Lighting control method of semiconductor light emitting element, lighting control device, and light emitting device

Abstract

The present invention provides a lighting control method, lighting control device, and light-emitting device for a semiconductor light-emitting element. The purpose is to suppress overshoot of LED current and shorten the time until lighting begins. Lighting control of the semiconductor light-emitting element is performed by controlling the current flowing through the semiconductor light-emitting element using a lighting control device. The lighting control device includes: a switching element having a control terminal for controlling the conduction state and connected in series with the semiconductor light-emitting element; and a control circuit for controlling the control terminal. The lighting control method for the semiconductor light-emitting element includes the following steps: a first step in which the control circuit causes the control voltage of the control terminal of the switching element to gradually increase from an initial value to a first value in a relatively short time; and a second step in which the control circuit causes the control voltage of the control terminal of the switching element to gradually increase from the first value to a second value in a relatively long time.

Description

Technical Field

[0001] The present invention relates to a lighting control technology for semiconductor light emitting elements such as LEDs (Light Emitting Diodes). Background Art

[0002] Flash devices using LEDs are known, for example, for illuminating a subject when taking photos with a camera. For example, Japanese Patent Application Publication No. 2019-144468 (Patent Document 1) describes a prior art example of a flash device using such an LED. In such a flash device, for example, a FET (field effect transistor) is connected in series with an LED and a driving voltage is supplied to them, so that the gate voltage of the FET gradually rises and the source and drain become conductive, thereby allowing current to flow through the LED. Furthermore, the current flowing through the LED (hereinafter referred to as "LED current") is detected. If the LED current reaches a specified value, the rise in the gate voltage of the FET is stopped and the gate voltage is maintained, thereby making it possible to light the LED with a constant current.

[0003] However, in the aforementioned flash device, to further shorten the time required to start lighting the LED, the FET gate voltage can simply be increased more quickly. However, in this case, the time lag between the control unit detecting the LED current and stopping the gate voltage increase causes a temporary excessive LED current (so-called overshoot). In contrast, slowing the rise of the FET gate voltage prevents overshoot, but in this case, the time required to start lighting the LED increases. This results in a delay in the emission of the irradiated light, making it undesirable for flash devices. This problem is not limited to flash devices; it generally applies to light-emitting devices.

[0004] [Prior Art Literature]

[0005] [Patent Document]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-144468 Summary of the Invention

[0007] [Problems to be solved by the invention]

[0008] One of the objects of a specific embodiment of the present invention is to provide a lighting control technology that can suppress overshoot of LED current and shorten the time until lighting starts in a light-emitting device using a semiconductor light-emitting element such as an LED.

[0009] [Methods used to solve the problem]

[0010] [1] One embodiment of the present invention provides a method for controlling the lighting of a semiconductor light-emitting element, which includes: (a) controlling the current flowing through the semiconductor light-emitting element by using a lighting control device, wherein the lighting control device includes: a switching element having a control terminal for controlling the conduction state and connected in series with the semiconductor light-emitting element; and a control circuit for controlling the control terminal. The method for controlling the lighting of the semiconductor light-emitting element includes the following steps: (b) a first step, wherein the control circuit causes the control voltage of the control terminal of the switching element to gradually increase from an initial value to a first value in a relatively short time; and (c) a second step, wherein the control circuit causes the control voltage of the control terminal of the switching element to gradually increase from the first value to a second value in a relatively long time.

[0011] [2] A lighting control device according to one embodiment of the present invention (a) controls the lighting of the semiconductor light-emitting element by controlling the current flowing through the semiconductor light-emitting element, and the lighting control device of the semiconductor light-emitting element comprises: (b) a switching element having a control terminal for controlling the conduction state and connected in series with the semiconductor light-emitting element; (c) a control circuit for providing a control voltage to the control terminal; (d) the control circuit causes the control voltage of the control terminal of the switching element to gradually increase from an initial value to a first value in a relatively short time, and then causes the control voltage of the switching element to gradually increase from the first value to a second value in a relatively long time.

[0012] [3] A light emitting device according to one embodiment of the present invention includes: the lighting control device described above; and a semiconductor light emitting element whose lighting is controlled by the lighting control device.

