil L10 when the NMOS transistor 303 is turned off. The capacitor 551 and the resistor 552 are connected to the cathode of the diode 550. Therefore, when the diode 550 is turned on, the current corresponding to the impedance of the capacitor 551 and the resistor 552 refluxes to the primary coil L10.

[0159] Fig.14 1 is a diagram showing an example of a waveform at the time of startup of the power supply circuit 22 using the switch control IC 12. Here, Fig.14 The time t50 is set as the timing when the power supply voltage Vcc (= Vx2) rises to the predetermined level Vt2 ( Figure 8 In addition, at Figure 8 In the example, for convenience, it is assumed that the voltage Vb of the terminal B immediately decreases to Vdd-R×Ib at the time t24 when the signal S1 changes to the “H” level. However, the actual voltage Vb is, for example, Fig.14 That way it gradually decreases.

[0160] First, at time t50, when the signal ENB of the switch control IC 12 becomes "L" level and the switch control IC 10 is activated, each circuit of the switch control IC 10 starts to operate. Fig.11When the determination circuit 33 outputs the signal S1 of "H" level, the switch 61 of the error voltage output circuit 44 becomes conductive. At this timing, power is not supplied to the secondary side of the power supply circuit 22, and thus the output voltage Vout2 is 0V. Therefore, the bias current Ib of the phototransistor 530 is zero, and thus the level of the voltage Vb becomes the power supply voltage Vdd. In addition, when the signal S1 becomes "H" level at time t50, the voltage output circuit 602 causes the voltage Vo to rise from 0V.

[0161] Then, when it comes to time t51, the conduction timer 600 outputs the pulse signal Vp2 of the "H" level, so the pulse signal Vp3 also becomes the "H" level. As a result, the drive signal Vdr2 becomes the "H" level, and the NMOS transistor 303 is turned on. In addition, every time the pulse signal Vp3 of the "H" level is input, the oscillation circuit 42 outputs the ramp wave Vr with a gradually increasing amplitude, so at the timing of time t51, the amplitude of the ramp wave Vr becomes larger.

[0162] When the ramp wave Vr becomes larger than the voltage Vb (here, the voltage Vo) at time t52, the comparator 603 outputs the signal Vc4 at the "H" level, so that the drive signal Vdr2 becomes the "L" level and the NMOS transistor 303 is turned off.

[0163] Furthermore, when it becomes time t53, the conduction timer 600 outputs the pulse signal Vp2 of the "H" level. As a result, the drive signal Vdr2 becomes the "H" level, and the NMOS transistor 303 is turned on. Furthermore, when the amplitude of the ramp wave Vr gradually increases at this timing, and it becomes time t54, the comparator 603 outputs the signal Vc4 of the "H" level, and therefore the drive signal Vdr2 becomes the "L" level. Here, the voltage output circuit 602 gradually increases the level of the voltage Vo from time t50, and therefore, the period T1 during which the NMOS transistor 303 is turned on also gradually becomes longer. Therefore, the power supply circuit 22 is soft-started.

[0164] In addition, if the NMOS transistor 303 is switched and power is supplied to the secondary side of the power supply voltage 22, the level of the output voltage Vout2 gradually increases. If the level of the output voltage Vout2 increases, the intensity of the light from the light emitting diode 308 also increases, so the bias current Ib flowing through the terminal B also increases. As a result, for example, if the signal ENB becomes "L" level and the NMOS transistor 303 starts switching, the error voltage Ve2 (=Vdd-R×Ib) decreases. Then, after the time 55 when the error voltage Ve2 becomes lower than the voltage Vo, the comparator 603 compares the error voltage Ve2 with the magnitude of the ramp wave Vr and changes the drive signal Vdr2 to the "L" level.

[0165] After time t55, for example, the switch control IC 12 performs the above Fig.10 Therefore, the output voltage Vout2 is controlled to the target level V2. Therefore, the switch control IC 12 can make the isolated power supply circuit 22 perform normal operation. As a result, the switch control IC 12 can gradually extend the period T1 during which the NMOS transistor 303 is turned on from the time t50 to the time t55 when the switch control IC 12 is started. Therefore, the prescribed period from the time t50 to the time t55 becomes the so-called soft start period Ts.

[0166] In addition, in the present embodiment, after the soft start period Ts, the period T2 (second period) during which the NMOS transistor 303 is turned on is longer than the period T1 (first period) during which the NMOS transistor 303 is turned on during the soft start period Ts. Therefore, in the present embodiment, when the power supply circuit 22 is started, a large current can be reliably prevented from flowing through the NMOS transistor 303.

[0167] In addition, the charge pump 701 of this embodiment is designed to output a voltage Vo at the level of the power supply voltage Vdd when the signal S1 of the "L" level is input, for example. Therefore, when the switch control IC 12 is used in a non-insulated power supply circuit, the comparator 603 compares the voltage of the error amplifier circuit 43 and the voltage of the ramp wave Vr, and therefore, the comparator 603 is not affected by the voltage output circuit 602a.

[0168] ==Other Embodiments of Voltage Output Circuit==

[0169] Fig.15 1 is a diagram showing an example of the structure of a voltage output circuit 602b that outputs a discretely changing voltage Vo. The voltage output circuit 602b is configured to include a counter 702 and a DAC (Digital to Analog Converter) 703.

[0170] The counter 702 is a circuit that increments the count value CNT by "1" at a predetermined interval during the soft start Ts period. Specifically, when the signal S1 at the "H" level is input, the counter 702 changes the count value CNT from "0" to "7" during the soft start period Ts (for example, a period of several ms to 10 ms). In addition, in the counter 702, for example, when the signal ENB changes to the "L" level, the reset is released.

