Integrated circuits, power supply circuits

Abstract

To provide an integrated circuit capable of detecting resonance current highly accurately even when load condition becomes light load.SOLUTION: An integrated circuit is for driving a switching element in a resonant type power supply circuit comprising a resonance circuit in which a coil and a capacitor are connected with each other in series and the switching element which controls a resonance current flowing in the resonance circuit. The integrated circuit includes: a first terminal to which a voltage according to the resonance current is applied; a first voltage output circuit for outputting a first voltage which is a first-fold of the voltage at the first terminal; a second voltage output circuit for outputting a second voltage which is second-fold of a voltage smaller than the first-fold of the voltage at the first terminal; and a drive circuit for driving the switching element based on a feedback voltage corresponding to the output voltage of the power supply circuit, the first voltage and the second voltage.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] An integrated circuit that controls an LLC current resonant converter generally drives a switching element based on a resonant current (for example, Patent Documents 1 to 4).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, the above-mentioned integrated circuit may change the driving pattern of the switching element according to the magnitude of the resonant current. Specifically, when the load state is a light load, the integrated circuit drives the switching element intermittently. However, generally, when the load state is a light load, the resonant current becomes small, and it is difficult to detect the resonant current.

[0005] The present invention has been made in view of the above conventional problems, and an object thereof is to provide an integrated circuit capable of accurately detecting a resonant current even when the load state is a light load.

Means for Solving the Problems

[0006] The present invention provides an integrated circuit for solving the aforementioned problems, which drives a switching element in a resonant power supply circuit comprising a resonant circuit in which a coil and a capacitor are connected in series, and a switching element for controlling the resonant current flowing through the resonant circuit, and comprises a first terminal to which a voltage corresponding to the resonant current is applied, a first voltage output circuit that outputs a first voltage which is the first time the voltage of the first terminal is output, a second voltage output circuit that outputs a second voltage which is the second time the voltage of the first terminal is smaller than the first time the voltage of the first terminal is output, and a drive circuit that drives the switching element based on a feedback voltage corresponding to the output voltage of the power supply circuit, the first voltage, and the second voltage.

[0007] The power supply circuit according to the present invention, which solves the aforementioned problems, is a resonant power supply circuit comprising: a resonant circuit in which a coil and a capacitor are connected in series; a switching element that controls the resonant current flowing through the resonant circuit; and an integrated circuit that switches the switching element, wherein the integrated circuit includes: a first terminal to which a voltage corresponding to the resonant current is applied; a first voltage output circuit that outputs a first voltage which is the first time the voltage of the first terminal is first; a second voltage output circuit that outputs a second voltage which is second time the voltage of the first terminal and is smaller than the first time the voltage of the first terminal is second; and a drive circuit that drives the switching element based on a feedback voltage corresponding to the output voltage of the power supply circuit, the first voltage, and the second voltage. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide an integrated circuit that can accurately detect resonant current even when the load condition is light load. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows an example of a switching power supply circuit 10. [Figure 2] This figure shows an example of the control IC40a. [Figure 3] This diagram shows an example of the relationship between voltage Vis and voltages V1 and V2. [Figure 4] This figure shows an example of a voltage generation circuit 72a. [Figure 5] This figure shows an example of drive signals Vdr1 and Vdr2 under heavy load conditions for load 11. [Figure 6] This figure shows an example of drive signals Vdr1 and Vdr2 when load 11 is under light load conditions. [Figure 7] This figure shows an example of the operation of control IC40a. [Figure 8] This figure shows an example of the control IC 40b. [Figure 9] This figure shows an example of a voltage generation circuit 72b. [Figure 10] This figure shows an example of the operation of control IC40b. [Modes for carrying out the invention]

[0010] The following matters become clear from this specification and the accompanying drawings:

[0011] =====Execution===== <<<Overview of Switching Power Supply Circuit 10>>> Figure 1 shows an example of the configuration of a switching power supply circuit 10, which is one embodiment of the present invention. The switching power supply circuit 10 is an LLC current resonant type power supply circuit that generates an output voltage Vout of a target level to a load 11 from a predetermined input voltage Vin.

[0012] The switching power supply circuit 10 is composed of capacitors 20, 21, 22, 32, resistor 23, NMOS transistors 24, 25, transformer 26, control block 27, diodes 30, 31, constant voltage circuit 33, and light-emitting diode 34.

[0013] The capacitor 20 stabilizes the voltage between the power line to which the input voltage Vin is applied and the ground line on the ground side, and removes noise and the like. The input voltage Vin is a DC voltage of a predetermined level. The capacitor 21 is a so-called resonance capacitor that forms a resonance circuit with the excitation inductance and leakage inductance (leakage inductance) based on the primary coil L1, secondary coils L2, and L3 of the transformer 26.

[0014] The capacitor 22 and the resistor 23 form a shunt circuit that shunts and detects the resonance current Icr flowing through the capacitor 21, and the capacitor 22 and the resistor 23 connected in series are connected in parallel to the capacitor 21.

[0015] Also, the resistor 23 generates a voltage Vis based on the current obtained by shunting the resonance current Icr. Therefore, the voltage Vis is a voltage corresponding to the resonance current Icr. When the resonance current Icr flows in the direction of the arrow shown in FIG. 1, the resonance current Icr is referred to as a positive resonance current Icr, and the voltage Vis in this case is a positive voltage.

[0016] Also, when the resonance current Icr flows in the direction of the arrow, that is, when the resonance current Icr flows in the order of the primary coil L1, the capacitor 22, and the resistor 23, the direction of the resonance current Icr is positive. Also, when the resonance current Icr flows in the direction opposite to the arrow, that is, when the resonance current Icr flows in the order of the resistor 23, the capacitor 22, and the primary coil L1, the direction of the resonance current Icr is negative.

[0017] NMOS transistor 24 is the high-side power transistor, and NMOS transistor 25 is the low-side power transistor. Specifically, NMOS transistors 24 and 25 are connected in series between the node to which the input voltage Vin is applied and the node to which the ground voltage is applied. In this embodiment, NMOS transistors 24 and 25 are used as switching elements, but for example, PMOS transistors or bipolar transistors may be used instead of NMOS transistors 24 and 25. Note that NMOS transistors 24 and 25 correspond to "switching elements".