[0013] According to the above configuration, in a light emitting device using a semiconductor light emitting element such as an LED, it is possible to shorten the time until lighting starts while suppressing overshoot of the LED current. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a circuit diagram showing the configuration of the flash device according to the first embodiment.

[0015] Figure 2 (A) is a timing chart for explaining the operation of the lighting control device. Figure 2 (B) is a local enlargement Figure 2 (A) is a diagram showing a waveform of a gate voltage.

[0016] Figure 3 This is a timing chart for explaining the operation of the lighting control device of the reference example.

[0017] Figure 4This is a circuit diagram showing the configuration of a flash device according to a second embodiment.

[0018] Figure 5 This is a circuit diagram showing the configuration of a flash device according to a third embodiment.

[0019] Figure 6 This is a timing chart for explaining the operation of the lighting control device.

[0020] Reference numerals

[0021] 10a: lighting control device; 11a: voltage addition circuit; 100a: flash unit; U1: control unit; R1, R2: resistors; C1, C2, C3: capacitors; Q1, Q2: field-effect transistors DETAILED DESCRIPTION

[0022] (First embodiment)

[0023] Figure 1 This is a circuit diagram showing the structure of a flash device according to a first embodiment. Flash device 100a of this embodiment includes a lighting control device 10a and LEDs 1 and 2 whose lighting is controlled by lighting control device 10a. Flash device 100a is used, for example, in a camera and receives a voltage V from a power supply circuit (not shown). in When a light emission signal is received from a control unit of the camera (not shown), the LEDs 1 and 2 are driven to generate a flash. The light intensity of the flash is set by a light intensity control signal supplied from the control unit of the camera.

[0024] In the example shown, two LEDs 1 and 2 are connected in series, but the number of LEDs is not limited to two and can be increased or decreased arbitrarily. In addition, several LEDs can be connected in parallel or in series and parallel.

[0025] The lighting control device 10a includes a control unit U1, capacitors (capacitive elements) C1, C2, and C3, resistors R1 and R2, a diode D1, and field-effect transistors Q1 and Q2. Field-effect transistor Q1 corresponds to the "switching element" of the present invention, and the remaining components correspond to the "control circuit" of the present invention (this also applies to the second and third embodiments).

[0026] The control unit U1 is configured using, for example, a microcomputer, and controls the overall operation of the lighting control device 10a. The control unit U1 receives a voltage V from a power supply circuit via a terminal IN and a terminal GND. in. The control unit U1 operates based on the supply of a light signal. Furthermore, the control unit U1 receives input of a light emission signal via terminal PWM1 and input of a light intensity control signal via terminal ICTRL. Furthermore, the control unit U1 detects current via terminals ISP and ISN1. Furthermore, the control unit U1 supplies a control voltage from terminal G1 to the gate of the field-effect transistor Q1. For example, a device identified by the well-known model number TPS92830-Q1 manufactured by Texas Instruments can be used as such a control unit U1.

[0027] The resistor element R1 is connected in series with the LEDs 1 and 2. Specifically, one end of the resistor element R1 is connected to the voltage V in The resistor element R1 is connected to the supply terminal of the control unit U1 and the other end to the anode of LED 1. One end of the resistor element R1 is connected to terminal ISP of the control unit U1 and the other end is connected to terminal ISN1. This resistor element R1 is used to detect current in the control unit U1. The current detected here corresponds to the current flowing through LEDs 1 and 2. The resistance value of the resistor element R1 is, for example, 0.1Ω.

[0028] The current path (source-drain region) of field-effect transistor Q1 is connected in series with LEDs 1 and 2, and its gate (control terminal) is connected to terminal G1 of control unit U1. Specifically, one end of the current path of field-effect transistor Q1 is connected to the cathode of LED 2, and the other end is connected to the GND terminal (reference potential terminal).

[0029] One end of the current path of the field effect transistor Q2 is connected to a 1.6V power supply via a resistor R2 , and the other end is connected to the gate of the field effect transistor Q1 via a diode D1 . The gate is connected to an input terminal of a light emission signal.

[0030] The anode of diode D1 is connected to the current path of field effect transistor Q2, and the cathode is connected to the gate of field effect transistor Q1. One end of resistor R2 is connected to the current path of field effect transistor Q2, and the other end is connected to a 1.6V power supply.

