Power supply circuit, power supply device

Abstract

To provide a power supply circuit and a power supply device that reduce power consumption of the power supply circuit for generating an output voltage of a predetermined level from an AC voltage.SOLUTION: A power supply circuit is a step-down power supply circuit for generating an output voltage of a predetermined level from an AC voltage and includes a rectifier circuit for rectifying the AC voltage, a first line connected to the rectifier circuit without an inductor as an electrical element, a second line on the ground side, a switch connected between the first and second lines, and a control circuit for controlling the switch so that the level of the output voltage becomes the predetermined level.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a power supply circuit and a power supply device. [Background technology]

[0002] There are power supply circuits that generate an output voltage of a predetermined level from an AC voltage (for example, Patent Documents 1 to 5). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-096902 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-153451 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-193018 [Patent Document 4] Japanese Patent Application Laid-Open No. 2014-220867 [Patent Document 5] Japanese Patent Application Laid-Open No. 2014-233129 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, some power supply circuits use Zener diodes to generate an output voltage at a predetermined level.

[0005] However, in general, in a power supply circuit using a Zener diode, when generating an output voltage of a predetermined level, a current flows steadily through the Zener diode, making it difficult to reduce power consumption.

[0006] The present invention has been made in view of the above-mentioned problems in the prior art, and has as its object to reduce the power consumption of a power supply circuit that generates an output voltage of a predetermined level from an AC voltage. [Means for solving the problem]

[0007] The main power supply circuit of the present invention that solves the above-mentioned problems is a step-down power supply circuit that generates an output voltage of a predetermined level from an AC voltage, and includes a rectifier circuit that rectifies the AC voltage, a first line connected to the rectifier circuit without passing through an inductor as an electric element, a second line on the ground side, a switch connected between the first and second lines, and a control circuit that controls the switch so that the level of the output voltage becomes the predetermined level.

[0008] The power supply device of the present invention, which primarily solves the above-mentioned problems, is a power supply device comprising a first step-down power supply circuit that generates a first output voltage of a predetermined level from an AC voltage, a second step-up power supply circuit that generates a second output voltage from the AC voltage, and a first control circuit, wherein the first power supply circuit comprises a first rectifier circuit that rectifies the AC voltage, a first line connected to the first rectifier circuit without passing through an inductor as an electric element, a second line on the ground side, a first switch connected between the first and second lines, and a first control circuit that controls the first switch so that the level of the first output voltage becomes the predetermined level. the second power supply circuit comprises a second switch having one end to which the AC voltage is applied, a second rectifier circuit to which the other end of the second switch is connected and which rectifies the AC voltage when the second switch is turned on, and an output circuit including an inductor connected to the second rectifier circuit and a third switch which controls a current flowing through the inductor, and which outputs the second output voltage based on the second rectified voltage from the second rectifier circuit, and the first control circuit operates using the first output voltage as a power supply voltage and controls the second switch based on a predetermined instruction. [Effects of the Invention]

[0009] According to the present invention, it is possible to reduce the power consumption of a power supply circuit that generates an output voltage of a predetermined level from an AC voltage. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram illustrating an example of a power supply device 10. FIG. [Figure 2] FIG. 2 is a diagram illustrating an example of a power supply circuit 12. [Figure 3] 3 is a diagram showing an example of a current path during a charging operation of the power supply circuit 12. FIG. [Figure 4] 10 is a diagram showing an example of a current path during reflux operation of the power supply circuit 12. FIG. [Figure 5] FIG. 2 is a diagram illustrating an example of a power factor correction circuit 20. [Figure 6] 2 is a diagram illustrating an example of an LLC resonant circuit 21. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] At least the following matters will become clear from the description of this specification and the accompanying drawings.

[0012] =====This embodiment===== <<<Outline of Power Supply Unit 10>>> 1 is a diagram showing an example of a power supply device 10. The power supply device 10 is used, for example, as a power supply for a television (not shown). The power supply device 10 includes power supply circuits 12 and 13, a load 14, a microcomputer (MCU) 15, a capacitor 16, a photodiode 17, and a switch 18. Note that nodes N0 and N1 are input nodes of the power supply circuit 12, and nodes N2 and N3 are input nodes of the power supply circuit 13.

[0013] An AC power supply 11 supplies an AC voltage Vac to power supply circuits 12 and 13. The power supply circuit 12 is a step-down power supply circuit that steps down the AC voltage Vac applied to nodes N0 and N1 to generate an output voltage Vdd. Here, the effective value of the AC voltage Vac is 100 to 240 V, and the voltage value of the output voltage Vdd is approximately 5 V to 10 V.

[0014] The power supply circuit 13 generates an output voltage Vout from an AC voltage Vac applied to nodes N2 and N3, and supplies power to a load 14 (for example, a television).

[0015] The microcomputer 15 controls the power supply device 10 based on instructions from the user. The microcomputer 15 operates by receiving the output voltage Vdd from the power supply circuit 12, and the capacitor 16 is provided to stabilize the output voltage Vdd.

[0016] Furthermore, when the microcomputer 15 receives a signal transmitted from a remote control (not shown) to cause the photodiode 17 to turn on the load 14, it sends a signal SW_sig to turn on the switch 18, which functions as a relay. As a result, the switch 18 is turned on, and the AC voltage Vac is applied to the power supply circuit 13. Thereafter, the microcomputer 15 sends a signal Wup_sig to the power supply circuit 13 to start up the power supply circuit 13. Then, upon receiving the signal Wup_sig to start up the power supply circuit 13, the power supply circuit 13 starts up and supplies power to the load 14.

