JP2013055330A - Semiconductor light-emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor light-emitting device in which luminous efficiency of a semiconductor light-emitting element can be improved.SOLUTION: The semiconductor light-emitting device includes: a semiconductor light-emitting element D1; and a pulse timing control unit 1 which interrupts a pulse current flowing to the semiconductor light-emitting element D1 to control the quantity of light emitted from the semiconductor light-emitting element D1 and controls a timing at which a pulse signal to be applied to the semiconductor light-emitting element D1 is turned on/off, so that the pulse current flows to the semiconductor light-emitting element D1 before discharge of diffusion capacitance of the semiconductor light-emitting element D1 which is caused by the interruption of the pulse current is terminated.

Description

  The present invention relates to a semiconductor light emitting element such as a light emitting diode (LED), a laser light emitting diode, or an organic EL element, and a semiconductor light emitting device using these.

  Semiconductor light-emitting devices such as LEDs, laser light-emitting diodes, and organic EL devices are light-emitting power efficiency that suppresses heat generation by utilizing the light-emitting phenomenon that occurs when free electrons and holes, which are charge carriers in semiconductors, are recombined. It is a high element. By replacing a conventional light emitting element with a semiconductor light emitting element, power consumption of an illumination device, an electronic display, an electronic signature, or the like can be reduced. In addition, it suppresses the consumption of scarce resources of the earth during production, and also suppresses the discharge of environmental pollutants, so that it has exploded explosively around the world as an element friendly to the global environment in recent years.

  In principle, the semiconductor light emitting element emits light having a light amount substantially proportional to the driving current. However, in reality, since there are changes in recombination efficiency and temperature dependence, nonlinearity appears in the amount of emitted light or the peak emission wavelength shifts with changes in the drive current value. For this reason, PWM (Pulse Width Modulation) is mainly used for controlling the semiconductor light emitting element, in which a pulse current having a constant peak current is passed to vary the current flow time width.

  FIG. 23 is a block diagram showing a configuration of a conventional semiconductor light emitting device. FIG. 24 is a waveform diagram of each part for explaining the operation of the conventional semiconductor light emitting device. In FIG. 23, a series circuit of a resistor Ro, LEDD1, and switching element Q1 is connected to both ends of the DC power supply Vdd. The pulse generator 10 applies the pulse signal VIN to the gate of the switching element Q1 at time t10 shown in FIG. Then, the current ILED flows through the LEDD1 along the path of Vdd → Ro → D1 → Q1, and the voltage VLED is generated between both ends of the LEDD1. The voltage VLED and current ILED increase rapidly and then reach a constant value. Thereafter, LEDD1 emits light, and light L is output.

  The operation of the LED at this time will be described using an equivalent circuit of the LED shown in FIG. A series circuit of a resistor r and a diffusion capacitor Cd is connected between the anode A and the cathode K of the LED D1, and a current source ILED and a resistor Rd are connected in parallel to the diffusion capacitor Cd. . In this configuration, when the switching element Q1 is turned on / off by the pulse signal from the pulse generator 10, the LEDD1 is also turned on / off. When the LEDD1 is turned off at time t11 in FIG. 24, the charge (voltage VLED) of the diffusion capacitor Cd is self-discharged via the resistor Rd. When LEDD1 is turned on at time t12, a current flows through the current source ILED and the diffusion capacitor Cd is charged. Thereafter, carriers of free electrons and holes recombine, and light L is output from LEDD1.

  As a conventional technique of this type, for example, a technique described in Patent Document 1 is known. Patent Document 1 discloses a storage unit that stores a luminance level of a light source that illuminates a display unit of a liquid crystal display, and a pulse generation unit that continuously generates a pulse signal having a width corresponding to the luminance level stored in the storage unit. By controlling the current flowing through the light source (LED) repeatedly by turning on and off with the generated continuous pulse signal, it is possible to easily adjust the brightness and obtain higher luminous efficiency.

JP 2000-132115 A

  However, in the conventional pulse current control, the diffusion capacitance Cd of the LED D1 is charged / discharged before the carriers recombine at the flow (on) and cutoff (off) timing of the pulse current. Due to this charging / discharging, power loss due to the voltage VLED and the current ILED occurred at the rising timing of the voltage VLED and the current ILED (for example, immediately after the time t10 and the time t12). That is, extra power that does not contribute to the light emission of the LEDD1 is consumed, and the light emission amount of the LEDD1 is reduced. This phenomenon has lowered the luminous efficiency of the semiconductor light emitting device.

