Integrated circuit for driving high-voltage LED lamp

1. Field of the Invention

The present invention relates to an integrated circuit, and more particularly to an integrated circuit for driving high-voltage LED lamp.

2. Description of Prior Art

At present, the LEDs (light-emitting diodes) are widely used, such as LED lamps. However, the prior arts of LED lamp drivers generally have a drawback that the driving circuit can not be integrated into one single semiconductor chip.

The following patents: US 2006/0038542 A1, US 2008/0129220 A1, US 2003/0122502 A1, U.S. Pat. Nos. 6,798,152 B2, 7,135,825 B2, 7,489,086 B2, 7,528,551 B2 , 7,592,755 B2, 6,441,558 B1, 7,288,900 B2, US 2002/0140379 A1, and U.S. Pat. No. 7,642,725 B2 disclosed the lighting applications of the LEDs. All of the above-mentioned lighting applications use at least one of the following devices: transformer, DC power supply, large inductor, large capacitor, and light sensor. Thus, it is impossible to integrate all the bulky devices into one semiconductor chip by using the existing semiconductor processes.

WO 2007/001116 A1 disclosed high-voltage switches with different potentials. In the existing semiconductor manufacturing processes for high voltage resistance, however, there are not suitable components for using. Accordingly, if the integration can not be realized, the production costs can not be effectively reduced. In addition, the current is instantaneously opened or shorted due to the open-circuit voltage switching, this will result in higher EMI. Furthermore, the conduction current is fixed and the total harmonic distortion (THD) is larger than 42%. The existing lighting regulation that the THD has to be smaller than 33% can not be satisfied.

U.S. Pat. No. 6,989,807 disclosed the detection of the voltage level of the input power to turn on and turn off the current-driving circuits in order. However, the temperature variation is neglected due to the forward voltage. This will easily result in higher voltage across the current-driving circuits to reduce the use efficiency. In addition, the optimal switching time can not be controlled and it causes the EMI and the harmonic distortion. Furthermore, the driving current is fixed and the THD is larger than 42%. The existing lighting regulation demanding THD to be smaller than 33% can not be satisfied, even though the power factor is larger than 90%.

In order to overcome the above-mentioned disadvantages, an integrated circuit for driving high-voltage LED lamp is disclosed that the integrated circuit can be integrated and conform the demands of the existing lighting regulation.

In order to achieve the above-mentioned objects, the integrated circuit for driving high-voltage LED lamps is applied to a rectified power and a plurality of LED stacks. The integrated circuit for driving high-voltage LED lamps includes a control unit, a plurality of current-clamping units electrically connected to the control unit and the respective LED stacks, and a plurality of current-sensing unit electrically connected to the respective current-clamps units and the control unit. The first stage of the current-clamping could permit without electrically connecting a current-sensing unit. When the rectified power is switched on, the current-sensing unit constantly monitors the electrical current flowing through the respective current-clamping unit and feeds back the monitored data to the control unit. The control unit sequentially switches on or off the current-clamping units according to the combinatorial logic state of the monitored data.

It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. Other advantages and features of the invention will be apparent from the following description, drawings and claims.

The features of the invention believed to be novel are set forth with particularity in the appended claims. The invention itself, however, may be best understood by reference to the following detailed description of the invention, which describes an exemplary embodiment of the invention, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram of an embodiment of an integrated circuit for driving high-voltage LED lamp according to the present invention;

FIG. 2 is a circuit diagram of an LED stack;

FIG. 3 is a voltage-current curve of an LED stack;

FIG. 4 is a block diagram of an embodiment of a current-clamping unit and a current-sensing unit;

FIG. 5 is a block diagram of an embodiment of a control unit;

FIG. 6 is a timing diagram of a control unit;

FIG. 7 is a curve of conduction currents v.s. a rectified power;

FIG. 8 is a curve of a total consumption current v.s. the rectified power; and

FIG. 9 is a truth table of the logic gates inside the control unit.

Reference will now be made to the drawing to describe the present invention in detail.

