TWI444099B - Light source device and dimming control circuit thereof - Google Patents

Description

Light source device and dimming control circuit thereof

The present invention relates to a light source device and a dimming control circuit thereof, and more particularly to a light source device of a diode and a dimming control circuit thereof.

Light Emitting Diode (LED) is small, power-saving and durable, and as the process matures, the price drops. Recently, products using light-emitting diodes as light sources are becoming more and more popular. And with the technological trend of energy saving and carbon reduction, the light-emitting diode has gradually become a new generation of light source. The light-emitting diode has a low working voltage, can actively emit light and has a certain brightness, and the brightness can be adjusted by voltage or current, and has the characteristics of impact resistance, vibration resistance and long life (100,000 hours). Therefore, LEDs are widely used in a variety of terminal equipment, from automotive headlights, traffic lights, text displays, billboards and large-screen video displays, to general-purpose architectural lighting and LCD backlighting.

Traditional luminaires can be dimmed with a dimmer. The dimmer inside the home can be placed separately from the luminaire, for example on a wall, allowing the user to easily adjust the intensity of the light. Since the dimmer is only suitable for adjusting the resistive bulb, it is not suitable for directly adjusting the brightness of the LED. Therefore, when LED lamps are used to directly replace traditional lamps, the flashing of the conventional lamps and LED lamps may be caused by different driving methods.

A dimming circuit 100 of the conventional light-emitting diode shown in FIG. 1 includes resistors R1 R R3 and capacitors C1 C C3. A low-pass filter composed of resistors R1 R R3 and capacitors C1 C C3 can convert a dimming signal dim_in into a driving signal dim_out to dim the light emitting diode. Since the dimming circuit 100 has a limit of the cutoff frequency, when the frequency of the dimming signal dim_in exceeds the cutoff frequency, the driving signal dim_out generated by the dimming circuit 100 is affected, so that the light emitting diode cannot emit the desired brightness. Further, the dimming circuit 100 also has a problem that the dimming ratio is small (its dimming ratio is about 100:1).

The invention provides a light source device and a dimming control circuit thereof, which can provide a higher dimming ratio and a larger dimming frequency range.

The invention provides a dimming control circuit comprising a triangular wave generator and a comparator. The triangular wave generator is used to generate a triangular wave signal. The positive input terminal of the comparator receives a dimming signal, and the negative input end of the comparator is coupled to the triangular wave generator. The comparator is configured to compare the triangular wave signal and the dimming signal to generate a driving signal.

The invention also provides a light source device comprising a light emitting diode unit, an inductor and a dimming module. One end of the LED unit is coupled to an input voltage. One end of the inductor is coupled to the other end of the LED unit. The dimming module is coupled to the other end of the inductor to adjust the brightness of the LED unit. The dimming module includes a switch unit and a dimming control circuit. The switch unit is coupled between the other end of the inductor and a ground. The dimming control circuit is coupled to the switch unit to generate a driving signal according to a dimming signal to control the conduction state of the switching unit, thereby adjusting the brightness of the LED unit. The dimming control circuit includes a triangular wave generator and a comparator. The triangular wave generator is used to generate a triangular wave signal. The positive input terminal of the comparator receives the dimming signal, and the negative input end of the comparator is coupled to the triangular wave generator to compare the triangular wave signal and the dimming signal to generate a driving signal.

In an embodiment of the invention, the light source device further includes a resistor coupled between the input voltage and the LED unit, and the dimming control circuit controls the conduction of the switch unit according to the current flowing through the resistor. status.

In an embodiment of the invention, the light source device further includes a buffer unit coupled to the dimming signal and the dimming control circuit for buffering the dimming signal.

In an embodiment of the present invention, the light source device further includes a second comparator, wherein the positive input end is coupled to the common contact of the resistor and the LED unit, and the negative input end of the second comparator is coupled. A reference voltage outputs a current detecting signal according to a voltage at a common contact of the resistor and the LED unit and a reference voltage.

