integrated circuit

Abstract

The present invention provides an integrated circuit capable of properly determining the type of a power supply circuit. The integrated circuit is an integrated circuit that switches a power transistor that controls an inductor current based on the inductor current flowing through an inductor and an output voltage, comprising: a first terminal that connects a first circuit when the integrated circuit is used for a first power supply circuit of a non-isolated type and connects a second circuit when the integrated circuit is used for a second power supply circuit of an isolated type; a voltage generation circuit that generates a voltage lower than a first level and corresponding to the output voltage in a first state, generates a voltage higher than a second level in a second state, and generates a voltage higher than the first level and lower than the second level in a third state; a determination circuit that determines that the integrated circuit is used for the first power supply circuit when the voltage of the first terminal is lower than the second level, and determines that the integrated circuit is used for the second power supply circuit when the voltage of the first terminal is higher than the second level; and a drive circuit that drives the power transistor based on the determination result.

Description

Technical Field

[0001] This invention relates to integrated circuits. Background Technology

[0002] Integrated circuits that control power supply circuits typically switch power transistors to enable the power supply circuit to generate a target level output voltage based on the input voltage (see, for example, Patent Documents 1-5).

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2014-82924

[0006] Patent Document 2: Japanese Patent Application Publication No. 2012-105424

[0007] Patent Document 3: International Publication No. 2018 / 207880

[0008] Patent Document 4: Japanese Patent Application Publication No. 2019-122240

[0009] Patent Document 5: International Publication No. 2020 / 213399 Summary of the Invention

[0010] The technical problem that the invention aims to solve

[0011] Furthermore, in integrated circuits, there is a determination circuit that corresponds to both non-insulated and insulated power supply circuits and determines which type of power supply circuit to use based on the state of the terminals. However, due to faults in the manufacturing process of the power supply circuit, such as poor connection to the terminals, the determination circuit may sometimes fail to operate properly.

[0012] The present invention was made in view of the above-mentioned problems, and its object is to provide an integrated circuit that can properly determine the type of power supply circuit.

[0013] Technical means for solving technical problems

[0014] The main integrated circuit of the present invention, which solves the above problems, is an integrated circuit that switches a power transistor 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. It includes: a first terminal, which is connected to a first circuit when the integrated circuit is used in a non-isolated first power supply circuit, and connected to a second circuit when the integrated circuit is used in an isolated second power supply circuit; and a voltage generation circuit, which, in a first state where the first terminal is connected to the first circuit, generates a voltage at the first terminal that is lower than a first level and corresponds to the output voltage, and generates a voltage at the first terminal that is connected to the first circuit. In a second state where the second circuit is connected, a voltage higher than the second level is generated at the first terminal; in a third state where the circuit to be connected to the first terminal is disconnected from the first terminal, a voltage higher than the first level and lower than the second level is generated at the first terminal; a determination circuit, which determines that the integrated circuit is used in the first power supply circuit when the voltage at the first terminal is lower than the second level, and determines that the integrated circuit is used in the second power supply circuit when the voltage at the first terminal is higher than the second level; and a driving circuit, which drives the power transistor based on the determination result of the determination circuit.

[0015] Invention Effects

[0016] According to the present invention, an integrated circuit capable of appropriately determining the type of power supply circuit can be provided. Attached Figure Description

[0017] Figure 1 This is a diagram showing an example of a switch control IC10.

[0018] Figure 2 This is a diagram showing an example of a voltage generation circuit 33a.

[0019] Figure 3 (a) is a diagram of the first state in which terminal A is connected to voltage divider circuit 800a. Figure 3 (b) is a diagram of the second state in which terminal A is connected to circuit 800b. Figure 3 (c) is a diagram showing an example of the voltage generated by the voltage generation circuit 33.

[0020] Figure 4 This is a diagram showing an example of the decision circuit 34.

[0021] Figure 5 This is a diagram showing an example of a non-insulated power supply circuit 20.

[0022] Figure 6This is a diagram used to illustrate the operation of the power supply circuit 20 during startup.

[0023] Figure 7 This is a diagram showing a partial structure of the switch control IC10.

[0024] Figure 8 This is a diagram used to illustrate the operation of the power supply circuit 20.

[0025] Figure 9 This is a diagram showing an example of an isolated power supply circuit 21.

[0026] Figure 10 This is a diagram used to illustrate the operation of the power supply circuit 21 during startup.

[0027] Figure 11 This is a diagram showing a partial structure of the switch control IC10.

[0028] Figure 12 This is a diagram used to illustrate the operation of the power supply circuit 21.

[0029] Figure 13 This is a diagram illustrating the operation of the power supply circuit 20 when a faulty connection occurs at terminal A.

[0030] Figure 14 This is a diagram showing an example of voltage generation circuit 33b. Detailed Implementation

[0031] Based on the description in this specification and the accompanying drawings, at least the following matters are clearly defined.

[0032] ======This implementation method======

[0033] <<<Structure of Switch Control IC10>>>

[0034] Figure 1 This diagram illustrates the structure of a switch control IC 10, an embodiment of the present invention. The switch control IC 10 is an integrated circuit that determines whether it is used in a non-isolated power supply circuit or an isolated power supply circuit, and controls the operation of the power supply circuit based on the determination result. Specifically, when used in a non-isolated switching power supply circuit, the switch control IC 10 operates based on a feedback voltage corresponding to the output voltage. On the other hand, when used in an isolated switching power supply circuit, the switch control IC 10 operates based on a current representing the error from the target level of the output voltage.

[0035] The switch control IC10 has terminals VCC, ZCD, A, B and OUT. Additionally, the switch control IC10 may include a GND terminal or other terminals for applying ground voltage, but these are omitted here for convenience.

[0036] Terminal VCC is the terminal to which the power supply voltage Vcc is applied to enable the switch control IC10 to operate.

[0037] Terminal ZCD is used to detect the inductor current in the power supply circuit using switch control IC10.

[0038] Terminal A is a terminal to which a voltage is applied to determine whether the power supply circuit using the switch control IC 10 is non-isolated or isolated. Additionally, when the switch control IC 10 is used for a non-isolated power supply circuit, a feedback voltage corresponding to the output voltage of the power supply circuit is applied to terminal A. Furthermore, when the switch control IC 10 is used for an isolated power supply circuit, a voltage divider resistor is connected to terminal A to divide the power supply voltage Vcc. Moreover, if the voltage at terminal A is set to voltage Va, terminal A is equivalent to the "first terminal".

[0039] Terminal B is used to connect a phase compensation component when the switch control IC10 is used in a non-isolated power supply circuit, and to connect a phototransistor when the switch control IC10 is used in an isolated power supply circuit. Furthermore, with the voltage of terminal B set to voltage Vb, terminal B is equivalent to a "second terminal".

[0040] Terminal OUT is the terminal to which the drive signal Vdr, which controls the switching of the switching element, is applied.

[0041] The switch control IC10 includes a power supply circuit 30, voltage detection circuits 31 and 32, voltage generation circuit 33a, judgment circuit 34, comparator 40 and 45, pulse circuit 41, oscillation circuit 42, error amplifier circuit 43, error voltage output circuit 44, comparator 46, OR gate element 47, and drive circuit 48.

[0042] The power supply circuit 30 generates a power supply voltage Vdd (e.g., a series regulator) based on a power supply voltage Vcc applied externally to the switch control IC 10, which is used to operate the internal circuitry of the switch control IC 10. Additionally, within the circuitry included in the switch control IC 10, the circuitry providing the power supply voltage Vdd is other than the power supply circuit 30 and the buffer circuit 71 of the drive circuit 48 (described later). In this embodiment, the buffer circuit 71 of the drive circuit 48 operates based on the power supply voltage Vcc.

