PARALLEL SEQUENCED LED LIGHT STRING

Abstract

A parallel sequenced LED light string includes a plurality of LED modules. The LED modules are connected in parallel through a power wire with a plurality of wire resistances. Each of the LED modules includes an impedance component capable of providing an impedance characteristic. The parallel-connected LED modules receive a supply power, and the LED modules respectively get different voltages through the wire resistances and the impedance components from the supply power so as to sequencing the LED modules.

Claims

1. A parallel sequenced LED light string, comprising: a plurality of LED modules, connected in parallel through a power wire with a plurality of wire resistances, wherein each of the LED modules comprises an impedance component capable of providing an impedance characteristic, wherein the parallel-connected LED modules receive a supply power, and the LED modules respectively get different voltages through the wire resistances and the impedance components from the supply power so as to sequencing the LED modules.

2. The parallel sequenced LED light string as claimed in claim 1, wherein the different voltages compare with a plurality of voltage ranges to determine the sequence the LED modules.

3. The parallel sequenced LED light string as claimed in claim 2, wherein the voltage ranges are built in a look-up table.

4. The parallel sequenced LED light string as claimed in claim 2, wherein the different voltages are determined according to the supply power, the number of the LED modules, the wire resistances, and the impedance component.

5. The parallel sequenced LED light string as claimed in claim 1, wherein the supply power is a constant-voltage source, wherein each of the impedance components is a controllable resistor with an adjustable resistance, and a resistance of the controllable resistor is designed to be decreased.

6. The parallel sequenced LED light string as claimed in claim 5, wherein a voltage generated by a front LED module is greater than a voltage generated by a rear LED module.

7. The parallel sequenced LED light string as claimed in claim 1, wherein the supply power is a constant-current source, wherein each of the impedance components is a controllable resistor with an adjustable resistance, and a resistance of the controllable resistor is designed to be increased.

8. The parallel sequenced LED light string as claimed in claim 7, wherein a voltage generated by a front LED module is less than a voltage generated by a rear LED module.

9. The parallel sequenced LED light string as claimed in claim 1, further comprising: a signal generation unit, configured to provide a sequence signal, wherein each of the impedance components is a controllable resistor with an adjustable resistance.

10. The parallel sequenced LED light string as claimed in claim 9, wherein the sequence of the LED modules is determined according to a cycle of the sequence signal, wherein the supply power is a constant-voltage source; when the sequence of one of the LED modules is completed, the corresponding impedance component is turned off, and the resistances of the remaining impedance components corresponding to the un-sequenced LED modules are decreased.

11. The parallel sequenced LED light string as claimed in claim 9, wherein the sequence of the LED modules is determined according to a cycle of the sequence signal, wherein the supply power is a constant-current source; when the sequence of one of the LED modules is completed, the corresponding impedance component is turned off, and the resistances of the remaining impedance components corresponding to the un-sequenced LED modules are increased.

12. The parallel sequenced LED light string as claimed in claim 9, further comprising: a switch unit connected to the controllable resistor in series.

13. The parallel sequenced LED light string as claimed in claim 1, wherein each of the LED modules comprises: a plurality of resistors, and a plurality of switch units correspondingly connected to the resistors in series.

14. The parallel sequenced LED light string as claimed in claim 1, further comprising: a compensation unit coupled to the last LED module in parallel, wherein the compensation unit comprises a controllable resistor with an adjustable resistance.

15. The parallel sequenced LED light string as claimed in claim 14, wherein the supply power is a constant-voltage source, when the LED modules are sequentially sequenced, the adjustable resistance of the controllable resistor is sequentially decreased.

16. The parallel sequenced LED light string as claimed in claim 14, wherein the supply power is a constant-current source, when the LED modules are sequentially sequenced, the adjustable resistance of the controllable resistor is sequentially increased.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0026] The present disclosure can be more fully understood by reading the following detailed description of the embodiment, with reference made to the accompanying drawings as follows:

[0027] FIG. 1A is a circuit diagram of a parallel sequenced LED light string supplied power by a constant-voltage source according to a first embodiment of the present disclosure.

[0028] FIG. 1B is a circuit diagram of the parallel sequenced LED light string supplied power by a constant-current source according to the first embodiment of the present disclosure.

[0029] FIG. 2A is a circuit diagram of a parallel sequenced LED light string supplied power by the constant-voltage source according to a second embodiment of the present disclosure.