In an embodiment of the invention, the light source device further includes a voltage dividing unit and a third comparator. The voltage dividing unit is coupled between the input voltage and the ground, and divides the input voltage to generate a divided voltage. The positive input end of the third comparator is coupled to a reference voltage, and the negative input end of the third comparator is coupled to the divided voltage, and outputs a voltage too low lock signal according to the reference voltage and the divided voltage, so that when the input voltage is too low Disable dimming control circuit.

In an embodiment of the invention, the dimming signal is a direct current signal, and the voltage level of the dimming signal is between the peak voltage level of the triangular wave signal and the valley voltage level.

In an embodiment of the invention, the dimming signal is a pulse width modulation signal, and the high voltage level of the pulse width modulation signal is greater than the peak voltage level of the triangular wave signal, and the low voltage of the pulse width modulation signal. The level is less than the valley voltage level of the triangular wave signal.

Based on the above, the present invention generates a conduction state of the driving signal control switch unit by using a triangular wave generator and a comparator, so that not only a high dimming ratio but also a dimming precision of the LED unit can be obtained, and dimming is performed. The signal frequency is not affected by the cutoff frequency as is known in the art.

The above described features and advantages of the present invention will be more apparent from the following description.

2 is a schematic diagram of a light source device according to an embodiment of the invention. Referring to FIG. 2 , the light source device 200 includes a light emitting diode unit 202 , an inductor L1 , and a dimming module 204 . The light-emitting diode unit 202 is coupled between an input voltage Vin and an inductor L1. The inductor L1 is coupled between the LED unit 202 and the dimming module 204, and the dimming module 204 is used to adjust the light-emitting diode. The brightness of the polar body unit 202. Further, the dimming module 204 can include a switch unit SW1 and a dimming control circuit 206. In this embodiment, the switch unit SW1 is implemented by using a transistor M1, but is not limited thereto. The gate of the transistor M1 is coupled to the inductor L1, the source of the transistor M1 is coupled to the ground, and the gate of the transistor M1 is coupled to the dimming control circuit 206.

The dimming control circuit 206 is configured to generate a driving signal SD1 according to a dimming signal Vdim to control the conduction state of the switching unit SW1, thereby adjusting the brightness of the LED unit 202. The dimming control circuit 206 includes a triangular wave generator 208 and a comparator OP1. The positive input terminal of the comparator OP1 receives the dimming signal Vdim, the negative input terminal of the comparator OP1 is coupled to the triangular wave generator 208, and the output end of the comparator OP1 is coupled to the switch unit SW1. The triangular wave generator 208 is configured to generate a triangular wave signal S1, and the comparator OP1 is configured to compare the triangular wave signal S1 with the dimming signal Vdim to generate the driving signal SD1. The dimming signal Vdim can be, for example, a direct current signal or a pulse width modulation signal, and the peak voltage level of the triangular wave signal S1 is Vh, and the valley voltage level is V1.

It is worth noting that when the dimming signal Vdim is a direct current signal, the voltage level of the dimming signal Vdim must be between the peak voltage level Vh of the triangular wave signal S1 and the valley voltage level V1. As shown in the schematic diagram of the analog dimming of FIG. 3A, the comparator OP1 compares the dimming signal Vdim with the triangular wave signal S1. When the voltage level of the dimming signal Vdim is higher than the voltage level of the triangular wave signal S1, the comparator OP1 The driving signal SD1 of the high voltage level is output, and the switching unit SW1 is turned on. At this time, the current supplied from the input voltage Vin can flow to the ground via the light-emitting diode unit 202, the inductor L1, and the switch unit SW1, and the light-emitting diode unit 202 can be made to emit light. At this time, the inductor L1 simultaneously accumulates energy.

When the voltage level of the dimming signal Vdim is lower than the voltage level of the triangular wave signal S1, the comparator OP1 outputs the driving signal SD1 of the low voltage level, so that the switching unit SW1 is turned off. At this time, the light-emitting diode unit 202 is supplied with light by the energy accumulated by the inductor L1 to emit light. Thus, by adjusting the voltage level of the dimming signal Vdim, the duty cycle of the driving signal SD1 can be changed, that is, when the voltage level of the dimming signal Vdim is higher, the duty cycle of the driving signal SD1 is higher, and when the dimming is performed, The lower the voltage level of the signal Vdim, the lower the duty cycle of the driving signal SD1. The duty cycle of the driving signal SD1 will affect the current flowing through the LED unit 202, that is, the higher the duty cycle of the driving signal SD1, the larger the current flowing through the LED unit 202, and the LED The brightness of the body unit 202 is stronger. Conversely, if the duty cycle of the driving signal SD1 is lower, the smaller the current flowing through the light emitting diode unit 202, the weaker the luminance of the light emitting diode unit 202.