[0018] The transformer 26 comprises a primary coil L1, secondary coils L2 and L3, and an auxiliary coil La, with insulation between the primary coil L1, the secondary coils L2 and L3, and the auxiliary coil La. In the transformer 26, voltage is generated in the secondary coils L2 and L3 and the auxiliary coil La in response to a change in the voltage across the primary coil L1 on the primary side.

[0019] Furthermore, the primary coil L1 has the source of NMOS transistor 24 and the drain of NMOS transistor 25 connected to one end, and the source of NMOS transistor 25 connected to the other end via capacitor 21.

[0020] Therefore, when the switching of NMOS transistors 24 and 25 begins, the voltages across the secondary coils L2 and L3 and the auxiliary coil La will change. Note that the primary coil L1 and the secondary coils L2 and L3 are electromagnetically coupled with opposite polarities, while the primary coil L1 and the auxiliary coil La are electromagnetically coupled with the same polarity.

[0021] Control block 27 is a circuit block for controlling the switching of NMOS transistors 24 and 25, and its details will be described later.

[0022] Diodes 30 and 31 rectify the voltages across secondary coils L2 and L3, and capacitor 32 smooths the rectified voltage. As a result, capacitor 32 generates a smoothed output voltage Vout. The output voltage Vout is a DC voltage of the desired level.

[0023] The constant voltage circuit 33 is a circuit that generates a constant DC voltage, and is configured, for example, using a shunt regulator.

[0024] The light-emitting diode 34 is an element that emits light of an intensity corresponding to the difference between the output voltage Vout and the output of the constant voltage circuit 33, and together with the phototransistor 52, which will be described later, it constitutes a photocoupler. In this embodiment, as the level of the output voltage Vout increases, the intensity of the light from the light-emitting diode 34 increases.

[0025] <<<Control Block 27>>> The control block 27 includes a control IC 40a, a diode 50, capacitors 51, 53, and 54, and a phototransistor 52.

[0026] Control IC 40a is an integrated circuit that controls the switching of NMOS transistors 24 and 25, and has terminals VCC, GND, FB, IS, CA, HO, LO, and VS.

[0027] Terminal VCC is the terminal to which the power supply voltage Vcc is applied to operate the control IC 40a. The cathode of diode 50 and capacitor 51, with one end grounded, are connected to terminal VCC. Capacitor 51 is charged by the voltage from the auxiliary coil La of transformer 26, resulting in the voltage Vcc. The control IC 40a is started by applying a divided voltage of the input voltage Vin, which is obtained by rectifying the AC input via a terminal (not shown), and after starting up, it operates based on the power supply voltage Vcc.

[0028] Terminal GND is a terminal to which a ground voltage is applied, and is connected, for example, to the casing of a device in which the switching power supply circuit 10 is installed.

[0029] Terminal FB is the terminal to which a feedback voltage Vfb corresponding to the output voltage Vout is generated, and a phototransistor 52 and a capacitor 53 are connected. The phototransistor 52 flows a bias current I1, whose magnitude corresponds to the light intensity from the light-emitting diode 34, from terminal FB to ground, and the capacitor 53 is provided to remove noise between terminal FB and ground. Therefore, the phototransistor 52 operates as a transistor that generates sink current.

[0030] Terminal IS is a terminal for detecting the resonant current value of the primary coil L1. Here, a voltage corresponding to the resonant current value of the primary coil L1 is generated at the node to which capacitor 22 and resistor 23 are connected. Therefore, a voltage Vis corresponding to the resonant current value of the primary coil L1 is applied to terminal IS.

[0031] Terminal CA is a terminal to which a voltage Vca is applied, generated based on the resonant current of the primary coil L1, and corresponding to the input power of the switching power supply circuit 10 (i.e., the power of the load 11). As will be described in more detail later, a capacitor 54 is connected to terminal CA.

[0032] Terminal HO is the terminal to which the drive signal Vdr1, which drives the NMOS transistor 24, is output, and the gate of the NMOS transistor 24 is connected to it.

[0033] Terminal LO is the terminal to which the drive signal Vdr2, which drives the NMOS transistor 25, is output, and the gate of the NMOS transistor 25 is connected to it.

[0034] Terminal VS is a terminal to which the voltage of the connection node, where the source terminal of NMOS transistor 24 and the drain terminal of NMOS transistor 25 are connected, is applied. When NMOS transistor 24 is turned on, the input voltage Vin is applied, and when NMOS transistor 25 is turned on, the ground voltage is applied.

[0035] Furthermore, the potential of the voltage Vs at terminal VS becomes the reference potential for the output voltage of the bootstrap circuit (not shown) used to turn on the NMOS transistor 24 when the input voltage Vin is applied to terminal VS.

[0036] <<<Details of Control IC 40a>>> Figure 2 shows an example of the control IC 40a. The control IC 40a is an integrated circuit that switches NMOS transistors 24 and 25 based on the magnitude of the resonant current Icr. The control IC 40a is composed of resistors 60-62, 64-67, diode 63, oscillator circuit 70, overcurrent protection circuit (OCP) 71, voltage generation circuit 72a, load detection circuit 73, and drive circuit 74. Note that the terminal VCC is omitted here for convenience.

[0037] ==Resistor 60== Resistor 60 generates a feedback voltage Vfb based on the bias current I1 from the phototransistor 52. One end of resistor 60 is connected to a predetermined voltage Vdd output by the internal power supply (not shown) of the control IC 40a, and the other end is connected to terminal FB. Therefore, if the resistance value of resistor 60 is "R", the feedback voltage Vfb generated at terminal FB is expressed by equation (1).

[0038] Vfb = Vdd - R × I1 ···(1) As described above, in this embodiment, the value of the bias current I1 increases in accordance with the increase in the output voltage Vout. Therefore, when the output voltage Vout increases, the feedback voltage Vfb decreases.

