JP2013008632A - Led power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LED power supply circuit which allows for switching to a control method that can minimize decrease of light by preventing the circuit loss from increasing when the driving voltage of an LED rises.SOLUTION: The LED power supply circuit comprises: a power supply means 8; a voltage detection means (R, R); a current detection means (R); and a control circuit 12. The power supply means 8 has a conversion section for converting an input power Pinto a drive power P. The voltage detection means detects the driving voltage Vto the LED, and the current detection means detects a driving current I2. Furthermore, an input power acquisition means 6 for acquiring the input power Pvalue is provided. The control circuit 12 has a difference operation section for calculating the difference (P-P) between the input power Pvalue and the product Pof the driving voltage value and the driving current value. A constant loss control section for controlling the conversion rate of the conversion section so that the difference becomes constant, and a constant current control section for controlling the driving current Ivalue to be constant are also provided, and switching is made to constant loss control when the driving voltage Vvalue exceeds a reference voltage.

Description

  The present invention relates to an LED power supply circuit used for lighting a light emitting diode (hereinafter referred to as an LED (Light Emitting Diode)).

  In recent years, the performance of LED elements has increased, and lighting fixtures using LEDs are in a state where they can be replaced with conventional light sources due to their long life. If the performance of LEDs is further improved in the future, it will be adopted in the field of general-purpose lighting equipment.

  Since the LED has a characteristic that the electrical resistance decreases as the temperature rises due to lighting, it is fundamental to perform constant current control in the lighting fixture. However, if the LED drive voltage rises due to environmental changes such as ambient temperature during constant current control, power exceeding the rated power will be supplied from the external power supply to the LED power supply circuit, resulting in increased circuit loss. End up. As a result, there is a problem that the failure rate of the LED power supply circuit increases. Further, when the LED element (or LED light emitting unit) is replaced, the drive voltage on the LED side may change, and the same problem may occur.

  Patent Document 1 discloses an LED drive device having a control method for switching between constant current control and constant power control based on the LED drive voltage (voltage between terminals).

Japanese Patent No. 4100400

  However, in the LED driving device of Patent Document 1, detailed investigation has not been made on the circuit loss after the transition from the constant current control to the constant power control, and the light reduction width increases with the transition. There was a problem.

  The present invention has been made in view of the above points, and suppresses an increase in light loss while preventing an increase in circuit loss when an LED drive voltage increases during constant current control. An object of the present invention is to provide an LED power supply circuit that can be switched to a control method capable of performing

  In order to achieve the above object, the present inventor paid attention to the fact that the upper limit value of the allowable circuit loss is determined by the size of the case of the LED power supply circuit, and the LED drive current so that the circuit loss becomes constant. Circuit loss constant control (hereinafter referred to as constant loss control) is realized. Then, when the LED drive voltage increases during constant current control and reaches a set value, a control switching method is executed to execute the transition from constant current control to constant loss control, and the present invention is completed. It was.

  That is, the LED power supply circuit according to the present invention includes power supply means, voltage detection means, current detection means, and control means. First, the power supply means includes an input unit that receives an external power supply, a conversion unit that converts input power into a drive voltage and a drive current necessary for the LED, and an output unit that outputs the drive voltage and the drive current to the LED. The voltage detection unit detects a drive voltage value of the output unit, and the current detection unit detects a drive current value of the output unit. The control means controls the power supply means based on the detected drive voltage value and drive current value.

  The LED power supply circuit is further provided with input power acquisition means for acquiring the input power value of the input unit. The control means includes a difference calculation unit, a constant loss control unit, a constant current control unit, and a control selection unit.

  The difference calculation unit calculates a difference between the acquired input power value and a product of the drive voltage value and the drive current value. The constant loss control unit controls the conversion rate of the conversion unit so that the calculated difference becomes constant. The constant current control unit controls the conversion rate of the conversion unit so that the detected drive current value becomes constant. The control selection unit selects the control by the constant current control unit when the drive voltage value is less than the reference voltage, and selects the control by the constant loss control unit when the drive voltage value is equal to or higher than the reference voltage. .

  The control means further includes an overvoltage protection control unit. The overvoltage protection control unit prevents application of a drive voltage higher than a predetermined voltage to the LED. The control means includes an overcurrent protection control unit. The overcurrent protection control unit prevents a drive current that is equal to or greater than a predetermined current from being supplied to the LED.

  The input power acquisition means has a data table including a plurality of preset input power values, and reads out one corresponding input power value from the data table according to the detected drive voltage value. ing.