[0043] The voltage detection circuit 31 is a circuit that detects whether the level of the power supply voltage Vdd is at a predetermined level X. Furthermore, "predetermined level X" represents the level at which the power supply voltage Vdd rises; when the target level of the power supply voltage Vdd is 5V, "predetermined level X" is, for example, 4.5V. Additionally, if the level of the power supply voltage Vdd rises to the predetermined 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). Furthermore, in this embodiment, the level of the power supply voltage Vcc when the level of the power supply voltage Vdd reaches the predetermined level X is defined as "predetermined level Vt1".

[0044] The voltage detection circuit 32 detects whether the power supply voltage Vcc reaches the "prescribed level Vt2" that triggers the internal circuitry of the switch control IC 10. When the power supply voltage Vcc rises to the prescribed level Vt2, the voltage detection circuit 32 changes the level of the signal ENB from "H" to "L". Furthermore, in this embodiment, the level Vt1 is lower than the prescribed level Vt2. Therefore, when the power supply voltage Vcc rises from zero, first, the voltage detection circuit 31 changes the signal UVLO to "L", and then the voltage detection circuit 32 changes the signal ENB to "L". Although... Figure 1 The values ​​are omitted, but in this embodiment, signals UVLO and ENB are input to the respective circuits of the switch control IC10.

[0045] Voltage generation circuit 33a is a circuit that generates a voltage Va corresponding to the external circuit connected to terminal A. For example... Figure 2 As shown, the voltage generation circuit 33a comprises a constant current source 90a and a voltage adjustment circuit 91a. The constant current source 90a provides a constant current IOa to terminal A.

[0046] The voltage adjustment circuit 91a adjusts the voltage Va of terminal A based on the state of terminal A and the constant current I0a supplied to terminal A. The voltage adjustment circuit 91a is constructed by including a PMOS transistor 92.

[0047] A reference voltage Vref5 is applied to the gate electrode of the PMOS transistor 92, a voltage Va is applied to the source electrode, and a ground voltage is applied to the drain electrode.

[0048] Here, with the external circuit connected to terminal A, when the voltage Va is low and the difference between voltage Va and the reference voltage Vref5 is less than the threshold voltage Vth of PMOS transistor 92, PMOS transistor 92 is turned off. In this case, a constant current IOa flows through terminal A to the connected external circuit. Although this will be explained in detail later, regarding the constant current I0a, it is set to a very small value (e.g., 2μA), so that even if the constant current I0a flows externally, the voltage Va at terminal A hardly changes. Therefore, in such a case, the voltage adjustment circuit 91a sets the voltage Va at terminal A to a value determined based on the circuit connected to terminal A.

[0049] Furthermore, when the external circuit is connected to terminal A, the PMOS transistor 92 turns on when the voltage Va is high and the difference between the voltage Va and the reference voltage Vref5 is greater than the threshold voltage Vth. Here, the PMOS transistor 92 is sized to allow a current slightly larger than the constant current I0a (e.g., 10 μA) to flow when it is turned on. In this state, if a large current (e.g., tens of μA) flows from the circuit connected to terminal A to terminal A, the voltage Va rises according to the current flowing into terminal A. Therefore, in this case, the voltage adjustment circuit 91a, together with the constant current source 90a, increases the voltage Va at terminal A.

[0050] Furthermore, when terminal A is not connected to the external circuit (i.e., terminal A is disconnected from the external circuit), the constant current I0a does not flow to the outside via terminal A, but instead flows to the PMOS transistor 92. In this case, the voltage Va becomes the drain / source voltage Vds of the PMOS transistor 92 generated by the constant current I0a flowing to the PMOS transistor 92. That is, the voltage adjustment circuit 91a sets the voltage Va at terminal A to the voltage corresponding to the constant current I0a. Additionally, the PMOS transistor 92 is equivalent to a "transistor".

[0051] The following shows the specific external circuit and explains what kind of voltage Va is generated by the voltage generation circuit 33a when each external circuit is connected to terminal A.

[0052] <Circuit connection case for non-isolated power supply circuits>

[0053] First, such as Figure 3(a) illustrates the first state where the voltage divider circuit 800a is connected to terminal A as an external circuit. Here, the voltage divider circuit 800a, composed of resistors 120 and 121, generates a divided voltage obtained by dividing the output voltage Vout1 of the non-isolated power supply circuit. Here, the output voltage Vout1 is controlled to a predetermined level (e.g., 400V). Therefore, by adjusting the voltage division ratio of resistors 120 and 121, the divided voltage can be set to the level that turns off the PMOS transistor 92.

[0054] In this embodiment, when used in a non-insulated power supply circuit Figure 3 When circuit (a) is connected to terminal A, the voltage level of the voltage divider is less than... Figure 3 (c) shows the first level V1, which reliably turns off the PMOS transistor 92. Additionally, the first level V1 is the level of the voltage divider voltage in the voltage divider circuit 800a when the output voltage Vout1 becomes an overvoltage. Although this will be explained in detail later, in a non-isolated power supply circuit, the output voltage Vout1 is controlled so that it does not exceed the overvoltage.

[0055] When such a voltage divider circuit 800a is connected to terminal A, the PMOS transistor 92 is turned off, and therefore, a constant current I0a flows to resistor 121. In this embodiment, for example, a sufficiently small current value is used as the constant current IOa. Therefore, when Figure 3 When the voltage divider circuit 800a in (a) is connected to terminal A, the voltage Va at terminal A becomes approximately the divided voltage (i.e., the feedback voltage obtained after dividing the output voltage Vout1). In addition, the voltage divider circuit 800a is equivalent to the "first circuit".

[0056] <Circuit connection for isolated power supply circuits>

[0057] Next, as Figure 3 (b) illustrates the second state where the voltage divider circuit 800b is connected to terminal A as an external circuit. Here, circuit 800b consists of resistor 520 and Zener diode 521, and generates a breakdown voltage Vz0 of Zener diode 521 at terminal A. In this embodiment, the breakdown voltage Vz0 is the level at which PMOS transistor 92 reliably conducts when circuit 800b is connected to terminal A. In this embodiment, the resistance value of resistor 520 is selected such that the current Ia flowing from circuit 800b through terminal A into voltage generation circuit 33a is sufficiently large relative to the sink current of PMOS transistor 92.

[0058] Therefore, when circuit 800b is connected to terminal A, current Ia flows into voltage generation circuit 33a. As a result, the voltage at the node connecting the constant current source 90a to the source electrode of PMOS transistor 92 (i.e., the voltage Va at terminal A) rises almost to the level of the power supply voltage Vdd. Therefore, as Figure 3 As shown in (c), when circuit 800b is connected to terminal A, the level of terminal A is higher than the second level V2, which is used by the determination circuit 34 described later to determine that the switch control IC10 is used in an isolated power supply circuit.

[0059] Furthermore, circuit 800b corresponds to the "second circuit," and resistor 520 and Zener diode 521 correspond to "components." Additionally, the breakdown voltage Vz0 corresponds to the "specified voltage." Furthermore, in this embodiment, circuit 800b is assumed to include resistor 520 and Zener diode 521; however, for example, it could also be a voltage divider resistor circuit that generates a voltage divider capable of turning on PMOS transistor 92.

[0060] <Case where the circuit used for power supply is not connected>

[0061] Furthermore, a third state will be described where the circuit to be connected to terminal A is disconnected from terminal A. In this case, the external circuit is not connected to terminal A, and a constant current I0a flows to the PMOS transistor 92. Therefore, the voltage adjustment circuit 91a sets the voltage Va to correspond to the constant current I0a. In this embodiment, the size ratio of the PMOS transistor is set such that when the constant current I0a flows to the PMOS transistor 92, the voltage at the source electrode of the PMOS transistor (i.e., the voltage Va at terminal A) is higher than the first level V1 and lower than the second level V2. Therefore, although this will be explained in detail later, when the external circuit is not connected to terminal A, it is possible to prevent the determination circuit 34 from mistakenly determining that the isolated circuit 800b is connected to terminal A (i.e., the switch control IC 10 is used for an isolated power supply circuit).

