Power supply device

Abstract

To provide a power supply device that can simplify the circuit configuration.SOLUTION: A power supply device 12 includes a power conversion circuit 21, a bottom detection circuit 25, a control circuit 22, and a mask circuit 26. The power conversion circuit 21 includes a switching element Q1 connected to a DC power supply 20, a winding L1, and a capacitor C1, and switching of the switching element Q1 supplies output current to a light emitting element 11 connected in parallel to the capacitor C1. The bottom detection circuit 25 detects the minimum voltage point of the voltage on both ends of the switching element Q1 during the off period of the switching element Q1, and outputs a detection signal. The control circuit 22 turns off the switching element Q1 according to the output of the power conversion circuit 21, and turns on the switching element Q1 by the detection signal from the bottom detection circuit 25. The mask circuit 26 restricts the switching element Q1 from turning on until a predetermined period of time elapses from the time when the switching element Q1 turns on.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present invention relate to a power supply device.

Background Art

[0002] Conventionally, there is a power supply device for lighting a light emitting element, which includes a switching element connected to a DC power supply, a winding, and a capacitor, and has a power conversion circuit that supplies an output current to the light emitting element connected in parallel to the capacitor by switching the switching element.

[0003] In such a power conversion circuit, when the current in the winding becomes zero after the switching element is turned off, voltage oscillation occurs at both ends of the switching element. By detecting the minimum voltage point of this voltage oscillation and turning on the switching element, switching loss can be reduced and efficiency can be improved. However, when the load is in a light load state, the on-period of the switching element becomes short and the switching frequency becomes high, so the number of occurrences of switching loss when the switching element turns on and off increases.

[0004] There is also a power supply device including a load determination means for determining whether the load is in a light load state, a bottom skip state determination means for determining whether the bottom skip state due to the light load state has continued for a first predetermined time, and a bottom skip operation determination means for determining a bottom skip operation when the load is in a light load state and the bottom skip state has continued for the first predetermined time, and shifting to a bottom skip operation in which the switching element is turned on at the minimum voltage point after the second time detected by the bottom detection means from the quasi-resonance operation.

[0005] In this power supply device, a load determination means, a bottom skip state determination means, a bottom skip operation determination means, etc. are required, resulting in a complex circuit configuration.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2010-45939 [Overview of the project] [Problems that the invention aims to solve]

[0007] The problem that this invention aims to solve is to provide a power supply device that can simplify the circuit configuration. [Means for solving the problem]

[0008] The power supply device of the embodiment includes a power conversion circuit and , regulation Your circuit and ,of The power conversion circuit includes a switching element connected to a DC power supply, a winding, and a capacitor, and supplies output current to a light-emitting element connected in parallel to the capacitor by switching the switching element. The control circuit includes an output detection circuit that detects when the output of the power conversion circuit exceeds a reference voltage and outputs a detection signal; a bottom detection circuit that detects the minimum voltage point of the voltage across the switching element during the off period of the switching element and outputs a detection signal; a flip-flop that outputs an L-level signal from the signal output terminal when a detection signal from the output detection circuit is input to the reset terminal and outputs an H-level signal from the signal output terminal when a detection signal from the bottom detection circuit is input to the set terminal; a mask circuit that restricts the input of a detection signal from the bottom detection circuit to the set terminal for a predetermined period of time from the time the switching element is turned on; and a driver that turns on the switching element when an H-level signal is input from the flip-flop and turns off the switching element when an L-level signal is input from the flip-flop. [Effects of the Invention]

[0009] According to the power supply device of this embodiment, a simplification of the circuit configuration can be expected. [Brief explanation of the drawing]

[0010] [Figure 1] This is a circuit diagram of a power supply device showing one embodiment. [Figure 2] The above shows the mask period from the time the switching element of the power supply is turned on, with (a) being the waveform of the drain current of the switching element and (b) being the waveform of the voltage across the switching element. [Figure 3] The mask period from the time the switching element of the same power supply is turned off is shown, with (a) being the waveform of the drain current of the switching element and (b) being the waveform of the voltage across the switching element. [Modes for carrying out the invention]

[0011] One embodiment will be described below with reference to the drawings.

