JP2011018557A - Power supply circuit for led lighting, and led electric bulb mounted with the power supply circuit for led lighting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply circuit for LED (light-emitting diode) lighting with a high power factor at use as a commercial alternating-current power source in an inverter system capable of controlling light by a general light controller varying a power supply voltage or an average power supply voltage, and an LED electric bulb mounted with the power supply circuit for the LED lighting.SOLUTION: The power supply circuit for the LED lighting inputs a voltage to be applied on an inverter circuit into a light-controlling terminal DM provided at a control IC 1 by dividing it at a given partial pressure ratio to the control IC 1 controlling the inverter circuit. By this, the light control of an LED element becomes possible by a general light controller varying the power supply voltage or the average power supply voltage.

Description

  The present invention relates to an inverter-type LED (light-emitting diode) lighting power circuit that can be dimmed by a general dimmer that varies a power supply voltage or an average power supply voltage, and an LED bulb equipped with the LED lighting power circuit.

  In recent years, bulb-type fluorescent lamps and LED bulbs have been manufactured and sold as alternative light sources to replace inefficient incandescent bulbs and halogen bulbs. In these bulb-type fluorescent lamps and LED bulbs, a power supply circuit including an inverter circuit is often used.

  The power supply circuit built in the LED bulb is usually composed of a rectifier circuit and an inverter circuit. Here, the rectifier circuit converts AC power supplied from a commercial power source into DC power, and includes, for example, a bridge-connected diode and a smoothing capacitor. The inverter circuit converts DC power input through the rectifier circuit into high-frequency power, and includes a transformer and a coil that perform step-down / step-up and a control IC that performs high-frequency switching.

JP 2004-192833 A

  Most of the above control ICs incorporate a circuit (constant current circuit) that keeps the current flowing through the LED element constant in order to prevent the luminance from changing when the input voltage to the inverter circuit fluctuates. (For example, cited document 1). Thereby, even if the power supply voltage input to the inverter circuit fluctuates, the LED element can emit light with a constant luminance. On the other hand, there arises a problem that light control cannot be performed by changing the power supply voltage (or the average value of the power supply voltages). In facilities such as hotels, wedding halls, restaurants, etc. where the brightness of lighting needs to be changed depending on events, weather, time zones, etc., dimming is generally performed by changing the power supply voltage or the average power supply voltage. Therefore, conventional LED bulbs cannot be used, and cannot be used as an alternative to incandescent bulbs that are scheduled to be discontinued in the future. In addition, there are an increasing number of cases where dimmers with a variable power supply voltage are incorporated in small-scale applications such as homes. Similarly, replacing incandescent bulbs with conventional inverter-type fluorescent lamps and LED bulbs Can not.

  Inverter circuits with a built-in constant current circuit exhibit negative resistance characteristics, so if the voltage supplied to the power supply circuit (power supply voltage) is decreased, a current exceeding the allowable value flows into the inverter circuit and damages the circuit. There is a fear. Therefore, it is prohibited to use a conventional inverter-type LED bulb for the dimmer that varies the power supply voltage. In addition, the conventional inverter type light bulb type fluorescent lamp and LED light bulb convert the voltage and current by the inverter circuit after rectifying the alternating current into the direct current, but a smoothing capacitor is added to the rectifier circuit. Therefore, it becomes a capacitor input type rectifier circuit. As a result, the current flowing into the inverter circuit has a pulse shape including many harmonics peculiar to the capacitor input type, and the power factor is about 0.6. Electricity companies discount or increase electricity charges even if the power factor is high or low. If many LED bulbs with such low power factor are used, the electricity charge becomes high. On the other hand, the delay power factor due to inductive loads such as motors and ballast-type fluorescent lamps can be easily improved by adding a phase advance capacitor, but a large capacity coil is required to improve such a lead phase. It is not easy. In addition, when a large amount of harmonics is generated, an excessive current may flow through the power factor improving phase-advancing capacitor connected to the same power system, causing a failure.

