The disclosure of Japanese Patent Application No. 2014-232574 filed on Nov. 17, 2014 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
The present invention relates to an LED drive method and an LED drive device, for example, relates to an LED drive method and an LED drive device which drive an LED by using an AC voltage as an input.
Japanese Unexamined Patent Application Publication No. 2014-13866 discloses an illumination device including a bleeder circuit on a secondary side of a transformer. Japanese Unexamined Patent Application Publication No. 2005-189902 discloses a control device including an H mode controller, an L mode controller, a mode switching device that switches outputs of the two controllers, and a bumpless auxiliary switching device that returns an output of the mode switching device to each of the two controllers.
For example, in an LED (Light Emitting Diode), flicking (in other words, flicker) may occur when the LED is in a low brightness state. As shown in Japanese Unexamined Patent Application Publication No. 2014-13866, it is considered to provide a bleeder circuit to reduce the flicker. However, when providing the bleeder circuit, a bleeder resistance and a switch that switches between coupling and uncoupling of the bleeder resistance are required, so that there is a risk that the downsizing and the cost reduction of the LED drive device are not achieved. When the bleeder resistance is coupled, useless power is consumed by the bleeder resistance, so that there is a risk that the power consumption of the LED drive device cannot be reduced (in other words, there is a risk that the power conversion efficiency cannot be improved).
Embodiments described later are made in view of the above, and other problems and new features will become clear from the description of the present specification and the accompanying drawings.
An LED drive method according to an embodiment drives an LED by using a voltage conversion unit, a constant current drive unit, and a control unit. A voltage conversion unit includes a coil and a first switch and converts an AC voltage into a first voltage which is a DC voltage by controlling the first switch to be on in an on-pulse period of a first drive signal. The constant current drive unit is supplied with the first voltage and generates a drive current Id having a current value according to light control information. The control unit compares brightness based on the light control information and reference brightness, generates the first drive signal based on an error between the first voltage and a target voltage representing a target of the first voltage when the brightness is higher than the reference brightness, and generates the first drive signal having a predetermined fixed on-pulse period when the brightness is lower than the reference brightness.
According to an embodiment, for example, it is possible to reduce the flicker when the LED is in a low brightness state.
The following embodiments will be explained, divided into plural sections or embodiments, if necessary for convenience. Except for the case where it shows clearly in particular, they are not mutually unrelated and one has relationships such as a modification, details, and supplementary explanation of some or entire of another. In the following embodiments, when referring to the number of elements, etc. (including the number, a numeric value, an amount, a range, etc.), they may be not restricted to the specific number but may be greater or smaller than the specific number, except for the case where they are clearly specified in particular and where they are clearly restricted to a specific number theoretically.
Furthermore, in the following embodiments, it is needless to say that an element (including an element step etc.) is not necessarily indispensable, except for the case where it is clearly specified in particular and where it is considered to be clearly indispensable from a theoretical point of view, etc. Similarly, in the following embodiments, when shape, position relationship, etc. of an element etc. is referred to, what resembles or is similar to the shape substantially shall be included, except for the case where it is clearly specified in particular and where it is considered to be clearly not right from a theoretical point of view. This statement also applies to the numeric value and range described above.
Further, in the embodiments, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) (abbreviated as MOS transistor) is used as an example of a MISFET (Metal Insulator Semiconductor Field Effect Transistor). However, non-oxide film is not excluded as a gate insulating film.
Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings. In all the drawings for explaining the embodiments, the same symbol is attached to the same member, as a principle, and the repeated explanation thereof is omitted.
The voltage conversion unit VCU generally includes a coil (here, a transformer TR1) and a first switch SW1, and converts an input voltage Vi outputted from the rectifier DB into an output voltage (a first voltage) Vo by controlling on/off of the first switch SW1 by a first drive signal GD1. In this case, the voltage conversion unit VCU controls the first switch SW1 to be on during an on-pulse period of the first drive signal GD1. In
More specifically, the voltage conversion unit VCU includes a capacitor C1, a transformer TR1, a switching control unit SWU, a photocoupler PCL, a diode DD1, and a smoothing capacitor Co1. The capacitor C1 is coupled between the input voltage Vi and the ground voltage GND and performs removal of noise included in the input voltage Vi and the like. The transformer TR1 includes a primary coil Lt1 and a secondary coil Lt2.
One end of the primary coil Lt1 is coupled to the input voltage Vi and the other end is coupled to the ground voltage GND through the first switch SW1 in the switching control unit SWU. Here, on/off of the first switch SW1 is controlled by the first drive signal GD1 through the photocoupler PCL. One end of the secondary coil Lt2 is coupled to the anode of the diode DD1 and the other end is coupled to the ground voltage GND. The smoothing capacitor Co1 is provided between the cathode of the diode DD1 and the ground voltage GND. The output voltage (the first voltage) Vo is generated at a coupling node between the smoothing capacitor Co1 and the diode DD1.