In addition, the frequency of the driving signal SD1 can be adjusted by adjusting the frequency of the triangular wave signal S1. When the frequency of the triangular wave signal S1 becomes high, the frequency of the driving signal SD1 is increased, thereby increasing the switching frequency of the switching unit SW1, and the dimming of the LED unit 202 is more accurate.

4A and FIG. 4B are schematic diagrams showing waveforms of current flowing through a light emitting diode unit according to an embodiment of the invention. In the embodiment of FIGS. 4A and 4B, the peak voltage Vh of the triangular wave signal S1 is 2.5 volts (V), and the valley voltage V1 is 0.6V. 4A is a waveform of a current flowing through the light emitting diode unit 202 when the voltage value of the dimming signal Vdim is 0.6V, and FIG. 4B is a light emitting diode when the voltage value of the dimming signal Vdim is 2.4V. The waveform of the current of the body unit 202. As shown in FIG. 4A and FIG. 4B, when the voltage value of the dimming signal Vdim is 0.6V and 2.4V, the average current flowing through the LED unit 202 is 2.67 milliamperes (mA) and 1 amp (1 amp, respectively). A), therefore, the dimming ratio of the present embodiment can reach 1A: 2.67 mA = 375: 1, which is obviously larger than the dimming ratio achievable by the dimming circuit 100 of the prior art.

FIG. 3B is a schematic diagram of digital dimming according to an embodiment of the invention, please refer to FIG. 3B. In this embodiment, the dimming signal Vdim is a pulse width modulation signal, and the high voltage level of the dimming signal Vdim is greater than the peak voltage level Vh of the triangular wave signal S1, and the low voltage level of the dimming signal Vdim is smaller than the triangular wave signal S1. The valley voltage level V1. Similarly, when the voltage level of the dimming signal Vdim is higher than the voltage level of the triangular wave signal S1, the comparator OP1 outputs the driving signal SD1 of the high voltage level, and the switching unit SW1 is turned on, thereby causing the light emitting diode unit 202 to emit light. . At this time, the inductor L1 simultaneously accumulates energy. When the voltage level of the dimming signal Vdim is lower than the voltage level of the triangular wave signal S1, the switching unit SW1 is turned off. At this time, the energy accumulated by the inductor L1 is supplied to the light emitting diode unit 202 to emit light.

In this way, the duty cycle of the driving signal SD1 can be changed according to the duty cycle of the dimming signal Vdim, and when the duty cycle of the dimming signal Vdim is higher, the working period of the driving signal SD1 is higher, and the light is transmitted through the second light. The greater the current of the polar body unit 202, the stronger the brightness of the light emitting diode unit 202. Conversely, the lower the duty cycle of the dimming signal Vdim, the lower the duty cycle of the driving signal SD1, and the smaller the current flowing through the LED unit 202, the weaker the luminance of the LED unit 202.

5A and FIG. 5B are schematic diagrams showing waveforms of current flowing through a light emitting diode unit according to an embodiment of the invention. In the embodiment of Figures 5A and 5B, the frequency of the dimming signal Vdim is 20 KHz. 5A is a waveform of a current flowing through the LED unit 202 when the duty cycle of the dimming signal Vdim is 4%, and FIG. 5B is a dimming signal when the duty cycle of the dimming signal Vdim is 100%. The waveform of the current of the body unit 202. As shown in FIG. 5A and FIG. 5B, when the duty cycle of the dimming signal Vdim is 4% and 100%, the average values of the currents flowing through the LED unit 202 are 18.2 mA and 1 A, respectively. The dimming ratio can reach 1A: 18.2 mA = 55:1.