[0031] Capacitor C1 is connected between terminal IN and terminal GND of the control unit U1. One end of capacitor C2 is connected to terminal G1 of the control unit U1 and the gate of field-effect transistor Q1, and the other end is connected to the GND terminal. Capacitor C3 has one end connected to a 1.6V power supply and the other end connected to the GND terminal. The capacitance of capacitor C1 is, for example, 100 μF, the capacitance of capacitor C2 is, for example, 0.013 μF, and the capacitance of capacitor C3 is, for example, 0.1 μF.

[0032] The voltage adding circuit 11a includes a field effect transistor Q2, a resistor R2, a capacitor C3, and a diode D1. The voltage adding circuit 11a is a circuit for adding a further voltage to the gate of the field effect transistor Q1 to the voltage supplied from the control unit U1.

[0033] Next, refer to Figure 2 (A) Figure 3 The operation of the lighting control device 10a will be described with reference to the timing chart shown. Figure 2 (A) is a timing chart of the lighting control device 10a of this embodiment. Figure 3 This is a timing diagram of the lighting control device of the reference example. Figure 2 (B) is a partial enlargement of the Figure 2 The waveform of the gate voltage shown in (A) is shown in FIG. In addition, the lighting control device of the reference example here is from Figure 1 The lighting control device 10a shown in the figure omits the voltage application circuit 11a formed by the field-effect transistor Q2, the resistor R2, the capacitor C3, and the diode D1. In each figure, the first section shows the waveform of the light emission signal, the second section shows the waveform of the gate voltage of the field-effect transistor Q1, the third section shows the waveform of the cathode voltage of the LED 2, and the fourth section shows the waveform of the current (LED current) flowing through the LEDs 1 and 2.

[0034] First, let's explain the overall operation. At terminal PWM1 of control unit U1, when the light-emission signal changes from a low level to a high level (light-emission instruction), a current (e.g., 0.3 mA) flows from terminal G1 of control unit U1 to charge capacitor C2, causing the gate voltage of field-effect transistor Q1 to rise. When the gate voltage exceeds a threshold, the current path of field-effect transistor Q1 becomes conductive, and current flows through LEDs 1 and 2. This current also flows through resistor R1, and is detected by terminals ISP and ISN1 of control unit U1. In other words, control unit U1 functions as a current detector. Control unit U1 controls the current flowing from terminal G1 so that the voltage detected between terminals ISP and ISN1 is constant with the voltage of the light-intensity control signal supplied to ICTRL (e.g., a voltage five times the voltage between terminals ISP and ISN1 is equal to the voltage of the light-intensity control signal). This allows LEDs 1 and 2 to be illuminated with the desired current.

[0035] Here, the time required from the time the light emission signal changes to a high level until the current flowing through LEDs 1 and 2 reaches the desired level is basically determined by the current from terminal G1 of control unit U1, the capacitance of capacitor C2, and the gate-source coupling capacitance of field effect transistor Q1. In the lighting control device of the reference example, for example, if the gate voltage when the desired current flows through LEDs 1 and 2 is 1.6V and the capacitance of capacitor C2 is 0.013μF, the time required for the current flowing through LEDs 1 and 2 to reach the desired level (for example, 1.8A) is ( Figure 3 The time from time t0 to time t2' shown is approximately 70 μs.

[0036] In contrast, in the lighting control device 10a of this embodiment, when the light emission signal reaches a high level, the field effect transistor Q2 is turned on accordingly, and a voltage is applied to the gate of the field effect transistor Q1 from the 1.6V power supply via the resistor R2 and the diode D1. The voltage at this point is 1.0V, minus the forward drop voltage Vf of the diode D1 (e.g., 0.6V).

[0037] The voltage applied by the voltage adding circuit 11a composed of the field effect transistor Q2, the diode D1, the resistor R2, etc. rises sharply, so Figure 2 As shown in the enlarged view of (B), the gate voltage of field effect transistor Q1 also increases rapidly from 0 V (initial value) to 1.0 V (first value) in a relatively short period of time (from time t0 to time t1). Then, from time t1 to time t2, the gate voltage of field effect transistor Q1 increases slowly from 1.0 V to 1.6 V (second value) in a relatively long period of time (from time t1 to time t2) due to the current from terminal G1 of control unit U1. After the gate voltage rises to 1.6 V (after time t2), it is maintained at this gate voltage.