Generally, the constant current drive unit IDU is supplied with the output voltage Vo, generates a drive current Id having a current value according to light control information BI inputted from outside, and drives the LED array LEDA with the drive current Id. Although described in detail in
The LED control unit LEDCU1 includes a voltage feedback control unit VFBU1, a fixed pulse control unit PCU, a selection unit SELU, a storage unit MEM, and a current feedback control unit IFBU1. The voltage feedback control unit VFBU1 generates a first drive signal GD1a based on an error between the output voltage (the first voltage) Vo and a target voltage representing a target of the output voltage Vo. Specifically, the voltage feedback control unit VFBU1 generates, for example, the first drive signal GD1a having an on-pulse period based on the error. The fixed pulse control unit PCU generates a first drive signal GD1b having a predetermined fixed on-pulse period or additionally a predetermined fixed cycle. The fixed on-pulse period and cycle are held in the storage unit MEM as a voltage pulse setting value PVS in advance.
The selection unit SELU selects either one of the first drive signal GD1a from the voltage feedback control unit VFBU1 and the first drive signal GD1b from the fixed pulse control unit PCU and outputs the selected first drive signal GD1 to the first switch SW1 of the voltage conversion unit VCU. Specifically, the selection unit SELU determines whether brightness based on the light control information BI is higher than or lower than predetermined reference brightness. The selection unit SELU selects the first drive signal GD1a in a first case in which the brightness is higher than the reference brightness and selects the first drive signal GD1b in a second case in which the brightness is lower than the reference brightness. In some cases, the selection unit SELU can perform the selection operation by determining the magnitude of the drive current Id instead of the brightness based on the light control information BI.
The current feedback control unit IFBU1 generates the second drive signal GD2 based on an error between the drive current Id and a target current representing a target of the drive current Id. In this case, the target current is variably set according to the light control information BI. Although the light control information BI is not particularly limited, the light control information BI is generated by a remote control or the like that adjusts the brightness of the LED.
In step S101, when there is no change in the brightness, the LED control unit LEDCU1 ends the processing. On the other hand, when there is a change in the brightness, the LED control unit LEDCU1 (for example, the selection unit SELU) determines whether or not the brightness is lower than predetermined reference brightness (in this example, 10%) (in other words, whether or not the brightness represents low brightness light control) (step S102). When the brightness does not represent the low brightness light control, the LED control unit LEDCU1 (for example, the selection unit SELU) selects the first drive signal GD1a from the voltage feedback control unit VFBU1 (step S103).
On the other hand, when the brightness represents the low brightness light control in step S102, the LED control unit LEDCU1 sets the voltage pulse setting value PVS (that is, a fixed on-pulse period or additionally a predetermined fixed cycle) stored in the storage unit MEM to the fixed pulse control unit PCU (step S104). Thereafter, the LED control unit LEDCU1 starts operation of the fixed pulse control unit PCU (step S105). Further, along with step S105, the LED control unit LEDCU1 (for example, the selection unit SELU) selects the first drive signal GD1b from the fixed pulse control unit PCU (step S106).
By the operations described above, the first drive signal GD1 that controls the first switch SW1 is generated by the fixed pulse control unit PCU in the case of low brightness light control (in a second case) and is generated by the voltage feedback control unit VFBU1 in the case of no low brightness light control (in a first case). The fixed pulse control unit PCU can stop the operation in the case of no low brightness light control.
In this case, the voltage feedback control unit VFBU1 determines an on-pulse period Ton of the first drive signal GD1 by, for example, proportional-integral control (so-called PI control) using a certain fixed control parameter (a phase compensation parameter). During the low brightness light control, it is possible to sufficiently maintain the output voltage Vo by a short on-pulse period Ton, so that the on-pulse period Ton is determined to be a small value.
On the other hand, the voltage feedback control unit VFBU1 determines the on-pulse period Ton for controlling the output voltage Vo to be constant in a range of the drive current Id according to a brightness of 0% to 100% by a fixed control parameter (a phase compensation parameter), so that it may not be possible to follow variation of phase characteristics when the brightness is changed and an operation area of the drive current Id is changed. For example, when using a control parameter that is set so that optimal control is performed during high brightness light control, the responsivity of feedback may not be sufficient during the low brightness light control. Specifically, a sufficient control band (in other words, a high zero crossing frequency) may not be secured.
Thereby, even when the voltage feedback control unit VFBU1 determines the on-pulse period Ton to be a small value, there is a risk that the voltage feedback control unit VFBU1 determines the on-pulse period Ton to be longer than a required length. Further, there is a risk that the voltage feedback control unit VFBU1 generates the first drive signal GD1 having such an on-pulse period Ton continuously until, for example, an overvoltage of the output voltage Vo is detected. As a result, different from a steady operation where pulses are continuously generated as shown in
In the period T1, the next on-pulse period Ton appears before power supplied during one on-pulse period Ton is consumed in the LED array LEDA, so that the output voltage Vo rises significantly. When the voltage feedback control unit VFBU1 detects an overvoltage of the output voltage Vo or the like, in the period T2, the voltage feedback control unit VFBU1 stops outputting pulses until the overvoltage state is eliminated (in other words, until the output voltage Vo lowers to a predetermined value). By such an intermittent operation, the output voltage Vo fluctuates in a large fluctuation width ΔVo.
