JP2012134100A - Led drive power supply device and led lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to perform dimming with stability even when the dimming is performed in a range including ultra-low brightness.SOLUTION: A dimming pulse signal is inputted into a secondary-side control circuit 120 of a feedback control circuit 101. At a smoothing circuit 121, smoothing processing is performed so that there remains a ripple corresponding to a pulse frequency of the dimming pulse signal and a voltage after the smoothing processing is given to a non-inverting input terminal of an operational amplifier OP of a controller 122. Feedback control by the controller 122, insulating means 130, and a primary-side control circuit 110 is performed based on the voltage where there remains the ripple. Because of the remaining ripple, at the time of low brightness, in other words, when a feedback voltage VFB of the primary-side control circuit 110 becomes low, a voltage composed only of a ripple component is inputted into a Q1 control signal generation circuit 111. The Q1 control signal generation circuit 111 performs burst dimming control based on the voltage composed only of the ripple component.

Description

  The present invention relates to an LED driving power supply device and an LED lighting device that drive LEDs at a constant current.

  LEDs are used in various forms such as lighting devices and backlights of display devices. An LED drive circuit that supplies electric power to an LED is generally driven by constant current control. Currently, various LED lighting devices having a dimming function have been put into practical use.

  The LED lighting device described in Patent Document 1 has a dimming function. The power converter of the LED lighting device of Patent Document 1 receives an alternating current (AC) voltage Vac at an input terminal, converts the AC voltage into a direct current (DC) voltage Vdc, and outputs a current for driving the LED. The power converter 10 converts the high AC input voltage to a desired voltage level that may be higher or lower than the rectified AC input level so that the LED current can be properly controlled for the desired luminance level. ing.

Special table 2008-537459 gazette

  By the way, when it is going to suppress the brightness | luminance of a LED lighting apparatus by light control, you have to reduce a drive current.

  However, when the driving current of the LED lighting device is decreased, the current flowing through the LED (LED current) becomes very small near the lower limit (minimum) of the dimmable range, and the LED current becomes unstable. Therefore, there has been a problem that flickering occurs when dimming is performed in a range including the extinguished state.

  Such instability of the LED current is caused by constant current control. Specifically, current feedback from the LED lighting device is necessary for constant current control. However, when the LED current becomes very small, the amount of current feedback is not sufficient.

  Therefore, the LED current temporarily increases once and the feedback control is performed until the minimum current feedback amount necessary for operation is obtained. However, the LED current is excessively reduced by the feedback control, and the LED current increases again. Since such control is repeated, the above flickering occurs.

  An object of the present invention is to realize an LED drive power supply device and an LED illumination device capable of stable dimming even when dimming to extremely low luminance.

  The present invention relates to an LED drive power supply device including a power conversion circuit and a feedback control unit. The power conversion circuit inputs power from an input power supply and outputs power to the LED. The feedback control unit performs feedback control on the basis of the dimming pulse signal for setting the luminance of the LED or the power supplied to the LED, and gives a control signal for controlling the power supplied to the LED to the power conversion circuit. With this configuration, the feedback control unit includes a smoothing circuit that smoothes the dimming pulse signal so that a predetermined ripple remains. The gain of feedback control is set high at the frequency of the dimming pulse signal.

  In the LED drive power supply device of the present invention, it is preferable that the gain of the feedback control is set to a value such that the influence of the ripple remains on the control signal.

  In this configuration, the dimming pulse signal is smoothed so that ripples repeated at a predetermined frequency remain, that is, the waveform is not completely smoothed (direct current). Also, the feedback control gain is high at the ripple frequency. For this reason, the influence of the ripple remains on the control signal given to the power conversion circuit.

  When the brightness of the LED is set high, that is, when the average voltage value of the control signal is set high, the ripple amplitude ratio is reduced with respect to the DC voltage value of the control signal, and normal DC voltage control is performed. On the other hand, when the LED brightness is set low, that is, when the voltage value of the control signal is set extremely low, the ripple amplitude ratio becomes large, and only the ripple component remains, and the burst operation is performed. As a result, stable power supply is possible regardless of whether the luminance is high or low.