  The subject of this invention is providing the semiconductor light-emitting device which can improve the luminous efficiency of a semiconductor light-emitting device.

  In order to solve the above-described problems, the present invention relates to a semiconductor light emitting device and a pulse current flowing through the semiconductor light emitting device to control a light emission amount of the semiconductor light emitting device and to be generated along with the interruption of the pulse current. A pulse timing control unit that controls on / off timing of a pulse signal to be applied to the semiconductor light emitting element so that a pulse current flows through the semiconductor light emitting element before the discharge of the diffusion capacitance of the semiconductor light emitting element is completed It is characterized by providing.

  The present invention also provides a first semiconductor light emitting element that emits light when a pulse current flows, and a second semiconductor light emitting element that is disposed opposite to the first semiconductor light emitting element and emits light when a pulse current flows. In addition, a pulse current is passed through one of the first and second semiconductor light emitting elements to emit light, and the other semiconductor light emitting element is irradiated with this light, thereby being included in the other semiconductor light emitting element. A pulse timing control unit for controlling on / off timing of a pulse signal to be applied to the first and second semiconductor light emitting elements so that a pulse current flows through the other semiconductor light emitting element after charging the diffusion capacitor It is characterized by providing.

  According to the present invention, the pulse current is allowed to flow through the semiconductor light emitting device before the discharge of the diffusion capacitance of the semiconductor light emitting device that occurs due to the interruption of the pulse current is completed by the on / off timing control of the pulse signal. The capacity discharge is reduced, and the pulse current can be effectively utilized for recombination of carriers of the semiconductor light emitting device. Therefore, the power consumption of the semiconductor light emitting element can be reduced and the amount of light emission can be increased, so that the light emission efficiency of the semiconductor light emitting element and the power efficiency of the semiconductor light emitting device can be improved.

It is a block diagram which shows the structure of the semiconductor light-emitting device based on Example 1 of this invention. It is a wave form diagram of each part for demonstrating operation | movement of the semiconductor light-emitting device based on Example 1 of this invention. It is a figure which shows the rising / falling waveform of LED provided in the semiconductor light-emitting device. It is a figure which shows the rising waveform of LED driven by the conventional semiconductor light-emitting device. It is a figure which shows the falling waveform of LED driven with the conventional semiconductor light-emitting device. It is a figure which shows the rising waveform of LED driven by the semiconductor light-emitting device which concerns on Example 1 of this invention. It is a figure which shows the falling waveform of LED driven by the semiconductor light-emitting device based on Example 1 of this invention. It is a figure which shows the loss area | region at the time of LED rising, the area | region of an ideal light, and the gain area | region at the time of falling. It is a figure which shows the improvement of the light emission loss of LED. It is a figure which shows the analysis of the charging / discharging loss of LED. It is a figure which shows the charging / discharging electric power per pulse, and a reduction rate. It is a block diagram which shows the structure of the semiconductor light-emitting device based on Example 2 of this invention. It is a wave form diagram of each part for demonstrating operation | movement of the semiconductor light-emitting device based on Example 2 of this invention. It is a block diagram which shows the structure of the specific example of the semiconductor light-emitting device based on Example 2 of this invention. It is a block diagram which shows the structure of the semiconductor light-emitting device based on Example 3 of this invention. It is a block diagram which shows the structure of the semiconductor light-emitting device based on Example 4 of this invention. It is a block diagram which shows the structure of the semiconductor light-emitting device based on Example 5 of this invention. It is a wave form diagram of each part for demonstrating operation | movement of the semiconductor light-emitting device based on Example 5 of this invention. It is a figure which shows the structure of the semiconductor light-emitting device based on Example 5 of this invention. It is a block diagram which shows the structure of the semiconductor light-emitting device based on Example 6 of this invention. It is a block diagram which shows the structure of the semiconductor light-emitting device based on Example 7 of this invention. It is a block diagram which shows the structure of the semiconductor light-emitting device based on Example 8 of this invention. It is a block diagram which shows the structure of the conventional semiconductor light-emitting device. It is a wave form diagram of each part for demonstrating operation | movement of the conventional semiconductor light-emitting device. It is a figure which shows the equivalent circuit of LED provided in the semiconductor light-emitting device.