On the other hand, the constant current drive unit IDU normally generates the drive current Id at a PWM on-duty close to a minimum value during the low brightness light control. Therefore, when the output voltage Vo rises significantly in the period T1, the constant current drive unit IDU cannot further decrease the PWM on-duty accordingly, so that the constant current drive unit IDU causes the drive current Id to increase. As a result, the brightness of the LED array LEDA increases. On the contrary, in the period T2, the constant current drive unit IDU decreases the drive current Id according to the decrease of the output voltage Vo. As a result, the brightness of the LED array LEDA decreases. In this manner, the fluctuation width ΔVo of the output voltage Vo is increased by the intermittent operation and the drive current Id is not controlled at a constant level, so that flicking (flicker) of the LED array LEDA may occur during the low brightness light control.
In this case, the transformer TR1 accumulates power during the on-pulse period Ton of the first drive signal GD1b. Then, the transformer TR1 discharges the accumulated power from the secondary side of the transformer TR1 through the diode DD1 during an off-pulse period Toff. The LED array LEDA is driven by the discharged power and the smoothing capacitor Co1 is charged by the discharged power. Here, the off-pulse period Toff of the first drive signal GD1b is longer than the off-pulse period of the first drive signal GD1a. Therefore, during the off-pulse period Toff, the power discharged from the transformer TR1 is sufficiently consumed, and the output voltage Vo rises once and then falls to some extent.
While the transformer TR1 is being charged with power during the next on-pulse period Ton, the LED array DEDA is driven by the smoothing capacitor Co1 and the output voltage Vo falls to a predetermined target voltage. Thereafter, the same operation is repeated in the off-pulse period Toff. As a result, the variation of the output voltage Vo is sufficiently smaller than that in the case of
In this case, the power accumulated in the transformer TR1 in the on-pulse period Ton of the first drive signal GD1b is smaller than the power accumulated in the on-pulse period of the first drive signal GD1a. Therefore, different from the case of
As described above, it is possible to sufficiently reduce the variation of the output voltage Vo during the low brightness light control, so that it is possible to reduce flicking (flicker) of the LED array LEDA. In this case, it is not necessary to provide a bleeder circuit as shown in Japanese Unexamined Patent Application Publication No. 2014-13866, so that it is possible to reduce the size and cost of the LED drive system. Further, it is not necessary to provide a bleeder circuit, so that it is possible to realize reduction of power consumption (in other words, improvement of power conversion efficiency in the voltage conversion unit VCU) of the LED drive system.
In the examples in
Further, in the examples in
The fixed pulse control unit PCU defines the on-pulse period Ton of the first drive signal GD1b to be a fixed value. On the other hand, the fixed pulse control unit PCU defines the cycle Tsw of the first drive signal GD1b to be a fixed value, and further when the switching system of the voltage feedback control unit VFBU1 is an asynchronous system, the fixed pulse control unit PCU can use a switching cycle of the voltage feedback control unit VFBU1 as the cycle Tsw of the first drive signal GD1b. In other words, while the fixed pulse control unit PCU generates the first drive signal GD1b at the switching cycle of the voltage feedback control unit VFBU1, the fixed pulse control unit PCU can also define the on-pulse period Ton for each switching cycle to be a fixed value.
However, in practice, the on-pulse period Ton of the first drive signal GD1b may be able to be shortened only to a certain extent due to restriction of hardware or the like, so that the variation of the output voltage Vo may not be able to be sufficiently reduced by only defining the on-pulse period Ton. Therefore, from this viewpoint, it is desirable to define both of the on-pulse period Ton and the cycle Tsw of the first drive signal GD1b to be fixed values. The on-pulse period Ton and the cycle Tsw can be defined to be appropriate values by, for example, performing simulation or the like in advance.
In
The commercial power supply AC is coupled between the external terminal PN1 and the external terminal PN2. The LED array LEDA is coupled between the external terminal PN3 and the external terminal PN4. The light control information BI is inputted into the external terminal PN5. Hereinafter, explanation related to portions overlapping with
A rectifier DB full-wave rectifies the AC voltage Vac from the commercial power supply AC by using four diodes. The voltage conversion unit VCU includes a photocoupler PCL, a pre-driver circuit PDV1, a transistor Q1, a transformer TR2, a capacitor C1, a diode DD1, a smoothing capacitor Co1, a feedback resistance circuit FBC, and a zero current detection circuit ZCDC. The transistor Q1 corresponds to the first switch SW1 in
The pre-driver circuit PDV1 is provided with a power supply voltage VCC of, for example, 12 V or the like and controls on/off of the transistor Q1 by using the power supply voltage VCC according to the first drive signal GD1 inputted through the photocoupler PCL. A photodiode included in the photocoupler PCL is provided with a power supply voltage VDD of, for example, 5V. For example, the first drive signal GD1 outputs a level of the power supply voltage VDD during the on-pulse period Ton and outputs a level of the ground voltage GND during the off-pulse period Toff.