  According to the present invention, even if the LED drive voltage increases during execution of constant current control, switching from constant current control to constant loss control can prevent an increase in circuit loss, and Thus, the amount of decrease in light of the LED illumination can be suppressed smaller than the conventional switching to constant power control.

It is a whole block diagram of the LED lighting fixture which concerns on this invention. It is a block diagram of the LED power supply circuit of this invention. It is a figure explaining the case where a drive voltage rises during the conventional constant current control. It is a figure for demonstrating the problem of the constant power control in the conventional power supply circuit. It is a figure for demonstrating the effect of the constant loss control in the power supply circuit of this invention. It is a drive power characteristic figure of the said LED power supply circuit. It is a circuit loss characteristic view of the LED power supply circuit.

  Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the overall configuration of an LED lighting apparatus according to this embodiment. The LED lighting apparatus includes an LED element array 2 and an LED power supply circuit 4 that supplies DC power to the LED element array 2. The power source of the LED power circuit 4 is an AC power source AC.

<Overall configuration of LED power supply circuit>
The LED power circuit 4 includes input power acquisition means 6, power supply means 8, voltage detection means (R ₁ , R ₂ ), and current detection means (R ₃ ). Input power acquisition unit 6 detects the input voltage V ₁ and an input current I1 from AC, to calculate the input power P ₁ from these detected values. A specific method for calculating the input power P ₁ is to first calculate the instantaneous power value (V ₁ × I ₁ ), add the instantaneous power value for one cycle, and then add the total value as the number of additions in one cycle. a method to input power P ₁ a numerical value obtained by dividing. Gives the P ₁ value, an input power value supplied to the input of the power supply means 8, the built-in control means (control circuit 12) to the power supply means 8.

Power supply means 8 generates a drive power P ₂ required from the AC power to the lighting of the LED element array 2, for example, a like flyback converter that will be described later. In the present embodiment, an IC chip is built in the power supply means 8 as the control circuit 12. However, the control circuit 12 may be a circuit provided independently from the power supply unit 8.

The voltage detection means has a series connection of resistors R ₁ and R ₂ . This series connection connects a pair of output terminals of the power supply means 8. Then, the terminal voltage of the resistor R ₁ is detected as a divided voltage V ₃ of the drive voltage, and this V ₃ value is given to the control circuit 12 of the power supply means 8. The control circuit 12 calculates the drive voltage V ₂ from the detected value of the divided voltage V ₃ based on the resistance values of the resistors R ₁ and R ₂ . Therefore, the voltage detection means substantially detects the drive voltage V ₂ from the output part of the power supply means 8.

The current detection unit includes a resistor R ₃ that connects the negative output terminal of the power supply unit 8 and the negative terminal of the LED element array 2. Then, the voltage V ₄ between the terminals of the resistor R ₃ is detected, and this V ₄ value is given to the control circuit 12. In the control circuit 12, based on the resistance value of the resistor _{R 3,} calculated from the detected value of the voltage _{V 4} of the resistor _{R 3} a driving current _{I 2.} Accordingly, the current detecting means so that detects the driving current I ₂ from the output section of substantially the power supply unit 8.

The control circuit 12 controls the power supply means 8 based on the given input power P ₁ value, drive voltage V ₂ value, and drive current I ₂ value.

<Control system for power supply means>
The control system of the power supply means 8 will be described in detail based on FIG. The power supply means 8 includes an AC power input unit 14, a power conversion unit 16, and a drive power output unit 18.

The input unit 14 includes a full-wave rectifying circuit DB constituted by such as a diode bridge, and a bypass capacitor C _1. Bypass capacitor C ₁ is intended for connecting an output terminal to each other in the full-wave rectifying circuit DB, to partial smoothing the rectified current from the full-wave rectifying circuit DB, and was intermittently by off driving of the charging switching element Q ₁ It is provided to prevent the influence of current from reaching the AC power supply side.

The output unit 18 includes an output capacitor C ₃ (electrolytic capacitor) connected in parallel to the LED element array 2. Then, stable driving power P ₂ is supplied to the LED element array 2 using the energy stored in the output capacitor C ₃ .

Converter 16 is connected downstream of the full-wave rectifying circuit DB, charging the output capacitor C ₃ a rectified current to the power converter. Converter 16 of the present embodiment is called a flyback converter, for supplying a constant current to the LED element array 2 through the output capacitor C _3. The conversion unit 16 also functions as a power factor correction circuit, and is a circuit capable of shaping an alternating current input to the full-wave rectifier circuit DB into a sine wave without distortion.