[0062] The determination circuit 34 determines whether the switch control IC 10 is used for a non-isolated power supply circuit or an isolated power supply circuit based on the voltage Va at terminal A. Specifically, when the voltage Va is lower than the voltage of the second level V2, the determination circuit 34 determines that the switch control IC 10 is used for a non-isolated power supply circuit; when the voltage Va is higher than the voltage of the second level V2, the determination circuit 34 determines that the switch control IC 10 is used for an isolated power supply circuit. Figure 4 This is a diagram illustrating an example of the structure of the decision circuit 34, which includes a comparator 50 and a D flip-flop 51.

[0063] Comparator 50 compares the reference voltage Vref1 (i.e., the voltage of the second level V2) and the voltage Va used to distinguish between non-isolated and isolated power supply circuits. Furthermore, when the switch control IC 10 is used for a non-isolated power supply circuit, a feedback voltage Vfb corresponding to the output voltage is applied to terminal A. On the other hand, when the switch control IC 10 is used for an isolated power supply circuit, the switch control IC 10 operates without using the voltage Va at terminal A. Therefore, by setting the level of the voltage Va of the isolated power supply circuit outside the range of the voltage Va of the non-isolated power supply circuit (the voltage range of the feedback voltage Vfb variation), the two can be distinguished.

[0064] For example, when the feedback voltage Vfb in a non-isolated power supply circuit varies within a range of, for example, 0 to 3V, the voltage Va of an isolated power supply circuit is set to a specified level outside of 0 to 3V (e.g., 5.4V), thereby enabling the distinction between the two based on the voltage at terminal Va.

[0065] In this embodiment, in order to distinguish the voltage range of the feedback voltage Vfb (e.g., 0 to 3V) and the voltage Va (e.g., 5.4V) of the isolated power supply circuit in the non-isolated power supply circuit, a reference voltage Vref1 (e.g., 4V) that is higher than the voltage range of the feedback voltage Vfb and lower than the voltage Va of the isolated power supply circuit is used.

[0066] Therefore, comparator 50 can determine whether the power supply circuit using switch control IC 10 is non-isolated or isolated by comparing the reference voltage Vref1 and the voltage Va.

[0067] The D flip-flop 51 is a circuit that holds the comparison result of the comparator 50 when the switch control IC 10 is activated. The D flip-flop 51 inputs the signal UVLO to the R input and the signal ENB to the CK input. Therefore, if the power supply voltage Vcc rises, the voltage detection circuit 31 causes the signal UVLO to change to an "L" level, thus releasing the reset of the D flip-flop 51. Subsequently, if the power supply voltage Vcc rises further, the voltage detection circuit 32 causes the signal ENB to change to an "L" level, thus holding the comparison result of the comparator 50 input to the D input. Then, the comparison result held in the D flip-flop 51 is output from the Q output as the signal S1.

[0068] In addition, in this embodiment, when it is determined that the switch control IC10 is used in a non-insulated power supply circuit, a signal S1 of level "L" is output, and when it is determined that the switch control IC10 is used in an isolated power supply circuit, a signal S1 of level "H" is output.

[0069] Comparator 40 is a so-called zero-current detection circuit that detects whether the inductor current IL (described later) of the power supply circuit has become zero based on the voltage Vzcd at terminal ZCD. Here, "zero" is, for example, a current value where the inductor current IL is almost zero (e.g., 0.1mA). Therefore, comparator 40 compares the voltage Vzcd with a reference voltage Vref2 corresponding to a current of, for example, 0.1mA, to detect that the inductor current IL is zero. In addition, if comparator 40 detects that the inductor current IL is zero, it causes the signal Vc2 to change to the "L" level.

[0070] If the inductor current IL is detected to be zero and the signal Vc2 changes to the "L" level, then the pulse circuit 41 outputs the "H" level pulse signal Vp.

[0071] Whenever a pulse signal Vp of level "H" is input, the oscillation circuit 42 outputs a ramp wave Vr with gradually increasing amplitude.

[0072] When the switch control IC10 is determined to be used in a non-isolated power supply circuit, the error amplifier circuit 43 outputs an error voltage Ve1 to set the output voltage level of the power supply circuit to a first target level. Specifically, when the "L" level signal S1 is input, the error amplifier circuit 43 amplifies the error between the voltage Va and the specified reference voltage Vref3 and outputs the error voltage Ve1. Furthermore, the error voltage Ve1 is equivalent to the "first error voltage".

[0073] Furthermore, when the "H" level signal S1 is input, the error amplifier circuit 43 stops outputting the error voltage Ve1. Additionally, the reference voltage Vref3 is determined based on the target level of the output voltage Vout1 of the non-isolated power supply circuit. Furthermore, for example, the stopping of the error voltage Ve1 is achieved by having the output of the error amplifier circuit 43 in a high-impedance state. Moreover, the error amplifier circuit 43 is equivalent to a "first error voltage output circuit," and the error voltage Ve1 is equivalent to a "first error voltage."

[0074] The error voltage output circuit 44 is a circuit that outputs an error voltage Ve2 to set the output voltage level of the power supply circuit to a second target level when the switch control IC 10 is determined to be used in an isolated power supply circuit. It includes a resistor 60 and a switch 61. Furthermore, although this will be explained in detail later, when the switch control IC 10 is used in an isolated power supply circuit, a phototransistor generating a current corresponding to the error from the target level of the output voltage is connected to terminal B. Additionally, the error voltage output circuit 44 generates the error voltage Ve2 based on the current of the phototransistor.

[0075] Switch 61 is positioned between resistor 60 and terminal B, wherein a power supply voltage Vdd is applied to one end of resistor 60. Switch 61, which is connected in series with resistor 60, is turned on when a signal S1 of “H” level is input and turned off when a signal S1 of “L” level is input.

[0076] Therefore, if an "H" level signal S1 is input, switch 61 is turned on, and the current in the phototransistor (described later) flows to resistor 60. Then, an error voltage Ve2 corresponding to the error from the target level of the output voltage is output from resistor 60. On the other hand, if an "L" level signal S1 is input, switch 61 is turned off, and the output of error voltage Ve2 is stopped. In addition, error voltage output circuit 44 is equivalent to a "second error voltage output circuit", and error voltage Ve2 is equivalent to a "second error voltage".

[0077] Thus, the error amplifier circuit 43 outputs an error voltage Ve1 when the input signal S1 is at an "L" level, and the error voltage output circuit 44 outputs an error voltage Ve2 when the input signal S1 is at an "H" level. Therefore, in this embodiment, only one of the error amplifier circuit 43 and the error voltage output circuit 44 operates, and outputs a voltage corresponding to the error of the output voltage. Furthermore, the voltage applied to terminal B is voltage Vb; therefore, when signal S1 is at an "L" level, voltage Vb is the error voltage Ve1, and when signal S1 is at an "H" level, voltage Vb becomes the error voltage Ve2.

[0078] Comparator 45 compares the voltage Vb at terminal B with the magnitude of the ramp wave Vr and outputs signal Vc3 as the comparison result. Here, voltage Vb is applied to the inverting input terminal of comparator 45, and ramp wave Vr is applied to the non-inverting input terminal of comparator 45. Therefore, when the level of ramp wave Vr becomes lower than the level of voltage Vb, signal Vc3 becomes "L" level, and when the level of ramp wave Vr becomes higher than the level of voltage Vb, signal Vc3 becomes "H" level.

[0079] Comparator 46 is a protection circuit to prevent the output voltage Vout1 from becoming an overvoltage. Specifically, when the switch control IC 10 is used in a non-isolated power supply circuit, if the voltage Va at terminal A becomes the voltage of the first level V1, comparator 46 causes the drive circuit 48 (described later) to stop driving the power transistor (described later).

[0080] Specifically, comparator 46 outputs a "H" level signal Vc4 when the voltage Va is above the reference voltage Vref4 (i.e., the voltage of the first level V1), and outputs a "L" level signal Vc4 when the voltage Va is lower than the reference voltage Vref4.

[0081] The logical sum of the output signals Vc3 and Vc4 of OR gate element 47.

