Load detecting method and power supply device where the method is applied

1. A method for detecting connection or detachment between a power supply device and a load, the method comprising steps of:

determining whether a load detection operation is necessary based on a detection voltage corresponding to an output voltage from the power supply device;

when determining the load detection operation to be necessary, estimating a specific time point in a first period during which the output voltage of the power supply device decreases from a first level to a second level; and

applying a test signal to the output voltage for a predetermined detection period with reference to the specific time point, wherein switching operation of a power switch of the power supply device does not occur in the first period.

2. The method of claim 1 , wherein estimating the specific time point comprises:

detecting the specific time point within current switching cycle of the power switch; and

estimating a next specific time point in a first period for next switching cycle based on the detected specific time point.

3. The method of claim 1 , wherein when the power switch switches in a burst mode, estimating the specific time point comprises:

detecting a specific time point of a non-switching period of current burst cycle of the power switch; and

estimating a next specific time point in a first period of next burst cycle based on the detected specific time point.

4. The method of claim 1 , further comprising:

detecting connection or detachment of the power supply device to or from the load based on a result of comparing a waveform of the test signal to a waveform detected from the output voltage to which the test signal is applied.

5. The method of claim 1 , wherein the specific time point is a middle time point of the first period.

6. A power supply device, comprising:

a power switch;

a power delivery device configured to convert an input into an output according to switching operation of the power switch; and

a load detecting device configured to determine whether a load detection operation is necessary based on a detection voltage corresponding to the output, and when it is determined that the load detection operation is necessary, estimate a specific time point in a first period during which the output decreases from a first level to a second level, and apply a test signal to the output for a predetermined detection period with reference to the specific time point, wherein switching operation of the power switch does not occur in the first period.

7. The power supply device of claim 6 , wherein the load detecting device is configured to detect the specific time point within current switching cycle of the power switch, and estimate a next specific time point in a first period for next switching cycle based on the detected specific time point.

8. The power supply device of claim 6 , wherein, when the power switch switches in a burst mode, the load detecting device is configured to detect the specific time point of a non-switching period of current burst cycle of the power switch, and estimate a next specific time point in a first period of next burst cycle based on the detected specific time point.

9. The power supply device of claim 6 , wherein the load detecting device is configured to detect connection or detachment of the power supply device to or from the load, depending on a result of comparing a waveform of the test signal to a waveform detected from the output voltage to which the test signal is applied.

10. The power supply device of claim 6 , further comprising a connection switch configured to deliver the output to a load, wherein the load detecting device is configured to turn off the connection switch when the load is detected to be detached from the output.

11. The power supply device of claim 6 , wherein the specific time point is a middle time point of the first period.