[0171] DAC 703 is a circuit that outputs a voltage Vo whose level increases as the count value CNT increases. For example, when the count value CNT is "0", DAC 703 outputs a voltage Vo of "0" V. Then, when the count value increases by "1", the voltage Vo is increased by "Vdd / 7". As a result, when the count value CNT is "7", DAC 703 increases the voltage Vo to the power supply voltage Vdd. Therefore, even when such a voltage output circuit 602b is used, the power supply circuit can be soft-started.

[0172] In addition, the DAC 703 is designed to output a voltage Vo at the level of the power supply voltage Vdd when the signal S1 at the "L" level is input, regardless of the count value CNT. Therefore, when the switch control IC 12 using the voltage output circuit 602b is used in a non-insulated power supply circuit, the comparator 603 is not affected by the voltage output circuit 602b.

[0173] Fig.16 2 is a diagram showing an example of the configuration of the voltage generating circuit 602 c . The voltage generating circuit 602 c includes a discharge circuit 704 , switches 706 and 709 , a current source 705 , a capacitor 707 , and a resistor 708 .

[0174] The discharge circuit 704 performs a discharge operation of the capacitor 707 when the signal ENB is at an "H" level, and stops the discharge operation when the signal ENB becomes an "L" level. When the signal S1 at an "H" level is input and the switch 706 becomes conductive, the current source 705 charges the capacitor 707 with a predetermined current. Here, the voltage Vo determined by the current of the current source 705 and the capacitance of the capacitor 707 is determined so that, for example, it rises from 0V to approximately the power supply voltage Vdd within the soft start period Ts. Therefore, when such a voltage output circuit 602c is used instead of the voltage output circuit 602a, the switch control IC 12 can soft-start the power supply circuit. In addition, the switch 706 is turned off when the signal S1 at an "L" level is input.

[0175] The switch 709 is turned on when the signal S1 at the "L" level is input, so the voltage Vo of the capacitor 707 is pulled up to the power supply voltage Vdd via the resistor 708. Therefore, when the switch control IC 12 using the voltage output circuit 602c is used in a non-insulated power supply circuit, the comparator 603 is not affected by the voltage output circuit 602c.

[0176] In the switch control IC 12 , the comparator 40 , the pulse circuit 41 , the on-timer 600 , and the OR gate circuit 601 correspond to a “first timing signal output circuit”, and the comparator 603 corresponds to a “second timing signal output circuit”.

[0177] <<<Structure of switch control IC13>>>

[0178] Fig.17 FIG. 1 is a diagram showing an example of a switch control IC 13 for soft-starting an isolated power supply circuit. The switch control IC 13 is a circuit as follows: Figure 1 The switch control IC 10 is added with a conduction timer 600, an OR gate circuit 601, a timer 610, an inverter 611, an AND gate circuit 612 and a charging circuit 613. The conduction timer 600 and the like are the same as the above-mentioned circuits, so the timer 610 and the like are described here.

[0179] When the signal S1 of the "H" level indicating that the switch control IC 13 is used for the isolated power supply circuit is input, the timer 610 starts to measure the soft start period Ts. Then, if the timer 610 measures the soft start period Ts after the signal S1 of the "H" level is input, the output of the timer 610 changes from the "L" level to "H". In addition, when the signal S1 of the "L" level indicating that the switch control IC 13 is used for the isolated power supply circuit is input, the timer 610 outputs the signal of the "L" level.

[0180] The inverter 611 inverts the logic level of the output of the timer 610, and the AND gate circuit 612 calculates the logic AND of the signal S1 and the output of the inverter 611, and outputs it to the charging circuit 613. In the AND gate circuit 612 in this embodiment, the signal S1 becomes "H" level, and before the soft start period Ts elapses, the signal of "H" level is output, and after the soft start period Ts elapses, the signal of "L" level is output.

[0181] The charging circuit 613 is a circuit that charges an element (eg, capacitor 531 ) connected to the terminal B while the AND circuit 612 outputs a signal at the “H” level, and is configured to include a current source 720 that generates a predetermined current and a switch 721 .

[0182] The switch 721 is turned on when the signal from the input of the AND gate circuit 612 is at the "H" level, and is turned off when the signal from the input of the AND gate circuit 612 is at the "L" level. Therefore, in this embodiment, the signal S1 is at the "H" level, and before the soft start period Ts has passed, the charging circuit 613 operates, and after the soft start period Ts has passed, the error voltage output circuit 44 operates.

[0183] In this way the switch control IC13 is used Fig.13In the case of the power supply circuit 22, the signal S1 is at the "H" level, and before the soft start period Ts, the capacitor 531 is charged by the current of the current source 720, so that the voltage Vb gradually increases. Therefore, during this period, the comparator 45 compares the gradually increasing voltage Vb with the magnitude of the ramp wave Vr, so that the period during which the NMOS transistor 303 is turned on gradually becomes longer.

[0184] Then, after the soft start period Ts has passed, the voltage Vb becomes the error voltage Ve2, and therefore the comparator 45 compares the voltage Vb determined by the error voltage Ve with the magnitude of the ramp wave Vr. Therefore, for example, the switch control IC 13 performs the above Fig.10 , so that the output voltage Vout2 is controlled to the target level V2.

[0185] In the switch control IC 13, the comparator 40, the pulse circuit 41, the conduction timer 600, and the OR gate circuit 601 are equivalent to the "first timing signal output circuit". In addition, the timer 610, the inverter 611, the AND gate circuit 612, and the charging circuit 613 are equivalent to the "voltage output circuit", and the comparator 45 is equivalent to the "second timing signal output circuit".