[0082] When the pulse signal Vp is output, the drive circuit 48 turns on the power transistor; when the OR gate element 47 outputs an "H" level signal, the drive circuit 48 turns off the power transistor. Specifically, when the switch control IC 10 is used in a non-isolated power supply circuit, the drive circuit 48 drives the power transistor based on the error voltage Ve1. On the other hand, when the switch control IC 10 is used in an isolated power supply circuit, the drive circuit 48 drives the power transistor based on the error voltage Ve2. The drive circuit 48 includes an SR flip-flop 70 and a buffer circuit 71.

[0083] The pulse signal Vp is input to the S input of the SR flip-flop 70, and the output of the OR gate element 47 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 OR gate element 47 outputs a signal of "H" level, the Q output becomes "L" level.

[0084] The buffer circuit 71 outputs a drive signal Vdr for driving the switching 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.

[0085] <<<An example of a non-isolated power supply circuit>>>

[0086] Figure 5 This diagram illustrates an example of the structure of a non-isolated power supply circuit 20. The power supply circuit 20 is a boost-chopper type AC-DC converter that uses the AC voltage Vac of a commercial power supply to generate an output voltage Vout1 at a target level V1 (e.g., 400V) for the load 11. The load 11 is, for example, a DC-DC converter or an electronic device such as a microcomputer. Furthermore, the power supply circuit 20 is equivalent to a "first power supply circuit".

[0087] The power supply circuit 20 is configured to include a switch 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.

[0088] Switch control IC10 is Figure 1 The control IC described herein controls the switching of the NMOS transistor 108 to improve the power factor of the power supply circuit 20, while simultaneously making the output voltage Vout1 level the target level Vo1.

[0089] The full-wave rectifier circuit 100 performs full-wave rectification on the applied specified AC voltage Vac and outputs it as voltage Vrec1 to capacitor 101. Furthermore, the AC voltage Vac is, for example, a voltage of 100–240V with a frequency of 50–60Hz.

[0090] To smooth out the voltage Vrec1, capacitor 101 applies the smoothed voltage Vrec1 to the main coil L1 of transformer 103. Additionally, the voltage applied to the main coil L1 (inductor) is equivalent to the input voltage.

[0091] The transformer 103 has a main coil L1 and an auxiliary coil L2 magnetically coupled to the main coil L1. Here, in this embodiment, the auxiliary coil L2 is wound such that the polarity of the voltage generated in the auxiliary coil L2 is opposite to the polarity of the voltage generated in the main coil L1.

[0092] Since a resistor 104 is provided between one end of the auxiliary coil L2 and the terminal ZCD, the voltage Vz1 generated by the auxiliary coil L2 is applied to the terminal ZCD as the voltage Vzcd.

[0093] Furthermore, since a diode 105 and a capacitor 106 are provided between one end of the auxiliary coil L2 and ground, the capacitor 106 is charged by voltage Vz1. In this embodiment, the charging voltage Vx1 of the capacitor 106 is provided as the power supply voltage Vcc of the switch control IC 10.

[0094] Capacitor 102, together with main coil L1, diode 107, and NMOS transistor 108, constitutes a boost chopper circuit. Therefore, the charging voltage of capacitor 102 becomes the DC output voltage Vout1.

[0095] The NMOS transistor 108 is a power transistor used to control the power supplied to the load 11. In this embodiment, the NMOS transistor 108 is a MOS (Metal Oxide Semiconductor) transistor, but it is not limited to this. The NMOS transistor 108 can be any transistor capable of controlling power; for example, it could also be a bipolar transistor.

[0096] Resistors 120 and 121 form a voltage divider circuit for dividing the output voltage Vout1, and generate a feedback voltage Vfb used when switching the NMOS transistor 108. Furthermore, the feedback voltage Vfb generated at the node where resistors 120 and 121 are connected is applied to terminal A. Therefore, in the power supply circuit 20, the voltage Va at terminal A becomes the feedback voltage Vfb. In this case, resistors 120 and 121 are... Figure 2 (a) shows the voltage divider circuit 800a.

[0097] Resistor 122 functions as a startup resistor when the power supply circuit 20 starts up. Resistor 131, capacitor 132, and capacitor 133 are phase compensation components used to stabilize the feedback loop of the power supply circuit 20. They are located between terminal B and ground and generate an error voltage Ve1.

[0098] ==Operation of Non-Insulated Power Supply Circuits==

[0099] Figure 6 This diagram illustrates the operation of the power supply circuit 20 during startup. Additionally, here, the power supply voltage Vcc is referred to as voltage Vx1, and voltage Va as the feedback voltage Vfb.

[0100] First, at time t0, when an AC voltage Vac is supplied to the power supply circuit 20, the voltage Vrec1 obtained after full-wave rectification 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, so the power supply voltage Vcc (=Vx1) at terminal VCC also increases.

[0101] Furthermore, when the voltage Vrec1 increases, capacitor 102 is charged via diode 107, thus increasing the output voltage Vout1. As a result, the feedback voltage Vfb, obtained by dividing the output voltage Vout1, also increases. Additionally, at this time, the output voltage Vout1 will not be higher than the effective value of the AC voltage Vac. Therefore, the feedback voltage Vfb will not make the effective value of the AC voltage Vac higher than the value obtained by dividing the effective value of the AC voltage Vac by resistors 120 and 121. That is, before the switch control IC 10 starts switching control, the feedback voltage Vfb varies from zero to the voltage value obtained by dividing the effective value of the AC voltage Vac by resistors 120 and 121.

[0102] Then, if at time t1, the power supply voltage Vcc (=Vx1) rises and reaches the specified level Vt1, the voltage detection circuit 31 causes the signal UVLO to change to the "L" level. As a result, the reset of the D flip-flop 51 is released.

[0103] Furthermore, if at time t2, the power supply voltage Vcc (=Vx1) rises further to the specified level Vt2, then the voltage detection circuit 32 causes the signal ENB to change to the “L” level.

[0104] Here, the voltage Vref1 of comparator 50 in the determination circuit 34 is set to be, for example, higher than the value obtained by dividing the effective value of AC voltage Vac by resistors 120 and 121. Therefore, at time t2, D flip-flop 51 maintains the comparison result from comparator 50 at the "L" level, and thus the level of signal S1 remains at the "L" level.

[0105] As a result, in Figure 1 In the switch control IC10, the error amplifier circuit 43, and the error voltage output circuit 44, such as Figure 7 As shown, only the error amplifier circuit 43 operates. Additionally, in Figure 7 For ease of understanding, the error voltage output circuit 44 has been omitted.

[0106] Furthermore, when the signal ENB is at the "L" level at time t2, the operation of each circuit in the switch control IC 10, including the error amplifier circuit 43, begins. 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. Additionally, although this will be explained in detail later, in the power supply circuit 20, the error amplifier circuit 43 operates to make the level of the feedback voltage Vfb consistent with the level of the reference voltage Vref3. Therefore, after time t2, the voltage Va (=Vfb) rises and becomes the reference voltage Vref3. Furthermore, in this case, since the state of terminal A is the first state, the voltage generation circuit 33a generates a voltage Va that is almost the same as the feedback voltage Vfb. In this embodiment, for convenience, when the state of terminal A is the first state, it will be described as if the voltage Va and the feedback voltage Vfb are the same.

[0107] Figure 8 This diagram illustrates the operation of the power supply circuit 20 after startup. Furthermore, the startup timing of the power supply circuit 20 is, for example, when the signal ENB becomes "L" level at time t2 and the operation of each circuit of the switch control IC 10 begins.

[0108] First, if the pulse signal Vp is output at time t10, the drive signal Vdr1 becomes "H" level, and the NMOS transistor 108 turns on. As a result, the inductor current IL1 increases. Furthermore, when the pulse signal Vp is output, the amplitude of the ramp wave Vr from the oscillation circuit 42 increases.