[0039] ==Resistors 61, 62== Resistors 61 and 62 output a voltage V1 to make it easier to detect the voltage Vis when the resonant current Icr is small. Resistors 61 and 62 output a voltage V1 that is A1 times the voltage Vis at terminal IS. Specifically, resistors 61 and 62 are voltage divider resistors that divide the difference ΔVis between a predetermined voltage Vdd and the voltage Vis using a voltage division ratio corresponding to A1, and output it as voltage V1.

[0040] Furthermore, resistors 61 and 62 are connected in series between the node to which a predetermined voltage Vdd is applied and terminal IS, and output voltage V1 from the connection point. As will be explained in more detail later, if the resistance value of resistor 61 is 4 × R1 and the resistance value of resistor 62 is R1, then A1 will be 0.8. Terminal IS corresponds to the "first terminal," and resistors 61 and 62 correspond to the "first voltage output circuit" and the "first voltage divider resistor circuit," respectively. Voltage V1 corresponds to the "first voltage," and the difference ΔVis corresponds to the "first difference." A1 times corresponds to the "first time."

[0041] ==Diode 63== Diode 63 prevents the voltage at the connection point of resistors 61 and 62 from dropping further than the forward voltage even when the voltage at the connection point becomes negative. Therefore, the cathode of diode 63 is connected to the connection point of resistors 61 and 62, and the anode is grounded.

[0042] ==Resistors 64, 65== Resistors 64 and 65 output a voltage V2 to detect the voltage Vis when the resonant current Icr is large. Specifically, resistors 64 and 65 output a voltage V2 that is A2 times the voltage Vis at terminal IS. Furthermore, resistors 64 and 65 are a voltage divider resistor circuit that divides the difference ΔVis with a voltage division ratio corresponding to A2 and outputs it as voltage V2.

[0043] Furthermore, resistors 64 and 65 are connected in series between the node to which a predetermined voltage Vdd is applied and terminal IS, and output a voltage V2 from the connection point. As will be described in detail later, if the resistance value of resistors 64 and 65 is R2, then A2 is 0.5. Note that "A2 times" in this embodiment is smaller than "A1 times". Also, resistors 64 and 65 correspond to the "second voltage output circuit" and the "second voltage divider resistor circuit", and the voltage V2 corresponds to the "second voltage". Also, A2 times corresponds to "2 times".

[0044] <<<Operation of resistors 61, 62, 64, 65 and diode 63>>> Figure 3 shows an example of the relationship between voltage Vis and voltages V1 and V2. Resistors 61 and 62 output voltage V1 by multiplying the difference ΔVis between a predetermined voltage Vdd (for example, 5V) and voltage Vis by A1. In other words, voltage V1 is the voltage obtained by dividing the difference ΔVis by a voltage division ratio determined by the resistance values ​​of resistors 61 and 62.

[0045] As mentioned above, for example, let the resistance value of resistor 61 be 4 × R1 and the resistance value of resistor 62 be R1. In this case, as shown in Figure 3, when the voltage Vis changes between voltage Vismin and voltage Vismax (for example, -5V to 5V), without diode 63, the voltage V1 will change in the range of -3V to 5V. In this case, "A1" will be 0.8.

[0046] Furthermore, if the voltage Vis falls below, for example, -1.25V, the voltage V1 becomes negative. Also, if the voltage V1 falls below -0.3V, parasitic elements, for example, may activate in the internal circuitry of the control IC 40a, potentially causing circuit malfunction.

[0047] Therefore, in this embodiment, diode 63 is connected between the connection point of resistors 61 and 62 and ground, as shown in Figure 2. As a result, voltage V1 is clamped at a voltage that is only forward voltage lower than the ground voltage, thereby suppressing malfunctions in the internal circuit of control IC 40a. In addition, by not using negative voltage, the circuit of control IC 40a can be designed simply. Furthermore, due to the combination of resistors 61 and 62 and diode 63, voltage V1 changes according to voltage Vis, as shown by the dotted line in Figure 3.

[0048] Furthermore, resistors 64 and 65 output voltage V2 by multiplying the difference ΔVis between a predetermined voltage Vdd (for example, 5V) and voltage Vis by A2. In other words, voltage V2 is the voltage obtained by dividing the difference ΔVis by a voltage division ratio determined by the resistance values ​​of resistors 64 and 65.

[0049] For example, let R2 be the resistance value of resistor 64 and R2 be the resistance value of resistor 65. In this case, as shown in Figure 3, when the voltage Vis changes between voltage Vismin and voltage Vismax (for example, -5V to 5V), the voltage V2 changes in the range of 0V to 5V, as shown by the dashed line in Figure 3. In this case, "A2" is 0.5.

[0050] As mentioned above, even if the resonant current Icr is small (for example, the voltage Vis changes between 0V and 100mV), resistors 61 and 62 multiply the difference ΔVis by "A1 (for example, 0.8)", so the voltage V1 changes between 1V and 80mV.

[0051] On the other hand, resistors 64 and 65 multiply the difference ΔVis by "A2 (for example, 0.5 times)," so if the voltage Vis changes in the same way as above, the voltage V2 will change by 2.5V ± 50mV. Therefore, when the resonant current Icr is small, using the voltage V1 makes it easier for the control IC 40a to detect changes in the voltage Vis.

[0052] However, as will be discussed later regarding the overcurrent protection circuit (OCP) 71, if the voltage Vis corresponding to the resonant current Icr that causes overcurrent is a large negative voltage (for example, voltage Vis = Vismin), it becomes difficult to detect overcurrent based on voltage Vis if the voltage V1 from resistors 61 and 62 is used.

[0053] Therefore, in order to detect the voltage Vis when the resonant current Icr becomes an overcurrent, in addition to the voltage divider circuit consisting of resistors 61 and 62, a voltage divider circuit consisting of resistors 64 and 65 is provided.

[0054] Furthermore, if there is no limit on the voltage range of the internal circuit of the control IC 40a, A1 may be made larger, and the voltage based on the voltage Vis may be generated using only resistors 61 and 62. However, in reality, the voltage range is limited to a narrow range. Therefore, in this embodiment, resistors 61 and 62 are provided separately from resistors 64 and 65.