[0038] By controlling the gate voltage of the field effect transistor Q1 in this manner, under the same conditions as those in the reference example, the time required for the current flowing through the LEDs 1 and 2 to reach the desired level is ( Figure 2 The time from time t0 to time t2 shown in (A) is shortened to about 20 μs. In addition, since the gate voltage is gradually increased in two steps, overshoot, a phenomenon in which the current flowing through LEDs 1 and 2 greatly exceeds the desired value, can be suppressed.

[0039] In the above description, 1.0 V is used as an example of the first value of the gate voltage, and 1.6 V is used as an example of the second value. However, considering the solid-state variation and temperature changes of the field-effect transistor Q1, it is preferable to set the first value of the gate voltage to a value that is 50% or more and 70% or less of the second value. From another perspective, it is preferable to set the first value of the gate voltage so that the magnitude of the current flowing through the LEDs 1 and 2 at the first value is 0.1% or more and 10% or less of the magnitude of the current flowing through the LEDs 1 and 2 at the second value.

[0040] (Second embodiment)

[0041] Figure 4 This is a circuit diagram showing the configuration of a flash device according to a second embodiment. The basic configuration of flash device 100b of this embodiment is the same as that of flash device 100a of the first embodiment described above. However, the configuration of voltage application circuit 11b in lighting control device 10b differs from that of voltage application circuit 11a in the first embodiment. The following description will omit any overlapping sections, focusing on the modified sections.

[0042] The voltage application circuit 11b includes field-effect transistors Q2, Q3, and Q4, resistors R2, R3, R4, and R5, and a capacitor C3. The connection configuration of the field-effect transistor Q2, resistor R2, and capacitor C3 is the same as that of the first embodiment. However, a 1.6V power supply is not provided on one end of each of the resistor R2 and capacitor C3.

[0043] The resistor R3 is connected between the input terminal of the light emitting signal and the gate of the field effect transistor Q2. The gate of the field effect transistor Q3 is connected between the cathode of the LED 2 and the field effect transistor Q1. One end of the current path is connected to the voltage V in The gate of field effect transistor Q4 is connected between the current path of field effect transistor Q3 and resistor R5, one end of the current path is connected to the gate of field effect transistor Q2, and the other end is connected to the GND terminal.

[0044] Next, refer to Figure 2 The operation of the lighting control device 10b will be described with reference to the timing chart shown in (A). The overall operation of the lighting control device 10b is the same as that of the lighting control device 10a of the first embodiment, so the description will focus on the differences.

[0045] In the lighting control device 10b of the present embodiment, when the light emission signal becomes high level, the field effect transistor Q2 is turned on accordingly, thereby supplying a voltage to the gate of the field effect transistor Q1.

[0046] When the gate voltage of the field effect transistor Q1 reaches the threshold, the current path of the field effect transistor Q1 is turned on. As a result, the cathode voltage of the LED 2 decreases (see Figure 2 MOSFET Q3 detects this drop. Specifically, MOSFETs Q3 and Q4 are turned on, and each current path is connected. Consequently, the gate of MOSFET Q2 is connected to the GND terminal, turning MOSFET Q2 off, and stopping the application of voltage to the gate of MOSFET Q1.

[0047] Then, the current from the terminal G1 of the control unit U1 gradually increases the gate voltage of the field effect transistor Q1 to 1.6 V. After the gate voltage rises to 1.6 V (after time t2), the gate voltage is maintained at that level.

[0048] As described above, according to the lighting control device 10 b of the second embodiment, it is also possible to suppress overshoot of the current flowing through the LEDs 1 and 2 and shorten the time until lighting starts.

[0049] (Third embodiment)

[0050] Figure 5 This is a circuit diagram showing the configuration of a flash device according to a third embodiment. The basic configuration of flash device 100c of this embodiment is the same as that of flash device 100b of the second embodiment described above. However, the configuration of voltage application circuit 11c in lighting control device 10c differs from that of voltage application circuit 11b of the second embodiment. The following description will omit any overlapping sections, focusing on the modified sections.