During the on-pulse period Ton of the first drive signal GD1, no current flows in the photodiode included in the photocoupler PCL and a transistor included in the photocoupler PCL is turned off. As a result, the pre-driver circuit PDV1 charges a gate capacitance of the transistor Q1 and an inner capacitor C10 by using the power supply voltage VCC through inner diodes and resistances appropriately. On the other hand, during the off-pulse period of the first drive signal GD1, the transistor included in the photocoupler PCL is turned on. As a result, the pre-driver circuit PDV1 discharges the inner capacitor C10, drives the inner transistor Q10 to be turned on, and discharges the gate capacitance of the transistor Q1 to the ground voltage GND.
The transformer TR2 includes an auxiliary coil Lt3 to detect zero current in addition to the primary coil Lt1 and the secondary coil Lt2 shown in
Specifically, in the case of flyback system, the power accumulated in the transformer TR2 is discharged from the secondary side of the transformer TR2 during the off-pulse period Toff of the transistor Q1. While the power is discharged, the transistor Q11 is controlled to be on by using the auxiliary coil Lt3 as an electromotive force. As a result, the zero current detection signal ZCD becomes a level of the ground voltage GND. On the other hand, when the power of the transformer TR2 is exhausted (in other words, a zero current state is reached), the electromotive force of the auxiliary coil Lt3 disappears and the transistor Q11 is controlled to be off. As a result, the zero current detection signal ZCD changes to the level of the power supply voltage VDD.
The feedback resistance circuit FBC resistance-divides an output voltage (a first voltage) Vo controlled to be 80 V or the like and generates a feedback voltage Vfb proportional to the output voltage Vo. For example, the resistance ratio of the feedback resistance circuit FBC is adjusted so that the feedback voltage Vfb is within a range between the power supply voltage VDD and the ground voltage GND.
The constant current drive unit IDU includes a transistor (a second switch) Q2, a diode DD2, a coil L2, a smoothing capacitor Co2, a current detection resistance Rs, and a pre-driver circuit PDV2. The transistor (a second switch) Q2 is composed of, for example, an n-type LDMOS transistor or the like. The transistor (the second switch) Q2 is provided between a node of the output voltage Vo and one end of the coil L2, and on/off of the transistor Q2 is controlled through the pre-driver circuit PDV2 coupled to the gate.
The cathode of the diode DD2 is coupled to one end of the coil L2 and the anode of the diode DD2 is coupled to the ground voltage GND. The other end of the coil L2 is coupled to the external terminal PN3. One end of the smoothing capacitor Co2 is coupled to the external terminal PN3 and the other end is coupled to the external terminal PN4 through the current detection resistance Rs. The pre-driver circuit PDV2 controls on/off of the transistor Q2 according to the second drive signal GD2.
When the transistor Q2 is controlled to be on, the diode DD2 is biased in the opposite direction and the current flowing through the coil L2 rises at a predetermined inclination (an inclination according to a difference between the output voltage Vo and the voltage of the external terminal PN3). On the other hand, when the transistor Q2 is controlled to be off, the diode DD2 is biased in the forward direction and the current flowing through the coil L2 decreases at a predetermined inclination (an inclination according to a difference between the voltage of the external terminal PN3 and the ground voltage GND). The drive current Id is controlled to be a target current by controlling the current flowing through the coil L2 by on/off of the transistor Q2. A voltage according to the number of serially coupled LEDs is applied between the external terminals PN3 and PN4, and a voltage (for example, 30 V) lower than the output voltage Vo is applied.
In the same manner as in
Instead of the output voltage Vo shown in
The interrupt control unit INTC receives the zero current detection signal ZCD and generates a start signal ST. For example, the interrupt control unit INTC receives a transition of the zero current detection signal ZCD to an “H” level (a level of the power supply voltage VDD) which is generated when the zero current is received and generates the start signal ST. The overvoltage detection unit OVP includes a comparator circuit and generates a forced stop signal when the feedback voltage Vfb exceeds a predetermined upper limit voltage.
The analog/digital conversion unit (a first analog/digital conversion unit) ADC1 converts the feedback voltage Vfb into a digital value (a first digital value) Dfb. In other words, the analog/digital conversion unit ADC1 converts the output voltage (a first voltage) Vo into the digital value Dfb proportional to the output voltage Vo. The PI control unit (a first digital control unit) PICUv1 calculates an error between the digital value Dfb and a target voltage digital value Dvtg representing a target of the output voltage Vo and determines the on-pulse period Ton of the first drive signal GD1a by a digital calculation using the error as an input. Here, the on-pulse period Ton is determined as a timer setting value TST.
The PI control unit (the first digital control unit) PICUv1 can be formed by software processing performed by a CPU (Central Processing Unit) or the like. More specifically, the PI control unit PICUv1 calculates the timer setting value TST, which is an operation amount U(n), by proportional (P)-integral (I) control. For example, an operation amount U(n) is calculated by an expression (1).
