TWI795208B - A driving circuit and light-emitting device using the same - Google Patents

Abstract

This application discloses a driving circuit and light-emitting device using the same. The driving circuit includes an external control unit, a digital control unit, a trigger unit and a current source. The digital control unit generates an internal control signal. The trigger unit generates a trigger signal to control the current source according to the internal control signal.

Description

A driving circuit and a light emitting device using the driving circuit

The present invention relates to a driving circuit for a light emitting device, and in particular to a circuit for adjusting the light intensity of the light emitting device by using a digital control unit.

With the development of technology, more and more devices in daily life use light-emitting diodes (light-emitting diodes; LEDs) as light sources. In order to be more widely used in daily life, some light sources are equipped with dimmers that can adjust the brightness, so that users can change the intensity of the light source according to the needs of the environment. Common dimmers can be divided into digital dimming and analog dimming. Compared with the digital dimming method, although the analog dimming method can also dim without a digital controller, it is limited by the dimmer used in the analog dimming method (such as TRIAC dimmer) A maintenance current is required to maintain the normal operation of the dimmer, which leads to the fact that the current passing through the dimmer is lower than the maintenance current of the dimmer in low-brightness applications, causing the dimmer to turn off abnormally and causing the light source to flicker . Therefore, the present invention proposes a digital dimming method, which not only avoids flickering at low brightness, but also improves the stability of the dimming method.

The invention discloses a light emitting device, which includes a digital control unit, a trigger unit, a current source, and a light source. The digital control unit provides a first current signal, wherein the first current signal is a pulse width modulation (PWM) signal; the trigger unit includes a first transistor, electrically connected to the digital control unit, and receives the first current signal; the current The source is electrically connected to the trigger unit, and the light source is electrically connected to the current source.

The invention discloses a light-emitting device that can be connected to a power supply, including a digital control unit, a trigger unit, a current source, and a light source. The digital control unit provides a first current signal, and the first current signal is a pulse width modulation (PWM) signal, and the trigger unit includes a transistor electrically connected to the digital control unit, and receives the first current signal; The trigger unit is electrically connected, and the light source is electrically connected to the current source.

FIG. 1A is a circuit diagram of a light emitting device 1000 according to an embodiment of the present invention. The light emitting device 1000 includes a light source 18 and a driving circuit 300 . The driving circuit 300 has an external control unit 10 , a digital control unit 12 , a trigger unit 14 and a current source 16 . The current source 16 is a certain current source and includes a transistor Q1. The transistor Q1 may be a high electron mobility field effect transistor (HEMT), more specifically, a depletion type high electron mobility field effect transistor. Transistor (Depletion-mode HEMT). The transistor Q1 has a gate G1 , a drain D1 and a source S1 . The drain D1 is electrically connected to the light source 18 , and the gate G1 is electrically connected to the trigger unit 14 .