[0186] <<<Structure of switch control IC14>>>

[0187] Fig.18 FIG. 1 is a diagram showing an example of a switch control IC 14 for soft-starting an isolated power supply circuit. The switch control IC 14 is a circuit as follows: Figure 1 The switch control IC 10 is added with a conduction timer 600, an OR gate circuit 601, a timer 610 and a control circuit 620. The conduction timer 600 and the like are the same as the above-mentioned circuits, so the control circuit 620 is described here.

[0188] The control circuit 620 is a circuit that, when the switch control IC 14 is used in an isolated power supply circuit, causes the error amplifier circuit 43 to operate as a constant current source only during the soft start period Ts. Specifically, the control circuit 620 controls the transconductance amplifier, i.e., the error amplifier circuit 43, based on the signal S1 and the output of the timer 610. For example, when the signal S1 is at an "H" level, the control circuit 620 causes the error amplifier circuit 43 to output a predetermined current from the time when the signal S1 becomes "H" level until the soft start period Ts passes. Then, if the signal S1 becomes "H" level and the soft start period Ts passes, the control circuit 620 sets the output of the error amplifier circuit 43 to a high impedance state. On the other hand, when the signal S1 is at an "L" level, the control circuit 620 causes the error amplifier circuit 43 to output an error voltage Ve1.

[0189] By using such a control circuit 620, the error amplifier circuit 43 can gradually increase the voltage Vb during the soft start period Ts. During this period, the comparator 45 compares the gradually increasing voltage Vb with the magnitude of the ramp wave Vr, so that the power supply circuit 22 performs a soft start at startup.

[0190] In the switch control IC 14, the comparator 40, the pulse circuit 41, the conduction timer 600 and the OR gate circuit 601 are equivalent to the "first timing signal output circuit". In addition, the timer 610, the control circuit 620 and the error amplifier circuit 43 are equivalent to the "voltage output circuit", and the comparator 45 is equivalent to the "second timing signal output circuit".

[0191] <<<Structure of switch control IC15>>>

[0192] Fig.19 FIG. 1 is a diagram showing an example of a switch control IC 15 for soft-starting an isolated power supply circuit. The switch control IC 15 is a circuit as follows: Figure 1 The switch control IC 10 is added with a conduction timer 600, an OR gate circuit 601, a timer 630 and an oscillation circuit 631. The conduction timer 600 and the OR gate circuit 601 are the same as the above-mentioned circuits, so here, the timer 630 and the oscillation circuit 631 are mainly described.

[0193] When the signal S1 is at the "H" level and the switch control IC15 is used for an isolated power supply circuit, the timer 630 starts timing the soft start period Ts. When the signal S1 is at the "H" level, each time the pulse signal Vp3 is input, the oscillation circuit 631 outputs a ramp wave Vr having a slope corresponding to the output of the timer 630. Specifically, the oscillation circuit 631 outputs a triangular wave-shaped ramp wave Vr whose slope gradually becomes gentle (or smaller) during the soft start period Ts. Then, if the soft start period Ts has passed since the signal S1 becomes the "H" level, the oscillation circuit 631 stops making the slope of the ramp wave Vr gentle, and outputs a ramp wave Vr with a predetermined slope.

[0194] On the other hand, when the signal S1 is at the "L" level and the switch control IC15 is used for a non-insulated power supply circuit, the oscillation circuit 631 outputs a predetermined ramp wave Vr whenever the pulse signal Vp3 is input, regardless of the output of the timer 630. In addition, the drive circuit 46 turns off the switching transistor (for example, NMOS 303) when the ramp wave Vr becomes larger than the voltage Vb. Therefore, if the slope of the ramp wave Vr from the oscillation circuit 631 becomes gentle, the period during which the switching transistor is turned on gradually becomes longer. Therefore, by using the oscillation circuit 631 in this way, the switch control IC15 can soft-start the isolated power supply circuit.

[0195] In the switch control IC 15 , the comparator 40 , the pulse circuit 41 , the on-timer 600 , and the OR circuit 601 correspond to a “first timing signal output circuit”, and the comparator 45 corresponds to a “second timing signal output circuit”.

[0196] <<<Structure of switch control IC16>>>

[0197] Fig. 20 FIG. 1 is a diagram showing an example of a switch control IC 16 for soft-starting a non-insulated power supply circuit. The switch control IC 16 is a circuit as follows: Figure 1 The switch control IC 10 is added with a conduction timer 600, an OR gate circuit 601, and a discharge circuit 650. The conduction timer 600 and the OR gate circuit 601 are the same as the above-mentioned circuits, so here, the discharge circuit 650 is described. In addition, here, it is assumed that the switch control IC 16 is used for example Figure 3 The power supply circuit 20 is shown.

[0198] When the switch control IC 16 is activated and a signal S1 indicating an "L" level for a non-insulated power supply circuit is input, the discharge circuit 650 discharges the capacitors 132 and 133 connected to the terminal B for a certain time. Thus, the voltage Vb decreases to 0V.

[0199] Thereafter, when the error amplifier circuit 43 charges the capacitors 132 and 133, the voltage Vb gradually increases from 0 V, so the period during which the switching transistor, namely the NMOS transistor 108, is turned on also gradually increases. Therefore, by using such a structure, the switch control IC 16 can soft-start the non-insulated power supply circuit 20.

[0200] ===Switch control IC including masking circuit===

[0201] <<<Structure of switch control IC17>>>

[0202] For example, in Figure 3 , Figure 7 In the power supply circuits 20 and 21, if the switching transistor is turned off and the current flowing through the transformers 103 and 302 changes, noise may be generated at the terminal ZCD. Figure 1 The comparator 40 of the switch control IC 10 may change the signal Vc2 to "H" level due to the noise of the terminal ZCD. Then, if the signal Vc2 becomes "H" level due to the noise, the switch control IC 10 turns on the switch transistor at an erroneous timing. In addition, the switch transistor here refers to, for example, the NMOS transistors 108 and 303.