[0055] ==Resistors 66, 67== The resistors 66 and 67 in Figure 2 divide a predetermined voltage Vdd at a voltage division ratio corresponding to A1 and output a voltage V3. Specifically, resistors 66 and 67 are voltage divider resistors that divide the difference ΔVgnd between the predetermined voltage Vdd and the ground voltage at a voltage division ratio corresponding to A1 and output a voltage V3. Resistors 66 and 67 are connected in series between the node to which the predetermined voltage Vdd is applied and the terminal GND, and output a voltage V3 from the connection point. As will be described in detail later, voltage V3 is used so that the voltage generation circuit 72a (described later) can accurately output voltage Vca. Note that resistors 66 and 67 correspond to the "third voltage divider resistor circuit," the difference ΔVgnd corresponds to the "second difference," and voltage V3 corresponds to the "third voltage."

[0056] ==Oscillator Circuit 70== The oscillator circuit 70 is a voltage-controlled oscillator circuit that outputs an oscillation signal Vosc to the drive circuit 74 (described later) for switching NMOS transistors 24 and 25 based on the input feedback voltage Vfb. The oscillation signal Vosc is, for example, a signal with a high-level (hereinafter referred to as "H" level) duty cycle of 50%. The oscillator circuit 70 outputs a high-frequency oscillation signal Vosc when the voltage Vfb level becomes low.

[0057] ==Overcurrent protection circuit (OCP)71== The overcurrent protection circuit 71 detects whether the resonant current Icr is an overcurrent. Specifically, the overcurrent protection circuit 71 detects whether the resonant current Icr is an overcurrent based on the voltage V2. The overcurrent protection circuit 71 also detects that the resonant current Icr is an overcurrent if the voltage V2 falls outside a predetermined range. Here, "overcurrent" means a current large enough to destroy one of the NMOS transistors 24 and 25 if it flows through either of them (for example, a current larger than a predetermined rated current). The "predetermined range" is the range of voltage V2 when the resonant current Icr is not an overcurrent.

[0058] Furthermore, the overcurrent protection circuit 71 outputs a signal ocp to the drive circuit 74 to stop switching the NMOS transistor 24 or 25 when the resonant current Icr becomes an overcurrent. On the other hand, if the resonant current Icr is not an overcurrent, the overcurrent protection circuit 71 outputs a signal ocp to the drive circuit 74 to switch the NMOS transistor 24 or 25. The overcurrent protection circuit 71 corresponds to the "first detection circuit".

[0059] ==Voltage Generation Circuit 72a== The voltage generation circuit 72a generates a voltage Vca at terminal CA that indicates the state of the load 11, based on voltage V1 corresponding to the resonant current Icr and voltage V3.

[0060] Figure 4 shows an example of a voltage generation circuit 72a. The voltage generation circuit 72a is composed of resistors 80 and 81 and a charge / discharge circuit 82a.

[0061] ===Resistors 80, 81=== Resistors 80 and 81 divide the voltage Vs and generate the signal sw_ctrl at the connection point. When NMOS transistor 24 is on and NMOS transistor 25 is off, the voltage Vs becomes the input voltage Vin. When NMOS transistor 24 is off and NMOS transistor 25 is on, the voltage Vs becomes the ground voltage. In other words, the on / off state of NMOS transistors 24 and 25 causes the voltage Vs to become either the input voltage Vin or the ground voltage. Consequently, the logic level of the signal sw_ctrl changes depending on whether NMOS transistors 24 and 25 are on or off.

[0062] ===Charging / discharging circuit 82a=== The charge / discharge circuit 82a charges and discharges the capacitor 54 with voltages V1 and V3, and outputs a voltage Vca that indicates the state of the load 11. Specifically, the charge / discharge circuit 82a averages the voltage V1, which is based on the voltage Vis corresponding to the resonant current Icr of the primary coil L1 detected at terminal IS, across the capacitor 54 connected to terminal CA, and outputs a voltage Vca that indicates the state of the load 11. The charge / discharge circuit 82a averages the voltage V1 based on the positive resonant current Icr based on the signal sw_ctrl.

[0063] Furthermore, the charge / discharge circuit 82a switches the voltage at node A to either voltage V1 or voltage V3 based on the signal sw_ctrl. The charge / discharge circuit 82a then charges or discharges the capacitor 54 connected to terminal CA via resistor 93 (described later) and outputs voltage Vca.

[0064] Furthermore, the resonant current Icr of the primary coil L1 increases in accordance with the input power of the switching power supply circuit 10. Also, the input power of the switching power supply circuit 10 increases in accordance with the power consumed by the load 11. For this reason, the voltage Vca increases as the load 11 becomes heavier (i.e., as the load current Iout of the load 11 increases).

[0065] Furthermore, "Load 11 being under heavy load" refers to a situation where, for example, the load current Iout flowing through load 11 is greater than a predetermined value (e.g., 1A). "Load 11 being under light load" refers to a situation where, for example, the load current Iout flowing through load 11 is less than a predetermined value (e.g., 1A). "Load 11 being unloaded" refers to a situation where the load current Iout flowing through load 11 is extremely small or 0A. In addition, while it was explained that the load current Iout used to determine whether load 11 is under heavy load or light load is, for example, 1A, this current value can be set in various ways.

[0066] The charge / discharge circuit 82a is composed of switches 90, 92, an inverter 91, and a resistor 93.

[0067] Switch 90 is an element that turns on when a high-level signal sw_ctrl is input. When switch 90 is turned on, the voltage Va at node A, to which switches 90 and 92 are connected, becomes voltage V1.

[0068] Switch 92 is an element that turns on when a low-level signal (hereinafter referred to as "L" level) sw_ctrl is input and the inverter 91 outputs a "H" level signal. When switch 92 is turned on, the voltage Va at node A becomes voltage V3. The reason why voltage V3 is applied to node A is that if, for example, a ground voltage were applied to node A when switch 92 is turned on, the capacitor 54 would be excessively discharged, and the voltage generation circuit 72a would not be able to output an accurate voltage Vca according to the state of the load 11.