[0012] In Figure 1, 10 is a lighting device, which comprises a light-emitting element 11 and a power supply device 12 for lighting the light-emitting element 11. The lighting device 10 may be, for example, a base light, a downlight, or any other lighting equipment installed on the ceiling.

[0013] The light-emitting element 11 is, for example, a semiconductor light-emitting element such as an LED. One or more light-emitting elements 11 are used, and if multiple are used, the multiple light-emitting elements 11 are connected in series or in series-parallel.

[0014] Furthermore, the power supply unit 12 includes a DC power supply 20 that supplies DC power, a power conversion circuit 21 that converts the DC power supplied from the DC power supply 20 into lighting power for the light-emitting element 11, and a control circuit 22 that controls the power conversion circuit 21.

[0015] The DC power supply 20 supplies DC power to the power conversion circuit 21 and may be an AC / DC circuit that, for example, rectifies and smooths the AC voltage supplied from the AC power supply to obtain a DC voltage, and further boosts the DC voltage to improve the power factor.

[0016] The power conversion circuit 21 converts the DC power supplied from the DC power supply 20 into the power to illuminate the light-emitting element 11. For example, it is composed of a DC / DC circuit that includes a step-down chopper circuit that steps down the DC voltage supplied from the DC power supply 20 to a DC voltage that illuminates the light-emitting element 11.

[0017] The power conversion circuit 21 includes a switching element Q1, a transformer T1, a capacitor C1, a diode D1, and a resistor R1.

[0018] The switching element Q1 is, for example, an n-channel MOSFET. The drain of the switching element Q1 is connected to the high potential side of the DC power supply 20, the source is connected to one end side of the transformer T1 and the cathode of the diode D1, and is connected to the low potential side of the power conversion circuit 21 via these transformer T1 and capacitor C1, and the gate is connected to the control circuit 22.

[0019] The transformer T1 includes a primary winding L1 which is an inductor and a secondary winding L2. One end side of the primary winding L1 is connected to the source of the switching element Q1, and the other end side is connected to one end side of the capacitor C1. One end side of the secondary winding L2 is connected to the low potential side of the power conversion circuit 21, and the other end side is connected to the control circuit 22.

[0020] One end side of the capacitor C1 is connected to the other end side of the winding L1, and the other end side is connected to the low potential side of the power conversion circuit 21. The light emitting element 11 is connected in parallel across both ends of the capacitor C1. The anode of the light emitting element 11 is connected between the other end side of the winding L1 and one end side of the capacitor C1, and the cathode is connected to the other end side of the capacitor C1. <​​​​​​​​​When the switching element Q1 is turned on, the power conversion circuit 21 forms a closed circuit between the high-potential side and the low-potential side of the DC power supply 20 by the switching element Q1, the winding L1, the capacitor C1, the light-emitting element 11, and the resistor R1. When the switching element Q1 is turned off, the winding L1, the capacitor C1, the light-emitting element 11, the resistor R1, and the diode D1 form a closed circuit.

[0024] The control circuit 22 includes a bottom detection circuit 25, a mask circuit 26, an output detection circuit 27, a flip-flop 28, and a driver 29. The control circuit 22 may consist entirely of ICs, or some of its elements may be configured outside of ICs. Alternatively, all of its elements may consist entirely of analog circuits.

[0025] The bottom detection circuit 25 is connected to the other end of the secondary winding L2 of the transformer T1. It monitors the voltage across the switching element Q1 detected by this winding L2 (drain-source voltage), detects the minimum voltage point across the switching element Q1 during the off period of the switching element Q1, and outputs the detection signal to the set terminal S of the flip-flop 28 through the mask circuit 26.

[0026] The mask circuit 26 acquires turn-on and turn-off information of the switching element Q1 within the control circuit 22. The mask circuit 26 is equipped with a timer that starts timing from the moment the switching element Q1 turns on or turns off. The mask circuit 26 restricts the switching element Q1 from turning on for a predetermined period (predetermined time), which is the mask period, from the moment the switching element Q1 turns on or turns off until the mask period has elapsed. The restriction of the switching element Q1 from turning on by the mask circuit 26 in this embodiment is performed indirectly. For example, the mask circuit 26 is provided between the bottom detection circuit 25 and the set terminal S of the flip-flop 28. During the mask period, the detection signal output from the bottom detection circuit 25 is disabled so that it is not output to the set terminal S of the flip-flop 28, and after the mask period has elapsed, the detection signal output from the bottom detection circuit 25 is output to the set terminal S of the flip-flop 28. The mask period is a period slightly shorter than the period of one cycle of the predetermined switching frequency of the switching element Q1.