[0203] Fig.21FIG. 1 is a diagram showing an example of a switch control IC 17 that can turn on a switch transistor at a correct timing. The switch control circuit IC 17 is configured to include Figure 1 The switch control IC 10 further includes a masking circuit 660 .

[0204] The masking circuit 660 is a circuit that masks and outputs the signal Vc2 of the comparator 40 for a predetermined period corresponding to the structure of the power supply circuit after the switching transistor is turned off. Specifically, when the switch control IC 17 is used for a non-insulated power supply circuit, the masking circuit 660 masks the signal Vc for a masking period Tm1, and when the switch control IC 17 is used for an insulated power supply circuit, the masking circuit 660 masks the signal Vc for a masking period Tm2 (>Tm1).

[0205] like Fig. 22 As shown, the mask circuit 660 includes a period setting circuit 750 and a logic circuit 751. The period setting circuit 750 is a circuit for setting a mask period corresponding to the signal S1, and includes an NMOS transistor 800, a switch 801, capacitors 802, 803, and a current source 804.

[0206] When the Q output of the SR flip-flop 70 included in the drive circuit 46 becomes "H" level, the NMOS transistor 800 is turned on, and when the Q output becomes "L" level, the NMOS transistor 800 is turned off. When the "H" level signal S1 indicating that the switch control IC 17 is used for the isolated power supply circuit is input, the switch 801 is turned on, and when the "L" level signal S1 indicating that the switch control IC 17 is used for the non-isolated power supply circuit is input, the switch 801 is turned off.

[0207] Therefore, during the period when the NMOS transistor 800 is turned off, the voltage Vcap of the node connecting the capacitor 802 and the current source 804 rises. In this embodiment, when the switch 801 is turned off, the period during which the voltage Vcap becomes "H" after the Q output of the SR flip-flop 70 becomes "L" level is set as "masking period Tm1 (first masking period)". In addition, when the switch 801 is turned on, the period during which the voltage Vcap becomes "H" after the Q output of the SR flip-flop 70 becomes "L" level is set as "masking period Tm2 (second masking period)". In addition, the masking period Tm2 in the state where the switch 801 is turned on becomes longer than the masking period Tm1.

[0208] The logic circuit 751 is a circuit that causes the signal Vc to mask for the masking periods Tm1 and Tm2, ​​and is configured to include an inverter 810, and AND gate circuits 811 and 812. Here, when the Q output of the SR flip-flop 70 is at the "L" level, the output of the inverter 810 becomes the "H" level. Therefore, from the time when the switching transistor is turned off to the time when the voltage Vcap becomes the "H" level, the AND gate circuit 811 outputs the signal Vm at the "L" level. Therefore, during this period, the AND gate circuit 812 outputs the signal Vmask at the "L" level, regardless of the level of the signal Vc. On the other hand, when the voltage Vcap becomes the "H" level, the signal Vm also becomes the "H" level, so the AND gate circuit 812 can output the signal Vmask at the same logic level as the signal Vc2.

[0209] <<<Operation of switch control IC17>>>

[0210] ==When the switch control IC 17 is used in a non-insulated power supply circuit==

[0211] Fig.23 is used to illustrate the use of switch control IC17 Figure 3 The operation diagram of the non-insulated power supply circuit 20 is shown in FIG. Figure 6 , the basic circuit operation of the switch control IC 17 used for the non-insulated power supply circuit is described in , but here, the operation of the circuit related to the masking circuit 660 is mainly described.

[0212] At time t70, if the pulse circuit 41 outputs the pulse signal Vp of the "H" level, the Q output of the SR flip-flop 70 becomes the "H" level, and therefore, Figure 3 The NMOS transistor 108 is turned on. As a result, the voltage Vds1 between the drain and the source of the NMOS transistor 108 becomes approximately zero. In addition, at this timing, the voltage Vzcd (= Vz1) is lower than the reference voltage Vref2, so the comparator 40 outputs a signal Vc2 of the "H" level.

[0213] At time t70, the Q output of the SR flip-flop 70 is at the "H" level, so Fig. 22 The NMOS transistor 800 of the mask circuit 660 is turned on. Therefore, both the signal Vm and the signal Vmask of the mask circuit 660 become "L" level.

[0214] At time t71, based on the signal Vc3 from the comparator 45, when the Q output of the SR flip-flop 70 changes to the "L" level, the NMOS transistor 108 turns off. As a result, the voltage Vds1 and the voltage Vzcd change to the "H" level. In addition, when the NMOS transistor 108 is turned off, the diode 107 is turned on, and the current flowing through the NMOS transistor 108 decreases sharply. As a result, the voltage Vds and the voltage Vzcd generate ringing noise.

[0215] Then, if the voltage Vzcd generates ringing noise and the voltage Vzcd becomes lower than the reference voltage Vref2, the signal Vc2 changes to the "H" level. However, from the time t71 when the NMOS transistor 108 is turned off to the time t72 after the masking period Tm1, the signal Vm is at the "L" level. Therefore, during the period from time t71 to t72, the signal Vc2 is masked, and the masking circuit 660 continues to output the signal Vmask at the "L" level. In addition, when the time t71 changes to the time t72 after the masking period Tm1, the signal Vm becomes the "H" level.