The light source 18 includes one or more light-emitting diodes. The light-emitting diodes may include semiconductor layers made of III-V semiconductor materials to emit non-coherent light. The III-V semiconductor materials are, for example, Al _x In _y Ga _{1-xy )} N or _{AlxInyGa ( 1-xy )} P, where 0≤x≤1; _0≤y≤1 ; (x+y)≤1. And depending on the material, the light-emitting diode can emit red light with a peak wavelength between 610nm and 650nm, green light with a peak wavelength between 495nm and 570nm, blue light with a peak wavelength between 450nm and 495nm, and a peak wavelength of Violet light between 400nm and 440nm or ultraviolet light with a peak wavelength between 200nm and 400nm. In one embodiment, the light-emitting diode has a light-emitting layer, and a wavelength conversion material formed on the light-emitting layer. The wavelength conversion material includes quantum dot material, phosphor material or a combination thereof. Wherein, the phosphor material may include yellow-green phosphor, red phosphor or blue phosphor. Yellow-green phosphors include YAG, TAG, silicates, vanadates, alkaline earth metal selenides, and metal nitrides. Red phosphors include fluorides (such as K ₂ TiF ₆ : Mn ⁴⁺ or K ₂ SiF ₆ : Mn ⁴⁺ ), silicates, vanadates, alkaline earth metal sulfides, metal oxynitrides, and tungstates and molybdate mixtures. The blue phosphor includes BaMgAl ₁₀ O ₁₇ :Eu ²⁺ . Quantum dot materials can be zinc sulfide, zinc selenide, zinc telluride, zinc oxide, cadmium sulfide, cadmium selenide, cadmium telluride, gallium nitride, gallium phosphide, gallium selenide, gallium antimonide, gallium arsenide, Aluminum nitride, aluminum phosphide, aluminum arsenide, indium phosphide, indium arsenide, tellurium, lead sulfide, indium antimonide, lead telluride, lead selenide, antimony telluride, ZnCdSeS, CuInS, CsPbCl ₃ , CsPbBr ₃ , CsPbI ₃ . In one embodiment, the LED including the wavelength conversion material can emit a white light. For example, in the backlight module of the display, the color temperature of white light is between 10000K~20000K, and has a color point coordinate (x, y) in the CIE1931 chromaticity diagram, where 0.27≦x≦0.285; 0.23≦y≦ 0.26. In another embodiment, for example, in the case of general lighting, the white light emitted by the light emitting diode has a color temperature between 2200~6500K (such as 2200K, 2400K, 2700K, 3000K, 5700K, 6500K) and is in the CIE1931 chromaticity In the figure, the coordinates (x, y) of a point with one color are located in the 7th order MacAdam ellipse (MacAdam ellipse).

As shown in FIG. 1A , if the operating voltages of different elements in the light emitting device 1000 are different, the light emitting device 1000 can be respectively connected to power sources 110 and 111 suitable for the requirements of individual elements. In one embodiment, the operating voltage of the digital control unit 12 is 5V, and the power supply 110 can provide a voltage of 3V~15V, such as 3.3V, 5V, 7V, and 12V; the operating voltage of the light source 18 is 110V, and the power supply 111 can provide 70V~230V voltage, such as 80V, 96V, 115V voltage. Connecting components that require different operating voltages to their respective power supplies not only makes the power supply more efficient, but also avoids mutual interference between components, which affects the stability of the components when they are operated. In one embodiment, the light emitting device 1000 further includes an AC/DC voltage conversion circuit (not shown in the figure) connected to the mains, and converts the mains into the power 110 and/or the power 111 respectively. The mains are, for example, 110V, 220V or 240V AC.

In the light emitting device 1000 , the digital control unit 12 generates a second control signal Si2 according to a first control signal Si1 from the external control unit 10 . The second control signal Si2 is input to the trigger unit 14 . The trigger unit 14 generates a third control signal Si3 according to the second control signal Si2, and uses the third control signal Si3 to control the current source 16 to be turned on or off (On or Off). Wherein, the first control signal Si1 is an external control signal, the second control signal Si2 is an internal control signal, and the third control signal Si3 is a trigger signal. Since the brightness of the light-emitting diode is related to the magnitude of the current flowing through it, by controlling the on or off state of the current source 16 , the magnitude of the current passing through the light source 18 within a period of time can be determined to achieve the effect of adjusting the luminous intensity of the light-emitting device 1000 .

The external control unit 10 can be a wired device or a wireless device, and is used to receive a user's command to generate the first control signal Si1. In one embodiment, the external control unit 10 is a wired device connected to the digital control unit 12 through physical wires to transmit the first control signal Si1 to the digital control unit 12 , such as a variable resistor or a sensor. In one embodiment, the external control unit 10 is a wireless device that transmits the first control signal Si1 to the digital control unit 12 through wireless transmission, such as a Bluetooth module or an Internet of Things device. In one embodiment, the digital control unit 12 is a microprocessor unit (Microcontroller Unit; MCU), for generating a second control signal Si2 according to the first control signal Si1, and the second control signal Si2 is a pulse width Modulation (Pulse Width Modulation; PWM) signal. More specifically, the digital control unit 12 adjusts the signal characteristics of the second control signal Si2 according to the first control signal Si1, and the signal characteristics include a duty ratio. As the duty ratio becomes lower, the conduction time of the current source 16 is longer, so that the light emitting time of the light source 18 is also longer, and the brightness provided by the light emitting device 1000 is also higher. Please refer to Figure 1B and related paragraphs for details.