U(n)=U(n−1)+K0·E(n)+K1·E(n−1) (1)
U(n) is the operation amount of this time and U(n−1) is the previous operation amount. E(n) is an error value of this time and is calculated by “(target voltage digital value Dvtg)−(digital value Dfb of this time)”. E(n−1) is a previous error value and is calculated by “(target voltage digital value Dvtg)−(previous digital value Dfb)”. K0 and K1 are coefficients which are control parameters (phase compensation parameters).
The timer unit TMC starts a count operation when receiving the start signal ST, and when the count operation reaches the timer setting value TST, the timer unit TMC stops the count operation and resets a count value. Then the timer unit TMC sets a period in which the timer unit TMC performs the count operation as the on-pulse period Ton of the first drive signal GD1a. The timer unit TMC forcibly stops the count operation from when the timer unit receives a forced stop signal FT to when generation of the forced stop signal FT is stopped. As a result, the first drive signal GD1a is fixed to an off level and the transistor G1 (the first switch SW1) is also fixed to off.
In this manner, the digital control is applied to the voltage feedback control unit VFBU1, so that it is possible to easily realize switching (selection) between the fixed pulse control unit PCU and the voltage feedback control unit VFBU1 according to the brightness as described above. In other words, for example, when the voltage feedback control unit VFBU1 includes a general analog circuit including an error amplifier circuit or the like, there is a risk that many artifices are required on the circuit in order to perform such switching (selection).
The current feedback control unit IFBU1 shown in
The target current setting unit TGI sets a target current digital value Ditg representing a target of the drive current Id according to the light control information BI. The PI control unit (a second digital control unit) PICUi1 calculates an error between the digital value Ds and the target current digital value Ditg and determines a PWM duty (a duty setting value DST) of the second drive signal GD2 by a digital calculation using the error as an input.
The PI control unit (the second digital control unit) PICUi1 can be formed by software processing performed by a CPU or the like. More specifically, the PI control unit PICUi1 performs calculation based on the expression (1) in the same manner as the PI control unit PICUv1 by defining the operation amount U(n) as the PWM duty (the duty setting value DST). The PWM generation unit PWMG generates the second drive signal GD2, which is the PWM signal, based on the duty setting value DST.
Here, when the output current Io of the secondary coil Lt2 becomes zero, the start signal ST is generated through the zero current detection signal ZCD. The first drive signal GD1a changes to an on level by receiving the start signal ST and maintains the on level during a period based on the timer setting value TST from the PI control unit PICUv1 (that is, during the on-pulse period Ton).
For example, in a stable state, the timer setting value TST from the PI control unit PICUv1 (the on-pulse period Ton) is maintained at substantially a constant value. Further, an inclination of the input current Ii in the on-pulse period Ton is proportional to the input voltage Vi. The input voltage Vi has a waveform of sinusoidal shape due to the rectifier DB, so that the inclination of the input current Ii increases or decreases by an amount of change based on the sinusoidal wave in a time series manner. Therefore, when the on-pulse period Ton is constant, an average current lave of the input current Ii is controlled to have a sinusoidal shape. As a result, it is possible to improve the power factor and to reduce higher harmonics with respect to the commercial power supply AC.
Here, the PI control unit PICUv1 and the PICUi1 are used as the first and the second digital control units. However, the first and the second digital control units are not particularly limited to those mentioned above. For example, it is also possible to use a PID control unit that performs proportional (P), integral (I), and differential (D) control.
The fixed pulse control unit PCU includes the storage unit MEM that holds the voltage pulse setting value PVS described above and a timer unit TMC2. The cycle Tsw of the first drive signal GD1b, which is included in the voltage pulse setting value PVS, is set in the timer unit TMC. Timer unit TMC2 outputs a trigger signal every time the cycle Tsw is reached. Regarding the selection unit SELUa, the output from the timer unit TMC2 is inputted into one of two input ports and the start signal ST is inputted into the other of the two input ports. Regarding the selection unit SELUb, the on-pulse period Ton of the first drive signal GD1b, which is included in the voltage pulse setting value PVS, is inputted into one of two input ports and the timer setting value TST is inputted into the other of the two input ports.
Thereby, when the selection units SELUa and SELUb select one of the two inputs based on the light control information BI, the timer unit TMC generates the on-pulse period Ton based on the fixed pulse control unit PCU and the first drive signal GD1 having the cycle Tsw. On the other hand, when the selection units SELUa and SELUb select the other of the two inputs based on the light control information BI, the timer unit TMC generates the first drive signal GD1a described in
Here, even in a period in which the selection units SELUa and SELUb select the fixed pulse control unit PCU, it is possible to quickly take an action when the switching of the selection units SELUa and SELUb is performed as described in
Here, a configuration example is shown in which the cycle Tsw is determined by the voltage pulse setting value PVS. However, in some cases, it is possible to determine the cycle Tsw by the start signal ST without providing the selection unit SELUa. Further, the fixed pulse control unit PCU is not necessarily limited to the method as shown in
The transformer TR2 is mounted near the center of the wiring substrate PCB. Various components provided on a primary side of the transformer TR2 are mounted on one side as seen from the transformer TR2, and various components provided on a secondary side of the transformer TR2 are mounted on the other side. The various components provided on the primary side of the transformer TR2 include the rectifier DB, the transistor Q1, the pre-driver circuit PDV1, the photocoupler PCL, and the like. In the primary side of the transformer TR2, the external terminals PN1, PN2, and PN5 are provided.