[0017] On the other hand, when the photodiode 17 receives a signal transmitted from the remote control to turn off the load 14, the microcomputer 15 sends a signal SW_sig to turn off the switch 18. As a result, the switch 18 turns off, and the supply of the AC voltage Vac to the power supply circuit 13 is stopped. Thereafter, the power supply circuit 13 stops supplying power to the load 14, and the load 14 enters a standby state. The microcomputer 15 will be described in detail later. The power supply circuit 12 corresponds to the "power supply circuit" and the "first power supply circuit," and the microcomputer 15 corresponds to the "first load."

[0018] <<<Outline of Power Supply Circuit 12>>> FIG. 2 is a diagram illustrating an example of the power supply circuit 12. The power supply circuit 12 is a step-down power supply circuit that steps down the AC voltage Vac applied to nodes N0 and N1 to generate a DC power supply voltage Vdd for the microcomputer 15. The power supply circuit 12 can supply a maximum power P1 to the microcomputer 15. The power supply circuit 12 includes capacitors 30, 31, and 39, diodes 32 to 36, a control IC 37, and an NMOS transistor 38. The power supply circuit 12 is a circuit that generates the power supply voltage Vdd without including a coil (i.e., an inductor) as an electric element. The power supply voltage Vdd corresponds to the "output voltage" and the "first output voltage." The maximum power P1 corresponds to the "first power" that the power supply circuit 12 can supply to a load.

[0019] Capacitors 30 and 31 are used to remove noise generated in power supply circuit 12, limit the current from AC power supply 11, remove the DC component of AC voltage Vac, convert AC voltage Vac to current, etc. Capacitor 30 corresponds to the "first capacitor," and capacitor 31 corresponds to the "second capacitor."

[0020] The diodes 32 to 35 constitute a full-wave rectifier circuit RC0 that full-wave rectifies the AC voltage Vac. The full-wave rectifier circuit RC0 full-wave rectifies the AC voltage from the capacitors 30 and 31 and applies the rectified voltage Vrec0 to the anode of the diode 36 and the drain of the NMOS transistor 38, both of which are connected to the first line LN1. The cathodes of the diodes 32 and 33 are connected to the first line LN1 without a coil as an electric element, and the anodes of the diodes 34 and 35 are connected to the second line LN2 on the ground side. In other words, the power supply circuit 12 does not include a coil as an electric element between the full-wave rectifier circuit RC0 and the diode 36 (described later) (i.e., on the first line LN1). Here, the "electric element" refers to a so-called discrete electronic component. Therefore, "a state in which the first line LN1 is connected without a coil (or inductor) as an electrical element" means a state in which the diodes 32, 33 and the first line LN1 are connected without using any inductance other than the parasitic inductance of the wiring.

[0021] The anode of diode 32 and the cathode of diode 34 are connected to node N0 via capacitor 30. The anode of diode 33 and the cathode of diode 35 are connected to node N1 via capacitor 31. That is, AC voltage Vac is applied to capacitors 30 and 31. Diodes 32 to 35 correspond to a "rectifier circuit" and a "first rectifier circuit," and rectified voltage Vrec0 corresponds to a "first rectified voltage." The connection point between the anode of diode 32 and the cathode of diode 34 corresponds to a "first input terminal," and the connection point between the anode of diode 33 and the cathode of diode 35 corresponds to a "second input terminal."

[0022] Diode 36 prevents current from flowing back from capacitor 39 to the full-wave rectifier circuit RC0. Specifically, when the voltage at the anode of diode 36 is higher than the charging voltage of capacitor 39 by at least the forward voltage of diode 36, diode 36 turns on and supplies current to capacitor 39 to charge it.

[0023] On the other hand, when the voltage at the anode of diode 36 is lower than the charging voltage of capacitor 39, diode 36 turns off and stops supplying current to capacitor 39. As a result, in this case, capacitor 39 is not charged. Also, diode 36 has an anode connected to the first line LN1 and a cathode connected to capacitor 39.

[0024] <<<<<Details of Control IC37>>>> The control IC 37 controls the NMOS transistor 38 so that the power supply voltage Vdd is at a predetermined level. The control IC 37 includes resistors 40, 41, 45, and 46, a reference voltage circuit 42, a hysteresis comparator 43, and an NMOS transistor 44. The resistors 40 and 41 form a voltage divider circuit that divides the power supply voltage Vdd to generate a divided voltage Vdiv. The reference voltage circuit 42 outputs a reference voltage Vref0 to set the power supply voltage Vdd at a predetermined level.

[0025] The hysteresis comparator 43 compares the divided voltage Vdiv with a high threshold voltage VrefH and a low threshold voltage VrefL that correspond to the reference voltage Vref0, and turns on and off the NMOS transistor 44. The hysteresis comparator 43 has a high threshold voltage VrefH and a low threshold voltage VrefL that correspond to the reference voltage Vref0. The high threshold voltage VrefH is higher than the low threshold voltage VrefL.

[0026] Specifically, when the divided voltage Vdiv becomes higher than the high threshold voltage VrefH, the hysteresis comparator 43 outputs a low-level (hereinafter referred to as "L" level) signal Vhis to turn off the NMOS transistor 44.