Generally speaking, the lighting time of the light source 18 is determined by controlling the current source 16 to be turned on or off, so as to achieve the dimming effect. Wherein, by turning on or off the current source 16 at a switching frequency higher than human eyes can detect (for example, a frequency greater than 50, 60, or 120 Hz), it is possible to prevent human eyes from feeling the flicker of the light emitting device 1000 and causing discomfort. In other words, the light emitting device 1000 sequentially generates the second control signal Si2 and the third control signal Si3 according to the first control signal Si1 to turn on or turn off the current source 16, wherein the frequency of the second control signal Si2 and the third control signal Si3 higher than the switching frequency perceivable by the human eye.

In the light emitting device 1000, the transistor Q1 in the current source 16 is a depletion high electron mobility field effect transistor, so the trigger unit 14 provides a third control signal Si3 including a negative voltage to turn on or off the transistor Q1. Specifically, the trigger unit 14 includes a negative voltage generator or a clamping circuit for generating a third control signal Si3 including a negative voltage according to the second control signal Si2. Referring to FIG. 1A, the trigger unit 14 includes a capacitor Ca electrically connected to the digital control unit, and a diode Di connected to the capacitor Ca and the transistor Q1. The voltage ranges of the third control signal Si3 and the second control signal Si2 are different, for example, the voltage range of the second control signal Si2 is 0V~5V, while the voltage range of the third control signal Si3 is -5V~0V, so that the voltage range including negative voltage The third control signal Si3 can turn on or turn off the transistor Q1.

FIG. 1B is a waveform diagram of the second control signal Si2 of an embodiment in FIG. 1A. FIG. 1B includes five waveforms including waveform (a) to waveform (e), respectively representing the waveforms of the second control signal Si2 with duty ratios of 0%, 25%, 50%, 75% and 100%. With the difference of the duty ratio, the waveform of the second control signal Si2 also changes from the waveform (a) representing the duty ratio 0% to the state of the low voltage (VL) and the ratio of the high voltage (VH), for example, to represent A waveform with a duty ratio of 25% (b), a waveform representing a duty ratio of 50% (c), a waveform representing a duty ratio of 75% (d), or a waveform representing a duty ratio of 100% (e). In the light emitting device 1000, the trigger unit 14 generates a third control signal Si3 according to the second control signal Si2, and the frequency of the third control signal Si3 is the same or substantially the same as the second control signal Si2, but the responsibility of the third control signal Si3 than the second control signal Si2. In terms of frequency, the frequency difference between the third control signal Si3 and the second control signal Si2 is less than 5% of one of the frequencies. In terms of the duty ratio, the sum of the duty ratios of the two signals Si2 and Si3 is approximately equal to 100%. For example, in the lighting device 1000, when the second control signal Si2 is of waveform (b) and the duty ratio is 25%, the duty ratio of the third control signal Si3 is approximately 75%; When (b) is adjusted to waveform (d), the duty ratio of the third control signal Si3 is also adjusted from 75% to 25%. In one embodiment, the sum of duty ratios of the two signals Si2 and Si3 is between 90% and 110%. The higher the duty ratio of the second control signal Si2 is, the lower the duty ratio of the third control signal Si3 is, so that the time for the light source 18 to emit light in one cycle is also shorter, making the brightness of the light emitting device 1000 darker; otherwise, the second control signal Si3 The lower the duty ratio of the signal Si2 is, the higher the duty ratio of the third control signal Si3 is, so that the time for the light source 18 to emit light in one cycle is longer, so that the brightness of the light emitting device 1000 is brighter. In summary, the light-emitting device 1000 can receive the user's instruction from the external control unit 10 to generate the corresponding first control signal Si1 to control the duty ratio of the second control signal Si2, and then control the current source 16 through the third control signal Si3 to achieve The light emission brightness of the light emitting device 1000 is changed.

