Electronic Device

Abstract

An electronic device is provided. The electronic apparatus includes a controller and a dummy load. When the dummy load is turned on by the controller, the dummy load regulates a direct current (DC) output voltage outputted to the electronic device by a power conversion apparatus connected to the electronic device. Accordingly, the electronic device communicates with the power conversion apparatus using the dummy load to dynamically regulate the DC output voltage, so as to avoid power consumption.

Description

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the priority benefits of U.S. provisional application Ser. No. 61/740,431, filed on Dec. 20, 2012. The entirety of the above-mentioned patent applications is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND OF THE INVENTION

[0002] 1. Field of Invention

[0003] The invention relates generally to a power control technique, and more particularly to a power supply system and an electronic device having a power saving function.

[0004] 2. Description of Related Art

[0005] At present, due to the requirement for the reduced weight of consumers' electronic apparatuses (e.g., desktop computers, notebooks, mobile phones, digital cameras, tablet PCs, etc.), power may be supplied by batteries within the electronic apparatuses or by means of external power adapters. That is, the electronic apparatuses require the power conversion apparatuses (e.g., alternating-current (AC) to direct-current (DC) adapters) to supply power or to charge the internal batteries.

[0006] As to the existing power supply system, the power conversion apparatus is a passive equipment. Namely, when the input terminal of the power conversion apparatus is connected to AC power, this power conversion apparatus passively provides the stable DC power to an electronic apparatus connected to the power conversion apparatus. However, once the power conversion apparatus is connected to the AC power, the power conversion apparatus may continue providing the DC power even though the power conversion apparatus is not connected to any electronic apparatus or the electronic apparatus connected to the power conversion apparatus is in an off mode. Accordingly, the existing power conversion apparatus is unable to adjust the output power according to the state of the electronic apparatus connected to the power conversion apparatus, which leads to the significant amount of unnecessary power consumption.

SUMMARY OF THE INVENTION

[0007] The invention is directed to an electronic device capable of determining the state of the electronic device by the power value of the DC output voltage, and thereby dynamically regulate the voltage level of the DC output voltage, so as to effectively manage power consumption and achieve power savings.

[0008] In an embodiment of the invention, an electronic device is provided. The electronic device includes a controller and a first dummy load connected to the controller. The controller turns on the first dummy load according to a state of the electronic device. When the controller turns on the first dummy load, the first dummy load regulates a DC output voltage outputted to the electronic device by a power conversion apparatus connected to the electronic device.

[0009] According to an embodiment of the invention, the power conversion apparatus includes an AC to DC converter and a power conversion control unit. The AC to DC converter is coupled to the electronic device, and the AC to DC converter converts an AC input voltage to the DC output voltage according to a switch signal and provides the DC output voltage to the electronic device. The power conversion control unit is coupled to the AC to DC converter, and the power conversion control unit detects the DC output voltage to determine the state of the electronic device. When the electronic device is turned off, the power conversion control unit sets the DC output voltage as a standby voltage through the switch signal.

[0010] According to an embodiment of the invention, when the electronic device is turned on, the controller turns on the first dummy load, and the power conversion control unit sets the DC output voltage as a normal voltage through the switch signal, in which the normal voltage is higher than the standby voltage.

[0011] According to an embodiment of the invention, the electronic device further includes a second dummy load, in which the first dummy load and the second dummy are used to regulate the DC output voltage.

[0012] According to an embodiment of the invention, when the electronic device is turned off, the controller turns on the first dummy load, and the power conversion control unit sets the DC output voltage as the standby voltage through the switch signal. When the electronic device is turned on, the controller turns on the second dummy load, and the power conversion control unit sets the DC output voltage as a normal voltage through the switch signal, in which the normal voltage is higher than the standby voltage.

[0013] According to an embodiment of the invention, when the electronic device is cut off from the power conversion apparatus, the power conversion control unit sets the DC output voltage as a ground voltage through the switch signal.

[0014] According to an embodiment of the invention, the AC to DC converter includes a converter circuit, a transformer, and a rectifier circuit. The converter circuit converts the AC input voltage into a first power voltage according to the switch signal. The transformer converts the first power voltage into a second power voltage. The rectifier circuit converts the second power voltage into the DC output voltage.

[0015] According to an embodiment of the invention, the power conversion control unit includes a power detector, a counter, a feedback control circuit, and a pulse modulation controller. The power detector detects the power value of the DC output voltage. The counter counts a predetermined period when the power value of the DC output voltage is within a predetermined range. The voltage feedback circuit detects a voltage level of the DC output voltage, and the voltage feedback circuit outputs a voltage setting signal according to the voltage level of the DC output voltage and a count result of the counter. The pulse modulation controller outputs the switch signal according to the voltage setting signal.