  The problem to be solved by the present invention is to provide an LED lighting power supply circuit having a high power factor close to 1 using a general inverter circuit control IC, and to supply power voltage or an average value of the power supply voltage. It is providing the inverter-type LED lighting power supply circuit which can be dimmed using the dimmer which makes variable.

An LED lighting power supply circuit according to the present invention made to solve the above problems is as follows.
In an LED lighting power supply circuit including an inverter circuit that converts a DC voltage into a high-frequency voltage using a control IC having either a dimming terminal or a reference power supply input terminal for a current detection circuit, applied to the inverter circuit A voltage dividing unit that divides a power supply voltage or a voltage obtained by lowering the power supply voltage by a predetermined voltage at a predetermined voltage dividing ratio, and the voltage divided by the voltage dividing unit is used for the dimming terminal or the current detection circuit; Input to the reference power input terminal.

  According to the LED lighting power supply circuit of the present invention, the power supply voltage applied to the inverter circuit or a voltage obtained by lowering the power supply voltage by a predetermined voltage at a predetermined voltage dividing ratio or the dimming terminal of the control IC of the inverter circuit or Input to the reference power supply input terminal for the current detection circuit. Thereby, when the power supply voltage is changed, the voltage applied to the dimming terminal or the reference power supply input terminal for the current detection circuit also changes at the same ratio. Therefore, the amount of current supplied to the LED by changing the power supply voltage is also increased. Will change. Therefore, it is possible to perform dimming using a dimmer that varies the power supply voltage.

  The LED lighting power supply circuit of the present invention does not add any special circuits or components to the conventional power supply circuit. Therefore, it is possible to perform dimming using a dimmer that varies the power supply voltage without substantially increasing the cost for manufacturing the LED bulb. In addition, this makes it possible to replace incandescent light bulbs and halogen light bulbs in large facilities such as hotels and restaurants, which can greatly contribute to power saving.

  Further, the above inverter circuit has a characteristic that it does not have negative resistance characteristics. Therefore, by adding a rectifier circuit to the power supply circuit of the present invention and further removing or reducing the smoothing capacitor normally used in the rectifier circuit, the output of the rectifier circuit is pulsated and the current and voltage flowing from the commercial power supply The waveform and phase can be substantially matched. As a result, a power factor close to 1 can be obtained. In addition, since almost no harmonics are generated, even if the incandescent light bulb or halogen light bulb is replaced with an LED light bulb with a built-in power supply circuit according to the present invention in a large facility such as a hotel or restaurant, an extra charge is paid due to the power factor decrease. There is no worry and there is no risk of damage to the facility and surroundings due to harmonics, which can greatly contribute to power saving.

The circuit diagram which shows the power supply circuit for the conventional LED lighting connected to DC power supply. The circuit diagram which shows 1st Example of the power circuit for LED lighting which concerns on this invention. The schematic circuit diagram which shows the internal structure of control IC, and its periphery. The wave form diagram for operation | movement description of the power circuit for LED lighting of a prior art example. The wave form diagram at the time of changing the voltage of the light control terminal of control IC in the power supply circuit for LED lighting of a prior art example. The wave form diagram for operation | movement description of the power circuit for LED lighting of 1st Example. The circuit diagram which shows the power supply circuit for the conventional LED lighting connected to AC power supply. The circuit diagram which shows 2nd Example of the power circuit for LED lighting which concerns on this invention. The figure which shows the electric current and voltage waveform in a prior art example. The figure which shows the electric current and voltage waveform at the time of removing the smoothing capacitor in the rectifier circuit of a prior art example, or making capacity | capacitance small. The figure which shows the electric current and voltage waveform of 2nd Example. The wave form diagram for operation | movement description of the power circuit for LED lighting of 2nd Example. Circuit diagram (a) around the dimming terminal DM showing a first modification of the partial pressure to the dimming terminal DM, circuit diagram (b) around the dimming terminal DM showing a second modification, and a third modification The circuit diagram (c) around the dimming terminal DM shown.