[0069] A resistor 93 is connected between node A and terminal CA, and together with capacitor 54 connected to terminal CA, resistor 93 forms an RC integrating circuit that operates with a time constant τ. Here, if the resistance value of resistor 93 is R3 and the capacitance value of capacitor 54 is C1, then the time constant τ = R3 × C1. Note that the time constant τ is assumed to be sufficiently longer than the period of the drive signals Vdr1 and Vdr2 that drive the NMOS transistors 24 and 25.

[0070] Therefore, when a "H" level signal sw_ctrl is input, the charge / discharge circuit 82a charges the capacitor 54 via the resistor 93 with a voltage V1 based on a positive resonant current Icr corresponding to the power consumption of the load 11.

[0071] On the other hand, when the charge / discharge circuit 82a receives the "L" level signal sw_ctrl, it discharges the capacitor 54 through the resistor 93 at voltage V3. Note that voltage V1 is generated by dividing the difference ΔVis, and even if voltage Vis becomes 0V, voltage V1 does not become 0V. Therefore, as described above, when discharging the capacitor 54, the voltage at node A is set to voltage V3. This suppresses excessive discharge of the capacitor 54 and allows for the output of a voltage Vca that more accurately indicates the state of the load 11.

[0072] Based on the above, the charge / discharge circuit 82a can average the voltage V1 and output a voltage Vca that indicates the state of the load 11. Note that terminal CA corresponds to the "second terminal," and voltage Vca corresponds to the "voltage at the second terminal."

[0073] ==Load detection circuit 73== The load detection circuit 73 in Figure 2 detects the state of the load 11 based on the voltage Vca. Specifically, when the voltage Vca falls below a predetermined voltage Vref_burst level and the state of the load 11 becomes light load, the load detection circuit 73 outputs a "H" level signal burst to the drive circuit 74, causing the NMOS transistors 24 and 25 to switch intermittently.

[0074] On the other hand, the load detection circuit 73 outputs an "L" level signal burst to the drive circuit 74 to continuously switch the NMOS transistors 24 and 25 if the voltage Vca is higher than a predetermined voltage Vref_burst and the state of the load 11 is not a light load. Details about continuous switching and intermittent switching will be explained later when the drive circuit 74 is described. The load detection circuit 73 corresponds to the "second detection circuit".

[0075] ===Drive Circuit 74=== The drive circuit 74 drives the NMOS transistors 24 and 25 based on the feedback voltage Vfb, voltage V1, and voltage V2 corresponding to the output voltage Vout.

[0076] When the load 11 is not in a light load state, the drive circuit 74 continuously switches the NMOS transistors 24 and 25 based on the oscillation signal Vosc output by the oscillation circuit 70 according to the level of the voltage Vfb, as shown in Figure 5. In this case, the drive circuit 74 does not intermittently stop the switching operation.

[0077] When the resonant current Icr becomes an overcurrent and the overcurrent protection circuit 71 outputs a signal ocp that stops switching the NMOS transistor 24 or 25, the drive circuit 74 turns off the NMOS transistor 24 or 25.

[0078] Furthermore, when the load 11 becomes a light load and the load detection circuit 73 outputs a "H" level signal burst, the drive circuit 74 intermittently switches the NMOS transistors 24 and 25 as shown in Figure 6.

[0079] Furthermore, "intermittent switching" means switching the NMOS transistors 24 and 25 in such a way that switching periods, in which the NMOS transistors 24 and 25 are continuously switched, and stop periods, in which the switching is intermittently stopped, are alternately repeated.

[0080] Furthermore, in Figures 5 and 6, the drive circuit 74 is depicted as generating drive signals Vdr1 and Vdr2 with a 50% duty cycle corresponding to the transmitted signal Vosc, and alternately outputting drive signals Vdr1 and Vdr2 at the "H" level. However, in reality, the drive circuit 74 outputs drive signals Vdr1 and Vdr2, which have a dead time between the change of drive signal Vdrv1 from the "H" level to the "L" level and the change of drive signal Vdr2 from the "L" level to the "H" level.

[0081] Furthermore, the drive circuit 74 outputs drive signals Vdr1 and Vdr2, which also have a dead time while the levels of the drive signals Vdr1 and Vdr2 are changing in opposite directions. In this way, the drive circuit 74 outputs drive signals Vdr1 and Vdr2, which are generated with a duty cycle of approximately 50% corresponding to the oscillation signal Vosc, and alternately become "H" level.

[0082] Note that in Figure 6, the number of pulses for drive signals Vdr1 and Vdr2 are shown to be the same during switching operation, but this is merely an example, and the number of pulses may be different. Here, "dead time" refers to the period during which both drive signals Vdr1 and Vdr2 are at the "L" level.

[0083] <<Operation of control IC 40a>> Figure 7 shows an example of the operation of the control IC 40a.

[0084] At time t0, the drive circuit 74 of the control IC 40a outputs a drive signal Vdr2 at the "L" level, and the NMOS transistor 25 turns off.

[0085] Subsequently, the negative resonant current Icr causes the voltage Vs at terminal VS to rise, becoming the input voltage Vin at time t1. Consequently, resistors 80 and 81 in Figure 4 generate a high-level signal sw_ctrl corresponding to the voltage Vs.

[0086] At this time, switch 90 in Figure 4 is turned on based on the "H" level signal sw_ctrl, and the voltage Va at node A becomes voltage V1.

[0087] At time t2, after the dead time has elapsed from time t0, the drive circuit 74 outputs a drive signal Vdr1 at the "H" level, and the NMOS transistor 24 turns on. Then, the voltage Vis corresponding to the resonant current Icr flowing in the positive direction becomes positive.

[0088] At time t3, after the drive circuit 74 outputs a "L" level drive signal Vdr1, the voltage Vs at terminal VS decreases to 0V due to the positive resonant current Icr. Consequently, resistors 80 and 81 in Figure 4 generate a "L" level signal sw_ctrl corresponding to the voltage Vs.