  Hereinafter, a semiconductor light emitting device according to an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram showing a configuration of a semiconductor light emitting device according to Example 1 of the present invention. In FIG. 1, a series circuit of a resistor Ro, LEDD1 (semiconductor light emitting element), and a switching element Q1 is connected to both ends of a DC power supply Vdd.

  The pulse timing control unit 1 controls the light emission amount of the LEDD1 by cutting off the pulse current flowing through the LEDD1, and applies the pulse current to the LEDD1 before the discharge of the diffusion capacitor Cd of the LEDD1 that occurs due to the interruption of the pulse current is completed. The on / off timing of the pulse signal to be applied to the LEDD1 is controlled so as to flow. The pulse timing control unit 1 applies the controlled pulse signal VIN to the gate of the switching element Q1.

  When the diffusion capacitance of the LEDD1 is Cd and the equivalent resistance connected in parallel to the diffusion capacitance Cd is Rd, the pulse timing control unit 1 sets the OFF time toff of the pulse signal VIN as time Tdis = 2.2 × Cd × It is set smaller than Rd and larger than the afterglow time Tz of LEDD1.

  In addition, the pulse timing control unit 1 performs pulse width modulation (PWM) on the pulse signal and applies the PWM-modulated pulse signal to the switching element Q1, thereby performing pulse control on the LEDD1.

  Instead of performing pulse width modulation on the pulse signal, pulse frequency modulation (PFM) or pulse amplitude modulation (PAM) is performed, and the modulated pulse signal is applied to the switching element Q1, thereby causing the LED D1 to emit light. You may control.

  FIG. 2 is a waveform diagram of each part for explaining the operation of the semiconductor light emitting device according to the first embodiment of the invention. The operation of the semiconductor light emitting device will be described with reference to the waveform diagrams of the respective parts shown in FIG.

  First, when the pulse timing control unit 1 applies the pulse signal VIN shown in FIG. 2 to the gate of the switching element Q1 at time t0, the switching element Q1 is turned on, and the LEDD1 passes along the path of Vdd → Ro → D1 → Q1. Current ILED flows through the LEDD1, and a voltage VLED is generated across the LEDD1. The voltage VLED and current ILED increase rapidly and then reach a constant value. Thereafter, LEDD1 emits light, and light L is output.

  When the pulse signal VIN is turned off at the time toff between the times t1 and t2, the LEDD1 is turned off, and the charge (voltage VLED) of the diffusion capacitor Cd is self-discharged through the resistor Rd, but the voltage VLED of the LEDD1 is slightly Decrease. In this case, since the OFF time toff of the pulse signal is set to be smaller than the time Tdis = 2.2 × Cd × Rd, the charge of the diffusion capacitor Cd is not completely discharged even at the time t2, so that VLED is positive. Voltage.

  Then, before the discharge of the charge of the diffusion capacitor Cd ends, at time t2, a pulse current is passed through the LEDD1 by turning on the pulse signal. For this reason, the amount of charge released from the diffusion capacitor Cd is reduced, and by using the remaining amount of charge, light emission can be resumed quickly by effectively utilizing the pulse current for recombination of carriers of the LEDD1. .

  Therefore, the charge / discharge power of the diffusion capacity of the LEDD1 can be reduced, the power consumption in the LED itself and the drive circuit can be reduced, and the amount of light emission can be increased. Therefore, the light emission efficiency of the LEDD1 and the power efficiency of the semiconductor light emitting device can be reduced. Can be improved.

  FIGS. 3 to 6 show the results of detecting the LED by the light receiver. FIG. 3 is a diagram illustrating a rising / falling waveform of the LED D1 provided in the semiconductor light emitting device. In FIG. 3, VLED is the voltage across LEDD1, ILED is the current flowing through LEDD1, and L is the light from LEDD1.

  FIG. 4 is a diagram showing a rising waveform of the LED D1 driven by the conventional semiconductor light emitting device. FIG. 5 is a diagram showing a falling waveform of an LED driven by a conventional semiconductor light emitting device. In FIG. 5, the time Tz of 10% to 90% with respect to the zero value of the waveform of the light L is defined as the afterglow time.