In one embodiment, a resistor (not shown) is further provided between the light source 18 and the power source 111 to adjust the current flowing through the light source 18 . In one embodiment, a resistor and/or capacitor is further provided between the power supply 111 and the current source 16, so that the resistor and/or capacitor are connected in series or in parallel with the light source 18 to adjust the current flowing through the light source 18, and to filter out impurities. The information allows the luminescence of the light source 18 to be more stable. In one embodiment, a resistor (not shown) and/or a capacitor (not shown) is further provided between the source S of the transistor Q1 and the ground potential in the current source 16 to adjust the current flowing through the transistor Q1 .

FIG. 2 is a light emitting device 1002 according to an embodiment of the present invention. The light emitting device 1002 includes a light source 18 and a driving circuit 302 . The driving circuit 302 has an external control unit 10 , a digital control unit 12 , a trigger unit 14 , a resistor R and a current source 160 . The current source 160 includes a transistor Q1 and a transistor Q2 connected in parallel. Transistors Q1 and Q2 may be high electron mobility field effect transistors, more specifically depletion type high electron mobility field effect transistors. The transistor Q1 has a gate G1 , a drain D1 and a source S1 , and the transistor Q2 has a gate G2 , a drain D2 and a source S2 . The transistor Q1 and the transistor Q2 are connected in parallel, so that the drains D1 and D2 are electrically connected to the light source 18 , the sources S1 and S2 are connected, and the gates G1 and G2 are both connected to the trigger unit 14 . Please refer to the preceding paragraphs for the relevant descriptions of components with the same or similar labels and names in the light emitting device 1002 and the light emitting device 1000, and how the light emitting device 1002 receives the user's instruction through the external control unit 10 to generate the first control signal Si1, and then For the operation process of controlling the luminous intensity of the light source 18 through the second control signal Si2 and the third control signal Si3 generated by the digital control unit 12 and the trigger unit 14 , please also refer to the preceding paragraphs. In the light emitting device 1002, the current source 160 including the transistors Q1 and Q2 can provide more current to the light source 18 to increase the luminous intensity. In one embodiment, a resistor R is provided between the power source 110 and the trigger unit 14 to provide another additional current (current signal) to the trigger unit 14 . The current signal can provide more current, so that the capacitor Ca in the trigger unit 14 can receive more charges and output more stable current to the transistors Q1 and Q2. One end of the resistor R is connected to the power source 110 , and the other end is electrically connected to the digital control unit 12 and the trigger unit 14 . Through the setting of the resistor R, the trigger unit 14 not only receives the second control signal Si2, but also receives the current signal passing through the resistor R. As mentioned above, the current signal can provide more charge to the capacitor Ca, so as to provide a more stable output current to the transistors Q1 and Q2. In one embodiment, the current value of the current signal is greater than the current value of the second control signal Si2, for example, the second control signal Si2 is 100mA, and the current signal is 1A. In other words, if the current of the second control signal Si2 cannot meet the requirements of the transistors Q1 and Q2, the current signal can be used to supplement the demand. Here, the current signal can provide more charges for the capacitor Ca to output a more stable current to the transistor. Crystals Q1, Q2. Therefore, the capacitor Ca in the trigger unit 14 can receive the current signal from the digital control unit 12 (that is, the second control signal Si2) and the current signal from the power supply 110, and can store more charges due to receiving multiple current signals, Therefore, the third control signal Si3 will not be abnormal due to insufficient charge stored in the capacitor Ca during the conduction period of the transistors Q1 and Q2. For example, the duty ratio of the third control signal Si3 should be 75%, because the electric charge stored in the capacitor Ca is not enough, the state of high voltage is changed to low voltage in advance, and the duty ratio is, for example, 60%. Such an abnormal duty ratio will cause the transistors Q1 and Q2 to be turned off in advance, resulting in abnormal brightness of the light emitting device 1002 . It should be noted that when the trigger unit 14 is connected with more transistors, the capacity of the capacitor Ca must be increased to store more charges and output current to the connected transistors stably. In such a case, it is more likely to cause an abnormal situation of the third control signal Si3 due to insufficient charge stored in the capacitor Ca, so it is more necessary to set the resistor R as shown in Figure 2 to increase the input to the trigger unit 14 current flow. Wherein, the value of the resistor R can be changed according to the required current. If the current input to the trigger unit 14 is to be increased, a resistor R with a lower value should be set. Relatively, if excessive current is to pass through the resistor to avoid excess heat, the resistor R with a larger value is set instead, and the current is reduced under the condition that the abnormality of the third control signal Si3 can be avoided. In other embodiments, the resistor R can be set in the light emitting device 1000 in FIG. 1A to connect the power supply 110 and the trigger unit 14, so that the capacitor Ca in the trigger unit 14 can receive the current signal from the digital control unit 12 ( That is, the second control signal Si2) and the current signal passing through the resistor R store more charges, so as to avoid the abnormal brightness phenomenon that the transistor Q1 is turned off in advance.