[0089] At this time, switch 92 in Figure 4 is turned on based on the "L" level signal sw_ctrl, and the voltage Va at node A becomes voltage V3. Then, the same operation is repeated from time t4 onwards.

[0090] In this way, the voltage generation circuit 72a outputs a voltage Vca based on the voltage V1 output by resistors 61 and 62 and the voltage V3 output by resistors 66 and 67. By using a voltage V1 obtained by multiplying the small fluctuation of voltage Vis by A1, the voltage value of voltage Vca can be larger than when voltage V2 is used, even when the load 11 is in a light load state. Furthermore, by using a voltage V3 obtained by multiplying voltage Vdd by A1, the capacitor 54 will not be excessively discharged when switch 92 is on, and a more accurate voltage Vca can be generated.

[0091] =====Other Embodiments===== <<<Details of control IC 40b>>> Figure 8 shows an example of control IC 40b. Like control IC 40a, control IC 40b is an integrated circuit that switches NMOS transistors 24 and 25 based on the magnitude of the resonant current Icr. Note that in Figure 8, the same reference numerals are used for components identical to those in Figure 2. Therefore, identical components will not be explained. Control IC 40b is configured to include resistors 68 and 69, a voltage generation circuit 72b, a comparator 75, and a selection circuit 76, in addition to those of control IC 40a.

[0092] ==Resistors 68, 69== Resistors 68 and 69 divide a predetermined voltage Vdd at a voltage division ratio corresponding to A² and output voltage V4. Specifically, resistors 68 and 69 are voltage divider resistors that divide the predetermined voltage Vdd and the difference ΔVgnd between it and the ground voltage at a voltage division ratio corresponding to A² and output voltage V4. Resistors 68 and 69 are connected in series between the node to which the predetermined voltage Vdd is applied and the terminal GND, and output voltage V4 from the connection point. As will be described in detail later, voltage V4 is used so that the voltage generation circuit 72b (described later) can accurately output voltage Vca. Note that resistors 68 and 69 correspond to the "fourth voltage divider resistor circuit," and voltage V4 corresponds to the "fourth voltage."

[0093] ==Comparator 75== The comparator 75 determines whether the voltage generation circuit 72b (described later) should use voltages V1 and V3 or voltages V2 and V4 when outputting voltage Vca, and controls the selection circuit 76. Specifically, the comparator 75 determines whether voltage Vca is higher than the reference voltage Vref0, and controls the selection circuit 76 based on the determination result. The reference voltage Vref0 is the level of voltage Vca when the load 11 is neither light load nor heavy load. The comparator 75 corresponds to the "determination circuit".

[0094] ==Selection Circuit 76== The selection circuit 76 selects the voltage to be applied to the voltage generation circuit 72b based on the judgment result of the comparator 75. Specifically, the selection circuit 76 selects voltages V2 and V4 when voltage Vca is higher than the reference voltage Vref0, that is, when the load 11 is in a heavy load state. On the other hand, the selection circuit 76 selects voltages V1 and V3 when voltage Vca is lower than the reference voltage Vref0, that is, when the load 11 is in a light load state.

[0095] ==Voltage Generation Circuit 72b== The voltage generation circuit 72b detects the state of the load 11 based on the magnitude of the resonant current Icr. Specifically, the voltage generation circuit 72b generates a voltage Vca at terminal CA that indicates the state of the load 11, based on the voltage selected by the selection circuit 76. In other words, the voltage generation circuit 72b uses voltages V2 and V4 when the state of the load 11 is a heavy load, and uses voltages V1 and V3 when the state of the load 11 is a light load. Here, the voltage selected from voltage V1 or voltage V2 is designated as voltage V5, and the voltage selected from voltage V3 or voltage V4 is designated as voltage V6.

[0096] Figure 9 shows an example of the voltage generation circuit 72b. The voltage generation circuit 72b is composed of resistors 80 and 81 and a charge / discharge circuit 82b. Note that resistors 80 and 81 are the same as in the case of the voltage generation circuit 72a.

[0097] ===Charging / discharging circuit 82b=== The charge / discharge circuit 82b charges and discharges the capacitor 54 with voltages V5 and V6, and outputs a voltage Vca indicating the state of the load 11. Specifically, the charge / discharge circuit 82b outputs the state of the load 11 as voltage Vca from voltage V5, which is based on voltage Vis corresponding to the resonant current Icr of the primary coil L1 detected at terminal IS, and voltage V6. The charge / discharge circuit 82b averages the voltage V5 based on the positive resonant current Icr based on the signal sw_ctrl.

[0098] The charge / discharge circuit 82b comprises switches 90, 92, an inverter 91, resistors 100, 103, 104, 106, 108, 110, a capacitor 101, and operational amplifiers 102, 105, 107, 109. Based on the signal sw_ctrl, the charge / discharge circuit 82b turns switches 90, 92 on and off, switching the voltage at node A to voltage V5 or voltage V6.

[0099] ====Resistor 100 and Capacitor 101==== The resistor 100 and capacitor 101 constitute a low-pass filter, stabilizing the voltage Va at node A.

[0100] ====Op-amp 102==== Operational amplifier 102 is a unity-gain buffer that outputs a voltage Va.

[0101] ====Op-amps 105, 107 and resistors 103, 104, 106, 108==== Operational amplifier 105 and resistors 103, 104, 106, and 108 constitute a differential amplifier circuit. Specifically, operational amplifier 105 and resistors 103, 104, 106, and 108 amplify and output the difference between the voltage Va from operational amplifier 102 and the voltage V6 from operational amplifier 107. Operational amplifier 107 is a unity-gain buffer that outputs voltage V6.

[0102] ====Op-amp 109 and resistor 110==== The operational amplifier 109 is a unity-gain buffer that outputs the voltage from the differential amplifier circuit, and outputs the voltage Vca via the resistor 110.