[0016] According to an embodiment of the invention, the pulse modulation controller includes a trigger circuit and a logic circuit. The trigger circuit outputs a switch trigger signal according to the voltage setting signal. The logic circuit outputs the switch signal to the AC to DC converter according to the switch trigger signal.

[0017] According to an embodiment of the invention, the power conversion control unit further includes an optical coupling circuit transmitting the voltage setting signal to the pulse modulation controller.

[0018] According to an embodiment of the invention, when the AC to DC converter receives the AC input voltage, the power conversion control unit controls the AC to DC converter to output the DC output voltage having a normal voltage to the electronic device within a predetermined period, in which the normal voltage is higher than the standby voltage.

[0019] In view of the above, according to the embodiments of the invention, the power supply system has the first dummy load configured in the electronic device, such that the power value of the DC output voltage is adjusted according to the state of the electronic device. Therefore, the power conversion control unit in the power conversion apparatus is able to determine the state of the electronic device according to the power value of the DC output voltage. Moreover, the power conversion control unit is able to dynamically regulate the voltage level of the DC output voltage according to the power requirement of the electronic device, and thereby save power by preventing unnecessary power consumption.

[0020] In order to make the aforementioned and other features and advantages of the invention comprehensible, embodiments accompanied with figures are described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1A is a block diagram of a power supply system according to an embodiment of the invention.

[0022] FIG. 1B is a driving waveform diagram of a power supply system according to an embodiment of the invention.

[0023] FIG. 1C is a schematic view of a pulse modulation controller according to an embodiment of the invention.

[0024] FIG. 2A is a block diagram of a power supply system according to another embodiment of the invention.

[0025] FIG. 2B is a driving waveform diagram of a power supply system according to another embodiment of the invention.

[0026] FIG. 3 is a flow diagram of a power control method of a power conversion apparatus according to an embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

[0027] In order to prevent unnecessary power consumption for a power supply system, embodiments of the invention provide an electronic device suitable for application in the power supply system. The electronic device in the power supply system is configured with at least one dummy load. Thereby, the electronic device may turn on the dummy load based on a state of the electronic device, and regulate a direct current (DC) output voltage outputted by a power conversion apparatus. The power conversion apparatus may then obtain a power requirement of the connected electronic device according to a power value of the DC output voltage, and thereby dynamically regulate a voltage level of the DC output voltage. Accordingly, the power conversion apparatus can provide a suitable power source matching the requirement and achieve a power saving effect.

[0028] Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.

[0029] FIG. 1A is a block diagram of a power supply system according to an embodiment of the invention. With reference to FIG. 1A, a power supply system 100 includes an electronic device 110 and a power conversion apparatus 120. In the present embodiment, the electronic device 110 includes a controller 111, a first dummy load 113, and a battery 115. The controller 111 may be an embedded controller or a keyboard controller, and the controller 111 may operate by receiving a DC output voltage Vdc provided by the power conversion apparatus 120 or by receiving a power provided by the battery 115. The first dummy load 113 may be implemented by physical circuit elements, such as in a circuit framework including resistors, capacitors, inductors, transistors, and/or combines thereof. The first dummy load 113 receives the DC output voltage Vdc, and the first dummy load 113 regulates a power value of the DC output voltage Vdc. The controller 111 may determine whether to turn on the first dummy load 113 according to a state of the electronic device 110. In other words, when the electronic device 110 is turned off, the power value of the DC output voltage Vdc is reduced. On the other hand, when the electronic device 110 is turned on, the controller 111 may turn on the first dummy load 113, and therefore the power value of the DC output voltage Vdc is increased. When the DC output voltage Vdc reaches a predetermined value, the controller 111 turns off the first dummy load 113.

[0030] The power conversion apparatus 120 includes an AC to DC converter 121 and a power conversion control unit 123. The AC to DC converter 121 is coupled to the electronic device 110 and receives an AC input voltage AC and a switch signal Ssw. The AC to DC converter 121 converts the AC input voltage AC to the DC output voltage Vdc according to the switch signal Ssw and provides the DC output voltage Vdc to the electronic device 110. The power conversion control unit 123 is coupled to the AC to DC converter 121, and the power conversion control unit 123 detects the power value of the DC output voltage Vdc to determine the state of the electronic device 110.