[0030] FIG. 2B is a circuit diagram of the parallel sequenced LED light string supplied power by the constant-current source according to the second embodiment of the present disclosure.

[0031] FIG. 3A is a schematic voltage diagram of the parallel sequenced LED light string according to the first embodiment of the present disclosure.

[0032] FIG. 3B is a schematic voltage diagram of the parallel sequenced LED light string according to the second embodiment of the present disclosure.

[0033] FIG. 4 is a block circuit diagram of a controllable resistor according to the present disclosure.

[0034] FIG. 5 is a block circuit diagram of multi-resistor embodiment according to the present disclosure.

[0035] FIG. 6 is a block circuit diagram of counting operation according to the present disclosure.

DETAILED DESCRIPTION

[0036] Reference will now be made to the drawing figures to describe the present disclosure in detail. It will be understood that the drawing figures and exemplified embodiments of present disclosure are not limited to the details thereof.

[0037] Please refer to FIG. 1A, which shows a circuit diagram of a parallel sequenced LED light string supplied power by a constant-voltage source according to a first embodiment of the present disclosure. The parallel sequenced LED light string includes a plurality of (N) LED (light-emitting diode) modules 11,12, . . . ,1N. The LED modules 11,12, . . . ,1N are connected in parallel through a power wire 10. In terms of actual conditions, the power wire 10 has a plurality of wire resistances R.sub.L1,R.sub.L2, . . . ,R.sub.LN,R.sub.L1′,R.sub.L2′, . . . ,R.sub.LN′. Each of the LED modules 11,12, . . . ,1N has a resistance R.sub.1,R.sub.2, . . . ,R.sub.N and a parasitic capacitor C.sub.1,C.sub.2, . . . ,C.sub.N in parallel with the corresponding resistance R.sub.1,R.sub.2, . . . ,R.sub.N. That is, a first LED module 11 has a first resistance R.sub.1 and a first parasitic capacitor C.sub.1 connected in parallel, a second LED module 12 has a second resistance R.sub.2 and a second parasitic capacitor C.sub.2 connected in parallel, . . . , and a Nth LED module 1N has a Nth resistance R.sub.N and a Nth parasitic capacitor C.sub.N connected in parallel.

[0038] As shown in FIG. 1A, the parallel-connected LED modules 11,12, . . . ,1N receive a supply power Vdc. In this embodiment, the supply power Vdc is a constant-voltage source for providing a voltage source with a constant voltage value. The LED modules 11,12, . . . ,1N respectively get different voltages through the wire resistances R.sub.L1,R.sub.L2, . . . ,R.sub.LN,R.sub.L1′,R.sub.L2′, . . . ,R.sub.LN′ and the resistances R.sub.1,R.sub.2, . . . ,R.sub.N of the LED modules 11,12, . . . ,1N from the supply power Vdc.

[0039] At the time of power-on, since the circuits in each of the LED modules 11,12, . . . ,1N have not been started or operated, each of the LED modules 11,12, . . . ,1N may be equivalent to the corresponding resistances R.sub.1,R.sub.2, . . . ,R.sub.N. For the convenience of description, the wire resistance R.sub.L1 and the wire resistance R.sub.L1′ may be equivalent to the single-wire wire resistance R.sub.L1. Similarly, the wire resistance R.sub.L2 and the wire resistance R.sub.L2′ may be equivalent to the single-wire wire resistance R.sub.L2, . . . , and the wire resistance R.sub.LN and the wire resistance R.sub.LN′ may be equivalent to the single-wire wire resistance R.sub.LN.

[0040] After the time of power-on, the supply power Vdc supplies power to the LED modules 11,12, . . . ,1N. Due to the voltage difference caused by the current flowing through the wire resistances R.sub.L1,R.sub.L2, . . . ,R.sub.LN, the voltages generated on the LED modules 11,12, . . . ,1N are different. In this embodiment, the voltage difference caused by the power supply Vdc of the constant-voltage source through the wire resistances R.sub.L1,R.sub.L2, . . . ,R.sub.LN is the voltage drop. Please refer to FIG. 3A, which shows a schematic voltage diagram of the parallel sequenced LED light string according to the first embodiment of the present disclosure. A first voltage V.sub.1 on the first LED module 11 is greater than a second voltage V.sub.2 on the second LED module 12, the second voltage V.sub.2 is greater than a third voltage V.sub.3 on the third LED module 13, and the rest may be deduced by analogy. The voltage generated by the front (up-stream) LED module is greater than the voltage generated by the rear (down-stream) LED module, i.e., V.sub.1>V.sub.2> . . . >V.sub.N. Accordingly, the LED modules 11,12, . . . ,1N are sequenced according to the different generated voltages V.sub.1,V.sub.2, . . . ,V.sub.N. In the following, the different generated voltages V.sub.1,V.sub.2, . . . ,V.sub.N and the sequence principle of the LED modules 11,12, . . . ,1N are described.

