JP2013110430A - Semiconductor light source device and method of controlling semiconductor light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To drive a semiconductor light-emitting element at high speed and stably by a PWM signal.SOLUTION: A semiconductor light source device comprises: an LED 18; a power-supply voltage conversion unit 11 that supplies a DC operating power; an inductor 13 that stores and discharges the power from the power-supply voltage conversion unit 11; FETs 12, 15, 14, and 19 that switch a charge path R1 for supplying and storing the power from the power-supply voltage conversion unit 11 to and in the inductor 13 and a discharge path R2 for emitting and discharging the power stored in the inductor 13 by the LED 18; a driving circuit that intermittently drives the LED 18 by switching at the FETs 12, 15, 14, and 19; a constant-current control unit 21 that detects a voltage across the path at the time of selecting each of the charge path and the discharge path and switches the FETs 12, 15, 14, and 19 according to the detection result to maintain the current flowing through the inductor 13 to be constant; and a duty monitor unit 22 that adjusts a DC voltage value supplied from a power-supply circuit according to the switching duty ratio of the FETs 12, 15, 14, and 19 by the constant-current control unit 21.

Description

  The present invention relates to a semiconductor light source device and a semiconductor light source control method using semiconductor light emitting elements such as LEDs (light emitting diodes) and LD (laser diodes).

  As an LED driving circuit for reducing power consumption and controlling the luminance of an LED to be constant, technologies including the following patent documents are considered. (For example, Patent Document 1)

JP 2005-011895 A

  The semiconductor light emitting device including the technology described in the above-mentioned patent document is driven by a linear constant current circuit in which an operational amplifier and a power transistor are combined to provide current feedback, a constant current control type DC / DC converter, or the like. Is a common configuration.

  When performing high-speed PWM driving, it is necessary to accelerate the rise of the current of the PWM waveform. In the former linear constant current circuit, current overshoot occurs due to overdrive due to feedback delay. For this reason, it is difficult to achieve both high-speed operation and stable feedback control. Further, when realizing high speed, the burden on the transistor in the output stage is large, it is necessary to allow for a larger voltage margin, and it is essential to take measures against heat of the transistor.

  In the latter DC / DC converter, it takes at least several to dozens of switching cycles before the inductor current used in the circuit is restored to the original current value. For this reason, it has been difficult to increase the speed due to such current rising characteristics.

  Recently, in order to improve the above-described problems with the latter DC / DC converter, the feedback system voltage when the PWM waveform is on and the output voltage of the capacitor in the circuit are temporarily held, and the next A device capable of increasing the speed by making the current rise steep has been realized. Even so, speeding up of the PWM cycle is limited to about several tens [kHz], and further speeding up is difficult.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a semiconductor light source device and a semiconductor light source control method capable of stabilizing a semiconductor light emitting element at high speed and driving it with a PWM signal. It is to provide.

One embodiment of the present invention is a semiconductor light-emitting element, a power supply circuit that supplies operating power, a passive element that accumulates and discharges power from the power supply circuit, and power supplied from the power supply circuit to the passive element. Including a plurality of switching elements for switching between a charging path for storing and a discharging path for emitting and discharging the power stored in the passive element by the semiconductor light emitting element, and the charging path and the discharging path are switched by the plurality of switching elements. By switching, a voltage applied to the driving circuit that intermittently drives the semiconductor light emitting element and the charging path and the discharging path is detected, and the current flowing through the passive element is maintained at a constant value according to the detection result. A constant current switch control unit that calculates a switching duty ratio of the plurality of switching elements to switch the plurality of switching elements; Characterized by comprising a duty monitoring unit for adjusting the voltage value the power supply circuit supplies in response to the switching duty ratio calculated by the flow switch controller.

  According to the present invention, it is possible to drive a semiconductor light emitting element with a PWM signal at high speed and stability.

The figure which shows the structure of the PWM drive circuit of the semiconductor light-emitting device based on one Embodiment of this invention. The timing chart which shows each signal waveform in the circuit of FIG. 1 concerning the embodiment.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram showing a circuit configuration of the semiconductor light source device 10 according to the embodiment. In the figure, a power supply input supplied to the apparatus is supplied to a power supply voltage converter 11. In this power supply voltage conversion unit 11, a DC drive voltage Vin that changes according to control from a duty monitoring unit 22 to be described later is constantly given to the drain of the n-channel FET 12 used as the first switching element (SW1). .

  The source of the FET 12 is connected to one end of the inductor 13 and to the drain of an n-channel FET 14 used as the second switching element (SW2).