Reference is made to FIG. 1 which is a block diagram of an embodiment of an integrated circuit for driving high-voltage LED lamp according to the present invention. The integrated circuit for driving high-voltage LED lamps 40 is applied to an AC power 10 , a bridge rectifier 20 , and a plurality of LED stacks 30 _ 1 - 30 _ 6 . In this embodiment, the amount of the LED stacks 30 _ 1 - 30 _ 6 is six, but this example is for demonstration and not for limitation. The integrated circuit for driving high-voltage LED lamps 40 includes a control unit 42 , a plurality of current-clamping units 44 a - 44 f , and at least one current-sensing unit 46 b - 46 f . In particular, the amount of the current-clamping units 44 a - 44 f and the amount of the current-sensing units 46 b - 46 f are five, but this example is for demonstration and not for limitation.

In order to conveniently describe the integrated circuit for driving high-voltage LED lamps, an electrical wire between the control unit 42 and the current-clamping unit 44 a is referred to as G 1 , and an electrical wire between the control unit 42 and the current-clamping unit 44 b is referred to as G 2 . The rest of the electrical wires G 3 -G 6 can be deduced by the same analogy. An electrical wire between the control unit 42 and the current-sensing unit 46 b is referred to as S 2 . The rest of the electrical wires S 3 -S 6 can be deduced by the same analogy. In addition, a conduction current flowing through the current-clamping unit 44 a is referred to as I 1 , and a conduction current flowing through the current-clamping unit 44 b is referred to as I 2 . The rest of the conduction currents I 3 -I 6 can be deduced by the same analogy.

The control unit 42 is electrically connected to the bridge rectifier 20 , the LED stack 30 _ 1 , the current-clamping units 44 a - 44 f , and the current-sensing units 46 b - 46 f . The current-clamping unit 44 a is electrically connected to the LED stacks 30 _ 1 , 30 _ 2 . The current clamping-unit 44 b is electrically connected to the LED stacks 30 _ 2 , 30 _ 3 and the current-sensing unit 46 b . The current-clamping unit 44 c is electrically connected to the LED stacks 30 _ 3 , 30 _ 4 and the current-sensing unit 46 c . The current-clamping unit 44 d is electrically connected to the LED stacks 30 _ 4 , 30 _ 5 and the current-sensing unit 46 d . The current-clamping unit 44 e is electrically connected to the LED stacks 30 _ 5 , 30 _ 6 and the current-sensing unit 46 e . The current-clamping unit 44 f is electrically connected to the LED stack 30 _ 6 and the current-sensing unit 46 f . The bridge rectifier 20 is electrically connected to the AC power 10 , the control unit 42 , and the LED stack 30 _ 1 .

The bridge rectifier 20 is used to provide a full-wave rectification to the AC power 10 . It is assumed that the AC power 10 is 220 volts, thus full-wave rectified peak value of the AC power 10 is 311 volts. The AC power 10 is rectified to a full-wave rectified power 25 by the bridge rectifier 20 . Because the rectified power 25 is not filtered and regulated, the voltage variation of the rectified power 25 is significant (approximately the magnitude of the positive-half sinusoidal wave). The rectified power 25 is supplied to provide the required power to the integrated circuit for driving high-voltage LED lamps 40 and the LED stacks 30 _ 1 ˜ 30 _ 6 .

Reference is made to FIG. 2 which is a circuit diagram of an embodiment of the LED stacks. The LED stack 30 _ 1 includes a plurality of light-emitting diodes connected in series. Each of the light-emitting diodes is electrically connected to a Zener diode to provide an open-circuit protection. Because the rest of the LED stacks 30 _ 2 - 30 _ 6 are the same as the LED stack 30 _ 1 , the detailed description is omitted here for conciseness.

Typically, a light-emitting diode is driven by a 20 mA forward current, thus a 3.6-volt forward voltage is produced across the light-emitting diode. Hence, twelve LEDs are connected in series to form the LED stack 30 _ 1 , thus a 43.2-volt forward voltage is produced across the LED stack 30 _ 1 under the 20-mA forward current. Reference is made to FIG. 3 which is a voltage-current curve of the embodiment of the LED stacks. In this example, the LED stack 30 _ 1 with twelve light-emitting diodes is exemplified for further demonstration. The abscissa represents the forward voltage across the LED stack 30 _ 1 , and the ordinate represents the forward current through the LED stack 30 _ 1 .