Conversion unit 16 includes a specific flyback transformer T _1, the charge switching element Q _1, a diode D _2, and a control circuit 12 which controls the charge switching element Q _1. Transformer T ₁ is provided so as to apply a secondary voltage on the output capacitor C ₃ a rectified voltage after full-wave rectification as the primary voltage.

Charging switching element Q ₁ is, they are serially connected to the primary winding T _1a of the transformer T _1, to induce a secondary voltage in the secondary winding T _1b by on-off driving. The drain terminal of the charging switching element Q ₁ is connected to the primary winding T _1a, the source-side terminal of Q ₁ is connected to the ground line is a negative terminal side of the full-wave rectifying circuit DB. The switching element _{Q 1} using the enhancement type N-channel MOSFET. When the gate voltage is driven current is supplied to the gate of the switching element Q ₁ from the drive circuit provided in the control circuit 12 occurs, the drain - current flows between the source. This state of the ON state of the switching element Q _1. On the other hand, a state where no drive current is supplied to the gate and no drain current flows is called an off state. Diode D ₂ is connected in series to rectify the secondary current in the secondary winding T _1b, it supplies a secondary current after rectification to the positive electrode of the output capacitor C _3.

The conversion unit 16 is provided with a noise removal circuit. Noise removal circuit is constituted by a series circuit of a diode D ₁ and the noise removal capacitor C _2, a resistor R _4. The series circuit (D ₁ and C ₂ ) is connected so as to connect both terminals of the primary winding of the transformer T ₁ . Here, the anode terminal of the diode D ₁ is connected to the connection point of the charging switching element Q ₁ and the primary winding T _1a, the cathode-side terminal is connected to the noise removal capacitor C _2. Noise removal capacitor C ₂ and the resistor R ₄ forms a parallel circuit.

Conversion unit 16 is constructed as described above, storing energy based on the rectified current to the output capacitor C _3. The driving current I2 to the LED element array 2 is adapted to be supplied by being stored in the output capacitor C ₃ energy.

The control circuit 12 includes a microcomputer (CPU), an AD converter for detecting the voltage or the like, and the FET driving circuit for supplying a drive current to the charge switching element _{Q 1,} a ROM and RAM, the charge switching element We are building a drive control system of Q _1.
When the control circuit 12 is expressed by a functional block, as shown in FIG. 2, the control circuit 12 includes a difference calculation unit 22, a constant current control unit 24, a constant loss control unit 26, and a control selection unit 28. The control circuit 12 further includes an overvoltage protection control unit 32, an overcurrent protection control unit 34, and a protection control selection unit 36.

In the CPU, for example, the switching period is determined based on the divided voltage value of the voltage after full-wave rectification, and the ON width is determined based on the drive current I ₂ value of the LED element array 2 detected via the resistor R _3. (On-state time) is determined. CPU sends a command signal determined switching period and ON widths in the MOSFET drive circuit for the switching element _{Q 1.} Driving circuit for Q ₁ represents a drive current based on the command signal supplied to the Q _1, which turns on and off the drive.

<About constant current control>
Constant current control unit 24, by driving the charge switching element Q _1, power factor improvement control also the charge switching element Q ₁ to perform simultaneously while performing constant current control of the current flowing through the LED element array 2 High-frequency switching control. That is, the control circuit 12 controls the detected driving current I ₂ value preset by the switching of the charging switching element Q ₁ so as to approach the current value and ON width (conversion). In the on state the charge switching element Q _1, the full-wave rectified current is stored as energy in the magnetic field to the magnetic transformer T _1, current flows based on the secondary voltage induced in the secondary side in the off state, output capacitor _{C 3} is charged. By adjusting the ON width of the control circuit 12, the constant current control of the driving current I ₂ is performed, thereby stabilizing the driving current value of the LED element array 2.

Further, the control circuit 12, the input current I ₁ of the current waveform flowing from the AC power supply AC to approximate to a sine wave, the cycle of the switching of the charging switching element Q ₁ (switching ON width + off width of the switching) For example, the power factor is improved by controlling so as to be proportional to the instantaneous value of the rectified voltage.