[0027] On the other hand, when the divided voltage Vdiv becomes higher than the high threshold voltage VrefH and then becomes lower than the low threshold voltage VrefL, the hysteresis comparator 43 outputs a high-level (hereinafter referred to as “H” level) signal Vhis to turn on the NMOS transistor 44.

[0028] The level VL1 of the power supply voltage Vdd when the divided voltage Vdiv is at the low threshold voltage VrefL corresponds to the "first level," and the level VL2 of the power supply voltage Vdd when the divided voltage Vdiv is at the high threshold voltage VrefH corresponds to the "second level."

[0029] The resistors 45 and 46 generate a gate voltage Vg that changes depending on whether the NMOS transistor 44 is on or off. Specifically, when the NMOS transistor 44 is on, the resistors 45 and 46 generate a gate voltage Vg that turns off the NMOS transistor 38. On the other hand, when the NMOS transistor 44 is off, the resistors 45 and 46 generate a gate voltage Vg that turns on the NMOS transistor 38 in the linear region.

[0030] Therefore, when the power supply voltage Vdd reaches level VL1, the control IC 37 outputs a gate voltage Vg that turns off the NMOS transistor 38. On the other hand, when the power supply voltage Vdd reaches level VL2, the control IC 37 outputs a gate voltage Vg that turns on the NMOS transistor 38. Note that level VL2 is higher than level VL1.

[0031] <<<Charging current path in power supply circuit 12>>> The drain of the NMOS transistor 38 is connected to the first line LN1, and the source is connected to the second line LN2. The NMOS transistor 38 is controlled by a gate voltage Vg from the control IC 37 and operates as a switch. The NMOS transistor 38 is turned off when the power supply voltage Vdd reaches level VL1 (i.e., when the divided voltage Vdiv reaches the low threshold voltage VrefL). In this case, the rectified voltage Vrec0 is applied to the capacitor 39 via the diode 36. As a result, the capacitor 39 is charged with the rectified voltage Vrec0, generating the power supply voltage Vdd. The power supply voltage Vdd is, for example, 5 V. The current path in this case will be described in detail below with reference to FIG. 3.

[0032] 3 is a diagram showing an example of a current path during a charging operation of the power supply circuit 12. The current path shown by the dashed dotted line is the path of the current Ia when a positive AC voltage Vac is applied to the node N0. The current path shown by the dashed two dotted line is the path of the current Ib when a negative AC voltage Vac is applied to the node N0.

[0033] When the NMOS transistor 38 is turned off and a positive AC voltage Vac is applied to the node N0, a current Ia corresponding to the AC voltage Vac flows as shown by the dashed line.

[0034] Specifically, when the NMOS transistor 38 is turned off and the AC voltage Vac applied to the node N0 is a positive voltage, the current Ia input from the node N0 flows to the node N1 via the capacitor 30, the diodes 32 and 36, the capacitor 39, the diode 35, and the capacitor 31 in this order.

[0035] On the other hand, when the NMOS transistor 38 is turned off and a negative AC voltage Vac is applied to the node N0, a current Ib corresponding to the AC voltage Vac flows as shown by the two-dot chain line.

[0036] Specifically, when the NMOS transistor 38 is turned off and the AC voltage Vac applied to the node N0 is a negative voltage, the current Ib input from the node N1 flows to the node N0 via the capacitor 31, the diodes 33 and 36, the capacitor 39, the diode 34, and the capacitor 30 in this order.

[0037] Therefore, when the power supply voltage Vdd reaches the level VL1 and the NMOS transistor 38 turns off, the capacitor 39 is charged with currents Ia and Ib according to the AC voltage Vac. As a result, the power supply voltage Vdd rises from the level VL1.

[0038] <<<<Return current path in the power supply circuit 12>>> Furthermore, the NMOS transistor 38 turns on when the power supply voltage Vdd reaches the level VL2 (i.e., when the divided voltage Vdiv reaches the high threshold voltage VrefH). In this case, the rectified voltage Vrec0 is not applied to the capacitor 39 via the diode 36. Therefore, the capacitor 39 is not charged with the rectified voltage Vrec0. Instead, the NMOS transistor 38 returns a current corresponding to the rectified voltage Vrec0 to the AC power supply 11 via the diodes 32 to 35. The current path in this case will be described in detail below with reference to FIG. 4.

[0039] 4 is a diagram showing an example of a current path during reflux operation of the power supply circuit 12. The current path shown by the dashed dotted line is the path of the current Ic when a positive AC voltage Vac is applied to the node N0. The current path shown by the dashed double dotted line is the path of the current Id when a negative AC voltage Vac is applied to the node N0.

[0040] When the NMOS transistor 38 is turned on and a positive AC voltage Vac is applied to the node N0, a current Ic corresponding to the AC voltage Vac flows as shown by the dashed line.

[0041] Specifically, when the NMOS transistor 38 is turned on and the AC voltage Vac applied to the node N0 is a positive voltage, the current Ic input from the node N0 flows to the node N1 via the capacitor 30, the diode 32, the NMOS transistor 38, the diode 35, and the capacitor 31 in this order.

[0042] On the other hand, when the NMOS transistor 38 is turned on and a negative AC voltage Vac is applied to the node N0, a current Id corresponding to the AC voltage Vac flows as shown by the two-dot chain line.