An LED array for high voltage resistance can be formed by connecting the LED stacks 30 _ 1 - 30 _ 6 in series. In a practical application of a 220-volt AC power, six LED stacks connected in series are driven by the 20-mA current to approximately produce a 311-volt forward voltage, which is nearly equal to the peak of the full-wave rectified voltage.

Reference is made to FIG. 4 which is a block diagram of an embodiment of a current-clamping unit and a current-sensing unit. The current-clamping unit 44 b includes an N-channel MOS 442 and a feedback resistor 444 . The feedback resistor 444 is electrically connected to a source of the N-channel MOS 442 . A gate of the N-channel MOS 442 is electrically connected to the control unit 42 (not shown) through the electrical wire G 2 . A drain of the N-channel MOS 442 is electrically connected to the LED stacks 30 _ 2 , 30 _ 3 .

When the electrical wire G 2 is set at a fixed high-voltage level, representing logic 1, by the control unit 42 , the N-channel MOS 442 is turned on. The conduction current I 2 through the N-channel MOS 442 is controlled by a voltage difference between the gate and the source of the N-channel MOS 442 and the feedback resistor 444 . When the conduction current I 2 increases, a voltage difference is resulted across the feedback resistor 444 , the gate to source voltage of the N-channel MOS 442 is reduced and, thus, the conduction current I 2 is clamped to a fixed value.

Because the current-clamping unit 44 a and the current-clamping units 44 c - 44 f are similar to the current-clamping unit 44 b , the detail description of the current-clamping unit 44 a and the clamping-units 44 c - 44 f are omitted here for conciseness. In particular, the value of the feedback resistor 444 of the current-clamping unit 44 a is different from those of the current-clamping units 44 b - 44 f . The resistance value of the feedback resistor 444 of the current-clamping unit 44 a is 750 ohms, and those of the current-clamping units 44 b - 44 f are 550 ohms, 400 ohms, 300 ohms, 200 ohms, and 180 ohms, respectively. The purpose of the different value of the feedback resistors is in order to improve the power factor to nearly 100% and reduce the total harmonic distortion to nearly 0%.

The current-sensing unit 46 b includes an NPN transistor 469 , an inverter 464 , a buffer 462 , a pull resistor 466 , and a base resistor 468 . An input terminal of the inverter 464 is electrically connected to a collector of the NPN transistor 469 . An input terminal of the buffer 462 is electrically connected to an output terminal of the inverter 464 , and the output terminal of the inverter 464 is electrically connected to the control unit 42 through the electrical wire S 2 . The pull resistor 466 is electrically connected to the collector of the NPN transistor 469 . One terminal of the base resistor 468 is electrically connected to a base of the NPN transistor 469 , and the other terminal of the base resistor 468 is electrically connected to the feedback resistor 444 and the source of the N-channel MOS 442 .

The current-sensing unit 46 b is provided to detect the voltage across the feedback resistor 444 . When the conduction current I 2 is greater than a default current, the voltage across the feedback resistor 444 turns on the NPN transistor 469 . The pull resistor 466 is provided to amplify voltage signal. The inverter 464 with a hysteresis characteristic is used to be a simple hysteresis comparator when a voltage signal of a collector of the NPN transistor 469 is inputted to the inverter 464 . Hence, the current-sensing unit 46 b outputs a logical high level (logical 1) to the control unit 42 when the sufficient conduction current I 2 flows through the feedback resistor 444 . On the other hand, the current-sensing unit 46 b outputs a logical low level (logical 0) to the control unit 42 . Because the rest of the current-sensing units 46 c - 46 f are the same as the current-sensing unit 46 b , the detailed description is omitted here for conciseness.