  FIG. 6 is a diagram showing a rising waveform of an LED driven by the semiconductor light emitting device according to Example 1 of the invention. FIG. 7 is a diagram showing a falling waveform of an LED driven by the semiconductor light emitting device according to Example 1 of the invention. The time Toff in the first embodiment is set to be longer than the afterglow time Tz.

  Comparing the rising waveform of LEDD1 between FIG. 4 and FIG. 6, the voltage during the OFF period of VLED shown in FIG. 6 is a positive voltage, and the rising time tss is shorter than that shown in FIG. That is, since the amount of charge released from the diffusion capacitor Cd is reduced, the pulse current can be effectively used for recombination of carriers of the LEDD1. Further, since the rise time tsd of the light L shown in FIG. 6 is also shorter than that shown in FIG. 4, the light emission amount can be increased.

  The inventor of the present applicant paid attention to the following ideas and conducted experiments on the light emission of the LEDs based on this idea, which will be described below.

  First, it can be considered from the experimental result that the LED consumes electric power for charging the diffusion capacity almost independent of the light intensity from the LED. For this reason, it is conceivable that the power consumption can be reduced by passing a pulse current through the LED without charging the diffusion capacitor. Further, in the light emission, since the pulse current can be efficiently used for carrier recombination without loss, the light emission amount increases.

  Improvement in luminous efficiency is expected by using the LED driving method described above. As a result of the experiment, the loss of light emission of the LED can be reduced by being driven without charging its diffusion capacity as follows.

  FIG. 8A shows a loss region and an ideal light region at the time of rising of the LED. FIG. 8B shows a gain region when the LED falls. The loss area of light emission at the time of rising is obtained by subtracting the area that actually emits light from the area from when the current starts to flow until the light emission reaches its peak. The calculation method of the loss ratio is shown in Equation (1).

{(Rising loss) − (Falling loss)} × 100 / (Ideal light) …… (1)
Moreover, the improvement result of the light emission loss of the conventional LED when using red LED, green LED, blue LED, and white LED as a light source and LED of this invention is shown in FIG. As can be seen from FIG. 9, the reduced loss (improvement effect in FIG. 9) is 10.2% for the red LED, 6.2% for the green LED, 5.3% for the blue LED, and 7% for the white LED. 9% improvement.

  In addition, the applicant made measurements with a circuit element measuring instrument for each color in order to examine the influence of the charge / discharge power on the diffusion capacity of the LED. The measurement was performed by connecting an impedance analyzer to both ends of the LED. FIG. 10 shows an analysis of the charge / discharge loss of the LED. In FIG. 10, the horizontal axis represents the LED voltage VLED, and the vertical axis represents the charge Q (pC). Since the diffusion capacity of the LED has voltage dependence, as shown in FIG. 10, the capacity of the LED can be found by obtaining the charge Q (pC) from the measured value of the LED voltage VLED. By adjusting the applied voltage range at the time of capacity measurement and measuring the voltage dependence of the charge charge, the charge charge amount and charge energy of the diffusion capacitor having voltage dependence can be accurately obtained.

  FIG. 11 shows the charge / discharge power per pulse and the reduction rate. The energy of [power supply voltage] × [charged charge] supplied from the power supply of the drive circuit when the diffusion capacitor is charged is consumed every time the pulse current flows. This total energy consumption is the sum of the energy consumed by the drive circuit when the diffusion capacitor is charged and the energy consumed by the drive circuit during the discharge after being charged into the diffusion capacitor. As can be seen from the reduction rate in FIG. 11, the driving power consumed each time the diffusion capacitor is charged / discharged is 26.5% for the red LED, 40.9% for the green LED, and 25.0 for the blue LED. %, And for white LEDs, it was reduced to 30.0%.

  FIG. 12 is a block diagram showing a configuration of a semiconductor light emitting device according to Example 2 of the present invention. The semiconductor light emitting device of Example 2 shown in FIG. 12 is characterized in that a current source Io (t) connected to both ends of the LED D1 is provided.

  The current source Io (t) supplies a pulse current to the LEDD1, and has the same function as the pulse timing control unit 1 shown in FIG. That is, the current source Io (t) controls the light emission amount of the LED D1 by cutting off the pulse current flowing through the LED D1, and before the discharge of the diffusion capacitance Cd of the LED D1 that occurs due to the interruption of the pulse current is terminated to the LED D1. The on / off timing of the pulse current to be supplied to the LEDD1 is controlled so as to supply the pulse current.