[0109] Furthermore, when the amplitude level of the ramp wave Vr at time t11 becomes higher than the voltage level Vb (=Ve1), comparator 45 causes signal Vc3 to change to the "H" level. As a result, SR flip-flop 70 is reset, and signal Vdr1 also becomes the "L" level.

[0110] When signal Vdr1 becomes level L, NMOS transistor 108 is turned off, and thus the inductor current IL gradually decreases. Furthermore, when NMOS transistor 108 is turned off, the voltage on the input side (voltage Vrec1 side) of the main coil L1 becomes lower than the voltage on the output side (output voltage Vout1 side) of the main coil L1, therefore the voltage Vz1 at the other end of the auxiliary coil L2, which is grounded at one end, becomes positive. As a result, voltage Vzcd (=Vz1) becomes higher than the reference voltage Vref2, and signal Vc2 from comparator 40 becomes level "H".

[0111] Then, if the inductor current IL1 becomes almost zero at time t12, the voltage Vz1 of the auxiliary coil L2, which is 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 comparator 40 becomes "L" level.

[0112] If the signal Vc2 from comparator 40 becomes "L" level, the pulse signal Vp is output, and therefore the NMOS transistor 108 is turned on. Then, after time t13, the operation from time t10 to t13 is repeated.

[0113] ==Feedback control and power factor should be improved==

[0114] Here, in the power supply circuit 20, if the output voltage Vout1 increases from the target level Vo1 (e.g., 400V), the feedback voltage Vfb rises. As a result, the error voltage Ve1 decreases, the on-time of the NMOS transistor 108 shortens, and therefore, the output voltage Vout1 decreases. On the other hand, if the output voltage Vout1 decreases from the target level Vo1, the feedback voltage Vfb decreases. As a result, the error voltage Ve1 rises, the on-time of the NMOS transistor 108 lengthens, and therefore, the output voltage Vout1 rises. Thus, feedback control is performed in the power supply circuit 20 to make the output voltage Vout1 reach the target level Vo1.

[0115] Therefore, when the power supply circuit 20 generates an output voltage Vout1 of the target level Vo1 according to the specified AC voltage Vac and supplies power to the fixed load, the feedback voltage Vfb becomes constant. As a result, since the error voltage Ve1 output from the error amplifier circuit 43 also becomes constant, the period during which the NMOS transistor 108 is turned on (e.g., the period from time t10 to t11) also becomes constant.

[0116] Furthermore, when the NMOS transistor 108 is turned on, if the voltage Vrec1 obtained by rectifying the AC voltage Vac becomes higher, the inductor current IL1 also increases. As a result, the peak waveform of the inductor current IL1 becomes the same as the voltage Vrec1, and the power factor is improved. Therefore, the power supply circuit 20 operates as a PFC (Power Factor Correction) circuit. Thus, the switch control IC 10 enables the non-isolated power supply circuit 20 to perform the desired operation.

[0117] <<<An Example of an Insulated Power Supply Circuit>>>

[0118] Figure 9 This is a diagram illustrating an example of the structure of an isolated power supply circuit 21. Power supply circuit 21 is a flyback AC-DC converter that uses the AC voltage Vac from a commercial power supply to generate an output voltage Vout2 at a target level V2 (e.g., 15V) for the load 11. Furthermore, power supply circuit 21 is equivalent to a "second power supply circuit".

[0119] The power supply circuit 21 is configured to include a full-wave rectifier 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.

[0120] The full-wave rectifier circuit 300 performs full-wave rectification on the applied specified AC voltage Vac and outputs it as voltage Vrec2 to capacitor 301.

[0121] To smooth out the voltage Vrec2, capacitor 301 applies the smoothed voltage Vrec2 to transformer 302.

[0122] Transformer 302 includes a primary coil L10 (inductor), a secondary coil L11, and an auxiliary coil L12, all insulated from each other. In transformer 302, a voltage is generated in the secondary coil L11 on the secondary side according to the voltage change 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 the voltage change across the primary coil L10.

[0123] Furthermore, since the drain of NMOS transistor 303 is connected to one end of the primary coil L10, the voltages of the secondary coil L11 and the auxiliary coil L12 change when the NMOS transistor 303 is switched on. Additionally, the primary coil L10 and the secondary coil L11 are electromagnetically coupled with opposite polarities, while the secondary coil L11 and the auxiliary coil L12 are electromagnetically coupled with the same polarity. Therefore, NMOS transistor 303 is equivalent to a "power transistor".

[0124] Control block 304 is a circuit block used to control the switching of NMOS transistor 303, which will be described in detail later.

[0125] Diode 305 rectifies the voltage of the secondary coil L11, and capacitor 306 smooths the rectified voltage. As a result, a smoothed output voltage Vout2 is generated in capacitor 306. Furthermore, the output voltage Vout2 becomes the DC voltage (e.g., 15V) of the target level V2.

[0126] The constant voltage circuit 307 is a circuit that generates a constant DC voltage, for example, by using a shunt regulator.

[0127] The light-emitting diode 308 is a device that emits light of an intensity corresponding to the difference between the output voltage Vout2 and the output of the constant voltage circuit 307, and together with the phototransistor 530 described later, constitutes an optocoupler. In this embodiment, when the level of the output voltage Vout2 increases, the intensity of the light from the light-emitting diode 308 increases.

[0128] <<<Control Block 304>>>

[0129] The control block 304 includes a switch control IC10, a capacitor 500, diodes 501 and 510, resistors 502, 511 and 520, a Zener diode 521, and a phototransistor 530.

[0130] Switch control IC10 is Figure 1 The integrated circuit described herein controls the switching of the NMOS transistor 303.

[0131] Terminal VCC is connected to the other end of capacitor 500 (one end of which is grounded), the cathode of diode 501, and the cathode of diode 510. Therefore, capacitor 500 is charged by the current from diode 501 and the current from diode 510. The charging voltage Vx2 of capacitor 500 then becomes the power supply voltage Vcc that activates switch control IC 10. Additionally, since the current from diode 510 is generated after switch control IC 10 is started, switch control IC 10 is activated based on the charging voltage Vx2 generated by the current from diode 501.

[0132] Resistor 511 is connected between terminal ZCD and auxiliary coil L12. Therefore, the voltage Vz2 generated by auxiliary coil L12 is applied to terminal ZCD as voltage Vzcd. Furthermore, as described above, a voltage of opposite polarity to that of primary coil L10 is generated in auxiliary coil L12. Therefore, when the inductor current IL2 flowing through primary coil L10 decreases, auxiliary coil L12 generates a positive voltage Vz2; when the inductor current IL2 flowing through primary coil L10 increases, auxiliary coil L12 generates a negative voltage Vz2.

[0133] One end of resistor 520, to which a charging voltage Vx2 is applied, and the other end of Zener diode 521 are connected to terminal A. Therefore, when the charging voltage Vx2 becomes sufficiently high, the voltage Va applied to terminal A becomes the breakdown voltage Vz0 of Zener diode 521 (e.g., 5.1V). In this case, resistor 520 and Zener diode 521 are... Figure 3 (b) shows the circuit 800b.

[0134] Terminal B is a terminal that generates an error voltage representing the difference between the output voltage Vout2 and the target voltage V2, and is connected to phototransistor 530. Phototransistor 530 causes a bias current Ib, corresponding to the intensity of the light from light-emitting diode 308, to flow from terminal B to ground. Therefore, phototransistor 530 operates as a transistor that generates sink current. Additionally, components such as capacitors for noise removal can be provided between terminal B and ground.

[0135] Terminal OUT is connected to the gate of NMOS transistor 303, therefore, NMOS transistor 303 is switched by drive signal Vdr2. In addition, power supply circuit 21 is equivalent to a "second power supply circuit".

[0136] ==Operation of an Insulated Power Supply Circuit==

[0137] Figure 10 This diagram illustrates the operation of the power supply circuit 21 during startup. Additionally, here, the power supply voltage Vcc is referred to as voltage Vx2.