  In the LED drive power supply device of the present invention, the input power supply is a commercial power supply, the power conversion circuit inputs the voltage of the commercial AC power supply, and the supply current to the LED is in the same phase as the voltage of the commercial AC power supply and is sinusoidal. It is preferable that the power factor correction converter be controlled so as to change to.

  In this structure, the case where a power factor improvement converter is specifically used as an LED drive power supply device is shown. With this configuration, a high power factor LED drive power supply device is possible.

  In the LED drive power supply device of the present invention, the feedback control gain is preferably set to a value that does not respond to the pulsation of the commercial AC power supply.

  In the LED drive power supply device of the present invention, it is preferable that the feedback control gain is set to sufficiently decrease in a frequency band twice that of the commercial AC power supply.

  In this configuration, the feedback gain of the power factor correction converter is specifically shown. In general, the feedback gain of the power factor correction converter is designed to sufficiently decrease at twice the commercial frequency so that fluctuation of the commercial frequency component does not occur in the output. That is, a higher power factor LED drive power supply device can be realized.

  In the LED drive power supply device of the present invention, it is preferable that burst dimming operation is performed at the frequency of the dimming pulse signal when the LED is lightly loaded.

  In this configuration, even if extremely low luminance control is performed, burst dimming operation can be performed because the ripple component remains, and occurrence of flicker that occurs at extremely low luminance as in the conventional case can be suppressed.

  Further, in the LED drive power supply device of the present invention, the power conversion circuit is an insulation type power conversion circuit including an insulation transformer that performs power conversion in an insulated state, and the feedback control unit is a primary side that is an input side of a commercial AC power supply. It is preferable to include a side control circuit, a secondary side control circuit on a side to which the LED is connected, and an insulating unit that forms a state feedback loop that insulates the primary side control circuit and the secondary side control circuit.

  This configuration shows a case where an insulating power conversion circuit is specifically used as the LED drive power supply device.

  In the LED drive power supply device of the present invention, the power conversion circuit is preferably a non-insulated buck-boost converter.

  This configuration shows a case where a non-insulated power conversion circuit is specifically used as the LED drive power supply device.

  Moreover, as a preferable example of this invention, regarding the LED illumination device, the LED illumination device includes the LED drive power supply device described in any of the above and an LED that receives power supply from the LED drive power supply device.

  In this configuration, an LED illumination device including the above-described LED drive power supply device is shown. By providing the LED drive power supply device described above, an LED illumination device capable of stable light control operation can be realized.

  According to the present invention, it is possible to configure an LED drive power supply device and an LED lighting device capable of stably dimming even if dimming is performed in a range including extremely low luminance.

It is a figure which shows the structure of the LED lighting apparatus which concerns on embodiment of this invention. It is a circuit block diagram which shows the specific structure of the feedback control part 101 which concerns on embodiment of this invention. It is a figure which shows the gain characteristic and phase characteristic of the secondary side control circuit 120 and the primary side control circuit 110. It is a figure which shows the feedback voltage VFB waveform at the time of high-intensity control and ultra-low-intensity control.

  An LED drive power supply device and an LED illumination device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a configuration of an LED illumination device.

  The LED illumination device includes an LED drive power supply device 100 and an LED module 300. The LED module 300 is a light emitting module in which a plurality of LEDs are connected in a predetermined arrangement. A commercial AC power supply 200 is connected to the LED drive power supply device 100.

  The LED drive power supply device 100 inputs the voltage of the commercial AC power supply 200 from the power supply input terminals P11 and P12, and supplies DC power to the LED module 300 connected to the power supply output terminals P21 and P22. This LED drive power supply device 100 is basically an insulated PFC (power factor correction converter) that is driven in a discontinuous mode and a critical mode.

  The diode bridge DB performs full-wave rectification on the AC voltage input from the power input terminals P11 and P12. A series circuit of the primary winding of the transformer T and the switching element Q1 is connected to the output of the diode bridge DB. A capacitor Ci for removing current ripple and noise is connected to the output of the diode bridge DB.

  The transformer T is a transformer for constituting a flyback converter. The secondary winding of the transformer T is connected to a secondary side rectifying / smoothing circuit including a diode D1 and a capacitor C1.

  The diode bridge DB, the transformer T, the switching element Q1, the diode D1, and the capacitor C1 constitute a power conversion circuit.