  Further, the current source Io (t) has a pulse current OFF time toff as a time Tdis = 2.2 ×, where Cd is a diffusion capacitance of the LEDD1 and Rd is an equivalent resistance connected in parallel to the diffusion capacitance Cd. It is set to be smaller than Cd × Rd and larger than the afterglow time Tz of the LEDD1.

  FIG. 13 is a waveform diagram of each part for explaining the operation of the semiconductor light emitting device according to the second embodiment of the invention. According to the semiconductor light emitting device of the second embodiment, even when the current source Io (t) is used, the semiconductor light emitting device operates in the same manner as the semiconductor light emitting device of the first embodiment, and similar effects can be obtained.

  FIG. 14 is a block diagram showing a configuration of a specific example of the semiconductor light emitting device according to Example 2 of the invention. In FIG. 14, a series circuit of an LED D1, a switching element Q1, and a current detection resistor Rs is connected to both ends of the DC power supply Vdd. The timing of the output VIN of the pulse timing control unit 1 is the same as that of the pulse timing control unit 1 shown in FIG. 1, but the pulse amplitude is increased or decreased according to the light emission amount.

  According to the semiconductor light emitting device shown in FIG. 14, the pulse timing control unit 1 applies the pulse signal VIN to the gate of the switching element Q1, so that the switching element Q1 is turned on and off, and the amplitude is controlled by the current limiting resistor Rs. Since a constant current flows, the switching element Q1 can constitute a constant current circuit, that is, a current source Io (t). Therefore, it operates in the same manner as the semiconductor light emitting device of Example 1, and the same effect can be obtained.

  FIG. 15A is a block diagram showing the configuration of the semiconductor light emitting device according to the third embodiment of the present invention, and FIG. 15B shows the pulse signal of the PWM / PAM control unit 2 of the semiconductor light emitting device of the third embodiment. It is a waveform diagram.

  The semiconductor light emitting device according to Example 3 shown in FIG. 15 is characterized by using the PWM / PAM control unit 2. The PWM / PAM control unit 2 controls (PWM) the duty cycle D = TON / (TON + TOFF) of the pulse signal to be applied to the gate of the switching element Q1, and also controls the peak current value ILED (PEAK) of the pulse (PAM). ) The PWM / PAM control unit 2 may be only PWM control or only PAM control.

  That is, since the light emission amount is L∝D · ILED (PEAK), the PWM / PAM control unit 2 arbitrarily changes the light emission amount L by, for example, a pulse signal that variably controls ILED as shown in FIG. Can be made.

  However, since the discharge time of the diffusion capacitor Cd of LEDD1 may change as the peak current value ILED (PEAK) increases or decreases, the off time of the pulse signal depends on the variable range of the peak current value ILED (PEAK). TOFF needs to be set or controlled so as to be shorter than the discharge time.

  As another control method other than the third embodiment, the diffusion time Cd of the LEDD1 is not discharged and the LED voltage is not lowered too much while maintaining the short off time TOFF in which the pulse current is cut off. There is a method of controlling the pulse repetition frequency f (Hz) = (1 / (TON + TOFF)) by varying the length of the ON time TON in which the pulse current is conducted.

  The semiconductor light emitting device according to the fourth embodiment of the present invention shown in FIG. 16 controls the pulse repetition frequency f (Hz) = (1 / (TON + TOFF)). FIG. 16A is a block diagram showing the configuration of the semiconductor light emitting device according to the fourth embodiment of the present invention, and FIG. 16B shows the pulse signal of the PWM / PAM control unit 3 of the semiconductor light emitting device of the fourth embodiment. It is a waveform diagram.

  The PFM / PAM control unit 3 shown in FIG. 16 controls the pulse repetition frequency f of the pulse signal to be applied to the gate of the switching element Q1 (PFM) and also controls the peak current value ILED (PEAK) of the pulse (PAM). ) Note that the PFM / PAM control unit 3 may be only PFM control or PAM control.

That is, the light emission amount L∝D · ILED (PEAK) = {1− (f × TOFF)} · ILED (PEAK
Therefore, the PFM / PAM control unit 3 controls the ON time TON while keeping the OFF time TOFF constant as shown in FIG. 16B, for example, and changes the pulse repetition frequency f. The amount of light emission can be changed.