[0051] The voltage application circuit 11c includes field-effect transistors Q2, Q3, and Q4, resistors R2, R3, R4, R5, and R6, and a capacitor C3. The configuration differs from the second embodiment in that a resistor R6 is added, and the gate of field-effect transistor Q3 is connected to terminal G2 of the control unit U1. Resistor R6 is connected between resistor R1 and LED 1. The control unit U1 detects the current flowing through LEDs 1 and 2 by detecting the voltage across resistor R1 between terminals IPS and ISN1, and the voltage across resistor (R1 + R6) between terminals IPS and ISN2. In other words, the control unit U1 functions as a current detector.

[0052] Next, refer to Figure 6The timing chart shown in FIG. 1 illustrates the operation of the lighting control device 10c. The overall operation of the lighting control device 10c is similar to that of the lighting control device 10a of the first embodiment and the lighting control device 10b of the second embodiment, so the following description will focus on the differences.

[0053] In the lighting control device 10c of this embodiment, when the light emission signal becomes high, the field effect transistor Q2 is turned on accordingly. As a result, a voltage is supplied to the gate of the field effect transistor Q1. Here, since the resistors R1 and R6 are connected in series, if they are set to the same resistance value, when the current flowing through the LEDs 1 and 2 is 1 / 2 of the desired value (see Figure 6 At point b in the fourth waveform of the current waveform, control unit U1 detects this current using terminal IPS-ISN2. Since terminal G2 operates to sink current, the gate voltage of field-effect transistor Q3 reaches GND level (reference potential). As a result, field-effect transistors Q3 and Q4 turn on, field-effect transistor Q2 turns off, and the voltage applied to the gate of field-effect transistor Q1 stops.

[0054] Then, the gate voltage of the field effect transistor Q1 gradually increases to 1.6 V by the current from the terminal G1 of the control unit U1. After the gate voltage rises to 1.6 V (after time t2), the gate voltage is maintained at that level.

[0055] As described above, according to the lighting control device 10 c of the third embodiment, it is also possible to suppress overshoot of the current flowing through the LEDs 1 and 2 and shorten the time until lighting starts.

[0056] In the third embodiment, when the current flowing through the LEDs 1 and 2 reaches half of its desired value, the control unit U1 detects this current. However, the current level used as a reference for this detection is preferably set within a range of 30% to 70% based on the value of the current flowing through the LEDs 1 and 2 reaching the desired value. This can be adjusted by the resistance values ​​of the resistors R1 and R6.

[0057] In addition, the present invention is not limited to the contents of the above-mentioned embodiments and can be implemented in various modifications within the scope of the main purpose of the present invention. For example, in each embodiment, an LED is used as an example of a semiconductor light-emitting element, but semiconductor light-emitting elements are not limited to this. For example, semiconductor light-emitting elements such as semiconductor lasers (LDs) can also be used. Similarly, in each embodiment, a field-effect transistor is used as an example of a switching element, but switching elements are not limited to this.

[0058] Furthermore, the circuit configurations in each embodiment are merely examples, and any circuit configuration that achieves the desired operation may be implemented with appropriate modifications. Specifically, other components not shown in the embodiments may be added, and as long as the same lighting control method is achieved, the circuit configuration may be different.

[0059] Furthermore, the application scope of the lighting control device and lighting control method according to the present invention is not limited to flash devices, but the present invention can be generally applied to light-emitting devices that are expected to generate a high amount of light in a relatively short time.

Claims

1. A method for controlling lighting of a semiconductor light-emitting element, the method controlling lighting of the semiconductor light-emitting element by controlling a current flowing through the semiconductor light-emitting element using a lighting control device, the lighting control device comprising: a switching element having a control terminal for controlling a conductive state and connected in series with the semiconductor light-emitting element; and a control circuit for controlling the control terminal. in, The lighting control method of the semiconductor light emitting element comprises the following steps: In a first step, the control circuit gradually increases the control voltage of the control terminal of the switching element from an initial value to a first value in a relatively short time; as well as In a second step, the control circuit gradually increases the control voltage at the control terminal of the switching element from the first value to a second value over a relatively long period of time. In the first step, the control circuit gradually increases the control voltage of the control terminal from the initial value while detecting the cathode voltage of the semiconductor light emitting element, and stops the gradual increase of the control voltage when a decrease in the cathode voltage is detected. The magnitude of the control voltage at the time when the gradual increase is stopped corresponds to the first value.