  The power supply terminals P21 and P22 are connected to the output of the secondary side rectifying and smoothing circuit, and the LED module 300 is connected between the power supply terminals P21 and P22. A current detection resistor Rs is connected in series to the current path (ground side line) of the LED module 300.

  Although specific light control is described later, the feedback control circuit 101 performs the following control as a general feedback control function. In the present embodiment, a specific circuit configuration relating to feedback control of constant current supply is not illustrated, and only a circuit configuration used for dimming control is illustrated and described.

  The feedback control circuit 101 detects the voltage of the current Io flowing through the LED module 300 using the detection resistor Rs. The feedback control circuit 101 includes a secondary-side control voltage (a voltage at an inverting input terminal of an operational amplifier OP described later) obtained from the reference voltage Vref and the detected voltage, and a dimming pulse signal input from the dimming signal input terminal P31. A control signal for ON / OFF control of the switching element Q1 is generated so as to coincide with a reference voltage (voltage of a non-inverting input terminal of the operational amplifier OP described later) set by.

  Here, the dimming pulse signal is a signal for setting the current Io flowing through the LED module 300, that is, a signal for setting the luminance. The dimming pulse signal is a rectangular wave input from the outside of the LED drive power supply device 100. The luminance is set according to the on-duty (the ratio of the on-time in one cycle) of the dimming pulse signal. In the LED drive power supply device 100 of the present embodiment, the pulse frequency is set to 1000 Hz as the dimming pulse signal.

  When the switching element Q1 is turned on / off, the feedback control circuit 101 operates in a discontinuous mode so that the change in the current flowing through the power supply input terminals P11 and P12 is substantially sinusoidal in phase with the AC voltage Vac from the commercial AC power supply 200. Alternatively, the switching element Q1 is controlled in the critical mode. This allows the power conversion circuit to function as a PFC (power factor correction) converter.

  Specifically, the feedback control circuit 101 of this embodiment includes a primary side control circuit 110, a secondary side control circuit 120, and an insulating unit 130. FIG. 2 is a circuit configuration diagram showing a specific configuration of the feedback control circuit 101. In the following, description will be made in order from the secondary side according to the feedback path.

  The secondary side control circuit 120 includes a smoothing circuit 121 (corresponding to the “smoothing circuit” of the present invention) that smoothes the dimming pulse signal. The smoothing circuit 121 is a series circuit of a resistor Rf and a capacitor Cf, and the capacitor Cf is connected to the ground line. Here, the smoothing circuit 121 smoothes the dimming pulse signal so that a predetermined ripple remains. The predetermined ripple is set by the values of the resistor Rf and the capacitor Cf.

  At this time, the capacitor Cf is connected to the LED module 300 side of the current detection resistor Rs on the ground line.

  The collector of the pnp transistor Qp is connected to the resistance Rf side of the smoothing circuit 121. A reference voltage Vref is supplied to the emitter of the transistor Qp. The dimming signal input terminal P31 is connected to the base of the transistor Qp.

  A resistor Rb is connected in parallel to the transistor Qp. In addition, a discharge resistor Rd is connected in parallel to the capacitor Cf. The resistors Rb, Rf, and Rd are set to resistance values that make the voltage at the inverting input terminal and the voltage at the non-inverting input terminal of the operational amplifier OP the same in a state where no dimming pulse signal is input. .

  The connection point between the resistor Rf and the capacitor Cf of the smoothing circuit 121 is connected to the non-inverting input terminal of the operational amplifier OP via the resistor R10.

  In the series circuit of the resistor Rref and the resistor R1, the resistor R1 side is connected to the opposite side of the current detecting resistor Rs connected in series to the ground line to the smoothing circuit 121. A reference voltage Vref is supplied to the resistor Rref side. An inverting input terminal of the operational amplifier OP is connected to a connection point between the resistor Rref and the resistor R1. A series circuit of a capacitor C3 and a resistor R3 is connected in parallel to the resistor R1. Therefore, the divided voltage of the resistor Rref and the circuit composed of the resistors R1 and R3 and the capacitor C3 is applied to the inverting input terminal of the operational amplifier OP.