  It should be noted that the LED drive circuit according to the present invention is not limited to the circuit configuration including the resistor and the switch element illustrated as a simple example, but includes a low power drive circuit including a general coil, capacitor, and switch element. Yes.

  FIG. 17 is a block diagram showing a configuration of a semiconductor light emitting device according to Example 5 of the present invention. In FIG. 17, a series circuit of LED1 (first semiconductor light emitting element), resistor Rd1, and switching element Q1 is connected to both ends of the DC power supply Vdd1. A series circuit of LED2 (second semiconductor light emitting element), resistor Rd2, and switching element Q2 is connected to both ends of the DC power supply Vdd2.

  The LED 1 and the LED 2 are arranged to face each other and irradiate light emitted from one LED to the other LED.

  The pulse timing control unit 1a causes a pulse current to flow through one of the LEDs 1 and 2 to emit light, and irradiates the other LED with this light before the other LED emits light using the induced carrier. After charging the diffusion capacitor included in the other LED, the on / off timing of the pulse signal to be applied to the LED 1 and the LED 2 is controlled so that a pulse current flows through the other LED. The pulse timing controller 1a applies the controlled pulse signal Vin1 to the gate of the switching element Q1, and applies the pulse signal Vin2 to the gate of the switching element Q2.

  FIG. 18 is a waveform diagram of each part for explaining the operation of the semiconductor light emitting device according to the fifth embodiment of the invention. The operation of the semiconductor light emitting device will be described with reference to the waveform diagrams of the respective parts shown in FIG.

  First, when the pulse timing control unit 1a applies the pulse signal Vin2 to the gate of the switching element Q2 at time t12, the switching element Q2 is turned on, and the current ILED2 flows through the LED2 through the path Vdd2 → LED2 → Q2. The LED 2 starts to emit light, and at time t13, the light L2 reaches the maximum intensity and is output.

  Since the light L2 emitted from the LED2 irradiates the LED1, the LED1 receives the light L2. This light L2 raises the voltage VLED1 of LED1. That is, carriers are induced in the LED 1 by the light L2 from the LED 2, and the diffusion capacity of the LED 1 is charged by the induced carriers.

  When the pulse timing control unit 1a applies the pulse signal Vin1 to the gate of the switching element Q1 at time t14, the switching element Q1 is turned on, and the current ILED1 flows through the LED1 along the path Vdd1 → LED1 → Q1. Emits light sharply without light emission delay, and the light L1 is output. When the pulse signal Vin1 is turned off at time t15, the light L1 is gradually turned off with afterglow.

  Next, when the pulse timing control unit 1a applies the pulse signal Vin1 to the gate of the switching element Q1 at time t16, the switching element Q1 is turned on, and the current ILED1 flows through the LED1 through the path of Vdd1 → LED1 → Q1. Thus, the LED 1 starts to emit light, and at time t17, the light L1 is output with the maximum intensity.

  Since the light L1 emitted from the LED1 irradiates the LED2, the LED2 receives the light L1. This light L1 raises the voltage VLED2 of the LED2. That is, carriers are induced in the LED 2 by the light L1 from the LED 1, and the diffusion capacity of the LED 2 is charged by the induced carriers.

  When the pulse timing control unit 1a applies the pulse signal Vin2 to the gate of the switching element Q2 at time t18, the switching element Q2 is turned on, and the current ILED2 flows through LED2 along the path Vdd2 → LED2 → Q2, and LED2 Emits light sharply without light emission delay, and the light L2 is output.

  Such drive control is repeated. That is, light irradiation is alternately performed between the LED 1 and the LED 2, and after the diffusion capacitance is charged mutually, the LED is caused to emit light. In particular, the time t18 shown in FIG. 18 is advanced to the same timing as the time t15, and the repeated drive waveform in which the time 14 is set to the same timing as the time t19 is used again, thereby minimizing the light emission delay and power consumption of both LEDs. To the limit.

  Thus, according to the semiconductor light emitting device according to Example 5, the pulse timing control unit 1a causes one of the LEDs 1 and 2 to emit light by passing a pulse current, and irradiates the other LED with this light. After charging the diffusion capacitance included in the other LED before the other LED emits light using the induced carrier, the pulse signal to be applied to LED1 and LED2 is turned on so that a pulse current flows through the other LED. Since the timing of / off is controlled, the pulse current can be utilized only for recombination of the carriers of LED1 and LED2.

