This application claims priority of Taiwan Patent Application No. 098138597, filed on Nov. 13, 2009, the entirety of which is incorporated by reference herein.
1. Field of the Invention
The invention relates to a Light Emitting Diode (LED), and more particularly to an LED dimming technique.
2. Description of the Related Art
Light Emitting Diode (LED) lamps have the advantages of long lifespan, low power consumption, short response time, low operating temperature . . . etc. Therefore, LED lamps have gradually replaced tungsten lamps in everyday life. However, since LED lamps can only be driven by a direct current (DC) source, it is difficult for designers of LED lamps to directly match the direct current (DC) of LEDs with the alternating current (AC) provided in most homes; whereas traditional tungsten lamps do not have this problem. Also, while brightness of traditional tungsten lamps can be controlled by standard dimmers, brightness of LEDs can not.
A light emitting diode (LED) lamp and an LED lamp module are provided. The brightness of the LED lamp is controlled by a dimmer and the LED lamp receives an external alternating current (AC) source via the dimmer. An exemplary embodiment of the LED lamp comprises at least one LED, a rectifying-modulating-driving apparatus and a current holding compensator. The rectifying-modulating-driving apparatus is coupled between the LED and the dimmer for bridge-rectifying and modulating an AC source with a conducting angle from the dimmer to drive the LED. The current holding compensator is coupled to the rectifying-modulating-driving apparatus to provide a compensation current when the AC source with the conducting angle is lower than a voltage after being bridge-rectified.
The conducting angle is defined along rising or falling edge(s) of the AC source.
The current holding compensator comprises: a comparator, comparing a reference voltage and a sample voltage sampled from the rectifying-modulating-driving apparatus to output a control signal; and a control switch, coupled to an output terminal of the comparator and a ground node of the rectifying-modulating-driving apparatus to control the compensation current between the rectifying-modulating-driving apparatus and a ground according to the control signal.
The comparator comprises: a first input terminal, receiving the reference voltage; and a second input terminal, receiving the sample voltage.
The first input terminal is a positive input terminal and the second input terminal is a negative input terminal.
The current holding compensator further comprises a capacitor coupled between the negative input terminal and the output terminal of the comparator to prevent an output of the comparator from oscillating at a threshold point.
The current holding compensator further comprises a first resistor and a power supply, and the output terminal of the comparator is coupled to the power supply via the first resistor.
The current holding compensator further comprises: a reference voltage generator, coupled to power supply to generate the reference voltage; and a voltage sampler, coupled to the rectifying-modulating-driving apparatus to obtain the sample voltage from the rectifying-modulating-driving apparatus.
The rectifying-modulating-driving apparatus comprises a rectifier coupled to the dimmer to bridge-rectify the AC source with the conducting angle so as to generate a rectified source.
The rectifier is a bridge composed of a plurality of diodes.
The sample voltage is obtained by sampling the rectified source.
The rectifying-modulating-driving apparatus further comprises: a first voltage drop circuit, coupled to the rectifier and receiving the rectified source to generate a voltage drop source; an output current controller, coupled between the first voltage drop circuit and the LED; and a pulse width modulation phase controller, coupled to the first voltage drop circuit and the output current controller for modulating the voltage drop source and generating a pulse width modulation (PWM) signal, wherein the output current controller drives the LED according to the PWM signal.
The first voltage drop circuit comprises a first transistor, a Zener diode and a second resistor, one terminal of the second resistor is coupled to an output terminal of the rectifier and a drain of the first transistor, and another terminal of the second resistor is coupled to a gate of the first transistor and a cathode of the Zener diode, and an anode of the Zener diode is coupled to the ground and a source of the first transistor is coupled to the control switch of the current holding compensator.
The control switch comprises a second transistor, the second transistor comprises a gate, a first source/drain and a second source/drain, respectively coupled to an output terminal of the comparator, the first voltage drop circuit and the ground.
The rectifying-modulating-driving apparatus further comprises a power factor correction circuit coupled between the first voltage drop circuit and the output current controller to correct the power factor of the AC source so as to reduce switching power loss.
The power factor correction circuit comprises: a first diode; a second diode; a third diode; a first capacitor; and a second capacitor, wherein the first capacitor is coupled between an input terminal of the power factor correction circuit and an anode of the second diode; the second capacitor is coupled between a cathode of the second diode and the ground; an anode and a cathode of the first diode are respectively coupled to the ground and the anode of the second diode; an anode and a cathode of the third diode are respectively coupled to the cathode of the second diode and an output terminal of the power factor correction circuit; the input terminal of the power factor correction circuit is coupled to an output terminal of the rectifier; and the output terminal of the power factor correction circuit is coupled to an input terminal of the output current controller.