6A and FIG. 6 are schematic diagrams showing waveforms of current flowing through a light emitting diode unit according to an embodiment of the present invention. In the embodiment of FIGS. 6A and 6B, the frequency of the dimming signal Vdim is 100 Hz. 6A is a waveform of a current flowing through the light-emitting diode unit 202 when the duty cycle of the dimming signal Vdim is 0.02%, and FIG. 6B is a light-emitting diode when the duty cycle of the dimming signal Vdim is 100%. The waveform of the current of the body unit 202. As shown in FIG. 6A and FIG. 6B, when the duty cycle of the dimming signal Vdim is 0.02% and 100%, the average current flowing through the LED unit 202 is 55 microamperes (uA) and 1A, respectively. The dimming ratio of this embodiment can reach 1A: 55uA = 18000:1. It can be seen that the dimming control circuit 206 can accurately and efficiently dim the LED unit 202 regardless of the low frequency or the high frequency.

As described above, the driving signal is generated by the triangular wave generator 208 and the comparator OP1 in the dimming control circuit 206, which not only can obtain a higher dimming ratio, but also increase the dimming accuracy of the LED unit 202, and The frequency of the dimming signal Vdim is not affected by the cutoff frequency as is known in the art.

FIG. 7 is a schematic diagram of a light source device according to another embodiment of the present invention. Referring to FIG. 7, the light source device 700 of the present embodiment is different from the light source device 200 in that the light source device 700 of the embodiment further includes a resistor Rs, a Shottky diode Z1, and a buffer. 702, comparators OP2, OP3, and a voltage dividing unit 704. The resistor Rs is coupled between the LED unit 202 and the input voltage Vin. The Shorttky diode Z1 is coupled between the inductor L1 and the input voltage Vin. The positive input terminal of the comparator OP2 is coupled to the common contact of the resistor Rs and the LED unit 202, the negative input terminal of the comparator OP2 is coupled to a reference voltage Vrf, and the output terminal of the comparator OP2 is coupled to the dimming control circuit. 206. The positive input terminal of the comparator OP3 is coupled to the reference voltage Vrf, the negative input terminal of the comparator OP3 is coupled to the voltage dividing unit 704, and the output terminal of the comparator OP3 is coupled to the dimming control circuit 206. In addition, the voltage dividing unit 704 is coupled between the input voltage Vin and the ground.

The buffer unit 702 is configured to buffer the dimming signal Vdim. The comparator OP2 compares the voltage between the reference voltage Vrf and the common junction of the resistor Rs and the LED unit 202 to detect the current flowing through the resistor Rs, that is, to detect the current flowing through the LED unit 202. And a current detecting signal CS1 is outputted to the dimming control circuit 206. In this way, the dimming control circuit 206 can adjust the duty cycle of the driving signal SD1 according to the current detecting signal CS1 to dim the LED unit 202. The detailed operation of the dimming control circuit 206 for dimming the LED unit 202 has been disclosed in the above embodiments, and thus will not be described herein.

In addition, the voltage dividing unit 704 is configured to divide the input voltage Vin to obtain a divided voltage Vd. In the present example, the voltage dividing unit 704 includes a resistor RA and a resistor RB connected in series between the input voltage Vin and the ground. The comparator OP3 compares the reference voltage Vrf with the divided voltage Vd to output an UnderVoltage LockOut (UVLO) signal UVLO1 to disable the dimming control circuit 206 when the input voltage Vin is too low.

In summary, the present invention generates a driving signal by using a triangular wave generator and a comparator in the dimming control circuit, so that not only a higher dimming ratio but also a dimming accuracy of the LED unit can be obtained, and The frequency of the dimming signal is not affected by the cutoff frequency as is known in the art. The user can freely adjust the frequency of the dimming signal according to the actual application to avoid flickering of the LED unit, or to prevent the frequency of the dimming signal from falling within the range recognizable by the human ear, so that the user can hear the miscellaneous News. In addition, since the dimming signal can be a DC signal or a pulse width modulation signal, only one external pin is required for the hardware design, which can reduce the production cost.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the invention, and any one of ordinary skill in the art can make some modifications and refinements without departing from the spirit and scope of the invention. The scope of the invention is defined by the scope of the appended claims.