[0216] Then, when the inductor current IL1 becomes approximately zero at time t73, the voltage Vz1 of the auxiliary coil L2 magnetically coupled to the main coil L1 drops sharply. As a result, at time t73, the voltage Vzcd becomes lower than the reference voltage Vref2, and the signal Vc2 from the comparator 40 becomes "H" level. At this timing, the signal Vm becomes "H" level, so the signal Vmask also becomes "H" level. As a result, at time t74, the pulse circuit 41 outputs the pulse signal Vp of "H" level, and the NMOS transistor 108 is turned on. In addition, the operation of time t70 to t74 is repeated.

[0217] Thus, the masking circuit 660 of this embodiment can mask the signal Vc2 from time t71 when the NMOS transistor 108 is turned off to time t72 after the masking period Tm1. Therefore, the switch control IC 17 can turn on the NMOS transistor 108 at a desired timing regardless of ringing noise.

[0218] ==When the switch control IC 17 is used in an isolated power supply circuit ==

[0219] Fig.24 is used to illustrate the use of switch control IC17 Fig.13 The operation diagram of the insulating power supply circuit 22 is shown in FIG. Fig.10 , the basic circuit operation of the switch control IC 17 used for the isolated power supply circuit is described in , but here, the operation of the circuit related to the masking circuit 660 is mainly described.

[0220] At time t80, if the pulse circuit 41 outputs the pulse signal Vp of the "H" level, the Q output of the SR flip-flop 70 becomes the "H" level, and therefore, Fig.13 The NMOS transistor 303 is turned on. As a result, the voltage Vds2 between the drain and the source of the NMOS transistor 303 becomes approximately zero. In addition, at this timing, the voltage Vzcd (= Vz2) is lower than the reference voltage Vref2, so the comparator 40 outputs the signal Vc2 of the "H" level.

[0221] At time t80, the Q output of the SR flip-flop 70 is at the "H" level, so Fig. 22 The NMOS transistor 800 of the mask circuit 660 is turned on. Therefore, both the signal Vm and the signal Vmask of the mask circuit 660 become "L" level.

[0222] At time t81, if the Q output of the SR flip-flop 70 changes to the "L" level, the NMOS transistor 303 is turned off. As a result, the voltage Vds2 and the voltage Vzcd change to the "H" level. "In addition, if the NMOS transistor 303 is turned off, the energy of the primary coil L10 is transmitted to the secondary coil L11 on the secondary side and flows back through the diode 550, the capacitor 551 and the resistor 552. As a result, in the isolated power supply circuit 22, if the NMOS transistor 303 is turned off, the current flowing through the NMOS transistor 303 decreases sharply. In addition, in this embodiment, Fig.13 The current change when the NMOS transistor 303 is turned off becomes greater than Figure 3 The change in current when the NMOS transistor 108 is turned off is large. As a result, the voltage Vds2 and the voltage Vzcd generate very large ringing noise.

[0223] Then, if the voltage Vzcd generates ringing noise and the voltage Vzcd becomes lower than the reference voltage Vref2, the signal Vc2 changes to the "H" level. However, from the time t81 when the NMOS transistor 303 is turned off to the time t82 after the masking period Tm2, ​​the signal Vm is at the "L" level. Therefore, during the period from time t81 to t82, the signal Vc2 is masked, and the masking circuit 660 continues to output the signal Vmask at the "L" level. In addition, if the time t81 changes to the time t82 after the masking period Tm2, ​​the signal Vm becomes the "H" level.

[0224] Then, when the current flowing through the auxiliary coil L12 becomes zero at time t83, the voltage Vz2 of the auxiliary coil L12 drops sharply. As a result, at time t83, the voltage Vzcd becomes lower than the reference voltage Vref2, and the signal Vc2 from the comparator 40 becomes "H" level. At this timing, the signal Vm is "H" level, so the signal Vmask also becomes "H" level. As a result, at time t84, the pulse circuit 41 outputs the pulse signal Vp of "H" level, and the NMOS transistor 303 is turned on. Thereafter, the operation at time t80 to t84 is repeated.

[0225] Thus, the masking circuit 660 of this embodiment can mask the signal Vc2 from time t81 when the NMOS transistor 303 is turned off to time t82 after the masking period Tm2. Therefore, the switch control IC 17 can turn on the NMOS transistor 303 at a desired timing regardless of ringing noise.

[0226] In addition, in the switch control IC 17, the comparator 40 that outputs the signal Vc2 (first timing signal) corresponds to the "first timing signal output circuit". In addition, the comparator 45 that outputs the signal Vc3 (second timing signal) corresponds to the "second timing signal output circuit". In addition, in the present embodiment, for example, the signal Vmask of the masking circuit 660 may be directly input to the drive circuit 46 without using the pulse circuit 41.

[0227] ===Summary===

[0228] The switch control IC 10 of the present embodiment has been described above. When the signal S1 is at the "L" level, the drive circuit 46 of the switch control IC 10 switches the transistor based on the error voltage Ve1 of the error amplifier circuit 43, and when the signal S1 is at the "H" level, the drive circuit 46 controls the switching of the transistor based on the error voltage Ve2 of the error voltage output circuit 44. Therefore, the switch control IC 10 can be used for either the non-insulated power supply circuit 20 or the isolated power supply circuit 21.

[0229] In addition, when the signal S1 is at the "H" level, the error amplifier circuit 43 stops outputting the error voltage Ve1. Therefore, the drive circuit 46 can switch the transistor without being affected by the error voltage Ve1. In addition, in the present embodiment, the error amplifier circuit 43 stops outputting the error voltage Ve1 by setting the output to a high impedance state. Therefore, for example, there is no need to provide a switch or the like (not shown) between the error amplifier circuit 43 and the inverting input terminal of the comparator 45.

[0230] Furthermore, when the signal S1 is at the "L" level, the error voltage output circuit 44 stops outputting the error voltage Ve2. Therefore, the drive circuit 46 can switch the transistor without being affected by the error voltage Ve2.