On the other hand, the various components provided on the secondary side of the transformer TR2 include the zero current detection circuit ZCDC, the smoothing capacitors Co1 and Co2, the diodes DD1 and DD2, the transistor Q2, the pre-driver circuit PDV2, the coil L2, and the like. In the secondary side of the transformer TR2, the external terminals PN3 and PN4 are provided. Further, here, an IC chip (a semiconductor chip) of a micro control unit (MCU) that forms the LED control unit LEDCU1 is mounted near the center of the wiring substrate PCB.
In such a configuration example, for example, when a method as shown in Japanese Unexamined Patent Application Publication No. 2014-13866 described above is used, it is necessary to secure amounting area of a bleeder circuit BL in the secondary area of the transformer TR2 as shown in an LED drive device LEDCM′ in
As described above, by using the LED drive system, the LED drive device, and the LED drive method of the first embodiment, it is possible to realize, typically, reduction of the flicker when the LED is in a low brightness state and the reduction of the size of the LED drive device. Further, it is possible to realize the reduction of the flicker when the LED is in a low brightness state and the reduction of the power consumption of the LED drive device and the like.
A voltage conversion unit VCU2 in
The coil L1 is provided between the cathode of the diode DD1 and a node N2 which is the other output node of the rectifier DB. The smoothing capacitor Co1 is provided between the anode of the diode DD1 and the node N2. The pre-driver circuit PDV1 controls on/off of the transistor Q1 according to the first drive signal GD1 from the LED control unit LEDCU1. The voltage conversion unit VCU2 is an inversion-type step-down converter and generates an output voltage (a first voltage) Vo at the node N2 by causing the anode of the diode DD1 to have the ground voltage. Accordingly, in
For example, even when the non-insulated type voltage conversion unit VCU2 as described above is used, the method of the first embodiment can be applied, and thereby it is possible to obtain the same effect as that of the first embodiment.
The LED control unit LEDCU2 includes a voltage feedback control unit VFBU2 and a current feedback control unit IFBU2, but does not include the fixed pulse control unit PCU, which is included in
Different from the case in
The selection unit (a first selection unit) SELU1 selects a digital value Doh1 outputted from the PI control calculation unit (a first calculation unit) PICLh1 in a first case in which the brightness based on the light control information BI is higher than predetermined reference brightness. On the other hand, the selection unit SELU1 selects a digital value Dol1 outputted from the PI control calculation unit (a second calculation unit) PICLl1 in a second case in which the brightness based on the light control information is lower than the reference brightness.
The subtraction unit (a first output error calculating unit) SBh1 calculates a digital value (a first output error digital value) Doeh1, which is an error between the digital value Doh1 outputted from the PI control calculation unit PICLh1 and a digital value Do1 selected by the selection unit SELU1. The subtraction unit (a second output error calculating unit) SBl1 calculates a digital value (a second output error digital value) Doel1, which is an error between the digital value Dol1 outputted from the PI control calculation unit PICLl1 and a digital value Do1 selected by the selection unit SELU1.
Roughly, the PI control calculation unit (the first calculation unit) PICLh1 calculates the digital value Doh1 by a digital calculation using an addition result of the digital value (the first error digital value) Der1 and the digital value (the first output error digital value) Doeh1 as an input. More specifically, the digital value Doeh1 is multiplied by the multiplication unit MLh1. The addition unit ADh1 adds a digital value outputted from the multiplication unit MLh1 and the digital value Der1 and outputs the addition result to the PI control calculation unit PICLh1. The PI control calculation unit PICLh1 outputs the digital value Doh1 by using the output of the addition unit ADh1 as an input.
In the same manner, roughly, the PI control calculation unit (the second calculation unit) PICLl1 calculates the digital value Dol1 by a digital calculation using an addition result of the digital value (the first error digital value) Der1 and the digital value (the second output error digital value) Doel1 as an input. More specifically, the digital value Doel1 is multiplied by the multiplication unit MLl1. The addition unit ADl1 adds a digital value outputted from the multiplication unit MLl1 and the digital value Der1 and outputs the addition result to the PI control calculation unit PICLl1. The PI control calculation unit PICLl1 outputs the digital value Dol1 by using the output of the addition unit ADl1 as an input.
The pulse generation unit (a first drive signal generation unit) PGEN1 generates the first drive signal GD1 based on the digital value Do1 selected by the selection unit SELU1. The pulse generation unit PGEN1 can be formed by, for example, the timer unit TMC as shown in
Although not particularly limited, each of the PI control calculation units PICLh1 and PICLl1 performs a digital calculation by, for example, using the expression (1) in the same manner as in the case of the PI control unit PICUv1 in
Here, as described in
When the brightness based on the light control information BI is higher than the reference brightness (in other words, when load is heavy), the phase compensation parameters (the coefficients K0 and K1) are set so that the PI control calculation unit PICLh1 can sufficiently control the output voltage Vo. On the other hand, when the brightness based on the light control information BI is lower than the reference brightness (in other words, when load is light), the phase compensation parameters (the coefficients K0 and K1) are set so that the PI control calculation unit PICLl1 can sufficiently control the output voltage Vo. Specifically, for example, the two phase compensation parameters are set so that the control band (the zero crossing frequency) is the same in each corresponding load condition.