<About constant loss control>
The constant loss control characteristic of the present invention will be described. The constant loss control is mainly executed by the difference calculation unit 22 and the constant loss control unit 24. The difference calculation unit 22 calculates a difference (P ₁ −P ₂ ) between the acquired input power P ₁ value and the drive power P ₂ value (product of the drive voltage V ₂ value and the drive current I ₂ value). In addition, the constant loss control unit sets the ON width (conversion rate) of the charging switching element Q ₁ of the conversion unit 16 so that the calculated difference (P ₁ −P ₂ ) is constant, that is, the circuit loss is constant. Control.

The control selection unit 28 selects one of the constant loss control unit and the constant current control unit based on the drive voltage V ₂ value. That is, the increase in driving voltage V ₂ in the constant current control, the detected value reaches the reference value V _0, the control selecting part 28 performs switching to the constant loss control from the constant current control. The driving voltage V ₂ in the constant loss control Once below the reference value V _0, the control selecting part 28 performs switching to the constant current control from the constant loss control.

The overvoltage protection control unit 32 of the control circuit 12 prevents the drive voltage V <b> 2 greater than a predetermined voltage from being applied to the LED element array 2. In addition, the overcurrent protection control unit 34 prevents a drive current I _{2 that} is equal to or greater than a predetermined current from being supplied to the LED element array 2. The protection control selection unit 36 selects one of these two overvoltage protection control units 32 and overcurrent protection control units 34.

<Effect of this embodiment>
The effects of the present invention will be described with reference to FIGS. Figure 3 shows the time variation of the drive current I ₂ and the drive voltage V ₂ when the driving voltage V ₂ is temporarily increased during constant current control. Curve a is the detection value of the drive current I _2. The transition of the curve a during constant current control is almost constant. Curve b is the detection value of the drive voltage V _2. When the drive voltage V ₂ during the constant current control is temporarily increased, V ₂ value varies as the curve b.

For comparison, FIG. 4 shows temporal changes in the drive current I ₂ , the drive voltage V ₂ , and the drive power P ₂ when the constant current control is switched to the constant power control. In the conventional constant current control, when the drive voltage V ₂ increases, the input power P _{1 that} is equal to or higher than the rated power is supplied from the AC power supply AC to the LED power supply circuit 4, so the drive voltage V ₂ increases and the reference value V _{When the value} exceeds ₀ , the control method may be switched from constant current control to constant power control. In the constant power control, the control circuit controls the driving of the power supply means, and the drive power P2 value becomes substantially constant as shown by the curve c. However, the constant power control is not control that suppresses the increase of the drive voltage V ₂ itself (see curve d), and by maintaining the drive power P ₂ value constant, the drive current I ₂ value temporarily changes like the curve e. I feel depressed. As a result, the reduction amount of the luminous flux amount of the LED becomes large.

On the other hand, FIG. 5 shows temporal changes of the drive current I ₂ , the drive voltage V ₂ , and the drive power P ₂ when the constant loss control of the present invention is executed. A curve f is the input power P ₁ value acquired by the input power detection means 6. Curves h and i are detected values of the drive current I ₂ detected by the current detector and the drive voltage V ₂ detected by the voltage detector. Similar to FIG. 4, the case where the driving voltage V ₂ is temporarily raised (curve i). The input power P ₁ value (curve f) changes as the drive voltage V ₂ increases. Since the I ₂ value is kept constant during the constant current control, the drive power P ₂ value (curve g) increases as the drive voltage V ₂ increases. When the drive voltage V ₂ exceeds the reference value V ₀ , the control method is switched from constant current control to constant loss control. In the constant loss control, the control circuit 12 controls the driving of the power supply means to maintain the difference (P ₁ −P ₂ ) between the input power P ₁ and the drive power P ₂ at a substantially constant value (curve g). Thus the curve g the driving power P ₂ is a curve (broken line) in the case of the constant current control, so that transition between the curves in the case of constant power control (dashed line). Thus, when the constant loss control is executed, even if the driving voltage V ₂ is temporarily increased, the drop in the drive current I ₂ value can be small (curve h). As a result, the amount of decrease in the luminous flux of the LED can be suppressed smaller than in the case of constant power control, and a predetermined luminous flux can be maintained.