[0043] Specifically, when the NMOS transistor 38 is turned on and the AC voltage Vac applied to the node N0 is a negative voltage, the current Id input from the node N1 flows to the node N0 via the capacitor 31, the diode 33, the NMOS transistor 38, the diode 34, and the capacitor 30 in this order.

[0044] Therefore, when the power supply voltage Vdd reaches the level VL2 and the NMOS transistor 38 turns on, the currents Ic and Id corresponding to the AC voltage Vac are circulated back to the AC power supply 11 via the NMOS transistor 38. As a result, the capacitor 39 is not charged with the currents Ic and Id corresponding to the AC voltage Vac. As a result, the power supply voltage Vdd drops from the level VL2.

[0045] From the above, when the power supply voltage Vdd is at level VL1, the control IC 37 supplies currents Ia and Ib from the AC power supply 11 to the capacitor 39 in order to charge the capacitor 39. On the other hand, when the power supply voltage Vdd is at level VL2, the control IC 37 returns the currents Ic and Id input from nodes N0 and N1 to the AC power supply 11. In this way, the control IC 37 can stably apply a predetermined level of the power supply voltage Vdd to the microcomputer 15 while reducing the power consumption of the power supply circuit 12.

[0046] Furthermore, the power supply voltage Vdd is generated by a capacitor 39 to which the rectified voltage Vrec0 is applied. Therefore, the charging voltage of the capacitor 39 (i.e., the power supply voltage Vdd) has a ripple component corresponding to the rectified voltage Vrec0, and the average of the charging voltage of the capacitor 39 becomes a predetermined level of the power supply voltage Vdd. The control IC 37 corresponds to the "control circuit" and the "second control circuit," and the NMOS transistor 38 corresponds to the "first switch."

[0047] <<<Outline of Power Supply Circuit 13>>> 1 again, power supply circuit 13 generates output voltage Vout from AC voltage Vac and supplies power to load 14 (e.g., a television). Power supply circuit 13 includes a power factor correction circuit 20 and an LLC resonant circuit 21. Power factor correction circuit 20 is an AC-DC converter that generates DC voltage Vdc from AC voltage Vac, and LLC resonant circuit 21 is a DC-DC converter that steps down DC voltage Vdc to generate output voltage Vout.

[0048] <<<<<Outline of Power Factor Correction Circuit 20>>>> FIG. 5 illustrates an example of a power factor correction circuit 20. The power factor correction circuit 20 is a boost chopper-type power supply circuit that generates a DC voltage Vdc of a target level from an AC voltage Vac of a commercial power supply. Here, the effective value of the AC voltage Vac is 100 to 240 V, and the voltage value of the DC voltage Vdc is approximately 400 V. That is, the power factor correction circuit 20 is a boost-type power supply circuit that boosts the AC voltage Vac to generate the DC voltage Vdc. The power factor correction circuit 20 can supply a maximum power P2 to the LLC resonant circuit 21. The power factor correction circuit 20 includes a full-wave rectifier circuit RC1 and an output circuit 50. The maximum power P2 corresponds to a "second power" that the power factor correction circuit 20 can supply to a load. Furthermore, 100 times the maximum power P1 is smaller than the maximum power P2. That is, the maximum power P2 is greater than the maximum power P1 by two or more orders of magnitude.

[0049] The output circuit 50 includes a coil L0, capacitors 51, 54, 60, and 61, an NMOS transistor 52, a diode 53, resistors 55, 57, 58, and 59, and an integrated circuit (IC) 56.

[0050] The full-wave rectifier circuit RC1 full-wave rectifies the predetermined AC voltage Vac applied to nodes N2 and N3 to generate a rectified voltage Vrec1, which is applied to capacitor 51 and coil L0. Here, the AC voltage Vac is, for example, a voltage of 100 to 240 V and a frequency of 50 to 60 Hz. The capacitor 51 is an element that smoothes the rectified voltage Vrec1. The full-wave rectifier circuit RC1 corresponds to the "second rectifier circuit," and the rectified voltage Vrec1 corresponds to the "second rectified voltage."

[0051] The rectified voltage Vrec1 is applied directly to one end of the coil L0, but may also be applied to the coil L0 via an element such as a resistor (not shown).

[0052] The coil L0, together with the NMOS transistor 52, the diode 53, and the capacitor 54, constitute a boost chopper circuit. Therefore, the charging voltage of the capacitor 54 becomes the DC voltage Vdc. The other end of the coil L0 is connected to the third line LN3, and the NMOS transistor 52 is connected as a switch between the third line LN3 and the fourth line LN4 on the ground side. When the NMOS transistor 52 is turned on, an inductor current IL corresponding to the rectified voltage Vrec1 flows through the coil L0. When the NMOS transistor 52 is turned on, the inductor current IL increases while the NMOS transistor 52 is on, at a rate determined by the inductance value of the coil L0 and the rectified voltage Vrec1.

[0053] Thereafter, when the NMOS transistor 52 turns off, a back electromotive force is generated in the coil L0, and while the back electromotive force is sufficient to turn on the diode 53, an inductor current IL flows from the coil L0 to the capacitor 54, charging the capacitor 54. The DC voltage Vdc is, for example, 400 V.

[0054] The resistor 55 is an element that converts the inductor current IL flowing through the coil L0 into a voltage and outputs it as a negative voltage. The negative voltage generated across the resistor 55 is applied to a terminal CS of an integrated circuit 56, which will be described later. The integrated circuit 56 detects the timing at which the inductor current IL stops flowing based on the negative voltage generated across the resistor 55, and turns on the NMOS transistor 52.