In one embodiment, a resistor (not shown) is further provided between the light source 18 and the power source 111 to adjust the current flowing through the light source 18 . In one embodiment, a resistor and/or capacitor is further provided between the power source 111 and the current source 160, so that the resistor and/or capacitor are connected in parallel with the light source 18 to adjust the current flowing through the light source 18, which can further filter out noise and make the The light emitting condition of the light source 18 is more stable. In one embodiment, a resistor (not shown) and/or a capacitor (not shown) is further provided between the sources S1 and S2 of the transistors Q1 and Q2 in the current source 160 and the ground potential to adjust the current flowing through the transistors. The current of Q1 and Q2.

FIG. 3 is a light emitting device 2000 according to an embodiment of the present invention. The light emitting device 2000 includes a light source 18 and a driving circuit 320 . The driving circuit 320 has an external control unit 10 , a digital control unit 12 , a trigger unit 15 and a current source 160 . Please refer to the preceding paragraphs for the relevant descriptions of the elements with the same or similar numbers and names in the light emitting device 2000 and the light emitting device 1000 . The trigger unit 15 includes a transistor Q3, and the transistor Q3 may be a metal oxide semiconductor field effect transistor (MOSFET), more specifically, an enhanced high electron mobility field effect transistor (Enhancement -mode MOSFETs). The transistor Q1 has a gate G1 , a drain D1 and a source S1 , and the transistor Q3 has a gate G3 , a drain D3 and a source S3 . In the light emitting device 2000, the transistor Q1 in the current source 160 is connected in series with the transistor Q3, so that the gate G1 of the transistor Q1 is connected to the ground potential, the drain D1 is electrically connected to the light source 18, and the source S1 is connected to the electric potential. The drain D3 of the transistor Q3 is connected, the gate G3 of the transistor Q3 is connected to the digital control unit 12 , the drain D3 is connected to the source S1 of the transistor Q1 , and the source S3 is connected to the ground potential. In the lighting device 2000 , the digital control unit 12 generates a second control signal Si2 according to a first control signal Si1 from the external control unit 10 , and the second control signal Si2 is input to the trigger unit 15 . In one embodiment, the digital control unit 12 and the trigger unit 15 further have a resistor, and the voltage value and/or current value of the second control signal Si2 can be adjusted through the setting of the resistor. The trigger unit 15 receives the second control signal Si2, and adjusts the turn-on or turn-off of the transistor Q3 according to the second control signal Si2, thereby adjusting the light-emitting time length of the light source 18 in one cycle. More specifically, when the transistor Q3 is turned on by receiving the second control signal Si2, the current passes through the light source 18, the current source 160 (transistor Q1 inside) and the trigger unit 15 (transistor Q3 inside) in sequence, so that The light emitting device 2000 can emit light. In contrast, when the transistor Q3 is turned off by receiving the second control signal Si2, the current cannot pass through the trigger unit 15 (the transistor Q3 inside), so that the light emitting device 2000 cannot emit light. Therefore, in the light emitting device 2000, the length of time during which the trigger unit 15 (transistor Q3 inside) is turned on can be adjusted directly according to the second control signal Si2 generated by the digital control unit 12, so as to change the length of light emitting time of the light source 18 in one cycle. , to achieve the effect of changing the brightness. That is to say, the higher the duty ratio of the second control signal Si2, the longer the time for the light source 18 to emit light in one cycle, so that the brightness of the light emitting device 1000 is higher; on the contrary, the lower the duty ratio of the second control signal Si2, a The shorter the light-emitting time of the light source 18 in the period, the lower the brightness of the light-emitting device 1000 . It is worth noting that since the transistor Q3 can be directly controlled by the second control signal Si2, there is no need to convert the second control signal Si2 by other devices (such as the trigger unit 14 ).