[0027] The output detection circuit 27 uses, for example, a comparator to receive a detection voltage corresponding to the current flowing between the resistor R1 and the capacitor C1. This detection voltage is compared with a predetermined reference voltage, and if the detection voltage exceeds the reference voltage, a detection signal is output to the reset terminal R of the flip-flop 28. The output detection circuit 27 may also detect the output current flowing through the light-emitting element 11 as described above, or it may detect the output voltage supplied from the winding L1 to the light-emitting element 11. It is sufficient that the output of the power conversion circuit 21, including the output current or output voltage, can be detected.

[0028] The flip-flop 28 has a set terminal S to which the bottom detection circuit 25 is connected via the mask circuit 26, a reset terminal R to which the output detection circuit 27 is connected, and a signal output terminal Q to which a signal is output to the driver 29. When a detection signal from the output detection circuit 27 is input to the reset terminal R, the flip-flop 28 outputs a low-level signal from the signal output terminal Q to the driver 29, and when a detection signal from the bottom detection circuit 25 is input to the set terminal S via the mask circuit 26, the flip-flop 28 outputs a high-level signal from the signal output terminal Q to the driver 29.

[0029] The driver 29 drives the gate of the switching element Q1 in response to the signal input from the flip-flop 28, thereby switching the switching element Q1. When the driver 29 receives a high-level signal from the flip-flop 28, it outputs a high-level drive signal to the gate of the switching element Q1, turning it on. When the driver 29 receives a low-level signal from the flip-flop 28, it outputs a low-level drive signal to the gate of the switching element Q1, turning it off.

[0030] Therefore, the control circuit 22 turns off the switching element Q1 in response to the output of the power conversion circuit 21, that is, in response to the detection signal from the output detection circuit 27, and turns on the switching element Q1 in response to the detection signal from the bottom detection circuit 25.

[0031] Next, the operation of the power supply unit 12 will be explained.

[0032] When the switching element Q1 is turned on, a DC current from the DC power supply 20 flows through the winding L1 to the capacitor C1 and the light-emitting element 11, causing the light-emitting element 11 to light up. When the switching element Q1 is turned off, the potential stored in the winding L1 is released, causing a DC current from the winding L1 to flow to the light-emitting element 11, and also flowing back to the winding L1 through the diode D1, causing the light-emitting element 11 to light up. During dimming, the brightness of the light-emitting element 11 is adjusted by changing the on-period of the switching element Q1.

[0033] Next, the specific operation of the power supply unit 12 will be explained with reference to Figures 2 and 3. Figure 2 shows the mask period m from the time of turn-on, where (a) is the waveform of the drain current of the switching element Q1 and (b) is the waveform of the voltage across the switching element Q1 (drain-source voltage). Figure 3 shows the mask period m from the time of turn-off, where (a) is the waveform of the drain current of the switching element Q1 and (b) is the waveform of the voltage across the switching element Q1 (drain-source voltage). Note that while Figures 2(a) and 3(a) show the on and off states of the switching element Q1, the timing of the change in the voltage across the switching element Q1 in Figures 2(b) and 3(b) is also linked to the on and off states of the switching element Q1 shown in Figures 2(a) and 3(a).

[0034] In Figures 2 and 3, when the off-state switching element Q1 is turned on, the drain current gradually increases according to the inductance value of the winding L1, and output current flows to the light-emitting element 11.

[0035] When the output current flowing through the light-emitting element 11 reaches a predetermined current value and the detection voltage detected by the output detection circuit 27 exceeds the reference voltage, the output detection circuit 27 outputs a detection signal to the reset terminal R of the flip-flop 28. When the detection signal is input to the reset terminal R of the flip-flop 28, it outputs an L-level signal from the signal output terminal Q to the driver 29. The driver 29 receives the L-level signal from the flip-flop 28 and outputs an L-level drive signal to the gate of the switching element Q1, causing it to turn off.