[0231] In addition, the error voltage output circuit 44 includes a resistor 60 that converts the bias current Ib from the phototransistor 530 and generates the error voltage Ve2. The resistance value of the resistor 60 can be freely selected, so it is easy to adjust the conversion gain (gain) when generating the error amplification voltage Ve2 according to the bias current Ib. Therefore, the feedback loop of the power supply circuit 21 can be stabilized.

[0232] In addition, the switch control IC 10 may have a memory such as an EPROM that stores a signal of "H" level or "L" level instead of the signal S1, and selects the error voltages Ve1 and Ve2 based on the information stored in the memory. In such a case, the user needs to write the information in the memory at the timing before the switch control IC 10 is used in the power supply circuit. The switch control IC 10 of the present embodiment is provided with a determination circuit 33, which determines whether the power supply circuit using the switch control IC 10 is a non-insulated type or an insulated type based on the voltage Va of the terminal A. Therefore, the switch control IC 10 can determine whether the power supply circuit is a non-insulated type or an insulated type without the user performing an operation, thereby reducing the trouble of the user.

[0233] In addition, if Figure 8 As shown, the determination circuit 33 determines whether the power supply circuit is non-insulated or insulated at a timing (e.g., time t24) after the voltage Va reaches the breakdown voltage Vz0 of a predetermined level. Therefore, in this embodiment, it is possible to determine whether the power supply circuit is non-insulated or insulated with high accuracy.

[0234] In addition, the determination circuit 33 determines whether the power supply circuit is a non-insulated type or an insulated type at the timing when the signal ENB becomes "L" level (for example, time t24). In the switch control IC 10, the switching of the transistor starts after the signal ENB becomes "L". Therefore, in this embodiment, before starting the switching of the transistor, a circuit suitable for a non-insulated type or an insulated type power supply circuit can be selected.

[0235] In the case of the non-insulated power supply circuit 20 , a phase compensation element for generating the error voltage Ve1 is connected to the terminal B. In the case of the isolated power supply circuit 21 , the phototransistor 530 is connected to the terminal B.

[0236] Furthermore, when the soft start period Ts has elapsed since startup, the switch control ICs 12 to 16 keep the switching transistors on for a longer period than before the soft start period Ts has elapsed. This can prevent a large current from flowing through the switching transistors when the power supply circuits 20 to 22 are started.

[0237] In addition, during the soft start period Ts, the switch control ICs 12 to 16 are as follows. Fig.14 As shown in FIG. 1 , the period T1 during which the switching transistors are turned on is gradually extended. Therefore, the switching control ICs 12 to 16 can start the power supply circuits 20 to 22 more safely.

[0238] The comparator 603 of the switch control IC 12 determines the timing to turn off the NMOS transistor 303 based on the lower voltage of the voltage Vo and the error voltage Ve2. By using such a three-input comparator 603, the voltage Vo can be smoothly switched to the error voltage Ve2.

[0239] Furthermore, for example, as in the switching control IC 13 , when the soft start period Ts elapses, the voltage to be compared by the comparator 45 may be switched from the voltage Vo to the error voltage Ve2 .

[0240] Furthermore, when the voltage Vo is not used, the oscillation circuit 631 of the switching control IC 15 may be caused to change the slope of the harmonic Vr during the soft start period Ts. Even when such a configuration is used, the power supply circuit can be safely started.

[0241] Furthermore, in the switch control IC 16 , when the switch control IC 16 is activated, the discharge circuit 650 discharges the capacitors 132 and 133 at the terminal B. By using such a configuration, the soft start of the isolated power supply circuit can be performed.

[0242] Furthermore, after the switching transistor is turned off, the masking circuit 660 of the switch control IC 17 masks the signal Vc2 for masking periods Tm1 and Tm2 corresponding to the type of the power supply circuit. Therefore, the switch control IC 17 can turn on the switching transistor 108 at a desired timing.

[0243] In addition, the noise when the switch control IC 17 is used in an isolated power supply circuit may be greater than the noise when it is used in a non-isolated power supply circuit. Therefore, in this embodiment, the masking period Tm2 when the switch control IC 17 is used in an isolated power supply circuit is longer than the masking period Tm2 when the switch control IC 17 is used in a non-isolated power supply circuit. As a result, the switch control IC 17 can turn on the switching transistor at a more accurate timing.

[0244] The above-mentioned embodiments are used to facilitate understanding of the present invention, and are not used to limit and explain the present invention. In addition, the present invention can be changed or improved without departing from its main purpose, and its equivalent content is of course also included in the present invention.

[0245] For example, since the voltage Va is generated in the power supply circuit 21, the voltage Va exceeding the variation range of the feedback voltage is set using the resistor 520 and the Zener diode 521, but the present invention is not limited thereto. For example, a resistor may be used instead of the Zener diode 521, and the voltage Vx2 may be divided by two resistors, and the divided voltage may be set as the voltage Va.

[0246] In addition, as described above, when the power supply circuit 20 is started, the feedback voltage Vfb becomes a value obtained by dividing the effective value of the AC voltage Vac by the resistors 120 and 121. Therefore, in the power supply circuit 21, it is also possible to use an element (for example, the forward voltage of the diode, i.e., 0.7V) that outputs a voltage value smaller than the value obtained by dividing the effective value of the AC voltage Vac by the resistors 120 and 121 to generate the voltage Va. In this case, the reference voltage Vref1 is set between the value obtained by dividing the effective value of the AC voltage Vac by the resistors 120 and 121 and the forward voltage of the diode, i.e., 0.7V, so that the determination circuit 33 can determine whether the power supply circuit is a non-insulated type or an insulated type.