[0041] In one embodiment, it can be implemented by means of a built-in corresponding look-up table. For example, the circuit designer may build the look-up table in advance according to the power supply Vdc, the number of the LED modules 11,12, . . . ,1N, the (estimated) wire resistances R.sub.L1,R.sub.L2, . . . ,R.sub.LN, and the resistances R.sub.1,R.sub.2, . . . ,R.sub.N for the different generated voltages V.sub.1,V.sub.2, . . . ,V.sub.N, thereby sequencing the LED modules 11,12, . . . ,1N.

[0042] The following is an implementation of the look-up table, in which 100 LED modules 11,12, . . . ,1N are taken as an example for description.

TABLE-US-00001 sequence of the LED modules voltage ranges (volts) #1 5.10-4.90 #2 4.90-4.70 #3 4.70-4.54 #4 4.54-4.38 #5 4.38-4.26 #6 4.26-4.14 . . . . . . #100  2.36-2.32

[0043] When the LED light string is powered on, the supply power Vdc supplies power to the LED modules 11,12, . . . ,1N. Therefore, the first voltage V.sub.1 is generated on the first LED module 11, the second voltage V.sub.2 is generated on the second LED module 12, . . . , and the Nth voltage V.sub.N is generated on the Nth LED module 1N. For example, when the voltage (for example, the first voltage V.sub.1) acquired by a certain LED module (for example, the first LED module 11) is 5.00 volts, since the voltage is within the voltage range (5.10-4.90 volts) of the first sequence (#1), the LED module is sequenced as the first LED module 11. Similarly, when the voltage (for example, the second voltage V.sub.2) acquired by a certain LED module (for example, the second LED module 12) is 4.80 volts, since the voltage is within the voltage range (4.90-4.70 volts) of the second sequence (#2), the LED module is sequenced as the second LED module 12. Similarly, when the voltage (for example, the sixth voltage V.sub.6) acquired by a certain LED module (for example, the sixth LED module 16) is 4.20 volts, since the voltage is within the voltage range (4.26-4.14 volts) of the sixth sequence (#6), the LED module is sequenced as the sixth LED module 16.

[0044] Therefore, after the LED light string is powered on, the sequence of each of the LED modules 11,12, . . . ,1N can be acquired according the corresponding voltage ranges in the look-up table by detecting the voltages V.sub.1,V.sub.2, . . . ,V.sub.N generated by the LED modules 11,12, . . . ,1N. However, the above-mentioned voltage ranges in the look-up table are not limited by the voltage values of the examples, which can be built according to the power supply Vdc, the number of the LED modules 11,12, . . . ,1N, the (estimated) wire resistances R.sub.L1,R.sub.L2, . . . ,R.sub.LN, the resistances R.sub.1,R.sub.2, . . . ,R.sub.N, or other parameters.

[0045] Please refer to FIG. 1B, which shows a circuit diagram of the parallel sequenced LED light string supplied power by a constant-current source according to the first embodiment of the present disclosure. In addition to realizing the power supply Vdc by means of the constant-voltage source, the present disclosure may also be realized by means of a constant-current source. In this embodiment, the supply power Idc is a constant-current source for providing a current source with a constant current value. The LED modules 11,12, . . . ,1N respectively get different voltages through the wire resistances R.sub.L1,R.sub.L2, . . . ,R.sub.LN,R.sub.L1′,R.sub.L2′, . . . ,R.sub.LN′ and the resistances R.sub.1,R.sub.2, . . . ,R.sub.N of the LED modules 11,12, . . . ,1N from the supply power Idc.