[0138] First, if an AC voltage Vac is supplied to the power supply circuit 21 at time t20 and a voltage Vrec2 is generated, then capacitor 500 is charged via diode 501. As a result, due to the increase in the charging voltage Vx2 of capacitor 500, the power supply voltage Vcc (=Vx2) at the final terminal VCC also increases.

[0139] Furthermore, when the power supply voltage Vcc (=Vx2) increases, the voltage Va also rises, 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 the voltage Va becomes higher than the reference voltage Vref1 when the power supply circuit 21 is started. In addition, as described above, since the state of terminal A is the second state, the voltage generation circuit 33a causes the voltage Va to rise higher than the second level V2 (i.e., the reference voltage Vref1).

[0140] Furthermore, if the power supply voltage Vcc rises further, and at time t22 the voltage Va becomes higher than the breakdown voltage Vz0, then the voltage Va is clamped at the breakdown voltage Vz0. Additionally, in this embodiment, since the breakdown voltage Vz0 (e.g., 5.4V) is set to be higher than the reference voltage Vref1, the voltage Va will necessarily be higher than the reference voltage Vref1 when the Zener diode 521 is turned on.

[0141] Then, if at time t23, the power supply voltage Vcc (=Vx2) rises and reaches the specified level Vt1, the voltage detection circuit 31 causes the signal UVLO to change to the "L" level. As a result, the reset of the D flip-flop 51 is released.

[0142] Furthermore, if at time t24, the power supply voltage Vcc (=Vx2) rises further to the specified level Vt2, then the voltage detection circuit 32 causes the signal ENB to change to the "L" level. When the signal ENB becomes the "L" level, the D flip-flop 51 maintains the comparison result of the "H" level from the comparator 50, so the level of the signal S1 changes to the "H" level.

[0143] As a result, in Figure 1 In the switch control IC10, in the error amplifier circuit 43 and the error voltage output circuit 44, such as Figure 11 As shown, only the error voltage output circuit 44 operates. Furthermore, since the output of the error amplifier circuit 43 becomes high impedance, the output of the error amplifier circuit 43 does not affect the voltage Vb at terminal B.

[0144] Furthermore, if signal ENB changes to "L" level at time t24, switch 61 of error voltage output circuit 44 is turned on. Therefore, the error voltage Ve2 of resistor 60 becomes Ve2 = Vdd - R × Ib. Here, the resistance value of resistor 60 is set to "R", and the bias current Ib of phototransistor 530 is set to "Ib". Also, since the on-resistance of switch 61 is sufficiently small, the voltage Vb at terminal B becomes the error voltage Ve2.

[0145] Figure 12 This diagram illustrates the operation of the power supply circuit 21 after startup. Furthermore, the startup timing of the power supply circuit 21 is, for example, when the signal ENB becomes "L" level at time t24 and the operation of each circuit of the switch control IC 10 begins.

[0146] First, if the pulse signal Vp is output at time t30, the drive signal Vdr2 becomes "H" level, and the NMOS transistor 303 turns on. As a result, the inductor current IL2 increases. Furthermore, if the pulse signal Vp is output, the amplitude of the ramp wave Vr from the oscillator circuit 42 increases. When the NMOS transistor 303 is on, due to the opposite polarity electromagnetic coupling of the secondary coil L11, the diode 305 turns off, and energy is stored in the transformer 302.

[0147] Furthermore, when the amplitude level of the ramp wave Vr at time t31 becomes higher than the voltage level Vb (=Ve2), comparator 45 causes signal Vc3 to change to the "H" level. As a result, SR flip-flop 70 is reset, and signal Vdr2 also becomes the "L" level.

[0148] When signal Vdr2 becomes L level, NMOS transistor 303 turns off. As a result, inductor current IL2 decreases sharply, and the voltage Vz2 at the other end of the auxiliary coil L12, which is grounded at one end, becomes positive. Additionally, the energy stored in transformer 302 is output from the secondary coil L2 through diode 305. Consequently, voltage Vzcd (=Vz2) becomes higher than the reference voltage Vref2, and signal Vc2 from comparator 40 becomes "H" level.

[0149] Then, if the inductor current IL3 of the secondary coil L11 becomes almost zero at time t32, the voltage Vz2 of the auxiliary coil L12, which is 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 of comparator 40 becomes "L" level.

[0150] If signal Vc2 changes to "L" level, pulse signal Vp is output, and NMOS transistor 303 turns on. Then, after time t33, the operation from time t30 to t33 is repeated. Furthermore, the timing when inductor current IL3 becomes almost zero varies according to the current value of inductor current IL2. Therefore, switch control IC 10 turns on NMOS transistor 303 based on inductor current IL2.

[0151] ==Feedback Control==

[0152] Here, when load 11 is lightly loaded, the output voltage Vout2 rises above the target level V2. At this time, the current flowing through the shunt regulator (not shown) of the constant voltage circuit 307 increases, and therefore the current in the light-emitting diode 308 also increases. Since the phototransistor 530 increases the bias current Ib according to the amplification of the light from the light-emitting diode 308, the error voltage Ve2 (=Vb) decreases. As a result, the on-time of the NMOS transistor 303 becomes shorter, and therefore the output voltage Vout2 decreases.

[0153] On the other hand, when the output voltage Vout2 decreases from the target level V2, the current of the light-emitting diode 308 decreases, contrary to the above. As a result, the bias current Ib decreases, and the error voltage Ve2 (=Vb) increases. Therefore, the on-time of the NMOS transistor 303 becomes longer, and the output voltage Vout2 increases. Thus, feedback control is performed in the power supply circuit 21 to make the output voltage Vout2 reach the target level V2. Therefore, the switch control IC 10 enables the isolated power supply circuit 21 to perform the desired operation.

[0154] ==Operation of a non-insulated power supply circuit when terminal A is poorly connected==

[0155] Figure 13 This diagram illustrates the operation of the power supply circuit 20 during startup when a poor connection to terminal A occurs. Here, the power supply voltage Vcc is referred to as the voltage Vx1 described above. "Poor connection" means, for example, that the external circuit is not electrically connected to terminal A, and that the external circuit and terminal A are electrically disconnected (or the impedance becomes very high).

[0156] First, when an AC voltage Vac is supplied to the power supply circuit 20 at time t40, the voltage Vrec1 obtained after full-wave rectification by the full-wave rectifier circuit 100 is applied to the capacitor 106 via the start-up resistor 122. As a result, the power supply voltage Vcc (=Vx1) at terminal VCC also increases because the charging voltage Vx1 of capacitor 106 increases.

[0157] Additionally, when voltage Vrec1 increases, capacitor 102 is charged via diode 107, thus increasing the output voltage Vout1. However, since the feedback voltage Vfb is not applied to terminal A, voltage Va increases according to the constant current I0a. Furthermore, at this time, the output voltage Vout1 will not become higher than the effective value of the AC voltage Vac.

[0158] Furthermore, in this embodiment, at time t41, as described above, the PMOS transistor 92 of the voltage generation circuit 33a adjusts the voltage Va to the voltage of the third level V3 based on the constant current I0a. Then, the voltage generation circuit 33a sets the level of voltage Va to a level that is higher than the voltage Vref4 of the first level V1 and lower than the voltage Vref1 of the second level V2. Therefore, at time t41, the comparator 50 outputs a signal Vc1 of level "L".

[0159] Then, if at time t42, the power supply voltage Vcc (=Vx1) rises to the specified level Vt1, the voltage detection circuit 31 causes the signal UVLO to change to the "L" level. As a result, the reset of the D flip-flop 51 is released.

[0160] Furthermore, if at time t43, the power supply voltage Vcc (=Vx1) rises further to the specified level Vt2, the voltage detection circuit 32 causes the signal ENB to change to the "L" level. Here, the voltage Vref1 of the comparator 50 of the determination circuit 34 is set to, for example, a higher value than that obtained by dividing the effective value of the AC voltage Vac by resistors 120 and 121.