[0036] When the switching element Q1 is turned off, the potential accumulated in the winding L1 begins to be released, and current flows from the winding L1 to the light-emitting element 11 and also flows back to the winding L1 through the diode D1, causing the voltage across the switching element Q1 to rise.

[0037] When the potential accumulated in winding L1 becomes zero (timing t1 in Figures 2 and 3), a voltage oscillation occurs in which the voltage across the switching element Q1 fluctuates due to the resonant operation between winding L1 and the parasitic capacitance component of the switching element Q1, which is a MOSFET.

[0038] The bottom detection circuit 25 monitors the voltage across the switching element Q1 during the off period of the switching element Q1 and detects the minimum voltage point, which is the bottom of the voltage trough across the switching element Q1 as the voltage oscillates. When the bottom detection circuit 25 detects the minimum voltage point across the switching element Q1, it outputs a detection signal directed to the set terminal S of the flip-flop 28.

[0039] Here, when a detection signal from the bottom detection unit 25 is input to the set terminal S of the flip-flop 28 via the mask circuit 26, the flip-flop 28 outputs a high-level signal to the driver 29, and the driver 29 outputs a high-level drive signal to the gate of the switching element Q1 to turn it on.

[0040] By detecting the minimum voltage point of the voltage across the switching element Q1, which is oscillating in this manner, and turning on the switching element Q1, the voltage across the winding L1 becomes zero, and the voltage across the switching element Q1 is also close to zero. This reduces the switching loss of the switching element Q1 and improves efficiency.

[0041] As shown in Figures 2(a) and 3(a), the period t of the switching frequency is the time from one turn-on to the next turn-on of the switching element Q1 (or, although not shown, from one turn-off to the next turn-off). For example, if the switching frequency is 50 kHz, the period t is 20 μs.

[0042] Furthermore, as shown in Figure 2(b), the mask circuit 26 restricts the switching element Q1 from turning on until a predetermined mask period m has elapsed, starting from the moment the switching element Q1 turns on. Alternatively, as shown in Figure 3(b), the mask circuit 26 restricts the switching element Q1 from turning on until a predetermined mask period m has elapsed, starting from the moment the switching element Q1 turns off.

[0043] The mask circuit 26 is provided between the bottom detection circuit 25 and the set terminal S of the flip-flop 28. During the mask period m, even if a detection signal is output from the bottom detection circuit 25, the mask circuit 26 blocks the output of that detection signal to the set terminal S of the flip-flop 28, thereby rendering the detection signal ineffective. In the examples of Figures 2(b) and 3(b), during the mask period m, the bottom detection circuit 25 detects the minimum voltage point of the voltage across the switching element Q1 four times, and the bottom detection circuit 25 outputs a detection signal four times, but these four detection signals are rendered ineffective.

[0044] The mask period m is set to a period shorter than the period t of the initial switching frequency of the switching element Q1.

[0045] The mask circuit 26 enables the detection signal after the mask period m has elapsed by allowing the detection signal output from the bottom detection circuit 25 to pass through so that it is input to the set terminal S of the flip-flop 28.

[0046] In this way, the mask circuit 26 restricts the switching element Q1 from turning on or turning off until the mask period m has elapsed, thereby suppressing an increase in the switching frequency, reducing the number of switching losses that occur when the switching element Q1 turns on and off, and improving efficiency.

[0047] For example, if the mask circuit 26 is absent, dimming the brightness of the light-emitting element 11 to 50% or less shortens the on-period of the switching element Q1 compared to the 100% brightness case, increasing the switching frequency and thus increasing the number of times switching loss occurs when the switching element Q1 is turned on and off. In contrast, if a mask period m is provided by the mask circuit 26, even if the brightness is dimmed, the increase in the switching frequency can be suppressed, reducing the number of times switching loss occurs when the switching element Q1 is turned on and off, and improving efficiency.

[0048] Furthermore, in the power supply device 12 of this embodiment, the mask circuit 26 allows for the restriction of the switching element Q1 from turning on or turning off until this mask period m has elapsed, simply by providing a mask period m from the time the switching element Q1 is turned on or turned off. This simplifies the circuit configuration of the control circuit 22.

[0049] Furthermore, the mask circuit 26 simplifies the circuit configuration of the control circuit 22 by disabling the detection signal output from the bottom detection circuit 25, thereby restricting the switching element Q1 from turning on for a predetermined period of time, starting from the moment the switching element Q1 turns on or off.