[0046] At the time of power-on, since the circuits in each of the LED modules 11,12, . . . ,1N have not been started or operated, each of the LED modules 11,12, . . . ,1N may be equivalent to the corresponding resistances R.sub.1,R.sub.2, . . . ,R.sub.N. For the convenience of description, the wire resistance R.sub.L1 and the wire resistance R.sub.L1′ may be equivalent to the single-wire wire resistance R.sub.L1. Similarly, the wire resistance R.sub.L2 and the wire resistance R.sub.L2′ may be equivalent to the single-wire wire resistance R.sub.L2, . . . , and the wire resistance R.sub.LN and the wire resistance R.sub.LN′ may be equivalent to the single-wire wire resistance R.sub.LN.

[0047] After the time of power-on, the supply power Idc supplies power to the LED modules 11,12, . . . ,1N. Due to the voltage difference caused by the current flowing through the wire resistances R.sub.L1,R.sub.L2, . . . ,R.sub.LN, the voltages generated on the LED modules 11,12, . . . ,1N are different. In this embodiment, the voltage difference caused by the power supply Idc of the constant-current source through the wire resistances R.sub.L1,R.sub.L2, . . . ,R.sub.LN is the voltage rise. Please refer to FIG. 3B, which shows a schematic voltage diagram of the parallel sequenced LED light string according to the second embodiment of the present disclosure. A first voltage V.sub.1 on the first LED module 11 is less than a second voltage V.sub.2 on the second LED module 12, the second voltage V.sub.2 is less than a third voltage V.sub.3 on the third LED module 13, and the rest may be deduced by analogy. The voltage generated by the front (up-stream) LED module is less than the voltage generated by the rear (down-stream) LED module, i.e., V.sub.1<V.sub.2< . . . <V.sub.N. Accordingly, the LED modules 11,12, . . . ,1N are sequenced according to the different generated voltages V.sub.1,V.sub.2, . . . ,V.sub.N. In the following, the different generated voltages V.sub.1,V.sub.2, . . . ,V.sub.N and the sequence principle of the LED modules 11,12, . . . ,1N are described. In one embodiment, it can be implemented by means of a built-in corresponding look-up table. For example, the circuit designer may build the look-up table in advance according to the power supply Idc, the number of the LED modules 11,12, . . . ,1N, the (estimated) wire resistances R.sub.L1,R.sub.L2, . . . ,R.sub.LN, and the resistances R.sub.1,R.sub.2, . . . ,R.sub.N for the different generated voltages V.sub.1,V.sub.2, . . . ,V.sub.N, thereby sequencing the LED modules 11,12, . . . ,1N.

[0048] The following is an implementation of the look-up table, in which 100 LED modules 11,12, . . . ,1N are taken as an example for description.

TABLE-US-00002 sequence of the LED modules voltage ranges (volts) #1 2.36-2.32 #2 2.40-2.36 #3 2.46-2.40 #4 2.52-2.46 #5 2.60-2.52 #6 2.68-2.60 . . . . . . #100  5.10-4.90

[0049] When the LED light string is powered on, the supply power Idc supplies power to the LED modules 11,12, . . . ,1N. Therefore, the first voltage V.sub.1 is generated on the first LED module 11, the second voltage V.sub.2 is generated on the second LED module 12, . . . , and the Nth voltage V.sub.N is generated on the Nth LED module 1N. For example, when the voltage (for example, the first voltage V.sub.1) acquired by a certain LED module (for example, the first LED module 11) is 2.34 volts, since the voltage is within the voltage range (2.36-2.32 volts) of the first sequence (#1), the LED module is sequenced as the first LED module 11. Similarly, when the voltage (for example, the second voltage V.sub.2) acquired by a certain LED module (for example, the second LED module 12) is 2.38 volts, since the voltage is within the voltage range (2.40-2.36 volts) of the second sequence (#2), the LED module is sequenced as the second LED module 12. Similarly, when the voltage (for example, the sixth voltage V.sub.6) acquired by a certain LED module (for example, the sixth LED module 16) is 2.64 volts, since the voltage is within the voltage range (2.68-2.60 volts) of the sixth sequence (#6), the LED module is sequenced as the sixth LED module 16.

[0050] Therefore, after the LED light string is powered on, the sequence of each of the LED modules 11,12, . . . ,1N can be acquired according the corresponding voltage ranges in the look-up table by detecting the voltages V.sub.1,V.sub.2, . . . ,V.sub.N generated by the LED modules 11,12, . . . ,1N. However, the above-mentioned voltage ranges in the look-up table are not limited by the voltage values of the examples, which can be built according to the power supply Idc, the number of the LED modules 11,12, . . . ,1N, the (estimated) wire resistances R.sub.L1,R.sub.L2, . . . ,R.sub.LN, the resistances R.sub.1,R.sub.2, . . . ,R.sub.N, or other parameters.