  The other end of the inductor 13 is connected to the drain of the n-channel FET 15 used as the third switching element (SW3) and the anode of the diode 16. The cathode of the diode 16 is connected to one end of the capacitor 17 and the anode of a semiconductor light emitting element, for example, an LED (light emitting diode) 18.

  The cathode of the LED 18 is connected to the drain of an n-channel FET 19 used as the fourth switching element (SW4). The source of the FET 19 is connected to the other end of the capacitor 17 and the source of the FET 15. The capacitor 17 is inserted for the purpose of reducing the ripple current flowing through the LED 18 and for the purpose of forming a square wave.

  Further, the source of the FET 15 is connected to one end of the resistor 20. The other end of the resistor 20 is connected to the source of the FET 14 and grounded.

  A constant current control unit 21 is provided to control the on / off timing of light emission of this device. The constant current control unit 21 supplies the PWM signal a to the gates of the FETs 12 and 15 and the duty monitoring unit 22, while the PWM signal b obtained by inverting the PWM signal a is supplied to the gates of the FETs 14 and 19. And supplied to the duty monitoring unit 22.

Further, the constant current control unit 21 detects the potentials at both ends of the resistor 20 together.
The constant current control unit 21 sends the two inverted PWM signals a and b to the FETs 12 and 15 and the FETs 14 and 19 while monitoring the voltage across the resistor 20, and maintains the intended constant current. Control is performed as follows.

  That is, the constant current control unit 21, the inductor 13, the diode 16, the capacitor 17, and the resistor 20 constitute a drive circuit for the LED 18, and FETs 12 and 15 are used as switching elements for controlling the current path in the drive circuit. FETs 14 and 19 are provided. Bipolar transistors may be used as the plurality of switching elements. However, since the FET is voltage controlled, the number of components such as a resistor can be reduced by using the FET.

  The duty monitoring unit 22 monitors the on / off duty of the two PWM signals a and b output from the constant current control unit 21. Then, the duty monitoring unit 22 controls the value of the drive voltage Vin that is converted and output by the power supply voltage conversion unit 11 so that the duty is kept at a constant value intended.

Next, the operation of the above embodiment will be described.
The constant current control unit 21 applies the PWM signal a as shown in FIGS. 2A and 2C to the gates of the FETs 12 and 15 and simultaneously reverses them as shown in FIGS. 2B and 2D. Such a PWM signal b is applied to the gates of the FETs 14 and 19.

  The FETs 12 and 15 are turned on, a current flows along the charging current path R1 indicated by a broken line in FIG.

  Next, when the FETs 12 and 15 are turned off and the FETs 14 and 19 are turned on, the energy accumulated in the inductor 13 flows along the discharge current loop R2 indicated by a one-dot chain line in the figure, and this process. Then, the energy is emitted and emitted through the LED 18 as a load.

  As shown in FIG. 2E, the current flowing through the inductor 13 gradually increases from the current Ia (Ia> 0) when the FETs 12 and 15 are turned on and rises, and the FETs 12 and 15 are turned off and start to decrease. The current Ib (Ia <Ib) at the peak is peaked, and then the pattern is gradually lowered until the FETs 12 and 15 are turned on again and become the current Ia at the time of rising. At that time, as shown in FIG. 2F, the current flowing through the diode 16 does not flow when the FETs 12 and 15 are on, and the current flows when the FETs 12 and 15 are off. The pattern of flowing is repeated.

  On the other hand, as shown in FIG. 2G, the current flowing through the LED 18 which is a light emitting element flows as it is in the inductor 13 during the period when the FETs 14 and 19 are on, and is close to a square wave as shown in the figure. It is possible to obtain a current pulse waveform having high-speed rising characteristics.

The condition for keeping the current flowing through the LED 18 constant can be expressed by the following relational expression. That is,
Duty = Vf / (Vin + Vf) (1)
(However, Vf: voltage applied to the LED. Vin: drive voltage.)
It becomes. In order to perform constant current driving while maintaining the intended duty, it is only necessary to maintain the relationship between the driving voltage Vin satisfying the above equation (1) and the voltage Vf applied to the LED 18.

  Therefore, the constant current control unit 21 feeds back and detects the voltage value at both ends of the resistor 20 to maintain the intended constant current, so that the duty of each PWM signal a, b to the FETs 12, 15 and FETs 14, 19 is maintained. And the energy stored in the inductor 13 is adjusted.

  The duty monitoring unit 22 monitors the duty of the PWM signals a and b to the FETs 12 and 15 and the FETs 14 and 19, and gives a command to the power supply voltage conversion unit 11 so that the duty becomes an intended value. .