6 and 7, characteristic diagram of the drive power _{P 1} of the LED power supply circuit 4 of the present invention, and is a characteristic diagram of a circuit loss _(P 1 -P _2). For example, a point A in FIG. In the start mode when the LED power circuit 4 is turned on, the drive current I ₂ increases and reaches the point A as the drive voltage V ₂ increases. In the steady mode, the driving voltage V2 is constant current control is performed in less than the reference voltage V _0. As shown in FIG. 6, the drive voltage V ₂ value and the drive power P ₂ are in a proportional relationship by constant current control. On the other hand, when the drive voltage is equal to or higher than the reference voltage V ₀ , the constant current control is switched to the constant loss control. In the constant loss control, driving power P _2, instead of increasing in proportion to V ₂ values, the difference between the input power P ₁ when V ₂ value becomes larger (P 1 _{-P 2)} is constant Change to keep. In this constant loss control section, as shown in FIG. 7, since the circuit loss (P ₁ -P ₂ ) is kept constant, the heat generated by the circuit loss is also constant.

The purpose of limiting this way the driving power P ₂ from the LED power supply circuit 4 is to suppress the heat generated by the circuit losses. According to the constant loss control of the present invention, since the heat generation in the power supply circuit can be made constant as described above, the LED power supply circuit 4 can be used near the limit of the usable range. Therefore, it is possible to realize control that can fully bring out the performance of the power supply circuit.

In the overvoltage control mode, when the drive voltage V ₂ exceeds the reference voltage V ₀ and rises to a predetermined voltage, the power supply unit 8 stops supplying the drive power P ₂ . The overvoltage control mode, in either of the constant current control and the constant loss control even when the driving voltage V ₂ to the LED element array 2 becomes suddenly large, LED elements by stopping the supply of the driving power P ₂ Row 2 is protected. Similarly, the overcurrent control mode, the drive current I ₂ When raised to a current value to a predetermined greater than the reference current value in the constant current control, the power supply means 8 stops the supply of the driving power P _2. The overcurrent protection is also, at any constant current control and the constant loss control even when the driving current I ₂ supplied to the LED element array 2 becomes suddenly large, by stopping the supply of the drive power P2 LED The element array 2 is protected.

<Modification>
The input power acquisition means has a data table including a plurality of preset input power P ₁ values, and does not actually detect the input power value, but from the data table based on the detected drive voltage V ₂ value. It may be configured to read out one corresponding input power P ₁ value. An input power acquisition means utilizing the circuit loss of the LED power supply circuit 4 is dependent on the driving voltage V ₂ the LED.

Moreover, the LED power supply circuit of the present invention can also be applied to an LED lighting apparatus that uses a DC power supply DC instead of the AC power supply AC. In this case, a configuration of the input unit 14, may be only the bypass capacitor C ₁ is omitted diode bridge DB.

2 LED element array 4 LED power supply circuit 6 Input power acquisition means 8 Power supply means 12 Control circuit (control means)
14 input unit 16 conversion unit 18 output unit 22 difference calculation unit 24 constant current control unit 26 constant loss control unit 28 control selection unit 32 overvoltage protection control unit 34 overcurrent protection control unit 36 protection control selection unit R ₁ , R ₂ voltage detection resistance of the resistor R ₃ current detector means

Claims (4)

A power supply means having an input unit that receives an external power supply, a conversion unit that converts input power into a drive voltage and a drive current necessary for the LED, and an output unit that outputs the drive voltage and the drive current to the LED;
Voltage detection means for detecting a drive voltage value of the output unit;
Current detection means for detecting a drive current value of the output unit;
A control means for controlling the power supply means based on the detected drive voltage value and drive current value, and an LED power supply circuit comprising:
Furthermore, input power acquisition means for acquiring the input power value of the input unit is provided,
The control means includes
A difference calculator that calculates a difference between the acquired input power value and the product of the drive voltage value and the drive current value;
A constant loss control unit that controls the conversion rate of the conversion unit so that the calculated difference is constant;
A constant current control unit that controls the conversion rate of the conversion unit so that the detected drive current value is constant;
A control selection unit for selecting control by the constant current control unit when the drive voltage value is less than a reference voltage, and for selecting control by the constant loss control unit when the drive voltage value is equal to or higher than a reference voltage;
An LED power supply circuit comprising: The LED power circuit according to claim 1,
The LED power circuit according to claim 1, wherein the control means further includes an overvoltage protection control unit for preventing application of a drive voltage equal to or higher than a predetermined voltage to the LED. The LED power circuit according to claim 1,
The LED power supply circuit according to claim 1, wherein the control unit further includes an overcurrent protection control unit that prevents a drive current exceeding a predetermined current from being supplied to the LED. In the LED power supply circuit according to any one of claims 1 to 3,
The input power acquisition unit has a data table including a plurality of preset input power values, and reads out one corresponding input power value from the data table according to the detected drive voltage value. LED power circuit.

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