100. . . Dimming circuit

200, 700. . . Light source device

202‧‧‧Lighting diode unit

204‧‧‧ dimming module

206‧‧‧ dimming control circuit

208‧‧‧ triangle wave generator

702‧‧‧buffer

704‧‧‧Voltage unit

R1~R3, Rs, RA, RB‧‧‧ resistance

C1~C3‧‧‧ capacitor

Dim_in‧‧‧ dimming signal

Dim_out‧‧‧ drive signal

L1‧‧‧Inductance

Vin‧‧‧Input voltage

SW1‧‧‧Switch unit

M1‧‧‧O crystal

SD1‧‧‧ drive signal

OP1, OP2, OP3‧‧‧ comparator

S1‧‧‧ triangle wave signal

The Vh‧‧‧ crest voltage level is

The V1‧‧‧ trough voltage level is

UVLO1‧‧‧ voltage is too low to lock the signal

Z1‧‧‧Shottky diode

Vrf‧‧‧reference voltage

CS1‧‧‧ Current detection signal

Vd‧‧‧voltage voltage

FIG. 1 illustrates a conventional light emitting diode dimming circuit.

2 is a schematic diagram of a light source device according to an embodiment of the invention.

FIG. 3A is a schematic diagram of analog dimming according to an embodiment of the invention.

FIG. 3B is a schematic diagram of digital dimming according to an embodiment of the invention.

4A-6B are schematic diagrams showing waveforms of current flowing through a light emitting diode unit according to an embodiment of the invention.

FIG. 7 is a schematic diagram of a light source device according to another embodiment of the present invention.

200. . . Light source device

202. . . Light-emitting diode unit

204. . . Dimming module

206. . . Dimming control circuit

208. . . Triangle wave generator

L1. . . inductance

Vin. . . Input voltage

SW1. . . Switch unit

M1. . . Transistor

SD1. . . Drive signal

OP1. . . Comparators

S1. . . Triangle wave signal

Claims (6)

A light source device includes: a light emitting diode unit having one end coupled to an input voltage; an inductor having one end coupled to the other end of the LED unit; and a dimming module coupled to the inductor The dimming module includes: a switch unit coupled between the other end of the inductor and a ground; and a dimming control circuit coupled to the switch unit, Generating a driving signal according to a dimming signal to control a conduction state of the switching unit, thereby adjusting brightness of the LED unit, the dimming control circuit comprising: a triangular wave generator for generating a triangular wave signal; and a comparator The positive input terminal receives the dimming signal, and the negative input end of the comparator is coupled to the triangular wave generator, and compares the triangular wave signal with the dimming signal to generate the driving signal; a voltage dividing unit coupled to the input Between the voltage and the ground, dividing the input voltage to generate a divided voltage; and a third comparator having a positive input coupled to a reference voltage, and a negative input of the third comparator Coupled to the divided voltage, the output voltage is too low a locking signal for disabling the dimming at the low input voltage control circuit according to the reference voltage and the divided voltage. The light source device of claim 1, further comprising: a resistor coupled between the input voltage and the LED unit, wherein the dimming control circuit further controls the current according to the current flowing through the resistor switch The conduction state of the unit. The light source device of claim 2, further comprising: a buffer unit coupled to the dimming signal and the dimming control circuit to buffer the dimming signal. The light source device of claim 2, further comprising: a second comparator, wherein the positive input end is coupled to the common contact of the resistor and the LED unit, and the negative input of the second comparator The terminal is coupled to a reference voltage, and outputs a current detecting signal according to the voltage on the common contact of the resistor and the LED unit and the reference voltage. The light source device of claim 1, wherein the dimming signal is a direct current signal, and the voltage level of the dimming signal is between a peak voltage level and a valley voltage level of the triangular wave signal. The light source device of claim 1, wherein the dimming signal is a pulse width modulation signal, and the high voltage level of the pulse width modulation signal is greater than a peak voltage level of the triangular wave signal, the pulse The low voltage level of the width modulation signal is less than the valley voltage level of the triangular wave signal.