[0103] <<<Operation of control IC 40b>>> Figure 10 shows an example of the operation of control IC 40b. Note that the changes in drive signals Vdr1, Vdr2, voltage Vs, and signal sw_ctrl at each of the times t10-t14 and at each of the times t20-t24 are the same as the changes in these signals and voltages at each of the times t0-t4 in Figure 7. Therefore, only the parts of the operation at times t10-t14 and t20-t24 that differ from the operation at times t0-t4 in Figure 7 will be explained below.

[0104] Furthermore, the operation at times t10 to t14 is when the selection circuit 76 selects voltages V1 and V3, that is, when the load 11 is in a light load state. On the other hand, the operation at times t20 to t24 is when the selection circuit 76 selects voltages V2 and V4, that is, when the load 11 is in a heavy load state.

[0105] At time t11, switch 90 in Figure 9 is turned on based on the "H" level signal sw_ctrl, and the voltage Va at node A becomes voltage V5 (i.e., voltage V1).

[0106] At time t13, switch 92 in Figure 4 is turned on based on the "L" level signal sw_ctrl, and the voltage Va at node A becomes voltage V6 (i.e., voltage V3). Then, from time t14 onwards, the same operation is repeated.

[0107] Between times t10 and t14, the voltage Va at node A of the charge / discharge circuit 82b is generated from voltages V1 and V3. Furthermore, since voltages V1 and V3 are voltages obtained by multiplying voltage Vis and voltage Vdd by A1, respectively, the voltage generation circuit 72b can output voltage Vca that better reflects small fluctuations in voltage Vis.

[0108] At time t21, switch 90 in Figure 9 is turned on based on the "H" level signal sw_ctrl, and the voltage Va at node A becomes voltage V5 (i.e., voltage V2).

[0109] At time t23, switch 92 in Figure 4 is turned on based on the “L” level signal sw_ctrl, and the voltage Va at node A becomes voltage V6 (i.e., voltage V4). Then, from time t24 onwards, the same operation is repeated.

[0110] Between times t20 and t24, the voltage Va at node A of the charge / discharge circuit 82b is generated from voltages V2 and V4. Furthermore, since voltages V2 and V4 are voltages obtained by multiplying voltage Vis and voltage Vdd by A2, the voltage generation circuit 72b can output a voltage Vca that better reflects the state of the load 11 when voltage Vis fluctuates significantly.

[0111] In this way, the voltage generation circuit 72b outputs a voltage Vca based on voltages V1 to V4. Voltages V1 and V3 are voltages obtained by multiplying voltages Vis and Vdd by A1, while voltages V2 and V4 are voltages obtained by multiplying voltages Vis and Vdd by A2. By using voltages multiplied by A1 or A2 in this way, the voltage generation circuit 72b can output a more accurate voltage Vca from the state of the load 11, from light load to heavy load.

[0112] Furthermore, when the load 11 is under heavy load conditions, the resonant current Icr is large, and the voltage Vis fluctuates significantly, the voltage generation circuit 72b outputs a voltage Vca using a voltage V2 which is a voltage Vis multiplied by A2, which is smaller than A1. By using a voltage V2 which is a voltage Vis multiplied by A2, the voltage generation circuit 72b can output a voltage Vca without saturating it, even when the voltage Vis fluctuates significantly.

[0113] ===Summary=== The switching power supply circuit 10 of this embodiment has been described above. The control IC 40a includes an IS terminal, resistors 61 and 62, resistors 64 and 65, and a drive circuit 74. Resistors 61 and 62 output a voltage V1 that is "A1 times" the voltage Vis. Therefore, even when the load 11 is in a light load state and the resonant current Icr is small, the control IC 40a can output a voltage Vca that more accurately reflects the change in voltage Vis. This makes it possible to provide an integrated circuit that can accurately detect the resonant current even when the load state is light load.

[0114] Furthermore, resistors 61, 62 and 64, 65 constitute a voltage divider circuit. Therefore, by making the voltage division ratios of the two voltage divider circuits different, two different multipliers can be achieved.

[0115] Furthermore, the control IC 40a includes a diode between the connection point of resistors 61 and 62 and ground. Therefore, even if the voltage difference ΔVis is divided by resistors 61 and 62, it is possible to suppress the voltage V1 from becoming a large negative voltage. This can suppress malfunctions in the internal circuitry of the control IC 40a.

[0116] Furthermore, the control IC 40a includes terminal CA, resistors 66 and 67, and a voltage generation circuit 72a. Resistors 66 and 67 have the same voltage division ratio as resistors 61 and 62. As a result, the voltage generation circuit 72a can more accurately generate the voltage Vca that indicates the state of the load 11.

[0117] Furthermore, the control IC 40a is equipped with an overcurrent protection circuit 71. The overcurrent protection circuit 71 detects overcurrent based on the voltage V2 output by resistors 64 and 65. Therefore, when the resonant current Icr is large, the overcurrent is detected by the voltage V2 divided by a voltage division ratio corresponding to "A2 times". As a result, the two voltage divider resistor circuits can be used for different purposes depending on whether the resonant current Icr is small or large.

[0118] Furthermore, the control IC 40a includes a load detection circuit 73. This allows the state of the load 11 to be detected based on a highly accurate voltage Vca, even when the resonant current Icr is small.

[0119] Furthermore, the control IC 40b includes resistors 68 and 69, a comparator 75, and a selection circuit 76. This allows the control IC 40b to output a voltage Vca based on the voltage output of a voltage divider resistor circuit having different voltage division ratios depending on the level of the voltage Vca. Also, by using a voltage V2 obtained by multiplying the voltage Vis by A2, the voltage generation circuit 72b can output a voltage Vca without saturating it, even when the voltage Vis fluctuates greatly.