  A series circuit of a capacitor C2 and a resistor R2 is connected between the output terminal and the inverting input terminal of the operational amplifier OP.

  The operational amplifier OP, resistors R1, R2, R3, and capacitors C2, C3 constitute a controller 122. The gain and phase frequency characteristics shown in FIG. 3A are realized by appropriately setting the element values of the resistors R1, R2, and R3 and the capacitors C2 and C3. FIG. 3A is a diagram illustrating the feedback gain and phase characteristics of the secondary side control circuit 120. Specifically, as shown in FIG. 3A, the controller 122 of the present application has a characteristic that the gain becomes minimum near 100 Hz and increases to near 1000 Hz. As shown in FIG. 3A, the decrease in gain corresponding to the increase in frequency up to 100 Hz is determined by the capacitance of the capacitor C2, and the increase in gain from 100 Hz to 1000 Hz is determined by the resistance value of the resistor R1 and the capacitor C3. The gain of 1000 Hz or more is determined by the resistance value of the resistor R3.

  Thereby, the frequency characteristic of the feedback gain can be changed so as to decrease at a frequency near 100 Hz, which is twice the frequency of the commercial AC power supply supplied to the LED drive power supply device 100. That is, the gain can be set to a value that does not respond to the full-wave rectification pulsation of the commercial AC power supply, and noise caused by the commercial AC power supply can be prevented. Further, the gain at 1000 Hz which is the pulse frequency of the dimming pulse signal can be increased, and the ripple component of the dimming pulse signal can be left in the feedback voltage VFB described later. Here, the characteristics are set so as to suppress the gain decrease at 1000 Hz, but each element value may be set so as to suppress the gain decrease according to the pulse frequency. By doing so, the feedback signal can be attenuated in the vicinity of 100 Hz, and the feedback signal can be passed in the vicinity of 1000 Hz.

  Returning to FIG. 2, a photodiode of a photocoupler constituting the insulating means 130 is connected to the output terminal of the operational amplifier OP via a resistor. At this time, the cathode of the photodiode is connected to the output terminal of the operational amplifier OP via a resistor. A DC drive voltage Vcc2 is supplied from the anode of the photodiode.

  The collector and emitter of the phototransistor of the photocoupler constituting the insulating means 130 are connected to the primary side control circuit 110.

  The primary side control circuit 110 includes a constant current source Icom to which the drive voltage Vcc1 is supplied. The output terminal of the constant current source Icom is connected to the collector of the phototransistor, and the emitter of the phototransistor is connected to the ground line.

  Between the collector and emitter of the phototransistor, a series circuit of a resistor R5 and a capacitor C5 and a capacitor C4 are connected in parallel. The collector of the phototransistor is connected to the Q1 control signal generation circuit 111.

  Then, by appropriately setting the element values of the resistor R5 and capacitors C4 and C5, the gain and phase frequency characteristics shown in FIG. 3B are realized. FIG. 3B is a diagram showing the feedback gain and phase characteristics of the primary side control circuit 110. Specifically, as shown in FIG. 3B, the gain decreases as the frequency increases to around 100 Hz, and the gain maintains a predetermined level from around 100 Hz to around 1000 Hz, and the frequency further increases. Accordingly, the gain decreases.

  As shown in FIG. 3B, the gain corresponding to the increase in frequency up to 100 Hz is determined by the capacitance of the capacitor C5, and the gain from 100 Hz to 1000 Hz is determined by the resistance value of the resistor R5. The gain corresponding to the increase in frequency is determined by the capacitance of the capacitor C4.

  Thereby, similarly to the above-mentioned secondary side control circuit 120, the gain at 1000 Hz which is the pulse frequency of the dimming pulse signal can be maintained with respect to the frequency characteristic of the feedback gain, and the dimming is performed on the feedback voltage VFB described later. The ripple component of the pulse signal can be left. At this time, the gain of 100 Hz, which is twice the frequency of the commercial AC power supply, can be set so as not to be too high, and noise caused by the commercial AC power supply can be prevented. Here, as with the secondary side control circuit 120, the gain characteristics may be appropriately adjusted by appropriately setting each element value according to the frequency and pulse frequency of the commercial AC power supply.