[0247] For example, in the error voltage output circuit 44 , a MOS transistor operating in a linear region may be used instead of the resistor 60 .

[0248] The switch control IC 10 is a circuit that operates in a mode (so-called critical mode) in which the transistor is turned on when the inductor current IL becomes zero, but may be a circuit that operates in a mode (so-called continuous mode) in which the inductor current IL changes continuously.

[0249] The power supply circuit 21 is a flyback power supply circuit, but is not limited thereto, and may be, for example, a forward power supply circuit, a push-pull power supply circuit, a half-bridge power supply circuit, a full-bridge power supply circuit, or a chopper power supply circuit.

[0250] In addition, in this embodiment, for the sake of convenience, the circuit for soft starting of the isolated power supply circuit (for example, the voltage output circuit 602, the comparator 603), the circuit for soft starting of the isolated power supply circuit (for example, the discharge circuit 650), and the masking circuit are described in different embodiments, but the switch control IC preferably includes all of them. By using such a switch control IC, the power supply circuit can be soft started and the switching transistor can be switched at a desired timing.

[0251] Description of symbols

[0252] 10 Switch Control IC

[0253] 20, 21 Power supply circuit

[0254] 31, 32 Voltage detection circuit

[0255] 33 Decision circuit

[0256] 40, 45, 603 Comparator

[0257] 41 Pulse Circuit

[0258] 42 Oscillator Circuit

[0259] 43 Error amplifier circuit

[0260] 44 Error voltage output circuit

[0261] 46 Driving Circuit

[0262] 100, 300 full-wave rectifier circuit

[0263] 101, 102, 106, 132, 133, 301, 306, 500, 531, 551, 707, 802, 803 capacitors

[0264] 103, 302 Transformer

[0265] 105, 107, 305, 501, 510, 550 diodes

[0266] 108, 303 NMOS transistor

[0267] 104, 120, 122, 131, 502, 511, 520, 552, 708 resistors

[0268] 304 Control Block

[0269] 307 Constant Voltage Circuit

[0270] 308 LED

[0271] 521 Zener diode

[0272] 530 Phototransistor

[0273] 600 On timer

[0274] 601 OR Gate Circuit

[0275] 602 Voltage Output Circuit

[0276] 610, 630 Timer

[0277] 611, 810 Inverter

[0278] 612, 811, 812 AND gate circuit

[0279] 613 Charging Circuit

[0280] 620 Control Circuit

[0281] 631 Oscillator Circuit

[0282] 650 Discharge Circuit

[0283] 660 Masking Circuit

[0284] 700 Clock Generation Circuit

[0285] 701 Charge Pump

[0286] 702 Counter

[0287] 703 DAC

[0288] 704 Discharge Circuit

[0289] 705, 804 Current Source

[0290] 706, 709, 801 switches

[0291] 750 Period Setting Circuit

[0292] 751 Logic circuits.

Claims

1. A switch control circuit, Based on an inductor current flowing through an inductor to which an input voltage is applied and an output voltage generated according to the input voltage, a transistor for controlling the inductor current is switched, wherein the switch control circuit is characterized in that it includes: a first error voltage output circuit that outputs a first error voltage corresponding to an error between a level of the output voltage and a first level based on a feedback voltage corresponding to the output voltage and a reference voltage when a first signal indicating that the switch control circuit is used for a non-insulated first power supply circuit is input; a second error voltage output circuit that outputs a second error voltage based on an error signal corresponding to an error between the level of the output voltage and a second level when a second signal indicating that the switch control circuit is used for an isolated second power supply circuit is input; as well as A driving circuit that switches the transistor based on the inductor current and the first error voltage when the switch control circuit is used in the first power supply circuit, and switches the transistor based on the inductor current and the second error voltage when the switch control circuit is used in the second power supply circuit.

2. The switch control circuit according to claim 1, characterized in that: The first error voltage output circuit stops outputting the first error voltage when the second signal is input.

3. The switch control circuit according to claim 1, characterized in that: The second error voltage output circuit stops outputting the second error voltage when the first signal is input.

4. The switch control circuit according to claim 2, characterized in that: The second error voltage output circuit stops outputting the second error voltage when the first signal is input.

5. The switch control circuit according to claim 3, characterized in that: The error signal is a current corresponding to an error between the level of the output voltage and the second level, The second error voltage output circuit comprises: a switch, the switch being turned on based on the second signal and being turned off based on the first signal; as well as A resistor connected in series with the switch, wherein when the switch is turned on, a current corresponding to an error between a level of the output voltage and the second level flows through the resistor, thereby generating the second error voltage.

6. The switch control circuit according to any one of claims 1 to 5, characterized in that: The switch control circuit is an integrated circuit and comprises: a first terminal to which the feedback voltage is applied when the switch control circuit is used in the first power supply circuit, and to which a voltage of a predetermined level outside a voltage range in which the feedback voltage changes is applied when the switch control circuit is used in the second power supply circuit; as well as A determination circuit determines whether the switch control circuit is used for the first power supply circuit or the second power supply circuit based on the voltage of the first terminal, and outputs the first signal or the second signal according to the determination result.

7. The switch control circuit according to claim 6, characterized in that: After the voltage of the first terminal reaches the predetermined level when the switch control circuit is used for the second power supply circuit, the determination circuit determines whether the switch control circuit is used for the first power supply circuit or the second power supply circuit based on the voltage of the first terminal.

8. The switch control circuit according to claim 7, characterized in that: After the voltage of the first terminal reaches the specified level when the switch control circuit is used for the second power supply circuit, until the switching of the transistor starts, the determination circuit determines whether the switch control circuit is used for the first power supply circuit or the second power supply circuit based on the voltage of the first terminal.