[0055] The integrated circuit 56 drives the NMOS transistor 52 so that the level of the DC voltage Vdc becomes a target level (for example, 400 V) while correcting the power factor of the power factor correction circuit 20. Specifically, the integrated circuit 56 drives the NMOS transistor 52 based on the inductor current IL and the DC voltage Vdc.

[0056] The integrated circuit 56 is provided with terminals VCC, FB, CS, COMP, OUT, and GND. The integrated circuit 56 is also provided with terminals other than the six terminals VCC, FB, CS, COMP, OUT, and GND described above, but these are omitted here for convenience.

[0057] The NMOS transistor 52 is a transistor for controlling power to the LLC resonant circuit 21. In this embodiment, the NMOS transistor 52 is a MOS (Metal Oxide Semiconductor) transistor, but is not limited to this. The NMOS transistor 52 may be, for example, a bipolar transistor, as long as it is a transistor that can control power. The gate of the NMOS transistor 52 is connected so as to be driven by a signal from the terminal OUT.

[0058] The resistors 57 and 58 form a voltage divider circuit that divides the DC voltage Vdc and generates a feedback voltage Vfb_a used to drive the NMOS transistor 52. The feedback voltage Vfb_a generated at the node to which the resistors 57 and 58 are connected is applied to the terminal FB.

[0059] Resistor 59 and capacitors 60, 61 are elements for phase compensation of feedback-controlled integrated circuit 56. Resistor 59 and capacitor 60 are connected in series between terminal COMP and ground, with capacitor 61 connected in parallel. The voltage generated at terminal COMP is designated voltage Vcomp. Voltage Vcomp decreases when DC voltage Vdc increases and feedback voltage Vfb_a increases, and increases when DC voltage Vdc decreases and feedback voltage Vfb_a decreases.

[0060] As described above, the negative voltage generated across the resistor 55 is applied to the terminal CS. A power supply voltage Vcc generated by the LLC resonant circuit 21 (described later) is applied to the terminal VCC, and the terminal GND is grounded. A start-up signal Wup_sig from the microcomputer 15 is input to the integrated circuit 56. When the start-up signal Wup_sig is input, the integrated circuit 56 starts up the power factor correction circuit 20.

[0061] As described above, the integrated circuit 56 operates to improve the power factor of the power factor correction circuit 20 and cause the power factor correction circuit 20 to output a DC voltage Vdc of a target level. Specifically, the integrated circuit 56 turns on the NMOS transistor 52 when the negative voltage generated across the resistor 55 becomes zero.

[0062] When the ramp voltage that rises when the NMOS transistor 52 is turned on reaches the voltage Vcomp corresponding to the feedback voltage Vfb_a, the integrated circuit 56 turns off the NMOS transistor 52. As a result, when the DC voltage Vdc rises, the voltage Vcomp drops, shortening the on-time of the NMOS transistor 52. Accordingly, when the NMOS transistor 52 is turned off, the back electromotive force generated in the coil L0 decreases, and the current that charges the capacitor 54 decreases.

[0063] On the one hand, when the DC voltage Vdc decreases, the voltage Vcomp increases, so the on-time of the NMOS transistor 52 is extended. Along with this, the back electromotive force generated in the coil L0 when the NMOS transistor 52 turns off increases, and the current charging the capacitor 54 increases. Thus, the integrated circuit 56 causes the power factor improvement circuit 20 to generate a DC voltage Vdc at the target level by adjusting the on-time of the NMOS transistor 52.

[0064] Here, the maximum value of the inductor current IL flowing through the coil L0 while the NMOS transistor 52 is on becomes a value corresponding to the rectified voltage Vrec1. Therefore, the average value of the inductor current IL is similar to the rectified voltage Vrec1 obtained by full-wave rectifying the AC voltage Vac. Note that while the frequency of the AC voltage Vac is 50 Hz or 60 Hz, the switching frequency of the NMOS transistor 52 is a frequency having a frequency range in units of kHz.

[0065] In other words, the power factor improvement circuit 20 makes the waveform of the AC voltage Vac applied to the nodes N2 and N3 and the waveform indicating the average of the input current input from the nodes N2 and N3 similar, thereby improving the power factor. Note that the power factor improvement circuit 20 corresponds to the "second power supply circuit". Also, the DC voltage Vdc corresponds to the "second output voltage", and the NMOS transistor 52 corresponds to the "third switch".

[0066] <<<<Overview of LLC Resonant Circuit 21>>>> FIG. 6 is a diagram showing an example of the LLC resonant circuit 21. The LLC resonant circuit 21 generates an output voltage Vout from the DC voltage Vdc. Also, the LLC resonant circuit 21 is an LLC current resonant type converter that generates an output voltage Vout at the target level from a predetermined DC voltage Vdc for the load 14.

[0067] The LLC resonant circuit 21 is composed of NMOS transistors 70 and 71, a transformer 72, capacitors 73, 77, 79, and 82, a detection circuit 74, an integrated circuit (IC) 75, a phototransistor 76, diodes 78, 80, and 81, a constant voltage circuit 83, and a light emitting diode 84.