  The Q1 control signal generation circuit 111 generates a control signal for controlling the switching element Q1 based on the feedback voltage VFB that is the collector voltage of the phototransistor, and outputs the control signal to the switching element Q1. The Q1 control signal generation circuit 111 generates a control signal for controlling the switching element Q1 such that Ton = α · VFB when the on-time of the switching element Q1 is Ton. Further, the Q1 control signal generation circuit 111 detects the timing when the current flowing through the power input terminals P11 and P12 becomes zero, and turns on the switching element Q1. Thereby, the LED drive power supply device 100 operates in the critical mode. In a light load, the Q1 control signal generation circuit 111 turns on the switching element Q1 after a predetermined time has elapsed after detecting the timing when the current flowing through the power input terminals P11 and P12 becomes zero. Thereby, the LED drive power supply device 100 operates in the discontinuous mode.

  When generating the control signal for controlling the switching element Q1 based on the feedback voltage VFB, the gains of the primary side control circuit 110 and the secondary side control circuit 120 are adjusted as described above, so that the pulse frequency Since the gain is high, the ripple component of the dimming pulse signal remains in the feedback voltage VFB. In other words, it is possible to obtain the feedback voltage VFB that intentionally leaves the ripple of the dimming pulse signal.

  By using the feedback control circuit 101 having the above configuration, dimming control is performed by the following operation.

  In the LED drive power supply device 100 of the present embodiment, the pulse frequency is set to 1000 Hz as the dimming pulse signal. Here, the pulse frequency refers to the frequency of a signal whose pulse rise timing is a 1/1000 second period. The dimming pulse signal used in the present embodiment is a signal that increases the on-duty when the luminance is decreased and decreases the on-duty when the luminance is improved.

(I) When increasing the brightness When increasing the brightness, the on-duty of the dimming pulse signal is decreased. As the on-duty decreases, the off-time of the transistor Qp becomes shorter. As a result, the voltage at the non-inverting input terminal of the operational amplifier OP approaches the reference voltage Vref and rises.

  When the voltage at the non-inverting input terminal of the operational amplifier OP increases, the voltage at the non-inverting input terminal with respect to the voltage at the inverting input terminal increases, and the output terminal voltage of the operational amplifier OP increases. When the output terminal voltage of the operational amplifier increases, the voltage applied to the photodiode decreases.

  When the voltage applied to the photodiode decreases, the amount of light emission decreases, the amount of light detected by the phototransistor decreases, and the voltage between the collector and emitter increases. As a result, the feedback voltage VFB input to the Q1 control signal generation circuit 111 increases.

  The Q1 control signal generation circuit 111 generates a control signal that lengthens the on-time of the switching element Q1 in response to the increase of the feedback voltage VFB, and supplies the control signal to the switching element Q1. Since the on-time of the switching element Q1 becomes longer, the power supplied to the LED module 300 increases. Thereby, it can control to the direction which raises LED brightness.

  At this time, the feedback voltage VFB has a high voltage value as shown in FIG. 4A, and is composed of a DC component and a ripple component. FIG. 4A is a diagram showing a waveform of the feedback voltage VFB at the time of high luminance control. However, since the amplitude of the DC component is significantly higher than the amplitude of the ripple component, there is almost no influence of the ripple component. In such a case, normal DC dimming control can be performed.

(Ii) When reducing luminance When reducing luminance, the on-duty of the dimming pulse signal increases. As the on-duty increases, the on-time of the transistor Qp decreases. As a result, the voltage at the non-inverting input terminal of the operational amplifier OP approaches the ground potential and decreases.

  When the voltage at the non-inverting input terminal of the operational amplifier OP decreases, the voltage at the non-inverting input terminal becomes relatively lower than the voltage at the inverting input terminal, and the output terminal voltage of the operational amplifier OP decreases. When the output terminal voltage of the operational amplifier decreases, the voltage applied to the photodiode increases.

  As the voltage applied to the photodiode increases, the amount of light emission increases, the amount of light detected by the phototransistor increases, and the voltage between the collector and emitter decreases. As a result, the feedback voltage VFB input to the Q1 control signal generation circuit 111 decreases.