[0051] Take the first embodiment shown in FIG. 1A (that is, the power supply of the constant-voltage source) as an example. In order to increase the accuracy of comparison, determination, and identification between the detected voltage and the voltage ranges of the look-up table, each of the resistances R.sub.1,R.sub.2, . . . ,R.sub.N in each of the LED modules 11,12, . . . ,1N is a controllable resistor with an adjustable resistance. When the LED modules 11,12, . . . ,1N are sequenced at the time of power-on, the resistance value of each of the controllable resistors (that is, the resistances R.sub.1,R.sub.2, . . . ,R.sub.N) may be designed to be the minimum value so that the current flowing through each of the resistances R.sub.1,R.sub.2, . . . ,R.sub.N is maximized. Therefore, the voltages V.sub.1,V.sub.2, . . . ,V.sub.N generated on each of the LED modules 11,12, . . . ,1N can be maximized, thereby increasing the accuracy of comparison, determination, and identification between the detected voltage and the voltage ranges of the look-up table.

[0052] Furthermore, in circuit applications, due to the constant-voltage source of the power supply Vdc and the equivalent resistance effect, the rear (down-stream) current is smaller and a voltage difference between the two rear (down0stream) LED modules is smaller. As shown in FIG. 3A, for example, a voltage difference between the first voltage V.sub.1 generated on the first LED module 11 and the second voltage V.sub.2 generated on the second LED module 12 is greater than a voltage difference between the second voltage V.sub.2 generated on the second LED module 12 and the third voltage V.sub.3 generated on the third LED module 13, that is, V.sub.3−V.sub.2<V.sub.2−V.sub.1. Moreover, the voltage difference between the LED modules at the rear (down-stream) will be smaller. As also shown in FIG. 1B and FIG. 3B, for the power supply Idc that provides the constant-current source, it is similar to that of the constant-voltage power supply Vdc, but the circuit effect is opposite. Therefore, the operation principle of the power supply Vdc for the constant-voltage source in the following is also applicable to the power supply Idc for the constant-current source, and the detail description is omitted here for conciseness. Only the operation principle of the constant-voltage power supply Vdc is described as follows.

[0053] In order to avoid decreasing the accuracy of comparison, determination, and identification between the detected voltage and the voltage ranges of the look-up table due to the lower voltage difference between LED modules, the parallel sequenced LED light string of the present disclosure adjusts the values of the resistances R.sub.1,R.sub.2, . . . ,R.sub.N to maintain the same current so that the voltage difference between any two LED modules is fixed, thereby increasing the accuracy of comparison, determination, and identification between the detected voltage and the voltage ranges of the look-up table. The manner adopted is achieved by adjusting the value of each of the resistances R.sub.1,R.sub.2, . . . ,R.sub.N through a sequence signal. The specific description is as follows.

[0054] The sequence signal is a pulse signal, namely, a signal with high and low level interleaving changes, and each high level (or low level) may be used as a basis for the sequence. That is, the first cycle may be regarded as the first sequence, the second cycle may be regarded as the second sequence, and the rest may be deduced by analogy.

[0055] Therefore, when the power is turned on for the first time, since the resistances R.sub.1,R.sub.2, . . . ,R.sub.N are connected in parallel, the equivalent resistance value is the smallest so the current flowing through is the largest. The magnitude of the first voltage V.sub.1 corresponding to the first sequence (first cycle) of the pulse signal can be acquired.

[0056] When the (first time) power-on is finished, the current flowing through the first resistance R.sub.1 approaches zero by turning off the first resistance R.sub.1 for example, the value of the first resistance R.sub.1 is adjusted to a relatively large value, which is like an open circuit for current, or by turning off a switch connected to the first resistance R.sub.1 to make the current flowing through the first resistor R.sub.1 is zero. In addition, the value of the second resistance R.sub.2 of the second LED module 12 to the value of the last resistance of the last LED module (for example, 100th LED module), namely, the 99 remaining resistances are decreased, for example but not limited to 1/100 of the original resistance. Therefore, since the values of the remaining resistances are all decreased, the equivalent resistance values after the parallel connection will be the same so that the current flowing through may be the same. When the power is turned on again, the magnitude of the second voltage V.sub.2 corresponding to the second sequence (second cycle) of the pulse signal can be acquired.