The sample voltage is obtained from a node between the first capacitor and the first diode of the power factor correction circuit.
The sample voltage is obtained from a node between the rectifier and the output current controller.
The LED lamp further comprises a second voltage drop circuit, coupled between an output terminal of the rectifier and the control switch.
Another exemplary embodiment of a light emitting diode (LED) lamp module comprises: at least one LED; a dimmer, an external alternating current (AC) source is received and generating an AC source with a conducting angle; a rectifying-modulating-driving apparatus, coupled between the LED and the dimmer for bridge-rectifying and modulating the AC source with the conducting angle to drive the LED; and a current holding compensator, coupled to the rectifying-modulating-driving apparatus to provide a compensation current when the AC source with the conducting angle is lower than a voltage after being bridge-rectified.
A detailed description is given in the following embodiments with reference to the accompanying drawings.
The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:
The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims.
The principle of operations of the dimmer 510 has been described previously and is omitted here for brevity. The appearance of the LED lamp 500 may be in any form, such as a tube light or light bulb, and may be assembled with the lamp holder and dimmer in any form and dismantled therefrom.
The LED lamp 500 comprises at least one LED 520 and a rectifying-modulating-driving apparatus 530. The rectifying-modulating-driving apparatus 530 bridge-rectifies and modulates the AC source with the conducting angle from the dimmer 510 so as to drive the LED 520. The conducting angle is defined along rising or falling edge(s) of the AC source (as shown in
In the embodiments of the invention, the voltage drop circuit 535 as shown in
The Power Factor Correction (PFC) circuit 538 is coupled between the voltage drop circuit 535 and the output current controller 536 to correct the power factor of the AC source so as to reduce switching power loss. According to an embodiment of the invention, the PFC circuit 538 as shown in
In addition, the PFC circuit may also not be configured in the rectifying-modulating-driving apparatus. In this manner, the voltage sampler 544 may obtain the sample voltage by sampling at any node between the rectifier 532 and the output current controller 536.
The LED lamp 500 may further comprise a current holding compensator 540 to provide a compensation current when the AC source with the conducting angle is lower than a voltage after being bridge-rectified (i.e. the rectified source). The current holding compensator 540 comprises a reference voltage generator 542, a voltage sampler 544, a comparator 546 and a control switch 548. Details of these components are described as below.
In the embodiments, the comparator 546 comprises a positive input terminal (labeled by ‘+’) coupled to the reference voltage generator 542 to receive the reference voltage and a negative input terminal (labeled by ‘−’) coupled to the voltage sampler 544 to receive the sample voltage. However, according to other embodiments of the invention, the comparator 546 may also receive the sample voltage via the positive input terminal and receive the reference voltage via the negative input terminal (in this manner, the control switch 548 as shown in
In addition, a capacitor C3 may be added between the negative input terminal and the output terminal of the comparator 546 so that Hysteresis may occur to prevent the output of the comparator 546 from oscillating at a threshold point. In practice, the capacitor may be used to differentiate between an upward tuning point and a downward tuning point in the brightness tuning range of the LED.
The comparator 546 is used to generate a control signal by comparing the reference voltage and the sample voltage. The control switch 548 controls the compensation current between the rectifying-modulating-driving apparatus 530 and the ground GND according to the control signal. For example, when operating at a small conducting angle (reference may be made to
In the embodiment of the invention, the control switch 548 comprises a transistor Q2, the transistor comprises a gate G, a drain D and a source S, respectively coupled to the output terminal of the comparator 546, a source node of the rectifying-modulating-driving apparatus 530 and a ground GND. Note that the source node may be the output terminal (i.e. the source of the transistor Q1) of the voltage drop circuit 535. The purpose of coupling the drain of the transistor Q2 to the voltage drop circuit 353 is to obtain a low operating voltage, so as to reduce the size of a transistor and reduce fabrication costs thereof? In other embodiment of the invention, the drain of the transistor Q2 may also be coupled to another source node (for example, the drain of transistor Q1, that is, the output of rectifier 532) via another voltage drop circuit 735 as shown in
In addition to the LED lamp as previously described above, an LED lamp module is further proposed according to another embodiment of the invention. Referring to
While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. Those who are skilled in this technology can still make various alterations and modifications without departing from the scope and spirit of this invention. Therefore, the scope of the present invention shall be defined and protected by the following claims and their equivalents.
Number | Date | Country | Kind |
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98138597 | Nov 2009 | TW | national |