A first embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a circuit diagram showing a conventional LED lighting power supply circuit using a DC power supply, and the brightness can be adjusted by applying a prescribed voltage to the dimming terminal DM through a volume or the like. FIG. 2 is a circuit diagram of an LED lighting power supply circuit capable of dimming by varying the power supply voltage according to the present embodiment. The power supply voltage is divided by voltage dividing resistors R4 and R5 and input to the dimming terminal DM.
In the circuit diagrams of FIG. 1 and FIG. 2, a portion having an important meaning in the present embodiment is surrounded by a broken line.

  FIG. 3 shows a simplified internal structure of a general LED lighting inverter circuit control IC used in FIGS. 1 and 2. The general operation of this control IC will be described with reference to the circuit diagram of FIG. 3 and the waveform diagram of FIG. As the control IC, for example, LT3755 (or LT3755-1) manufactured by Linear Technology, Inc. can be used. In this LT3755 (LT3755-1), the CTRL terminal corresponds to the dimming terminal DM.

  The control IC 1 includes a stabilized power supply circuit that generates a stable power source used by the control IC 1, a reference clock (OSC) serving as a reference for operation, and a flip-flop whose output is normally rotated at a rising edge of the clock signal of the OSC ( FF), a driver for enhancing the driving capability required to drive the transistor or field effect transistor (FET) provided outside or inside the output of the FF, and current detection for detecting a current flowing through the transistor or FET There is a dimming terminal DM for inputting a comparison voltage for the terminal CS and the current detection terminal CS and changing the brightness.

  The top waveform in FIG. 4 is a clock signal in the OSC, and the output (Q) of the FF is normally rotated at the rising edge thereof, and the FET is turned on through the driver. As a result, the drain voltage VD of the FET drops from approximately the power supply voltage to approximately 0 V, a current flows through the FET via the coil L1, is converted into a voltage by the resistor R2, and is input to the current detection terminal CS.

  The current flowing through the coil L1 increases in proportion to time, and the proportionality coefficient (slope) is inversely proportional to the inductance of the coil L1 and proportional to the power supply voltage. When the voltage of the current detection terminal CS becomes equal to the voltage of the dimming terminal DM, that is, when the current of the coil L1 reaches a specified value, the output of the comparator is rotated forward, and the output is passed through the reset RST terminal of the FF. Is reset. As a result, the Q of FF falls to 0 and the FET is turned off.

Incidentally, the energy supplied to the LED element LED1~LEDn by energizing once FET corresponds to the energy stored in the coil L1, the (current flowing through the coil ^L1) 2/2 × (the inductance of the coil L1) Therefore, even if the power supply voltage fluctuates, the current value of the coil L1 is kept constant. Thereby, constant energy is always supplied to LEDn from LED1 connected in series.

  Next, since the gradient of the current flowing through the coil L1 is proportional to the voltage, the time required for the comparator to rotate forward is fast when the power supply voltage is high, and slow when the power supply voltage is low. This means that when the period of the OSC clock signal is constant, as shown in the waveform of the drain voltage VD in FIG. 4, the FET is energized only for a short time when the power supply voltage is high, and is energized for a long time when the power supply voltage is low. That is, when the power supply voltage is high, the average current of the power supply decreases, and when the power supply voltage is low, the average current increases. Therefore, it can be seen that the conventional power supply circuit shown in FIG. 1 exhibits a negative resistance characteristic in which voltage and current are inversely proportional.

  Although this is an advantage that the brightness of the illumination does not change even if the power supply voltage fluctuates, the commercial power supply is intermittently energized using semiconductor switches such as thyristors and triacs that are mainly used in the market. Therefore, dimming is possible not only when dimming the power supply voltage with a single winding transformer called slidac, but also when the power supply voltage drops. If a current several times the specified current flows through the protective circuit, the protection circuit such as a fuse may be burned out and damaged. Therefore, many LED bulbs and bulb-type fluorescent lamps are prohibited from being used for such dimmers that vary the power supply voltage.

On the other hand, the operation when the voltage of the dimming terminal DM in FIG. 3 is changed will be described with reference to FIG.
When the power supply voltage is constant, the slope of increase in the current flowing through the coil L1 is constant. Therefore, when the voltage at the dimming terminal DM is low, the current in the coil L1 reaches a specified value in a short time, and the output Vcmp of the comparator The output level becomes H (High), the FF is reset, and the FET is turned off. As a result, the energy stored in the coil L1 is controlled by the level of the terminal voltage of the dimming terminal DM.