  Therefore, the power consumed by the LEDs 1 and 2 can be reduced, and the amount of light emission can be increased. Thereby, the light emission efficiency of LED1, LED2 and the power efficiency of a semiconductor light-emitting device can further be improved.

  Moreover, since the diffusion capacitance can be charged at an arbitrary timing by irradiating the LEDs 1 and 2 with light, it is not necessary to pass a driving current (pulse current) to the LEDs 1 and 2 for charging the diffusion capacitance before light emission. The semiconductor light emitting device can be driven with high efficiency by a driving current having an arbitrary waveform.

  As for the power generation characteristics of each LED with respect to each wavelength, red to green LEDs having a long emission wavelength tend to exhibit higher power generation characteristics as the wavelength of irradiated light is longer as a result of experiments. As a result of experiments, a blue LED having a significantly different composition of the compound semiconductor and having the shortest emission wavelength tends to exhibit higher power generation characteristics as the wavelength of irradiated light is shorter.

  Therefore, in order to emit light with high efficiency while alternately irradiating light with a pair of LED1 and LED2, use LEDs of the same wavelength or different wavelengths from red LED to green LED having a long emission wavelength. The efficiency can be improved by alternately emitting light together with the LEDs.

  As an example, when two or more n-color LEDs are combined, nC1 + nC2 + nC3 +... NC (3 colors for 2 colors, 7 colors for 3 colors, 15 colors for 4 colors, etc. Colors of the type n-1) + nCn can be obtained. Among them, except for the case where the LED emits light alone, the luminous efficiency is improved in the color development of nC2 + nC3 +... NC (n-1) + nCn.

  Even in the blue LED having the shortest emission wavelength, if a yellow phosphor is used in combination, a long emission wavelength can be obtained. Therefore, the efficiency is improved even if the LEDs are alternately emitted together with the LEDs having different wavelengths.

  FIG. 19 is a diagram showing an example of the structure of the semiconductor light emitting device according to Example 5 of the invention. FIG. 19A is a layout diagram showing the structure of LED1 and LED2, and FIG. 19B is a circuit diagram of LED1 and LED2. The LED 1 and the LED 2 include, for example, a metal material 4 made of the same member, on which an n-type semiconductor layer 5a, an active layer 6a, and a p-type semiconductor layer 7a are stacked, an n-type semiconductor layer 5b, and an active layer 6b. The p-type semiconductor layer 7b and the stacked layer are arranged to face each other.

  Accordingly, light irradiation can be alternately performed between the LED 1 and the LED 2, and the LED can be generated after mutually charging the diffusion capacitance.

  FIG. 20 is a block diagram showing a configuration of a semiconductor light emitting device according to Example 6 of the present invention. The semiconductor light emitting device of Example 6 shown in FIG. 20 is characterized in that a current source I1 (t) connected to both ends of the LED 1 and a current source I2 (t) connected to both ends of the LED 2 are provided. .

  The current source I1 (t) supplies a pulse current to the LED 1 and has the same function as the pulse signal Vin1 of the pulse timing control unit 1a shown in FIG. The current source I2 (t) supplies a pulse current to the LED 2 and has the same function as the pulse signal Vin2 of the pulse timing control unit 1a shown in FIG.

  Even when such current source I1 (t) and current source I2 (t) are used, the same effect as that of the semiconductor light emitting device according to Example 5 can be obtained. Moreover, the light emission amount of each LED can be accurately controlled by adjusting the current value. In particular, this is an effective driving method when, for example, LEDs having different light emission colors and light emission areas are controlled by different currents optimum for each LED.

  FIG. 21 is a block diagram showing a configuration of a semiconductor light emitting device according to Example 7 of the present invention. The semiconductor light emitting device according to Example 7 shown in FIG. 21 is characterized in that a PFM control unit 8 that outputs pulse signals Vin1 and Vin2 is provided at the gates of the switching elements Q1 and Q2. The PFM control unit 8 performs pulse frequency modulation on the pulse signal, and applies the modulated pulse signals Vin1 and Vin2 to the switching elements Q1 and Q2, thereby controlling the light emission of the LEDs 1 and LED2.