[0057] Similarly, when the (second time) power-on is finished, the currents flowing through the first resistance R.sub.1 and the second resistance R.sub.2 approach zero by turning off the first resistance R.sub.1 and the second resistance R.sub.2, for example, the value of the first resistance R.sub.1 and the value of the second resistance R.sub.2 are adjusted to relatively large values, which is like an open circuit for current, or by turning off switches connected to the first resistance R.sub.1 and the second resistance R.sub.2 to make the currents flowing through the first resistor R.sub.1 and the second resistance R.sub.2 are zero. In addition, the value of the third resistance R.sub.3 of the third LED module 13 to the value of the last resistance of the last LED module (for example, 100th LED module), namely, the 98 remaining resistances are decreased, for example but not limited to 1/100 of the original resistance. Therefore, since the values of the remaining resistances are all decreased, the equivalent resistance values after the parallel connection will be the same so that the current flowing through may be the same. When the power is turned on again, the magnitude of the second voltage V.sub.3 corresponding to the third sequence (third cycle) of the pulse signal can be acquired. Accordingly, the sequence signal may be used as the basis of the sequence, and the values of the remaining resistances can be adjusted (decreased) to maintain the same current so that the voltage difference between any two LED modules is maintained constant, thereby increasing the accuracy of comparison, determination, and identification between the detected voltage and the voltage ranges of the look-up table.

[0058] In comparison with the constant-voltage power supply shown in FIG. 1A, the impedance compensation of the constant-current power supply shown in FIG. 1B is to increase the values of the remaining resistances so that the equivalent resistance values after the parallel connection will increase so that the current flowing through is decreased. Accordingly, the sequence signal may be used as the basis of the sequence, and the values of the remaining resistances can be adjusted (increased) to maintain the same current so that the voltage difference between any two LED modules is maintained constant, thereby increasing the accuracy of comparison, determination, and identification between the detected voltage and the voltage ranges of the look-up table.

[0059] Please refer to FIG. 2A and FIG. 2B, which show a circuit diagram of a parallel sequenced LED light string supplied power by the constant-voltage source and by the constant-current source according to a second embodiment of the present disclosure, respectively. For the convenience of description, take the constant-voltage power supply shown in FIG. 2A and FIG. 3A as an example. Therefore, the operation principle of the power supply Vdc for the constant-voltage source in the following is also applicable to the power supply Idc for the constant-current source, and the detail description is omitted here for conciseness. Only the operation principle of the constant-voltage power supply Vdc is described as follows.

[0060] The major difference between the LED light string shown in FIG. 2A and the LED light string shown in FIG. 1A is that the resistance value of each LED module 11,12, . . . ,1N in the LED light string of FIG. 2A does not have the controllable characteristics as shown in FIG. 1A. Therefore, In order to achieve the effect of resistance compensation, the LED light string shown in FIG. 2A further includes a compensation unit 20 to replace the controllable adjustment of the resistance in each LED module 11,12, . . . ,1N as shown in FIG. 1A. In other words, the compensation manner with adjustable resistance (that is, the resistance is controllable) shown in FIG. 1A and FIG. 1B will be implemented by the compensation unit 20. Therefore, not only simplify the circuit control, but also save the circuit costs. In particular, the compensation unit 20 is an integrated circuit (IC), which has a counting function, or the compensation unit 20 is a circuit self-designed by an analog circuit and a digital circuit, which has a counting function.

[0061] Therefore, when the power is turned on for the first time, since the resistances R.sub.1,R.sub.2, . . . ,R.sub.N are connected in parallel, the equivalent resistance value is the smallest so the current flowing through is the largest. The magnitude of the first voltage V.sub.1 corresponding to the first sequence (first cycle) of the pulse signal can be acquired.

[0062] When the (first time) power-on is finished, the first resistance R.sub.1 is turned off and the impedance of the compensation unit 20 is decreased (i.e., the impedance compensation of the compensation unit 20 is performed) so that the equivalent resistance values after the parallel connection will be the same and the current flowing through may be the same. When the power is turned on again, the magnitude of the second voltage V.sub.2 corresponding to the second sequence (second cycle) of the pulse signal can be acquired.