  The Q1 control signal generation circuit 111 generates a control signal for shortening the on-time of the switching element Q1 in response to a decrease in the feedback voltage VFB, and supplies the control signal to the switching element Q1. Since the ON time of the switching element Q1 is shortened, the power supplied to the LED module 300 is reduced. Thereby, it can control to the direction which reduces the brightness | luminance of LED.

  At this time, by performing the above-described feedback gain control, the feedback voltage VFB is composed only of a ripple component as shown in FIG. FIG. 4B is a diagram showing a waveform of the feedback voltage VFB at the time of extremely low brightness control. As described above, even if extremely low luminance control is performed, the burst dimming operation is performed because the ripple component remains. In burst dimming, the luminance is adjusted according to the current off period. Therefore, the current is not reduced as much as DC dimming in which the luminance is adjusted according to the magnitude of the current in all periods, and the current can be stably operated. In addition, blinking of about 1000 Hz does not appear as flicker in human eyes. Thereby, generation | occurrence | production of the flicker which generate | occur | produces at the time of extremely low brightness | luminance like the past can be suppressed.

  As described above, by using the configuration and processing of the present embodiment, it is possible to perform dimming in which stable luminance is obtained even from extremely high luminance to extremely low luminance close to a light-off state. At this time, there is no need to perform a structure or processing for switching to two kinds of control methods such as DC dimming control at high luminance and PWM dimming control at low luminance, and the circuit element values of the feedback control circuit 101 are appropriately set. Only by setting, stable dimming can be performed.

  In the above description, the frequency of the dimming pulse signal is 1000 Hz. However, if the frequency is not substantially the same as the frequency of the commercial AC power supply, it may be set to a predetermined frequency higher than the frequency of the commercial AC power supply. .

  In this embodiment, an insulated PFC (power factor improvement) converter is shown, but the same control can be performed also in a PFC (power factor improvement) converter using a non-insulated buck-boost converter as a circuit system. .

DESCRIPTION OF SYMBOLS 100: LED drive power supply device, 101: Feedback control part, 110: Primary side control circuit, 111: Q1 control signal generation circuit, 120: Secondary side control circuit, 121: Smoothing circuit, 122: Controller, 130: Insulation means , 200: commercial AC power supply, 300: LED module

Claims (9)

A power conversion circuit that inputs power from an input power source and outputs power to the LED;
A feedback control unit that performs feedback control based on a dimming pulse signal for setting the luminance of the LED or the power supplied to the LED, and gives a control signal for controlling the power supplied to the LED to the power conversion circuit And comprising
The feedback control unit includes a smoothing circuit that smoothes the dimming pulse signal so that a predetermined ripple remains,
The gain of the feedback control is an LED drive power supply device that is set high at the frequency of the dimming pulse signal. The LED drive power supply device according to claim 1,
The gain of the feedback control is an LED drive power supply device set to a value such that the ripple remains in the control signal. The LED driving power supply device according to claim 1 or 2,
The power conversion circuit is a power factor correction converter that inputs the voltage of the commercial AC power supply and controls the supply current to the LED to change in a sine wave shape in phase with the voltage of the commercial AC power supply. Drive power supply. The LED drive power supply device according to claim 3,
The gain of the feedback control is an LED drive power supply device that is set to a value that does not respond to the pulsation of the commercial AC power supply. The LED drive power supply device according to any one of claims 3 and 4,
The gain of the feedback control is an LED drive power supply device that is set to sufficiently decrease in a frequency band twice that of the commercial AC power supply. The LED drive power supply device according to any one of claims 1 to 5,
An LED drive power supply device that performs burst dimming operation at the frequency of the dimming pulse signal when the LED is lightly loaded. The LED drive power supply device according to any one of claims 1 to 6,
The power conversion circuit is an insulated power conversion circuit including an insulation transformer that performs power conversion in an insulated state,
The feedback control unit includes a primary side control circuit that is an input side of the commercial AC power supply, a secondary side control circuit that is a side to which an LED is connected, the primary side control circuit, and the secondary side control circuit. And an insulating means for forming an insulated state feedback loop. The LED drive power supply device according to any one of claims 1 to 6,
The LED power supply device, wherein the power conversion circuit is a non-insulated buck-boost converter. The LED drive power supply device according to any one of claims 1 to 8,
An LED lighting device comprising: an LED that receives power supply from the LED driving power supply device.

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