Constant-power power supply apparatus and method of supplying constant-power power

1. A method of supplying a loading with an electric power within a predetermined range of a default power, wherein at least two reference voltages are predetermined, and each two neighboring reference voltages are defined to have a voltage section therebetween, and each voltage section has a slope parameter accordingly; the method comprising the steps of:

detecting a working voltage of the electric power supplied to the loading;

obtaining the slope parameter of the voltage section in which the working voltage falls; and

generating a working current according to the working voltage and the obtained slope parameter, wherein a product of the working current and the working voltage is in the predetermined range of the default power.

2. The method of claim 1 , further comprising the step of comparing the working voltage with an upper limit voltage, and keeping the working voltage supplied to the loading identical to the highest reference voltage when the working voltage is higher than the upper limit voltage.

3. The method of claim 1 , wherein the working current supplied to the loading is kept no higher than an upper limit current.

4. The method of claim 2 , wherein the working current supplied to the loading is kept no higher than an upper limit current.

5. The method of claim 1 , wherein the predetermined range of the default power is between 90% and 110% of the default power.

6. The method of claim 1 , wherein number of the reference voltages is at least three.

7. The method of claim 6 , wherein absolute values of the slope parameters of the voltage sections decrease from the voltage section between the highest and the second highest reference voltages to the voltage section between the second lowest and the lowest reference voltages.

8. The method of claim 1 , wherein the loading has a LED chip.

9. A power supply apparatus for receiving power from a power source and supplying a loading with an electric power within a predetermined range of a default power, comprising:

a driving unit for receiving the power from the power source and supplying the loading with a working voltage and a working current;

a voltage sensing unit electrically connected to the driving unit to detect the working voltage; and

a feedback control unit electrically connected to the voltage sensing unit and the driving unit, wherein the feedback control unit keeps at least two reference voltages, and each two neighboring reference voltages are defined to have a voltage section therebetween, and each voltage section has a slope parameter accordingly;

wherein the feedback control unit receives the working voltage sensed by the voltage sensing unit, and finds the voltage section in which the working voltage falls to obtain the slope parameter of the voltage section, and then sends a current signal, which is according to the working voltage and the obtained slope parameter, to the driving unit to command the driving unit to change the working current accordingly, wherein a product of the working current and the working voltage is remained in the predetermined range of the default power.

10. The power supply apparatus of claim 9 , wherein the feedback control unit further keeps an upper limit voltage; the feedback control unit sends a voltage signal to the driving unit to keep the working voltage supplied to the loading identical to the highest reference voltage when the working voltage is higher than the upper limit voltage.

11. The power supply apparatus of claim 10 , further comprising a current sensing unit electrically connected to the driving unit and the feedback control unit to detect the working current, wherein the feedback control unit further keeps an upper limit current, and the feedback control unit sends a current signal to the driving unit when the working current is higher than an upper limit current, to keep the working current supplied to the loading identical to the upper limit current.

12. The power supply apparatus of claim 9 , wherein the feedback control unit has a comparator and a signal generator; the comparator is electrically connected to the voltage sensing unit, and the signal generator is electrically connected to the driving unit; the comparator keeps the reference voltages and the slope parameters; the comparator determines which voltage section the working voltage falls in, and then sends a slope signal according to the slope parameter of the voltage section to the signal generator; the signal generator generates the current signal according to the slope signal and the working voltage.

13. The power supply apparatus of claim 9 , wherein the predetermined range of the default power is between 90% and 110% of the default power.

14. The power supply apparatus as defined in claim 9 , wherein number of the reference voltages is at least three.

15. The power supply apparatus as defined in claim 14 , wherein absolute values of the slope parameters of the voltage sections decrease from the voltage section between the highest and the second highest reference voltages to the voltage section between the second lowest and the lowest reference voltages.

16. The power supply apparatus as defined in claim 9 , wherein the loading has a LED chip.