  The power supply voltage conversion unit 11 shifts the drive voltage Vin to a necessary voltage value based on a command from the duty monitoring unit 22.

  As described above, the capacitor 17 is inserted for the purpose of reducing the ripple current flowing through the LED 18 which is a semiconductor light emitting element. However, the charging current absorbs the rising current of the LED 18 and hinders the high-speed rising operation of the LED 18. It becomes a factor.

  Therefore, during the period in which the PWM signal a is on, the FET 19 that operates with the PWM signal b obtained by inverting the PWM signal a is turned off to turn off the discharge path of the capacitor 17 through the LED 18, that is, the positive electrode of the capacitor 17, the anode of the LED 18, By turning off the discharge path of the capacitor 17 composed of the cathode of the LED 18, the drain of the FET 19, the source of the FET 19, and the negative electrode of the capacitor 17, and suppressing the discharge of the capacitor 17 due to the current in the direction of the FET 15 by the diode 16, Next, the voltage at the capacitor 17 can be held until the PWM signal a is turned off.

  Therefore, the current for charging the capacitor 17 is not absorbed by the current for the LED 18, and the rising characteristic of the LED 18 can be made sufficiently steep and high speed.

  Here, the constant current control unit 21 can be realized with the same configuration as a constant current feedback type step-down DC / DC converter that is generally integrated into an IC. In this type, the switching frequency is already in the order of several [MHz]. Even things are being put into practical use. Therefore, by adopting these ICs as the current control circuit, it is possible to control the PWM cycle on the order of several [MHz].

  As described above in detail, according to the present embodiment, the property of the inductor 13 in which the current does not change suddenly in order to maintain a constant current is used, and in addition to the analog regions of the FETs 12 and 15 and the FETs 14 and 19 that are switching elements. Since the switching operation is performed using the saturation region, it is possible to realize driving with a PWM signal stabilized at high speed and with high efficiency.

  In the above embodiment, the case where the present invention is applied to a device for driving an LED (light emitting diode) as a semiconductor light emitting element has been described. However, the present invention is not limited to this, and other semiconductor light emitting elements such as an LD (laser diode) can be used. Or an organic EL (electroluminescence) device or the like. Further, the number of semiconductor light emitting elements used in the circuit is not limited.

  In the above-described embodiment, the case where the constant current control DC / DC converter type PWM drive circuit is used as the drive circuit has been described. However, the present invention is not limited to the drive circuit type.

  Furthermore, as a device using the semiconductor light source device, for example, a DLP (Digital Light Processing) (registered trademark) type projector device in which R, G, and B color LEDs are intermittently driven in a time-sharing manner by field sequential driving, for example. Application is also possible.

  In that case, in synchronization with the image display on the micromirror element for forming the optical image, for example, the frame frequency is 120 [Hz], and the duty of each color is set according to the projection mode set at that time. Even when it is necessary to switch in units of%, it becomes possible to respond sufficiently stably.

  In addition, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention in the implementation stage. Further, the functions executed in the above-described embodiments may be combined as appropriate as possible. The above-described embodiment includes various stages, and various inventions can be extracted by an appropriate combination of a plurality of disclosed constituent elements. For example, even if some constituent requirements are deleted from all the constituent requirements shown in the embodiment, if the effect is obtained, a configuration from which the constituent requirements are deleted can be extracted as an invention.

The invention described in the claims of the present application of the present application will be appended below.
According to the first aspect of the present invention, a semiconductor light emitting device, a power supply circuit for supplying operating power, a passive device for storing and discharging power from the power supply circuit, and supplying power from the power supply circuit to the passive device A plurality of switching elements for switching between a charging path for storing and discharging electric power stored in the passive element by causing the semiconductor light emitting element to emit light and releasing the power, and the charging path and the discharging path for the plurality of switching elements. And a voltage applied to the path when each of the charge path and the discharge path is selected, and a current flowing through the passive element is a constant value according to the detection result. A constant current switch controller that calculates the switching duty ratio of the plurality of switching elements so as to be maintained at Characterized by comprising a duty control unit for adjusting the power supply circuit for supplying a voltage value according to the switching duty ratio calculated by Kijo current switch controller.

  The invention described in claim 2 is the invention described in claim 1, further comprising a capacitor connected to the semiconductor light emitting element and the switching element.

  According to a third aspect of the invention, in the first or second aspect of the invention, the passive element is an inductor.

  According to a fourth aspect of the invention, in the invention according to any one of the first to third aspects, the plurality of switching elements are FETs.