[0068] The NMOS transistor 70 is a high-side power transistor, and the NMOS transistor 71 is a low-side power transistor. In this embodiment, the NMOS transistors 70 and 71 are used as switching elements, but they may also be PMOS transistors or bipolar transistors, for example.

[0069] The transformer 72 includes a primary coil L1, secondary coils L2 and L3, and an auxiliary coil La, and is insulated from the primary coil L1, the secondary coils L2 and L3, and the auxiliary coil La. In the transformer 72, a voltage is generated in the secondary coils L2 and L3 on the secondary side in response to a change in the voltage across the primary coil L1 on the primary side, and a voltage is generated in the auxiliary coil La on the primary side in response to a change in the voltage across the secondary coils L2 and L3.

[0070] The primary coil L1 has one end connected to the source of the NMOS transistor 70 and the drain of the NMOS transistor 71, and the other end connected to the source of the NMOS transistor 71 via a capacitor 73.

[0071] Therefore, when the NMOS transistors 70 and 71 start to be driven, there is a change in the voltage of each of the secondary coils L2 and L3 and the auxiliary coil La. The primary coil L1 and the secondary coils L2 and L3 are electromagnetically coupled with the same polarity, and the secondary coils L2 and L3 and the auxiliary coil La are also electromagnetically coupled with the same polarity.

[0072] The detection circuit 74 detects the resonance current Icr flowing through the capacitor 73. The detection circuit 74 outputs the polarity of the resonance current Icr to a later-described integrated circuit 75. The phototransistor 76, capacitors 77 and 79, and diode 78 will be described later.

[0073] Diodes 80 and 81 rectify the voltages of the secondary coils L2 and L3, and capacitor 82 smoothes the rectified voltage. As a result, a smoothed output voltage Vout is generated in capacitor 82. The output voltage Vout becomes a DC voltage at a target level.

[0074] The constant voltage circuit 83 is a circuit that generates a constant DC voltage, and is configured using, for example, a shunt regulator.

[0075] The light-emitting diode 84 is an element that emits light with an intensity corresponding to the difference between the output voltage Vout and the output of the constant voltage circuit 83, and together with the phototransistor 76 described below, constitutes a photocoupler. In this embodiment, as the level of the output voltage Vout increases, the intensity of the light emitted from the light-emitting diode 84 increases.

[0076] The integrated circuit 75 is an integrated circuit that drives the NMOS transistors 70 and 71, and has terminals VCC, GND, FB, IS, HO, and LO.

[0077] The terminal VCC is a terminal to which the power supply voltage Vcc for operating the integrated circuit 75 is applied. The terminal VCC is connected to the cathode of a diode 78 and a capacitor 79 with one end grounded. Therefore, the capacitor 79 is charged by a current from the diode 78, whose anode is connected to the auxiliary coil La, and the charging voltage of the capacitor 79 becomes the power supply voltage Vcc for operating the integrated circuit 75.

[0078] The terminal GND is a terminal to which a ground voltage is applied, and is connected to, for example, the housing of the device in which the power supply device 10 is installed.

[0079] The terminal FB is a terminal at which a feedback voltage Vfb_b corresponding to the output voltage Vout is generated, and is connected to a phototransistor 76 and a capacitor 77. The phototransistor 76 causes a bias current I1, the magnitude of which corresponds to the intensity of light from the light-emitting diode 84, to flow from the terminal FB to the ground, and the capacitor 77 is provided to remove noise between the terminal FB and the ground.

[0080] Therefore, the phototransistor 76 operates as a transistor that generates a sink current. The integrated circuit 75 also has an internal resistor (not shown) provided between the terminal FB and a power supply voltage (not shown). The feedback voltage Vfb_b is generated based on a voltage drop caused by the bias current I1 flowing through the resistor.

[0081] The terminal IS is a terminal to which a voltage corresponding to the current value of the resonance current Icr of the primary coil L1 is applied from the detection circuit 74.

[0082] The terminal HO is a terminal from which a drive signal Vdr1 for driving the NMOS transistor 70 is output, and the gate of the NMOS transistor 70 is connected.

[0083] Terminal LO is a terminal from which a drive signal Vdr2 for driving NMOS transistor 71 is output, and is connected to the gate of NMOS transistor 71. The integrated circuit 75 outputs drive signals Vdr1 and Vdr2 based on the polarity of the resonance current Icr detected by the detection circuit 74 to prevent so-called out-of-resonance. The drive signals Vdr1 and Vdr2 are pulse signals whose duty ratio is, in principle, constant (for example, 50%).

[0084] Furthermore, a start signal Wup_sig from the microcomputer 15 (described later) is input to the integrated circuit 75. When the start signal Wup_sig is input, the integrated circuit 75 starts up the LLC resonant circuit 21.

[0085] As described above, the integrated circuit 75 operates to cause the LLC resonant circuit 21 to generate an output voltage Vout at a target level. Specifically, when the output voltage Vout rises above the target level, the intensity of light from the light-emitting diode 84 increases, causing the bias current I1 to increase and the feedback voltage Vfb_b to decrease. In this case, the integrated circuit 75 increases the frequency of the drive signals Vdr1 and Vdr2 to decrease the gain, which is the ratio of the output voltage Vout to the DC voltage Vdc.

[0086] When the horizontal axis represents frequency and the vertical axis represents gain, the gain generally exhibits an upward convex shape with a peak at the resonance frequency of the coil L1 and capacitor 73. The frequencies of the drive signals Vdr1 and Vdr2 are set to be higher than the resonance frequency to prevent so-called out-of-resonance.