2. The lighting control method of a semiconductor light emitting element according to claim 1, wherein: The magnitude of the first value of the control voltage in the first step corresponds to not less than 50% and not more than 70% of the second value.

3. The lighting control method of a semiconductor light emitting element according to claim 1, wherein: The first value of the control voltage in the first step is set so that the magnitude of the current flowing through the semiconductor light emitting element corresponding to the first value is not less than 0.1% and not more than 10% of the magnitude of the current flowing through the semiconductor light emitting element corresponding to the second value.

4. A method for controlling the lighting of a semiconductor light-emitting element, the method comprising: controlling the current flowing through the semiconductor light-emitting element using a lighting control device, the lighting control device comprising: a switching element having a control terminal for controlling a conductive state and connected in series with the semiconductor light-emitting element; and a control circuit for controlling the control terminal. in, The lighting control method of the semiconductor light emitting element comprises the following steps: In a first step, the control circuit gradually increases the control voltage of the control terminal of the switching element from an initial value to a first value in a relatively short time; as well as In a second step, the control circuit gradually increases the control voltage at the control terminal of the switching element from the first value to a second value over a relatively long period of time. In the first step, the control circuit gradually increases the control voltage of the control terminal from the initial value while detecting the current flowing through the semiconductor light emitting element, and stops gradually increasing the control voltage when the current becomes greater than or equal to 30% and less than or equal to 70% of the current corresponding to the second value. The magnitude of the control voltage at the time when the gradual increase is stopped corresponds to the first value.

5. A lighting control device for a semiconductor light emitting element, the lighting control device controlling the lighting of the semiconductor light emitting element by controlling a current flowing through the semiconductor light emitting element. in, The lighting control device of the semiconductor light emitting element comprises: a switching element having a control terminal for controlling a conductive state and connected in series with the semiconductor light emitting element; as well as a control circuit providing a control voltage to the control terminal, The control circuit gradually increases the control voltage of the control terminal of the switching element from an initial value to a first value in a relatively short time, and then gradually increases the control voltage of the switching element from the first value to a second value in a relatively long time. The control circuit includes a voltage detection unit for detecting a cathode voltage of the semiconductor light emitting element. While detecting the cathode voltage using the voltage detection unit, the control voltage at the control terminal is gradually increased from the initial value. When the voltage detection unit detects a decrease in the cathode voltage, the gradual increase in the control voltage is stopped. The magnitude of the control voltage at the time when the gradual increase is stopped corresponds to the first value.

6. The lighting control device for a semiconductor light emitting element according to claim 5, wherein: The magnitude of the first value of the control voltage corresponds to not less than 50% and not more than 70% of the second value.

7. The lighting control device for a semiconductor light emitting element according to claim 5, wherein: The first value of the control voltage is set so that a magnitude of a current flowing through the semiconductor light emitting element corresponding to the first value is not less than 0.1% and not more than 10% of a magnitude of a current flowing through the semiconductor light emitting element corresponding to the second value.

8. A lighting control device for a semiconductor light emitting element, the lighting control device controlling the lighting of the semiconductor light emitting element by controlling a current flowing through the semiconductor light emitting element. in, The lighting control device of the semiconductor light emitting element comprises: a switching element having a control terminal for controlling a conductive state and connected in series with the semiconductor light emitting element; as well as a control circuit providing a control voltage to the control terminal, The control circuit gradually increases the control voltage of the control terminal of the switching element from an initial value to a first value in a relatively short time, and then gradually increases the control voltage of the switching element from the first value to a second value in a relatively long time. The control circuit includes a current detection unit for detecting a current flowing through the semiconductor light emitting element. While the current detection unit detects the current flowing through the semiconductor light emitting element, the control voltage at the control terminal is gradually increased from the initial value. When the current detection unit detects that the current is within a range of 30% to 70% of the current corresponding to the second value, the gradual increase of the control voltage is stopped. The magnitude of the control voltage at the time when the gradual increase is stopped corresponds to the first value.

9. A light-emitting device comprising: The lighting control device according to any one of claims 5 to 8; as well as A semiconductor light emitting element whose lighting is controlled by the lighting control device.

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