By using such a PI control unit PICUv2, the intermittent operation as shown in
Further, for example, the PI control calculation unit PICLh1 performs digital calculation by using the output of the addition unit ADh1 instead of the output of the subtraction unit SBe1 used as in the case of
The PI control calculation unit PICLh1 calculates a new digital value Doh1 for causing the error obtained by the addition to be close to zero. Therefore, the error between the digital value Doh1 and the digital value Dol1 becomes small. As a result, it is possible to suppress rapid variation of the digital value Do1 which may occur when a selection destination of the selection unit SELU1 is switched. In other words, when the rapid variation of the digital value Do1 occurs, this may cause the flicker of the LED. It is possible to prevent this kind of situation by using the PI control unit PICUv2.
The current feedback control unit IFBU2 includes the analog/digital conversion unit (the second analog/digital conversion unit) ADC2, a PI control unit PICUi2, a pulse generation unit PGEN2, and the target current setting unit TGI. The analog/digital conversion unit (the second analog/digital conversion unit) ADC2 converts the drive current Id into a digital value. However, in practice, the analog/digital conversion unit ADC2 converts the drive current Id into a digital value (a second digital value) Ds proportional to the drive current Id by using the current detection voltage IS and the like in the same manner as in the case of
The target current setting unit TGI sets a target current digital value Ditg representing a target of the drive current Id according to the light control information BI. The PI control unit PICUi2 includes two PI control calculation units PICLh2 and PICLl2, two addition units ADh2 and ADl2, two subtraction units SBh2 and SBl2, two multiplication units MLh2 and MLl2, a selection unit SELU2, and a subtraction unit SBe2. The configuration and the operation of the PI control unit PICUi2 are the same as those of the PI control unit PICUv2, so that only the configuration will be simply described below.
The subtraction unit (a second error calculating unit) SBe2 calculates a digital value (a second error digital value) Der2, which is an error between the digital value Ds and a target current digital value Ditg. The selection unit (a second selection unit) SELU2 selects a digital value Doh2 outputted from the PI control calculation unit (a third calculation unit) PICLh2 in the first case described above, selects a digital value Dol2 outputted from the PI control calculation unit (a fourth calculation unit) PICLl2, and outputs the selected digital value Do2.
The subtraction unit (a second output error calculating unit) SBh2 calculates a digital value (a third output error digital value) Doeh2, which is an error between the digital value Doh2 and the digital value Do2. The subtraction unit (a fourth output error calculating unit) SBl2 calculates a digital value (a fourth output error digital value) Doel2, which is an error between the digital value Dol2 and the digital value Do2.
Roughly, the PI control calculation unit (the third calculation unit) PICLh2 calculates the digital value Doh2 by a digital calculation using an addition result of the digital value Der2 and the digital value Doeh2 as an input. More specifically, the digital value Doeh2 is multiplied by the multiplication unit MLh2. The addition unit ADh2 adds a digital value outputted from the multiplication unit MLh2 and the digital value Der2 and outputs the addition result to the PI control calculation unit PICLh2. The PI control calculation unit PICLh2 outputs the digital value Doh2 by using the output of the addition unit ADh2 as an input.
In the same manner, roughly, the PI control calculation unit (the fourth calculation unit) PICLl2 calculates the digital value Dol2 by a digital calculation using an addition result of the digital value Der2 and the digital value Doel2 as an input. More specifically, the digital value Doel2 is multiplied by the multiplication unit MLl2. The addition unit ADl2 adds a digital value outputted from the multiplication unit MLl2 and the digital value Der2 and outputs the addition result to the PI control calculation unit PICLl2. The PI control calculation unit PICLl2 outputs the digital value Dol2 by using the output of the addition unit ADl2 as an input.
The pulse generation unit (a second drive signal generation unit) PGEN2 generates the second drive signal GD2 based on the digital value Do2 selected by the selection unit SELU2. The pulse generation unit PGEN2 can be formed by, for example, the PWM generation unit PWMG as shown in
It is possible to realize reduction of the flicker of the LED by using, in particular, the voltage feedback control unit VFBU2 as shown in
As another effect, the operation amount U(n) is optimized in a large adjustable range by using the two PI control calculation units, so that it is possible to improve adjustability toward a target value. The improvement of adjustability is particularly useful in the current feedback control unit IFBU2 which is required to precisely adjust the drive current Id according to the brightness. Therefore, from a viewpoint of realizing reduction of the flicker of the LED and improvement of the adjustability, it is desirable to use both the voltage feedback control unit VFBU2 and the current feedback control unit IFBU2.