[0087] On the other hand, when the output voltage Vout falls below the target level, the intensity of light from the light-emitting diode 84 decreases, causing the bias current I1 to decrease and the feedback voltage Vfb_b to increase. In this case, the integrated circuit 75 decreases the frequency of the drive signals Vdr1 and Vdr2 to increase the gain.

[0088] As a result, the integrated circuit 75 causes the LLC resonant circuit 21 to generate an output voltage Vout at a target level. The LLC resonant circuit 21 corresponds to a "second load."

[0089] <<<Details of Microcomputer 15>>> 1 again, microcomputer 15 controls power supply device 10. Microcomputer 15 has terminals VDD, RCV, and GND. Power supply voltage Vdd from power supply circuit 12 is applied to terminal VDD, and microcomputer 15 operates using power supply voltage Vdd as a power supply voltage. In addition, capacitor 16 is provided between terminal VDD and ground to stabilize power supply voltage Vdd.

[0090] The photodiode 17 is provided between the terminal RCV and the ground, and receives, for example, an infrared signal from a television remote control (not shown). The microcomputer 15 controls the operation of the television based on the signal received by the photodiode 17.

[0091] When the photodiode 17 of the microcomputer 15 receives a signal transmitted from the remote control to turn on the television, the microcomputer 15 outputs a signal SW_sig that turns on the switch 18. When the switch 18 is turned on, an AC voltage Vac is applied to the nodes N2 and N3, and the AC voltage Vac is applied to the power supply circuit 13. Thereafter, the microcomputer 15 outputs a start-up signal Wup_sig to the integrated circuits 56 and 75 in the power supply circuit 13. The signal SW_sig corresponds to a "predetermined instruction," and the switch 18 corresponds to a "second switch."

[0092] This activates the power factor correction circuit 20 and LLC resonant circuit 21 in the power supply circuit 13, and power is supplied to the load 14 (for example, a television).

[0093] Meanwhile, when the photodiode 17 of the microcomputer 15 receives a signal transmitted from the remote control to turn off the television, the photodiode 17 outputs a signal SW_sig to turn off the switch 18. When the switch 18 is turned off, the AC voltage Vac is no longer applied to the nodes N2 and N3, so the power supply circuit 13 stops supplying power to the load 14 and the television enters standby mode.

[0094] Although the television is in standby mode, AC voltage Vac is still being applied to power supply circuit 12, and power supply circuit 12 continues to apply power supply voltage Vdd to microcomputer 15. This allows microcomputer 15 to operate even when the television is in standby mode and receive signals from the remote control. Microcomputer 15 corresponds to the "first control circuit."

[0095] ===Summary=== The power supply device 10 of this embodiment has been described above. The power supply circuit 12 includes a full-wave rectifier circuit RC0, an NMOS transistor 38, and a control IC 37. The control IC 37 controls the NMOS transistor 38 so that the power supply voltage Vdd is at a predetermined level. When the NMOS transistor 38 is turned on, the power supply circuit 12 returns an input current corresponding to the AC voltage Vac to the AC power supply 11. This allows the power supply circuit 12 to maintain the power supply voltage Vdd at a predetermined level without wasting power from the AC power supply 11. This reduces the power consumption of the power supply circuit that generates an output voltage at a predetermined level from an AC voltage.

[0096] The power supply circuit 12 also includes a diode 36 and a capacitor 39. When the voltage at the anode of the diode 36 is higher than the charging voltage of the capacitor 39 by at least the forward voltage of the diode 36, the diode 36 turns on and supplies current to the capacitor 39. As a result, the capacitor 39 is charged. On the other hand, when the voltage at the anode of the diode 36 is lower than the charging voltage of the capacitor 39, the diode 36 turns off and stops supplying current to the capacitor 39. As a result, the capacitor 39 is not charged. In this way, the diode 36 prevents current from flowing back from the capacitor 39 to the full-wave rectifier circuit RC0.

[0097] Furthermore, the control IC 37 turns off the NMOS transistor 38 when the level of the power supply voltage Vdd reaches level VL1, and turns on the NMOS transistor 38 when the level of the power supply voltage Vdd reaches level VL2. As a result, the control IC 37 charges the capacitor 39 when the level of the power supply voltage Vdd reaches level VL1, and returns current to the AC power supply 11 via the NMOS transistor 38 when the level of the power supply voltage Vdd reaches level VL2. This allows the power supply circuit 12 to generate a power supply voltage Vdd at a predetermined level.

[0098] The power supply circuit 12 also has a full-wave rectifier circuit RC0 as a rectifier circuit, which allows the power supply circuit 12 to efficiently use the power from the AC power supply 11 to generate a power supply voltage Vdd at a predetermined level.

[0099] The power supply circuit 12 also has an NMOS transistor 38 as a switch, which allows the power supply circuit 12 to turn on the NMOS transistor 38 in the linear region and limit the current value of the reflux current.

[0100] The power supply device 10 also includes power supply circuits 12 and 13, a switch 18, and a microcomputer 15. As a result, the microcomputer 15 can receive a signal transmitted from the remote control based on the power supply voltage Vdd applied by the power supply circuit 12, even when the television is in standby mode.