[0063] Similarly, when the (second time) power-on is finished, the first resistance R.sub.1 and the second resistance R.sub.2 are turned off and the impedance of the compensation unit 20 is further decreased so that the equivalent resistance values after the parallel connection will be the same. In other words, when both the first resistance R.sub.1 and the second resistance R.sub.2 are turned off, the impedance of the compensation unit 20 is smaller than the impedance when only the first resistance R.sub.1 is turned off so that the current flowing through may be the same. When the power is turned on again, the magnitude of the second voltage V.sub.3 corresponding to the third sequence (third cycle) of the pulse signal can be acquired. Accordingly, the sequence signal may be used as the basis of the sequence, and the impedance of the compensation unit 20 is adjusted (decreased) to maintain the same current so that the voltage difference between any two LED modules is maintained constant, thereby increasing the accuracy of identifying the detected voltage.

[0064] In comparison with the constant-voltage power supply shown in FIG. 2A, the impedance compensation of the constant-current power supply shown in FIG. 2B is to increase the impedance of the compensation unit 20 so that the equivalent resistance values after the parallel connection will increase and the current flowing through is decreased. Accordingly, the sequence signal may be used as the basis of the sequence, and the impedance of the compensation unit 20 is adjusted (increased) to maintain the same current so that the voltage difference between any two LED modules is maintained constant, thereby increasing the accuracy of identifying the detected voltage.

[0065] Please refer to FIG. 4, which shows a block circuit diagram of a controllable resistor according to the present disclosure. As mentioned above, each of the resistances R.sub.1,R.sub.2, . . . ,R.sub.N in each of the LED modules 11,12, . . . ,1N is a controllable resistor with a controllable resistor R11. The controllable resistor R11 is connected in series to a switch unit Q11, such as but not limited to a transistor switch. Therefore, the resistance value of the controllable resistor R11 may be adjusted to decrease, especially when it is designed to be the minimum value, the current flowing through the control resistors R11 will be maximized. At this condition, the voltages V.sub.1,V.sub.2, . . . ,V.sub.N generated on each of the LED modules 11,12, . . . ,1N may be maximized, which can increase the accuracy of comparison, determination, and identification between the detected voltage and the voltage ranges of the look-up table.

[0066] Please refer to FIG. 5, which shows a block circuit diagram of multi-resistor embodiment according to the present disclosure. In comparison with the controllable resistor with adjustable resistance shown in FIG. 4, the present disclosure may also achieve designs with different resistance values through the way of multiple resistors in parallel, such as two resistors R21,R22. Each of the two resistors R21,R22 are respectively connected to a switch unit Q21,Q22 in series. That is, the resistor R21 is connected to the switch unit Q21 in series, and the resistor R22 is connected to the switch unit Q22 in series. Take two resistors R21,R22 and two switch units Q21,Q22 as an example. In order to generate a smaller resistance value, the switch units Q21,Q22 may be turned on so that the two resistors R21,R22 are connected in parallel. On the contrary, in order to generate a larger resistance value, at least one switch unit Q21,Q22 is turned off, or even both switch units Q21,Q22 are turned off, to become an open-circuited state. Therefore, this embodiment can achieve increasing the accuracy of comparison, determination, and identification between the detected voltage and the voltage ranges of the look-up table. Moreover, a voltage regulator 31 and an analog to digital conversion unit 32 are provided. The voltage regulator 31 is coupled to the resistors R21,R22 and the switch units Q21,Q22 in parallel for voltage regulation. The analog to digital conversion unit 32 is coupled to the voltage regulator 31 for an operation of converting analog signals into digital signals.

[0067] Please refer to FIG. 6, which shows a block circuit diagram of counting operation according to the present disclosure. It is also a block circuit diagram of the compensation unit to implement a compensation manner with adjustable resistance (that is, controllable resistor).

[0068] In summary, the present disclosure has the following features and advantages:

[0069] 1. The voltage range information provided by the built-in look-up table is used for corresponding the detected voltage, and the voltage difference is provided to determine the sequence of the LED modules, thereby simplifying the circuit design and quickly completing the sequencing of the LED light string.

[0070] 2. The controllable resistor with adjustable resistance, the compensation unit 20 with adjustable resistance, or the parallel-connected resistors is/are used to increase the accuracy of comparison, determination, and identification between the detected voltage and the voltage ranges of the look-up table.

[0071] Although the present disclosure has been described with reference to the preferred embodiment thereof, it will be understood that the present disclosure 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 present disclosure as defined in the appended claims.