[0161] Furthermore, in this embodiment, the D flip-flop 51 maintains the comparison result from the comparator 50 at the "L" level; therefore, the level of signal S1 remains at the "L" level. As a result, in Figure 1 In the switch control IC10, in the error amplifier circuit 43 and the error voltage output circuit 44, such as Figure 7 As shown, only the error amplifier circuit 43 is operating.

[0162] Furthermore, if the signal ENB changes to an "L" level at time t43, the operation of each circuit in the switch control IC 10, including the error amplifier circuit 43, begins. Since the voltage Va is higher than the reference voltage Vref4, the comparator 46 outputs an "H" level signal Vc4, and the switching of the NMOS transistor 108 is stopped. Therefore, the output voltage Vout1 in the power supply circuit 20 does not become an overvoltage, and damage to capacitors such as 102 is prevented.

[0163] <<Examples of Voltage Generation Circuits>>

[0164] Furthermore, the voltage generation circuit 33a consists of a constant current source 90a and a voltage adjustment circuit 91a, but it can also be configured as follows: Figure 14The voltage generation circuit 33b is shown. The voltage generation circuit 33b generates voltage Va according to the state of terminal A, from a first state to a third state. The specific operation of the voltage generation circuit 33b will be explained below. Furthermore, the voltage generation circuit 33b is configured to include a constant current source 90b, an operational amplifier 600, a control circuit 601, and a current output circuit 602.

[0165] A constant current source 90b provides a constant current IOb to terminal A. Operational amplifier 600 compares voltage Va with a reference voltage Vref6 and, based on their magnitudes, controls the on-resistance of the NMOS transistor 700 in the current output circuit 602 (described later). When voltage Va is higher than the reference voltage Vref6, control circuit 601 outputs a signal en that enables operational amplifier 600. Conversely, when voltage Va is lower than the reference voltage Vref6, control circuit 601 outputs a signal en that disables operational amplifier 600. In this case, operational amplifier 600 outputs a voltage that turns off NMOS transistor 700. Furthermore, the reference voltage Vref6 is lower than... Figure 3 (c) shows the voltage of the third level V3, which is higher than the voltage of the first level V1 (i.e., the reference voltage Vref4) and lower than the voltage of the second level V2 (i.e., the reference voltage Vref1).

[0166] The current output circuit 602 generates a current I3 corresponding to the output of the operational amplifier 600, and is composed of NMOS transistors 700, 703, and 704, and PMOS transistors 701 and 702. Further details will be provided later, but the current I3 is the current flowing through the NMOS transistor 704.

[0167] <Circuit connection case for non-isolated power supply circuits>

[0168] Here, as mentioned above Figure 3 (a) and Figure 3 As shown in (c), in the first state where the voltage divider circuit 800a is connected to terminal A, the voltage Va is set to the first level V1. Therefore, in this case, since the voltage Va becomes lower than the reference voltage Vref6, the control circuit 601 turns off the NMOS transistor 700 to disable the operational amplifier 600. Since the current I1 of the diode-connected PMOS transistor 701 does not flow, the current I2 of the PMOS transistor 702, which forms a current mirror circuit with the PMOS transistor 701, also does not flow. Since the current I2 is the current through the diode-connected NMOS transistor 703, when the current I2 does not flow, the current I3 of the NMOS transistor 704, which forms a current mirror circuit with the NMOS transistor 703, also does not flow.

[0169] Therefore, when terminal A is in its first state, the current output circuit 602 does not drive terminal A with current I3. As a result, the voltage generation circuit 33b generates a voltage Va that becomes a voltage divider. Here, the constant current I0b from the constant current source 90b flows to ground via resistor 121. Furthermore, similar to the constant current I0a, the constant current I0b is set to a very small value (e.g., 2μA), so that even if the constant current I0b flows externally, the voltage Va at terminal A hardly changes. That is, when the voltage divider circuit 800a used in a non-isolated power supply circuit is connected to terminal A, the voltage generation circuit 33b sets the level of the voltage Va at terminal A to approximately the level of the feedback voltage Vfb.

[0170] <Circuit connection for isolated power supply circuits>

[0171] In addition, as mentioned above Figure 3 As shown in (b) and 3(c), in the second state where circuit 800b is connected to terminal A, the Zener diode 521 of circuit 800b applies a breakdown voltage Vz0 to terminal A. Here, since the level of the reference voltage Vref6 in this embodiment is set to be lower than the level of the breakdown voltage Vz0, the control circuit 601 enables the operational amplifier 600. In this case, the voltage level of the non-inverting input terminal of the operational amplifier 600 is higher than the voltage level of the inverting input terminal, therefore, the operational amplifier 600 reduces the on-resistance of the NMOS transistor 700. As a result, current I1 increases, and current I2 also increases. Furthermore, when current I2 increases, current I3 also increases.

[0172] However, in this embodiment, the maximum value of current I3 is set to be greater than that from... Figure 3 (b) The current Ia of resistor 520 is smaller. Therefore, voltage adjustment circuit 91b cannot set the level of voltage Va to the level of reference voltage Vref6 through feedback control, and voltage Va rises to a voltage higher than the second level V2 (e.g., voltage Vdd). That is, in this case, voltage generation circuit 33b sets the level of voltage Va at terminal A to a voltage higher than the second level.

[0173] <Case where the circuit used for power supply is not connected>

[0174] Furthermore, a third state, in which the circuit to be connected to terminal A is disconnected from terminal A, will be explained. Assume that even when the voltage Va is lower than the reference voltage Vref6, the operational amplifier 600 is disabled, and the NMOS transistor 704 is turned off, the constant current source 90b generates a current I0b, thus making the voltage Va higher than the reference voltage Vref6. As a result, the operational amplifier 600 operates. Furthermore, in this embodiment, since the current I0b is set to be smaller than the maximum value of the current I3, the operational amplifier 600 can set the level of the voltage Va to the level of the reference voltage Vref6. That is, when terminal A is in the third state, the voltage generation circuit 33b generates a voltage Va that is the reference voltage Vref6 (i.e., the voltage of the third level V3). Therefore, when terminal A is in the third state, it is possible to prevent the determination circuit 34 from incorrectly determining that terminal A is in the second state.

[0175] ===Summary===

[0176] The switch control IC 10 of this embodiment has been described above. The switch control IC 10 includes terminal A, a voltage generation circuit 33a, a determination circuit 34, and a drive circuit 48. When terminal A is in the third state, the voltage generation circuit 33a generates a voltage at terminal A that is higher than the first level V1 and lower than the second level V2, representing a third level V3. Therefore, when terminal A is used in the power supply circuit 20, even if the state of terminal A is in the third state, the determination circuit 34 can determine that terminal A is used in the power supply circuit 20. Thus, an integrated circuit capable of appropriately determining the type of power supply circuit can be provided.

[0177] Additionally, the voltage generation circuit 33a includes a constant current source 90a and a voltage adjustment circuit 91a. The constant current source 90a provides a constant current IOa. Thus, the voltage adjustment circuit 91a can detect that the state of terminal A is in the third state and adjust the voltage Va based on the constant current IOa.

[0178] Furthermore, the voltage generation circuit 33a includes a PMOS transistor 92. When terminal A is in the third state, the PMOS transistor 92 generates a third level V3 voltage at terminal A, which is higher than the first level V1 and lower than the second level V2, based on a constant current I0a. Thus, when terminal A is in the third state, the determination circuit 34 can determine that the switch control IC 10 is being used in the power supply circuit 20.

[0179] Furthermore, when terminal A is in the first state, PMOS transistor 92 is off, and when terminal A is in the second and third states, PMOS transistor 92 is on. Thus, unless terminal A is in the third state, the determination circuit 34 can appropriately determine which of the power supply circuits 20 and 21 the switch control IC 10 is used for.