  FIG. 22 is a block diagram showing a configuration of a semiconductor light emitting device according to Example 8 of the present invention. The semiconductor light emitting device according to Example 8 shown in FIG. 22 is characterized in that a PAM control unit 9 that outputs pulse signals Vin1 and Vin2 is provided at the gates of the switching elements Q1 and Q2. The PAM control unit 9 performs amplitude modulation on the pulse signal and applies the modulated pulse signals Vin1 and Vin2 to the switching elements Q1 and Q2, thereby controlling the light emission amounts of the LEDs 1 and LED2, respectively. .

  In addition, this invention is not limited to the semiconductor light-emitting device based on Example 1 thru | or 8 mentioned above. For example, the timing control shown in FIG. 2 used in the semiconductor light emitting device according to the first embodiment may be added to the timing control of the LEDs 1 and 2 of the semiconductor light emitting device according to the fifth embodiment shown in FIG. According to this, the effect is further great.

  The present invention can be used for LED lighting devices, organic EL lighting devices, and the like.

Vdd, Vdd1, Vdd2 DC power supply Ro, Rs, Rd Resistance D1 LED
Q1, Q2 Switching elements Io (t), I1 (t), I2 (t) Power source 1 Pulse timing control unit 2 PWM / PAM control unit 3 PFM / PAM control unit 5a, 5b n-type semiconductor layers 6a, 6b Active layer 7a, 7b p-type semiconductor layer 8 PFM controller 9 PAM controller
10 Pulse generator Cd Diffusion capacitance

Claims (10)

A semiconductor light emitting device;
The semiconductor light emitting device emits light before controlling the amount of light emitted from the semiconductor light emitting device by cutting off a pulse current flowing through the semiconductor light emitting device, and before the discharge of the diffusion capacitance of the semiconductor light emitting device generated by the interruption of the pulse current is completed. A pulse timing control unit for controlling on / off timing of a pulse signal to be applied to the semiconductor light emitting element so that a pulse current flows through the element;
A semiconductor light emitting device comprising:   The pulse timing control unit sets an off time Toff of the pulse signal as time Tdis = 2.2 × Cd × Rd, where Cd is the diffusion capacitance and Rd is an equivalent resistance connected in parallel to the diffusion capacitance. 2. The semiconductor light emitting device according to claim 1, wherein the semiconductor light emitting device is smaller than the afterglow time of the semiconductor light emitting element.   The pulse timing control unit performs pulse width modulation, pulse frequency modulation, or pulse amplitude modulation on the pulse signal, and applies the modulated pulse signal to the semiconductor light emitting element. Item 3. A semiconductor light emitting device according to Item 2.   4. The semiconductor light emitting device according to claim 1, wherein the pulse timing control unit includes a current source, and causes a pulse current to flow from the current source to the semiconductor light emitting element. 5.   The pulse timing control unit performs pulse width modulation and pulse amplitude modulation on the pulse signal, and applies the modulated pulse signal to the semiconductor light emitting element. The semiconductor light emitting device according to claim 4.   The pulse timing control unit performs pulse frequency modulation and pulse amplitude modulation on the pulse signal, and applies the modulated pulse signal to the semiconductor light emitting element. The semiconductor light emitting device according to claim 4. A first semiconductor light emitting element that emits light when a pulse current flows;
A second semiconductor light emitting element that is disposed opposite to the first semiconductor light emitting element and emits light when a pulse current flows;
A diffusion capacitance included in the other semiconductor light emitting element is obtained by causing a pulse current to flow through one of the first and second semiconductor light emitting elements to emit light and irradiating the other semiconductor light emitting element with the light. A pulse timing control unit for controlling on / off timing of a pulse signal to be applied to the first and second semiconductor light emitting elements so that a pulse current flows to the other semiconductor light emitting element after charging
A semiconductor light emitting device comprising:   The pulse timing control unit performs pulse width modulation, pulse frequency modulation, or pulse amplitude modulation on the pulse signal, and applies the modulated pulse signal to the first and second semiconductor light emitting elements. The semiconductor light emitting device according to claim 7.   The pulse timing control unit includes a first current source and a second current source, and causes a pulse current to flow from the first current source to the first semiconductor light emitting element, and from the second current source to the second semiconductor. 9. The semiconductor light emitting device according to claim 7, wherein a pulse current is passed through the light emitting element.   10. The semiconductor light emitting device according to claim 7, wherein the first and second semiconductor elements are disposed opposite to and adjacent to each other in the same member.

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