[0120] The embodiments described above are provided to facilitate understanding of the present invention and are not intended to limit its interpretation. Furthermore, the present invention may be modified or improved without departing from its spirit, and it goes without saying that the present invention includes equivalents thereof. [Explanation of symbols]

[0121] 10 Switching power supply circuit 11 Load 20, 21, 22, 32, 51, 53, 54, 101 Capacitors 23, 60~62, 64~69, 80, 81, 93, 100, 103, 104, 106, 108, 110 Resistors 24,25 NMOS transistors 26 transformers 27 Control Block 30, 31, 50, 63 diodes 33 Constant Voltage Circuit 34 Light-emitting diodes 52 Phototransistors 70 Oscillator Circuit 71 Overcurrent protection circuit 72a, 72b Voltage generation circuit 73 Load detection circuit 74 Drive Circuit 75 Comparator 76 Selection Circuit 82a,82b Charge / discharge circuit 90, 92 switches 91 Inverter 102, 105, 107, 109 operational amplifiers

Claims

1. An integrated circuit for driving a switching element in a resonant power supply circuit comprising a resonant circuit in which a coil and a capacitor are connected in series, and a switching element for controlling the resonant current flowing through the resonant circuit, A first terminal to which a voltage corresponding to the resonant current is applied, A first voltage output circuit that outputs a first voltage which is a first predetermined multiplier of the first difference between a first predetermined voltage and the voltage of the first terminal, A second voltage output circuit outputs a second voltage which is smaller than the first predetermined multiplier of the first difference, and which is a second predetermined multiplier of the second difference between the second predetermined voltage and the voltage of the first terminal, A load detection circuit for detecting the load state of the power supply circuit, A drive circuit that drives the switching element based on a feedback voltage corresponding to the output voltage of the power supply circuit, the first voltage, and the second voltage, Equipped with, The aforementioned drive circuit is The drive method is switched upon receiving a signal output from the load detection circuit that indicates whether the load current of the load is less than a predetermined value, or whether it is a light load. When the load current is less than the predetermined value (light load), the switching element is driven based on the feedback voltage and the first voltage; when the load current is greater than the predetermined value (heavy load), the switching element is driven based on the feedback voltage. Integrated circuit.

2. The integrated circuit according to claim 1, The first voltage output circuit is, This is a first voltage divider resistor circuit that divides the first difference between a first predetermined voltage and the voltage of the first terminal by a voltage division ratio corresponding to the first predetermined magnification, and outputs it as the first voltage. The aforementioned second voltage output circuit is, This is a second voltage divider resistor circuit that divides the second difference using a voltage division ratio corresponding to the second predetermined magnification and outputs it as the second voltage. Integrated circuit.

3. The integrated circuit according to claim 2, An integrated circuit comprising a diode whose cathode is connected to the output of the first voltage divider resistor circuit and whose anode is grounded.

4. The integrated circuit according to claim 3, The second terminal and, A third voltage divider resistor circuit outputs a third voltage by dividing the third difference between the first predetermined voltage and the ground voltage at a voltage division ratio corresponding to the first predetermined multiplier, A voltage generation circuit that generates a voltage at the second terminal indicating the state of the load of the power supply circuit based on the first and third voltages, An integrated circuit equipped with the following features.

5. The integrated circuit according to claim 4, The system includes a first detection circuit that detects whether the resonant current is an overcurrent based on the second voltage, The drive circuit turns off the switching element when the resonant current becomes an overcurrent. Integrated circuit.

6. The integrated circuit according to claim 5, The system includes a second detection circuit that detects the state of the load based on the voltage of the second terminal, The drive circuit intermittently switches the switching element when the load state becomes a light load. Integrated circuit.

7. An integrated circuit according to any one of claims 4 to 6, A fourth voltage divider resistor circuit divides the third difference using a voltage division ratio corresponding to the second predetermined magnification and outputs it as a fourth voltage, A determination circuit that determines whether the voltage at the second terminal is higher than the reference voltage, A selection circuit that selects the second voltage and the fourth voltage when the voltage at the second terminal is higher than the reference voltage, and selects the first voltage and the third voltage when the voltage at the second terminal is lower than the reference voltage, Equipped with, The voltage generation circuit is Based on the selected voltage, a voltage indicating the state of the load is generated at the second terminal. Integrated circuit.

8. It is a resonant power supply circuit, A resonant circuit in which a coil and a capacitor are connected in series, A switching element that controls the resonant current flowing through the aforementioned resonant circuit, An integrated circuit that switches the aforementioned switching element, Equipped with, The aforementioned integrated circuit is A first terminal to which a voltage corresponding to the resonant current is applied, A first voltage output circuit that outputs a first voltage which is a first predetermined multiplier of the first difference between a first predetermined voltage and the voltage of the first terminal, A second voltage output circuit outputs a second voltage which is smaller than the first predetermined multiplier of the first difference, and which is a second predetermined multiplier of the second difference between the second predetermined voltage and the voltage of the first terminal, A load detection circuit for detecting the load state of the power supply circuit, A drive circuit that drives the switching element based on a feedback voltage corresponding to the output voltage of the power supply circuit, the first voltage, and the second voltage, Includes, The aforementioned drive circuit is The drive method is switched upon receiving a signal output from the load detection circuit that indicates whether the load current of the load is less than a predetermined value, or whether it is a light load. When the load current is less than the predetermined value (light load), the switching element is driven based on the feedback voltage and the first voltage; when the load current is greater than the predetermined value (heavy load), the switching element is driven based on the feedback voltage. power circuit.

9. The integrated circuit according to claim 1, The load detection circuit outputs the signal to the drive circuit based on the first voltage or the second voltage. The aforementioned drive circuit is When the load current is less than the predetermined value (light load), the switching element is driven based on the feedback voltage and the first voltage; when the load current is greater than the predetermined value (heavy load), the switching element is driven based on the feedback voltage and the second voltage. Integrated circuit.

10. An integrated circuit according to claim 1, The system includes a first detection circuit that detects whether the resonant current is an overcurrent based on the second voltage, The drive circuit turns off the switching element when the resonant current becomes an overcurrent. Integrated circuit.

11. An integrated circuit according to claim 9, The drive circuit drives the switching element to switch intermittently when there is a light load, and drives the switching element to switch continuously when there is a heavy load. Integrated circuit.

12. The integrated circuit according to claim 9, The system includes a comparator for determining the magnitude of the resonant current, The load detection circuit uses the first voltage when the comparator determines that the resonant current is smaller than a predetermined current, and uses the second voltage when the comparator determines that the resonant current is larger than the predetermined current. Integrated circuit.

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