[0101] The above-described embodiments are intended to facilitate understanding of the present invention and are not intended to limit the present invention. Furthermore, the present invention may be modified or improved without departing from the spirit thereof, and the present invention includes equivalents thereof. [Explanation of symbols]

[0102] 10 Power supply 11 AC power supply 12,13 Power circuit 14 Load 15 Microcomputer 16,30,31,39,51,54,60,61,73,77,79,82 Capacitors 17 Photodiode 18 Switch 20 Power factor correction circuit 21 LLC resonant circuit 32~36,53,78,80,81 Diodes 38, 44, 52, 70, 71 NMOS transistors 40, 41, 45, 46, 55, 57, 58, 59 Resistance 42 Reference voltage circuit 43 Hysteresis Comparator 50 Output circuit 56,75 Integrated circuits 72 Transformer 74 Detection circuit 76 Phototransistor 83 Constant voltage circuit 84 Light-emitting diode RC0,RC1 Full wave rectifier circuit

Claims

1. A step-down power supply circuit that generates an output voltage of a predetermined level from an AC voltage, a full-wave rectifier circuit that rectifies the AC voltage; a first line connected to the full-wave rectifier circuit without an inductor serving as an electric element; a second line on the ground side; a switch connected between the first and second lines; a control circuit that controls the switch so that the level of the output voltage becomes the predetermined level; a diode having an anode connected to the first line; a capacitor connected to the cathode of the diode and the second line, through which the output voltage is generated; Equipped with The switch is connected to the first line between the full-wave rectifier circuit and the anode of the diode; The control circuit a voltage divider circuit connected to the cathode of the diode and the second line; Including, the control circuit controls the switch based on a divided voltage generated in the voltage divider circuit; one node of the capacitor is connected to a first point of the first line, and the other node is connected to a second point of the second line; one node of the voltage divider circuit is connected to a third point of the first line, and the other node is connected to a fourth point of the second line; The anode of the diode is connected to a fifth point of the first line, and the cathode of the diode is connected to a sixth point of the first line; One node of the switch is connected to a seventh point of the first line, and the other node is connected to an eighth point of the second line; The first point, the third point, the sixth point, the fifth point, and the seventh point are arranged in this order on the first line, The second point, the fourth point, and the eighth point are arranged in this order on the second line. power circuit.

2. 2. The power supply circuit according to claim 1, a first capacitor connected to a first input terminal of the full-wave rectifier circuit; a second capacitor connected to a second input terminal of the full-wave rectifier circuit; Equipped with The AC voltage is applied to the first and second capacitors. power circuit.

3. 3. The power supply circuit according to claim 1, the control circuit includes a hysteresis comparator that turns off the switch when the level of the output voltage reaches a first level, and turns on the switch when the level of the output voltage reaches a second level higher than the first level; another switch whose gate receives the output of the hysteresis comparator; another voltage dividing circuit receiving an output of the other switch; the other voltage dividing circuit has a first resistor having one node connected to the ninth point of the first line and another node connected to the tenth point, and a second resistor having one node connected to the tenth point and another node connected to the eleventh point of the second line, The output of the other switch is connected to the tenth point, The output of the tenth point is input to the switch, thereby controlling the on / off of the switch. power circuit.

4. The power supply circuit according to any one of claims 1 to 3, the switch is a MOS transistor having a drain connected to the first line and a source connected to the second line; power circuit.

5. A power supply device comprising: a first step-down power supply circuit that generates a first output voltage at a predetermined level from an AC voltage; a second step-up power supply circuit that generates a second output voltage from the AC voltage; and a first control circuit, The first power supply circuit a first full-wave rectifier circuit that rectifies the AC voltage; a first line connected to the first full-wave rectifier circuit without an inductor serving as an electric element; a second line on the ground side; a first switch connected between the first and second lines; a second control circuit that controls the first switch so that the level of the first output voltage becomes the predetermined level; a diode having an anode connected to the first line; a capacitor connected to the cathode of the diode and the second line, through which the first output voltage is generated; Including, The first switch is connected to the first line between the first full-wave rectifier circuit and the anode of the diode; The second control circuit is a voltage divider circuit connected to the cathode of the diode and the second line; Including, the second control circuit controls the first switch based on a divided voltage generated in the voltage divider circuit; one node of the capacitor is connected to a first point of the first line, and the other node is connected to a second point of the second line; one node of the voltage divider circuit is connected to a third point of the first line, and the other node is connected to a fourth point of the second line; The anode of the diode is connected to a fifth point of the first line, and the cathode of the diode is connected to a sixth point of the first line; one node of the first switch is connected to a seventh point of the first line, and the other node is connected to an eighth point of the second line; The first point, the third point, the sixth point, the fifth point, and the seventh point are arranged in this order on the first line, The second point, the fourth point, and the eighth point are arranged in this order on the second line. The second power supply circuit a second switch having one end to which the AC voltage is applied; a second rectifier circuit that rectifies the AC voltage when the other end of the second switch is connected and the second switch is turned on; an output circuit including an inductor connected to the second rectifier circuit and a third switch that controls a current flowing through the inductor, and that outputs the second output voltage based on a second rectified voltage from the second rectifier circuit; the first control circuit operates using the first output voltage as a power supply voltage and controls the second switch based on a predetermined instruction. power supply.

6. 6. The power supply device according to claim 5, a first power that the first power supply circuit can supply to a first load of the first power supply circuit is smaller than a second power that the second power supply circuit can supply to a second load of the second power supply circuit; power supply.

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