FIG. 6 is a waveform diagram showing the operation of the LED lighting power supply circuit of this embodiment shown in FIG. 2, and a voltage obtained by dividing the power supply voltage at a predetermined ratio is inputted to the dimming terminal DM. Here, the power supply voltage is V, the inductance of the coil L1 is L, the current flowing in the coil L1 after time t after the FET is turned on is i, the value of the current detection resistor R2 is R, and the dimming terminal DM is input. I = (V / L) · t, where r is the voltage division ratio of the voltage to the power supply voltage V
i ・ R = V / r
When these two simultaneous equations are solved for t, t = L / r · R
Thus, the time during which the FET is turned on is constant regardless of the power supply voltage, and is determined by the value of the inductance L of the coil L1, the voltage dividing ratio r of the voltage input to the dimming terminal DM with respect to the power supply voltage V, and the current detection resistor R2. Value.

  From the above, by dividing the power supply voltage with a resistor or the like and inputting a voltage proportional to the power supply voltage to the dimming terminal DM, a current proportional to the power supply voltage flows as shown in the graph of FIG. Thus, dimming can be performed by changing the power supply voltage.

  A second embodiment of the LED lighting power supply circuit according to the present invention will be described with reference to FIGS. In this embodiment, a rectifier circuit is added in front of the circuit of the first embodiment, and a commercial power supply (AC power supply) is connected to the power supply circuit of this embodiment.

FIG. 7 is a circuit diagram of a conventional LED lighting power supply circuit using a commercial power supply. Further, FIG. 8 shows that the luminance of the LED element can be changed by using a dimmer for dimming the bulb by changing the power supply voltage or the average value of the power supply voltage according to this embodiment, and the power factor is 1 is a circuit diagram showing a high power factor LED lighting power supply circuit close to 1. FIG.
In the circuit diagrams of FIG. 7 and FIG. 8, like the first embodiment, portions having an important meaning in the present embodiment are surrounded by broken lines.

  In the conventional example shown in FIG. 7, the commercial power supply is rectified by a bridge-connected diode D2 via a protective element R6 made of a fuse or a minute resistance that breaks when the circuit is abnormal, and then smoothed by a smoothing capacitor C4. It passes through the prevention coil L2 and capacitor C3, and is input to an inverter circuit composed of the control IC1, coil L1, FET, and the like. The dimming terminal DM is connected to a power supply Vcc stabilized in the control IC 1 divided by a volume, and the current flowing from the LED 1 connected in series to the LED n can be changed to change the luminance thereof. it can. On the other hand, since the current flowing through these LED elements does not change even when the power supply voltage is changed, dimming by a general dimmer cannot be performed, and when the power supply voltage decreases, the power supply current reaches several times the rated current. In some cases, the diode D2 may burn out or the protective element R6 may break.

  The second embodiment shown in FIG. 8 is an example in which a commercial power supply is used as in the conventional example of FIG. 7, but unlike FIG. 7, the power supply voltage is divided by voltage dividing resistors R4 and R5, and the dimming terminal DM is used. Is entered. Accordingly, the current (or average current) flowing through the LED element can be changed by changing the power supply voltage (or average power supply voltage) as in the first embodiment, and the light is adjusted using an external dimmer. Is possible.