[0050] Thus, in the power supply unit 12, the circuit configuration of the control circuit 22 can be simplified, so the control circuit 22 does not need to use expensive components such as a microcontroller, as in the case where the minimum voltage point of a voltage-fluctuating switching element Q1 is counted and bottom skipping is performed, but can be implemented using inexpensive components such as analog ICs.

[0051] Furthermore, the mask circuit 26 provides a mask period m from the moment the switching element Q1 is turned on, thereby suppressing fluctuations in the switching frequency even if the on-period of the switching element Q1 changes due to dimming.

[0052] Furthermore, the mask circuit 26 only needs to acquire a detection signal from the output detection circuit 27 by setting a mask period m from the time the switching element Q1 is turned off, thus simplifying the circuit configuration.

[0053] In this embodiment, the mask circuit 26 is provided between the bottom detection circuit 25 and the flip-flop 28. However, it may also be provided in the bottom detection circuit 25, or between the winding L2 and the bottom detection circuit 25, so that the bottom detection circuit 25 does not output a detection signal during the mask period m. Alternatively, it may be provided between the flip-flop 28 and the driver 29, or in the driver 29, or between the driver 29 and the switching element Q1, so that the driver 29 does not output a high-level drive signal to the switching element Q1 during the mask period m.

[0054] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of Symbols]

[0055] 11 Light-emitting element 12 Power supply 20 DC power supply 21 Power Conversion Circuit 22 Control circuits 25 Bottom detection circuit 26 Mask Circuit C1 Capacitor L1 winding Q1 Switching element

Claims

1. A power conversion circuit comprising a switching element connected to a DC power supply, a winding, and a capacitor, wherein the switching of the switching element supplies output current to a light-emitting element connected in parallel to the capacitor; A control circuit for controlling the power conversion circuit; Equipped with, The aforementioned control circuit is An output detection circuit that detects when the output of the power conversion circuit exceeds a reference voltage and outputs a detection signal, A bottom detection circuit detects the minimum voltage point of the voltage across the switching element during the off period of the switching element and outputs a detection signal. A flip-flop that outputs a low-level signal from the signal output terminal when the detection signal from the output detection circuit is input to the reset terminal, and outputs a high-level signal from the signal output terminal when the detection signal from the bottom detection circuit is input to the set terminal, A mask circuit that restricts the input of the detection signal from the bottom detection circuit to the set terminal for a predetermined period of time from the time the switching element is turned on until a predetermined period of time has elapsed, A driver that turns on the switching element by inputting the H-level signal from the flip-flop, and turns off the switching element by inputting the L-level signal from the flip-flop, A power supply device characterized by having the following features.

2. The mask circuit disables the detection signal output from the bottom detection circuit to restrict the switching element from turning on, starting from the moment the switching element turns on until the predetermined period has elapsed. The power supply device according to claim 1, characterized in that it is a power supply device.

3. A power conversion circuit having a switching element connected to a DC power supply, a winding, and a capacitor, and supplying output current to a light-emitting element connected in parallel to the capacitor; A control circuit for controlling the power conversion circuit; Equipped with, The aforementioned control circuit is An output detection circuit that detects when the output of the power conversion circuit exceeds a reference voltage and outputs a detection signal, A bottom detection circuit detects the minimum voltage point of the voltage across the switching element during the off period of the switching element and outputs a detection signal. A flip-flop that outputs a low-level signal from the signal output terminal when the detection signal from the output detection circuit is input to the reset terminal, and outputs a high-level signal from the signal output terminal when the detection signal from the bottom detection circuit is input to the set terminal, A mask circuit that restricts the input of the detection signal from the bottom detection circuit to the set terminal for a predetermined period of time from the time the switching element is turned off until a predetermined period of time has elapsed, A driver that turns on the switching element by inputting the H-level signal from the flip-flop, and turns off the switching element by inputting the L-level signal from the flip-flop, A power supply device characterized by having the following features.

4. The mask circuit disables the detection signal output from the bottom detection circuit to restrict the switching element from turning on until the predetermined period has elapsed, starting from the moment the switching element turns off. The power supply device according to claim 3, characterized in that it is a power supply device.

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