[0180] Furthermore, the voltage divider circuit 800a generates a feedback voltage Vfb corresponding to the output voltage Vout1 at terminal A, and circuit 800b includes elements that generate a breakdown voltage Vz0 at terminal A. Therefore, when terminal A is in the first and second states, the voltage generation circuit 33a can generate a voltage Va for appropriately determining the type of the power supply circuit. Furthermore, when terminal A is in the third state, the voltage generation circuit 33a can generate a voltage Va at the third level V3. Then, the determination circuit 34 can appropriately determine the type of the power supply circuit.

[0181] Additionally, the switch control IC 10 includes a comparator 46. When the voltage Va becomes the first level V1, the comparator 46 causes the drive circuit 48 to stop driving the NMOS transistor 108. That is, when terminal A is in the third state, the voltage Va is higher than the first level V1, therefore, the drive circuit 48 does not drive the NMOS transistor 108. Thus, even if terminal A becomes the third state, the switch control IC 10 will not cause the output voltage Vout1 of the power supply circuit 20 to become an overvoltage by driving the NMOS transistor 108.

[0182] In addition, the switch control IC10 includes an error amplifier circuit 43 and an error voltage output circuit 44. Thus, regardless of which of the power supply circuits 20 or 21 the switch control IC10 is used in, it can switch the NMOS transistor 108 or 303, thereby enabling the power supply circuit 20 or 21 to generate an output voltage Vout1 or Vout2 based on the input voltage Vac.

[0183] Additionally, the switch control IC10 includes terminal B. Therefore, regardless of which of the power supply circuits 20 and 21 the switch control IC10 is used in, the power supply circuits 20 and 21 can generate target level output voltages Vout1 and Vout2 based on the voltage generated in terminal B.

[0184] The above embodiments are provided to facilitate understanding of the present invention, and are not intended to limit or restrict its interpretation. Furthermore, the present invention can be modified or improved without departing from its spirit, and the present invention naturally includes its equivalents.

[0185] For example, a voltage Va is generated in the power supply circuit 21, and a resistor 520 and a Zener diode 521 are used to set the voltage Va beyond the range of the feedback voltage, but this is not a limitation. For example, a resistor can be used instead of the Zener diode 521, and the voltage Vx2 can be divided by the two resistors, with the divided voltage set as the voltage Va.

[0186] Furthermore, as described above, when the power supply circuit 20 starts, the feedback voltage Vfb is the value obtained by dividing the effective value of the AC voltage Vac through resistors 120 and 121. Therefore, in the power supply circuit 21, it is also possible to use a component with a smaller output voltage value than the value obtained by dividing the effective value of the AC voltage Vac through resistors 120 and 121 (for example, the forward voltage of a diode, i.e., 0.7V) to generate 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 through resistors 120 and 121 and the forward voltage of the diode, i.e., 0.7V. Thus, the determination circuit 34 can determine whether the power supply circuit is non-insulated or insulated.

[0187] For example, in the error voltage output circuit 44, a MOS transistor that operates in the linear region can be used instead of resistor 60.

[0188] Furthermore, the switch control IC10 is a circuit that operates in a mode where the transistor is turned on (so-called critical mode) when the inductor current IL becomes zero. However, for example, it can also be a circuit that operates in a mode where the inductor current IL changes continuously (so-called continuous mode).

[0189] In addition, the power supply circuit 21 is a flyback power supply circuit, but it is not limited to this. For example, it can also be a forward, push-pull, half-bridge, full-bridge, or chopper power supply circuit.

[0190] Label Explanation

[0191] 10 Switch Control IC

[0192] 11 Load

[0193] Power supply circuits 20, 21, and 30

[0194] 31, 32 Voltage detection circuit

[0195] 33a, 33b Voltage generation circuits

[0196] 34. Decision Circuit

[0197] 40, 45, 46, 50 comparators

[0198] 41 Pulse Circuit

[0199] 42 Oscillating Circuit

[0200] 43 Error Amplifier Circuit

[0201] 44 Error Voltage Output Circuit

[0202] 47 OR gate components

[0203] 48 Drive Circuit

[0204] 51 D flip-flop

[0205] Resistors with ratings of 60, 104, 120, 121, 122, 131, 502, 511, and 520.

[0206] 61 Switch

[0207] 70 SR trigger

[0208] 71 Buffer Circuit

[0209] 90a, 90b constant current sources

[0210] 91a and 91b voltage regulation circuits

[0211] 92, 701, 702 PMOS transistors

[0212] 100 and 300 full-wave rectifier circuits

[0213] 101, 102, 106, 132, 133, 301, 306, 500 capacitors

[0214] Transformers 103 and 302

[0215] 105, 107, 305, 501, 510 diodes

[0216] 108, 303, 700, 703, 704 NMOS transistors

[0217] 304 control block

[0218] 307 Constant Voltage Circuit

[0219] 308 LED

[0220] 521 Zener diode

[0221] 530 phototransistor

[0222] 600 operational amplifier

[0223] 601 Control Circuit

[0224] 602 Current Output Circuit

[0225] 800A voltage divider circuit

[0226] 800b circuit.

Claims

1. An integrated circuit, The integrated circuit, which switches a power transistor controlling the inductor current based on the inductor current flowing through an inductor to which an input voltage is applied and an output voltage generated according to the input voltage, is characterized by comprising: A first terminal is connected to a first circuit when the integrated circuit is used for a non-insulated first power supply circuit, and connected to a second circuit when the integrated circuit is used for an insulated second power supply circuit. A voltage generation circuit, in a first state where the first terminal is connected to the first circuit, generates a voltage at the first terminal that is lower than a first level and corresponds to the output voltage; in a second state where the first terminal is connected to the second circuit, generates a voltage at the first terminal that is higher than a second level; and in a third state where the circuit to be connected to the first terminal is disconnected from the first terminal, generates a voltage at the first terminal that is higher than the first level and lower than the second level. The determination circuit determines that the integrated circuit is used in the first power supply circuit when the voltage of the first terminal is lower than the second level, and determines that the integrated circuit is used in the second power supply circuit when the voltage of the first terminal is higher than the second level. as well as A driving circuit that drives the power transistor based on the determination result of the determination circuit.

2. The integrated circuit as described in claim 1, characterized in that, The voltage generation circuit includes: A constant current source that provides a constant current to the first terminal; and A voltage adjustment circuit that adjusts the voltage of the first terminal based on the state of the first terminal and the constant current supplied to the first terminal.

3. The integrated circuit as described in claim 2, characterized in that, The voltage regulation circuit includes a transistor that, in the third state, generates a voltage at the first terminal that is higher than the first level and lower than the second level, based on the constant current.

4. The integrated circuit as described in claim 3, characterized in that, The transistor is off in the first state and on in the second and third states.

5. The integrated circuit according to any one of claims 1 to 4, characterized in that, The first circuit is a voltage divider circuit that generates a feedback voltage corresponding to the output voltage at the first terminal. The second circuit includes an element that generates the voltage at the first terminal.

6. The integrated circuit according to any one of claims 1 to 5, characterized in that, It also includes a protection circuit that, in the case that the integrated circuit is used in a non-isolated first power supply circuit, causes the drive circuit to stop driving the power transistor if the voltage at the first terminal becomes the first level.

7. The integrated circuit according to any one of claims 1 to 6, characterized in that, Also includes: A first error voltage output circuit, wherein when the integrated circuit is used in the first power supply circuit, outputs a first error voltage for setting the level of the output voltage to a first target level; as well as A second error voltage output circuit, when the integrated circuit is used in the second power supply circuit, outputs a second error voltage to set the level of the output voltage to a second target level. When the integrated circuit is used in the first power supply circuit, the driving circuit drives the power transistor based on the first error voltage; when the integrated circuit is used in the second power supply circuit, the driving circuit drives the power transistor based on the second error voltage.

8. The integrated circuit as described in claim 7, characterized in that, It also includes a second terminal, which is connected to a capacitor when the integrated circuit is used in the first power supply circuit, and connected to a phototransistor when the integrated circuit is used in the second power supply circuit. The first error voltage output circuit generates the first error voltage for the capacitor. The second error voltage output circuit generates the second error voltage based on the current of the phototransistor.

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