Next, the power factor of the LED lighting power supply circuit according to the second embodiment will be described.
First, FIG. 9 shows the operation of the capacitor input type rectifier circuit in the conventional example of FIG. The upper solid line in FIG. 9 shows the voltage waveform of the commercial power supply, which is converted into full-wave rectification by the diode D2, and smoothed by the smoothing capacitor C4. As a result, most of the pulsating flow of full wave rectification disappears, resulting in a voltage waveform (V (C4)) as shown by the broken line. The operation of this rectifier circuit is as follows. First, the smoothing capacitor C4 is charged to the peak value of the commercial power supply. After that, the voltage of the commercial power supply decreases with a sine curve, but the voltage of the smoothing capacitor C4 does not drop suddenly due to the electric charge accumulated in the capacitor, so that the diode D2 becomes non-conductive, and power is supplied from the commercial power supply. It will not be supplied. During this time, the inverter circuit continues to operate due to the electric charge accumulated in the smoothing capacitor C4, so that the voltage of the smoothing capacitor C4 decreases. When the absolute value of the voltage of the commercial power supply increases and exceeds the voltage of the smoothing capacitor C4, the diode D2 becomes conductive again.

  Since the capacitor input type rectifier circuit repeats the above-described operation, there are times when current flows and when current does not flow as indicated by the lower solid line in FIG. Further, the peak of the current waveform is advanced in phase from the voltage waveform, and further, the current waveform includes a large amount of harmonics instead of a sine wave of the commercial power supply frequency. When this smoothing capacitor C4 is removed or made smaller, the intermittent current specific to the capacitor input type and the phase-advanced current with respect to the power supply voltage does not flow, and the voltage waveform and phase match. However, since the relationship between the voltage and current of the inverter circuit of the load is a negative resistance, the current waveform is as shown in FIG. 10, and although the power factor and harmonic noise are improved as compared with the capacitor input type, the sine wave Far away, the power factor remains after 0.7-0.8.

  On the other hand, in the present embodiment in which the smoothing capacitor C4 is similarly removed or reduced, since the negative resistance characteristic of the inverter circuit has disappeared, a current proportional to the power supply voltage flows, and its current waveform is As shown in FIG. As a result, the phase of the voltage and current match, and a current proportional to the voltage flows. Therefore, the current waveform becomes a sine wave proportional to the voltage, the power factor becomes approximately 1 and almost no harmonics are included. become. It should be noted that the specific value of the capacity of the smoothing capacitor C4 is desirably 22 μF or less per 1 A of consumed current.

  FIG. 12 shows the operation of the AC power supply half cycle in the power supply circuit of this embodiment. From this figure, it can be seen that when a voltage correlated with the power supply voltage is input to the dimming terminal DM, a power supply current correlated with the power supply voltage flows.

  Further, in the conventional example of FIG. 7, the LED group composed of LEDs 1 to LEDn is supplied with a constant energy regardless of fluctuations in the power supply voltage. Therefore, the capacitor C1 connected in parallel with these LED groups is the chopping frequency of the inverter. In this case, it is only necessary to store a charge and to allow a stable current to flow through the LED. Further, since the chopping frequency is as high as several tens KHz to several hundreds KHz, the capacitance may be 1 μF or less. On the other hand, in the power supply circuit of the present embodiment shown in FIG. 8, the current flowing through the LED group becomes a full-wave rectified waveform of the commercial power supply, and therefore blinks at a frequency twice the commercial power supply frequency. Since this frequency is much shorter than the period in which the human eye can distinguish between light and dark, it does not give discomfort, but by using a capacitor of several hundred to several thousand μF that can be expected to have a storage effect in the power supply frequency band. , Can emit more stable light.

  1, 2, 7, and 8, the capacitor symbol is a common capacitor symbol and an electrolytic capacitor symbol, and this is used for different types of capacitors. It is not used to indicate the capacity value. Here, the general capacitor symbol indicates approximately 1 μF or less, and the electrolytic capacitor symbol indicates a capacitance value higher than that.

  In FIG. 2, FIG. 8, and the above description, the voltage input to the dimming terminal DM is obtained by dividing the power supply voltage by a resistor. However, as shown in FIG. There are many methods such as using a buffer amplifier as in (b).

  FIG. 13C is a circuit example that enables a more stable operation when a dimmer that varies the power supply voltage (or average power supply voltage) is used. When the power supply voltage is lowered for dimming from the outside, the power supply voltage of the control IC 1 is lowered and the operation of the control IC 1 becomes unstable. As a result, the lighting may flicker or the operation of the control IC may suddenly stop at a certain voltage. In order to prevent such a problem that the illumination suddenly disappears, in the modified example of FIG. 13C, a diode having a Zener effect is added to the voltage dividing circuit of the power supply voltage input to the dimming terminal DM.