The above-described embodiments are only to illustrate the technical ideas and characteristics of the present invention, and its purpose is to enable those skilled in this art to understand the content of the present invention and implement it accordingly, and should not limit the patent scope of the present invention. That is, all equivalent changes or modifications made according to the spirit disclosed in the present invention should still be covered by the patent scope of the present invention.

1000, 1002, 2000: light emitting device 300, 302, 320: drive circuit 110, 111: power supply 10: External control unit 12: Digital control unit 14, 15: trigger unit 16, 160: current source 18: light source Ca: Capacitance Di: diode R: resistance Q1, Q2, Q3: Transistor Si1: The first control signal Si2: Second control signal Si3: The third control signal

FIG. 1A is a circuit diagram of a light emitting device according to an embodiment of the present invention.

FIG. 1B is a waveform diagram of the second control signal.

Fig. 2 is a circuit diagram of a light emitting device according to an embodiment of the present invention.

Fig. 3 is a circuit diagram of a light emitting device according to an embodiment of the present invention.

none

1000: light emitting device

300: drive circuit

110, 111: power supply

10: External control unit

12: Digital control unit

14:Trigger unit

16: Current source

18: light source

Ca: Capacitance

Di: diode

Q1: Transistor

D1: drain

G1: Gate

S1: source

Si1: The first control signal

Si2: Second control signal

Si3: The third control signal

Claims (7)

A light emitting device, comprising: a digital control unit providing a first current signal, wherein the first current signal is a pulse width modulation (PWM) signal; a trigger unit including an enhanced metal oxide semiconductor field effect transistor , wherein the enhanced metal oxide semiconductor field effect transistor includes a first gate, a first drain, and a first source, the first gate is electrically connected to the digital control unit, and receives the first A current signal, the first source is connected to a ground potential; a current source includes a depletion type high carrier mobility transistor connected in series with the enhanced high electron mobility field effect transistor, wherein the depletion type high carrier The mobility transistor includes a second gate, a second drain, and a second source, the second gate is connected to the ground potential, and the second source is connected to the first drain; and a light source , electrically connected to the second drain. For the light-emitting device of claim 1, a resistor and/or a capacitor are further provided between the second source and the ground potential. For example, the light-emitting device of claim 1, wherein the light-emitting device can be connected to a power source, and further includes a resistor located between the power source and the light source. For example, the light-emitting device of claim 1, wherein the light-emitting device can be connected to a power source, and further includes a resistor and/or a capacitor between the power source and the current source. For example, the light-emitting device of item 1 of the scope of the patent application further includes a resistor located between the digital control unit and the trigger unit. For example, the light-emitting device in claim 1 of the patent application further includes an external control unit, wherein the external control unit generates an external control signal to adjust the signal characteristics of the first current signal. For example, the light emitting device according to claim 6 of the patent application, wherein the signal characteristic of the first current signal includes a duty ratio.

Images