9. The switch control circuit according to any one of claims 1 to 5, characterized in that: The switch control circuit is an integrated circuit, The device has a second terminal, to which the element for generating the first error voltage is connected when the switch control circuit is used in the first power supply circuit, and to which the phototransistor for generating the error signal is connected when the switch control circuit is used in the second power supply circuit.

10. The switch control circuit according to any one of claims 1 to 5, characterized in that: From the start of the switching control circuit until a prescribed period has passed, the driving circuit switches the transistor so that the period during which the transistor is turned on becomes a first period, and after the prescribed period has passed, the driving circuit switches the transistor so that the period during which the transistor is turned on becomes a second period longer than the first period.

11. The switch control circuit according to claim 10, characterized in that: From the time when the switch control circuit is activated until the predetermined period elapses, the drive circuit switches the transistor so that the first period gradually increases.

12. The switch control circuit according to claim 11, characterized in that: Include: a first timing signal output circuit that outputs a first timing signal indicating a timing for turning on the transistor based on a voltage corresponding to the inductor current; a voltage output circuit that outputs a first voltage higher than the second error voltage level if the predetermined period has elapsed after the switch control circuit is activated; as well as a second timing signal output circuit that outputs a second timing signal indicating a timing for turning off the transistor based on the voltage of the first voltage and the second error voltage, whichever has a lower level; The drive circuit switches the transistor based on the first timing signal and the second timing signal.

13. The switch control circuit according to claim 11, characterized in that: Include: a first timing signal output circuit that outputs a first timing signal indicating a timing for turning on the transistor based on a voltage corresponding to the inductor current; a voltage output circuit, wherein if the switch control circuit is activated, the voltage output circuit outputs a first voltage whose level becomes higher; as well as a second timing signal output circuit, which outputs a second timing signal indicating a timing for turning off the transistor based on the first voltage when the switch control circuit is activated, and outputs the second timing signal based on the second error voltage when the prescribed period elapses after the switch control circuit is activated, The drive circuit switches the transistor based on the first timing signal and the second timing signal.

14. The switch control circuit according to claim 11, characterized in that: Include: a first timing signal output circuit that outputs a first timing signal indicating a timing for turning on the transistor based on a voltage corresponding to the inductor current; An oscillating circuit that outputs a triangular-wave oscillating voltage; as well as a second timing signal output circuit that outputs a second timing signal indicating a timing for turning off the transistor based on the oscillation voltage and the second error voltage, The oscillation circuit changes the oscillation voltage so that when the predetermined period elapses after the switch control circuit is activated, the period during which the transistor is turned on becomes longer. The drive circuit switches the transistor based on the first timing signal and the second timing signal.

15. The switch control circuit according to claim 10, characterized in that: comprising a discharge circuit, which discharges the capacitor to which the first error voltage is applied for a predetermined period of time when the switch control circuit is activated, The drive circuit turns on the transistor based on a voltage corresponding to the inductor current, and turns off the transistor when a level of the charging voltage of the capacitor increases so that a period during which the transistor is turned on becomes longer.

16. The switch control circuit according to any one of claims 1 to 5, characterized in that: Include: a first timing signal output circuit that outputs a first timing signal indicating a timing for turning on the transistor based on a voltage corresponding to the inductor current; as well as a masking circuit that masks the first timing signal for a first masking period after the transistor is turned off and outputs the masking circuit based on the first signal, and masks the first timing signal for a second masking period different from the first masking period after the transistor is turned off and outputs the masking circuit based on the second signal, The driving circuit switches the transistor based on the output of the masking circuit and the first error voltage when the switching control circuit is used for the first power supply circuit, and switches the transistor based on the output of the masking circuit and the second error voltage when the switching control circuit is used for the second power supply circuit.

17. The switch control circuit according to claim 16, characterized in that comprising a second timing signal output circuit that outputs a second timing signal indicating a timing for turning off the transistor based on either the first error voltage or the second error voltage and a triangular wave oscillation voltage, The drive circuit switches the transistor based on an output of the masking circuit and the second timing signal.

18. The switch control circuit according to claim 16, characterized in that: The second masking period is a period longer than the first masking period.

19. The switch control circuit according to claim 17, characterized in that: The second masking period is a period longer than the first masking period.

20. A switch control circuit, Based on an inductor current flowing through an inductor to which an input voltage is applied and an output voltage generated according to the input voltage, a transistor for controlling the inductor current is switched, wherein the switch control circuit is characterized in that: The switch control circuit is an integrated circuit and comprises: a first terminal to which a feedback voltage corresponding to the output voltage is applied when the switch control circuit is used in a non-insulated first power supply circuit, and to which a voltage of a prescribed level outside a voltage range in which the feedback voltage changes is applied when the switch control circuit is used in an isolated second power supply circuit; and A determination circuit determines whether the switch control circuit is used for the first power supply circuit or the second power supply circuit based on the voltage of the first terminal.

21. A switch control method, The switching control method switches a transistor for controlling the inductor current based on an inductor current flowing through an inductor to which an input voltage is applied and an output voltage generated according to the input voltage. The switching control method is characterized in that: When a first signal indicating that the power supply circuit is a non-insulated first power supply circuit is input, a first error voltage corresponding to an error between a level of the output voltage and a first level is output based on a feedback voltage corresponding to the output voltage and a reference voltage, When a second signal indicating that the power supply circuit is an isolated second power supply circuit is input, a second error voltage is output based on an error signal corresponding to an error between the level of the output voltage and a second level, When the power supply circuit is the first power supply circuit, the transistor is switched based on the inductor current and the first error voltage, and when the power supply circuit is the second power supply circuit, the transistor is switched based on the inductor current and the second error voltage.

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