  According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, the semiconductor light emitting element is an LED, an LD, or an organic EL.

  According to a sixth aspect of the present invention, there is provided a semiconductor light emitting device, a power supply circuit that supplies operating power, a passive device that accumulates and discharges power from the power supply circuit, and supplies power from the power supply circuit to the passive device. A plurality of switching elements that switch between a charging path for storing and discharging electric power stored in the passive element by causing the semiconductor light emitting element to emit light and discharging, and the charging path and the discharging path for the plurality of switching elements, And a drive circuit for intermittently driving the semiconductor light emitting element by switching the voltage, the voltage applied to the path when each of the charging path and the discharging path is selected, and the detection result The switching duty ratio of the plurality of switching elements is calculated so that the current flowing through the passive element is maintained at a constant value according to the plurality of switching elements. A constant current switch control step of switching a child; and a duty control step of adjusting a voltage value supplied by the power supply circuit in accordance with the switching duty ratio calculated by the constant current switch control step. .

  A seventh aspect of the invention is characterized in that, in the sixth aspect of the invention, a capacitor is further connected to the semiconductor light emitting element and the plurality of switching elements.

  The invention according to claim 8 is the invention according to claim 6 or 7, wherein the passive element is an inductor.

  The invention according to claim 9 is the invention according to any one of claims 6 to 8, wherein the plurality of switching elements are FETs.

  According to a tenth aspect of the present invention, in the beginning of any of the sixth to ninth aspects, the semiconductor light emitting element is an LED, an LD, or an organic EL.

  DESCRIPTION OF SYMBOLS 10 ... Semiconductor light source device, 11 ... Power supply voltage conversion part, 12 ... FET (SW1), 13 ... Inductor, 14 ... FET (SW2), 15 ... FET (SW3), 16 ... Diode, 17 ... Capacitor, 18 ... LED, DESCRIPTION OF SYMBOLS 19 ... FET (SW4), 20 ... Resistance, 21 ... Constant current control part, 22 ... Duty monitoring part.

Claims (10)

A semiconductor light emitting device;
A power supply circuit for supplying operating power;
A passive element that stores and discharges power from the power supply circuit, a charging path that supplies and stores power from the power supply circuit to the passive element, and power that is stored in the passive element is emitted by the semiconductor light emitting element. A driving circuit that intermittently drives the semiconductor light emitting element by switching the charging path and the discharging path with the plurality of switching elements,
The voltage applied to the path is detected when each of the charge path and the discharge path is selected, and the switching duty ratio of the plurality of switching elements is calculated so that the current flowing through the passive element is maintained at a constant value according to the detection result. A constant current switch controller for switching the plurality of switching elements;
A semiconductor light source device, comprising: a duty monitoring unit that adjusts a voltage value supplied by the power supply circuit in accordance with the switching duty ratio calculated by the constant current switch control unit.   The semiconductor light source device according to claim 1, further comprising a capacitor connected to the semiconductor light emitting element and the switching element.   3. The semiconductor light source device according to claim 1, wherein the passive element is an inductor.   4. The semiconductor light source device according to claim 1, wherein the plurality of switching elements are FETs.   5. The semiconductor light source device according to claim 1, wherein the semiconductor light emitting element is an LED, an LD, or an organic EL. Semiconductor light emitting device, power supply circuit for supplying operating power, passive device for storing and discharging power from the power supply circuit, charging path for supplying and storing power from the power supply circuit to the passive device, and passive A semiconductor light emitting device including a plurality of switching elements for switching a discharge path for emitting electric power stored in the element by emitting light from the semiconductor light emitting element and switching the charge path and the discharge path with the plurality of switching elements; A control method in a semiconductor light source device comprising a drive circuit for intermittently driving,
The voltage applied to the path is detected when each of the charge path and the discharge path is selected, and the switching duty ratio of the plurality of switching elements is calculated so that the current flowing through the passive element is maintained at a constant value according to the detection result. A constant current switch control step for switching the plurality of switching elements,
A semiconductor light source control method comprising: a duty monitoring step of adjusting a voltage value supplied by the power supply circuit in accordance with the switching duty ratio calculated in the constant current switch control step.   7. The semiconductor light source control method according to claim 6, further comprising connecting a capacitor to the semiconductor light emitting element and the plurality of switching elements.   8. The semiconductor light source control method according to claim 6, wherein the passive element is an inductor.   9. The semiconductor light source control method according to claim 6, wherein the plurality of switching elements are FETs.   The semiconductor light source control method according to claim 6, wherein the semiconductor light emitting element is an LED, an LD, or an organic EL.

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