Reference is made to FIG. 5 which is a block diagram of an embodiment of a control unit. The control unit 42 includes at least one first NOT gate 424 , at least one second NOT gate 426 , and at least one OR gate 422 . In this embodiment, the amount of the first NOT gates 424 _ 1 - 424 _ 5 , the amount of the second NOT gates 426 _ 1 - 426 _ 5 are five, and the amount of the OR gates 422 _ 1 - 422 _ 4 is four. The input terminals of the second NOT gates 426 _ 1 - 426 _ 5 are electrically connected to the output terminals of the first NOT gates 424 _ 1 - 424 _ 5 and the electrical wires G 1 -G 5 , respectively. The output terminals of the OR gates 422 _ 1 - 422 _ 4 are electrically connected to the input terminals of the first NOT gates 424 _ 1 - 424 _ 4 . One input terminal of each of the OR gates 422 _ 1 - 422 _ 4 is electrically connected to the electrical wires S 2 -S 5 , respectively; the other terminal of each of the OR gates 422 _ 1 - 422 _ 4 is electrically connected to the output terminal of the second NOT gates 426 _ 2 - 426 _ 5 , respectively. The input terminal of the first “NOT” terminal 424 _ 5 is electrically connected to the electrical wire S 6 .

The control unit 42 receives logical signals of the current-sensing units 46 b - 46 f . The logical signals are operated to output corresponding fixed-voltage logical signals to control the current-clamping unit 44 a and the current-clamping units 44 b - 44 f . In particular, the conduction current I 1 does not require to be monitored, and the current-clamping unit 44 f is fixed at a logical high level. A truth table of operating the electrical wires is shown as follows. Because the logical operation is well known in the art, the detailed description of producing the truth table is omitted here for conciseness and only the truth table is shown in FIG. 9 .

Reference is made to FIG. 6 which is a timing diagram of the control unit. Reference is made to FIG. 7 and FIG. 8 which are a curve of conduction currents and a rectified power and a curve of a total consumption current and the rectified power, respectively. When the rectified power 25 drives the LED stacks 30 _ 1 - 30 _ 6 , the current-sensing units 46 b - 46 f monitor the current flowing in the current-clamping units 44 b - 44 f and feed back the monitored data to the control unit 42 . Accordingly, the control unit 42 sequentially switches on or off the current-clamping units 44 b - 44 f according to the combinatorial logic state of the monitored data.

An example is provided as follows. Initially, the rectified power 25 supplies a small voltage that can only drive the LED stack 30 _ 1 , thus only the current (namely, the conduction current I 1 ) flows through the current-clamping unit 44 a . Afterward, when the supplied voltage by the rectified power 25 is sufficiently large to drive the LED stacks 30 _ 1 - 30 _ 2 , the current-sensing unit 46 b monitors the conduction current I 2 and the monitored data are sent to the control unit 42 . Also, the current-clamping unit 44 a is turned off by the control unit 42 . Afterward, when the supplied voltage by the rectified power 25 is sufficiently large to drive the LED stacks 30 _ 1 - 30 _ 3 , the current-sensing unit 46 c monitors the conduction current I 3 and the control unit 42 is notified. Also, the current-clamping unit 44 a and the current-clamping unit 44 b are immediately turned off by the control unit 42 . The operation for the rest of the current-sensing units 46 c - 46 f can be deduced by the same analogy. On the other hand, when the rectified power 25 initially supplies a peak voltage, the operation of the control unit 42 is the same as the above-mentioned operation of the control unit 42 , the detailed description is omitted here for conciseness.

The integrated circuit for driving high-voltage LED lamps can be integrated and conform the demands of the existing lighting regulation. The test results are as follows:

1. The power factor (PF) is 96%.

2. The total harmonic distortion (THD) is 11.5%.

3. The efficiency is 90.5%.

4. The luminous efficacy is 104 lm/W.

In particular, the luminous efficacy of a typical LEDs is 115 lm/W.

Although the present invention has been described with reference to the preferred embodiment thereof, it will be understood that the invention is not limited to the details thereof. Various substitutions and modifications have been suggested in the foregoing description, and others will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.