As described above, by using the LED drive system, the LED drive device, and the LED drive method of the third embodiment, it is possible to obtain the same effect as that of the first embodiment in addition to the effect of improvement of the adjustability described above. In other words, the bleeder circuit is not required, so that it is possible to reduce the size, the cost, and the power consumption of the LED drive device and the like. The PI control unit PICUv2 and the PICUi2 shown in
The LED control unit LEDCU3 includes a voltage feedback control unit VFBU3, the current feedback control unit IFBU1, the fixed pulse control unit PCU, a selection unit SELU3, and the storage unit MEM. Different from the case in
Different from the case in
The voltage feedback control unit VFBU3 has the same configuration as that in
During the low brightness light control, the drive current Id of the LED array LEDA is small with respect to the target voltage of the output voltage Vo, so that the intermittent operation as shown in
Therefore, as shown in
Thereby, it is possible to reduce the flicker of the LED. Further, as another effect, it is possible to variably control the current value of the drive current Id based on the variable control of the output voltage Vo in a state in which the second drive signal GD2b is fixed during the low brightness light control. When using such a method, during the low brightness light control, for example, it may be possible to realize adjustment of the current value of the drive current Id according to the brightness at higher resolution than in a case in which the configuration example of
In step S201, when there is no change in the brightness, the LED control unit LEDCU3 ends the processing. On the other hand, when there is a change in the brightness, the LED control unit LEDCU3 (for example, the selection unit SELU3) determines whether or not the brightness is lower than predetermined reference brightness (in this example, 10%) (in other words, whether or not the brightness represents the low brightness light control) (step S202). When the brightness does not represent the low brightness light control, the LED control unit LEDCU3 (for example, the selection unit SELU3) selects the second drive signal GD2a from the current feedback control unit IFBU1 (step S203).
On the other hand, when the brightness represents the low brightness light control in step S202, the LED control unit LEDCU3 sets the current pulse setting value PIS (that is, fixed PWM cycle and PWM duty) stored in the storage unit MEM to the fixed pulse control unit PCU (step S204). Thereafter, the LED control unit LEDCU3 starts operation of the fixed pulse control unit PCU (step S205). Further, along with step S205, the LED control unit LEDCU3 (for example, the selection unit SELU3) selects the second drive signal GD2b from the fixed pulse control unit PCU (step S206). Further, along with step S205, the target voltage setting unit TGV sets a target voltage according to the light control information BI.
In the LED drive system of the fourth embodiment, as described above, sufficient adjustability to a target voltage is required during the low brightness light control in order to variably control the output voltage Vo during the low brightness light control. Therefore, as also described in the third embodiment, it is useful to use the PI control unit PICUv2 including the two PI control calculation units PICLh1 and PICLl1 as shown in
As described above, by using the LED drive system, the LED drive device, and the LED drive method of the fourth embodiment, it is possible to obtain the same effect as that of the first embodiment. Further, in some cases, it is possible to improve light control resolution during the low brightness light control.
While the invention made by the inventors has been specifically described based on the embodiments, the present invention is not limited to the above embodiments and can be variously modified without departing from the scope of the invention. For example, the above embodiments are described in detail in order to describe the present invention in an easily understandable manner, and the embodiments are not necessarily limited to those that include all the components described above. Further, some components of a certain embodiment can be replaced by components of another embodiment, and components of a certain embodiment can be added to components of another embodiment. Further, regarding some components of each embodiment, it is possible to perform addition/deletion/exchange of other components.
An LED drive device according to an embodiment of the present invention drives an LED provided outside by using an AC voltage inputted from outside. The LED drive device includes a rectifier, a voltage conversion unit, a constant current drive unit, and a control unit. The rectifier rectifies an AC voltage. The voltage conversion unit includes a coil and a first switch, and converts a voltage outputted from the rectifier into a first voltage which is a DC voltage by controlling on/off of the first switch by a first drive signal. The constant current drive unit is provided with the first voltage, includes a coil and a second switch, generates a drive current having a current value according to light control information inputted from outside by controlling on/off of the second switch by a second drive signal that is a PWM signal, and drives the LED by the drive current. The control unit includes a target current setting unit, a current feedback control unit, a fixed pulse control unit, a target voltage setting unit, and a voltage feedback control unit, and generates a first drive signal and a second drive signal. The target current setting unit sets a target current representing a target of the drive current according to the light control information. The current feedback control unit determines a PWM duty of the second drive signal based on an error between the drive current and the target current in a first case in which brightness based on the light control information is higher than predetermined reference brightness. The fixed pulse control unit generates the second drive signal having a predetermined fixed PWM cycle and PWM duty in a second case in which the brightness based on the light control information is lower than the reference brightness. The target voltage setting unit sets a target voltage representing a target of the first voltage according to the light control information. The voltage feedback control unit generates the first drive signal based on an error between the first voltage and the target voltage.
Number | Date | Country | Kind |
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2014-232574 | Nov 2014 | JP | national |
This application is a Continuation application of U.S. patent application Ser. No. 14/922,141, filed on Oct. 24, 2015, now U.S. Pat. No. ______.
Number | Date | Country | |
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Parent | 14922141 | Oct 2015 | US |
Child | 15354681 | US |