  In the case of voltage division by the resistors R3 and R4 shown in FIGS. 2 and 8, assuming that the power supply voltage is Vp, the voltage Vdm input to the dimming terminal DM is Vdm = Vp · R4 / (R3 + R4). On the other hand, when a Zener diode ZD1 having a Zener voltage of Vz is added as shown in FIG. 13C, Vdm = (Vp−Vz) · R4 / (R3 + R4). Therefore, when the power supply voltage becomes Vz or less, the DM terminal Input voltage becomes 0V. If the zener voltage Vz is set to be equal to or higher than the operating voltage of the control IC1, the LED current decreases to 0 in a state where the IC1 operates normally, so that the LED is turned off before the control IC1 becomes unstable.

  In the modification of FIG. 13C, a constant current element (or constant current circuit) CC is also used, and a substantially constant current can flow through the Zener diode ZD1 even if the power supply voltage changes. Furthermore, the phenomenon that the light is suddenly turned off also smoothly turns off when the power supply voltage Vp approaches the zener voltage Vz. Therefore, the LED light bulb using the power supply circuit of the present modification has the same dimming characteristics as the conventional incandescent light bulb. Can be prepared.

  The inverter circuit control IC is not limited to the above-described LT3755 (or LT3755-1), but may be one having a similar function such as LM3409 manufactured by National Semiconductor USA. In the case of LM3409, since the IADJ terminal corresponds to the dimming terminal DM, a voltage obtained by dividing the power supply voltage may be input to the IADJ terminal.

  In addition, when a reference power input terminal for the current detection circuit is used instead of the dimming terminal and a voltage obtained by dividing the power supply voltage is input to the reference power input terminal for the current detection circuit, the same result as in the above embodiment is obtained. Is obtained.

  Further, the circuit of the above embodiment shows general examples, and it goes without saying that the circuit is not limited to these embodiments.

1 ... Control IC
C1, C2, C3, C3 ', C4, C4' ... Capacitor CC ... Constant current element CS ... Current detection terminal DM ... Dimming terminal L1, L2 ... Coil LED1, ..., LEDn ... LED elements R1, R2, R3, R4 , R5 ... resistance

Claims (8)

  In an LED lighting power supply circuit including an inverter circuit that converts a DC voltage into a high-frequency voltage using a control IC having either a dimming terminal or a reference power supply input terminal for a current detection circuit, applied to the inverter circuit A voltage dividing means for dividing a power supply voltage or a voltage obtained by lowering the power supply voltage by a predetermined voltage at a predetermined voltage dividing ratio, and the voltage divided by the voltage dividing means for the dimming terminal or the current detection circuit; An LED lighting power supply circuit characterized by being input to a reference power supply input terminal.   2. The LED lighting power supply circuit according to claim 1, wherein an AC power supply voltage is supplied to the inverter circuit through a rectifier circuit.   The LED lighting power supply circuit according to claim 2, wherein the rectifier circuit does not have a capacitor for smoothing an AC power supply voltage.   3. The LED lighting power supply circuit according to claim 2, wherein the rectifier circuit has a smoothing capacitor of 22 μF or less per 1 A of consumption current.   5. The voltage division to the dimming terminal or the reference power supply input terminal for the current detection circuit is performed after the voltage is reduced by a constant voltage from the power supply voltage by an electronic component having a constant voltage effect. LED power supply circuit according to any one of the above.   6. The LED lighting power supply circuit according to claim 5, wherein the electronic component is a Zener diode or an electronic component having the same function.   In an LED lighting power supply circuit including an inverter circuit that converts a DC voltage into a high-frequency voltage, the output of the inverter circuit is always turned on for a first fixed time and turned off for a second fixed time regardless of the power supply voltage. Thus, the LED lighting power supply circuit, wherein the inverter circuit does not exhibit a negative resistance.   8. An LED bulb comprising the LED lighting power supply circuit according to claim 1 mounted thereon.

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