[0031] When the electronic device 110 is turned off, such as in a state S5 defined by Advanced Configuration and Power Interface (ACPI), the power conversion control unit 123 may set the DC output voltage Vdc as a standby voltage through the switch signal Ssw, such as 5V, for example. When the electronic device 110 is turned on, such as in a state S0 defined by ACPI, the power conversion control unit 123 may set the DC output voltage Vdc as a normal voltage through the switch signal Ssw, such as 19V, in which the normal voltage is typically higher than the standby voltage.

[0032] The AC to DC converter 121 includes a converter circuit 131, a transformer TR, and a rectifier circuit 133. The converter circuit 131 receives the AC input voltage AC, and the converter circuit 131 converts the AC input voltage AC to a first power voltage VP1 according to the switch signal Ssw. The transformer TR converts the first power voltage VP1 to a second power voltage VP2. The rectifier circuit 133 converts the second power voltage VP2 to the DC output voltage Vdc. The rectifier circuit 133 may be formed by a diode D1 and a capacitor C1, although embodiments of the invention are not limited thereto.

[0033] The power conversion control unit 123 includes a power detector 141, a counter 143, a voltage feedback circuit 145, an optical coupling circuit 147, and a pulse modulation controller 149. The power detector 141 detects the power value of the DC output voltage Vdc, in which the power of the DC output voltage Vdc is related to the power of the second power voltage VP2. Therefore, the present embodiment may determine the power value of the DC output voltage Vdc by detecting the power value of the second power voltage VP2, although embodiments of the invention are not limited thereto. The counter 143 is controlled by the power detector 141 to count for a predetermined period. For example, when the power value of the DC output voltage Vdc is within a predetermined range, the power detector 141 controls the counter 143 to count for the predetermined period.

[0034] The voltage feedback circuit 145 detects the voltage level of the DC output voltage Vdc, and the voltage feedback circuit 145 outputs a voltage setting signal Svs1 according to the voltage level of the DC output voltage Vdc and a count result CR1 of the counter 143. The optical coupling circuit 147 converts the voltage setting signal Svs1 to a voltage setting signal Svs2, and the optical coupling circuit 147 transmits the voltage setting signal Svs2 to the pulse modulation controller 149. Moreover, the voltage setting signals Svs1 and Svs2 are substantially the same. However, the signal type of the voltage setting signal Svs2 may be set according to a requirement of the pulse modulation controller 149. For example, when the pulse modulation controller 149 is a current mode controller, then the voltage setting signal Svs2 may be a current signal, although embodiments of the invention are not limited thereto. The pulse modulation controller 149 outputs the switch signal Ssw according to the voltage setting signal Svs2, so as to control the first power voltage VP1 outputted by the converter circuit 131.

[0035] In one embodiment of the invention, the voltage feedback circuit 145 may be further coupled to the power detector 141, such that the voltage feedback circuit 145 outputs the voltage setting signal Svs1 according to the voltage level and the power value of the DC output voltage Vdc and the count result CR1 of the counter 143.

[0036] FIG. 1B is a driving waveform diagram of a power supply system according to an embodiment of the invention. With reference to FIGS. 1A and 1B, similar or same elements are labeled with similar or same reference numerals. In a period T11, the AC to DC converter 121 receives the AC input voltage AC and outputs the DC output voltage Vdc, and the power conversion control unit 123 controls the AC to DC converter 121 to output the DC output voltage Vdc having a normal voltage Vnr. At this time, the power detector 141 detects that a power value PW1 of the DC output voltage Vdc is within a predetermined range (between 0 to a power detection level LPD). Therefore, the power detector 141 controls the counter 143 to count a predetermined time TD. Moreover, during the predetermined time TD, the voltage level of the DC output voltage Vdc is maintained at the normal voltage Vnr. The predetermined time TD may be set manually according to a circuit requirement, such as the response speed of the controller 111, although embodiments of the invention are not limited thereto.

[0037] In a period T12, the counter 143 has counted the predetermined time TD. Therefore, the count result CR1 of the counter 143 is maintained, and the power conversion control unit 123 controls the AC to DC converter 121 to output the DC output voltage Vdc having a standby voltage Vst. Assume here that the electronic device 110 electrically connects to the power conversion apparatus 120 at a time TA and provides the DC output voltage Vdc to the electronic device 110. However, assume that the electronic device 110 is turned off at this time, which means that the first dummy load 113 has not been turned on. Here, the power value PW1 of the DC output voltage Vdc is lower than the power detection level LPD, and therefore the voltage level of the DC output voltage Vdc is maintained at the standby voltage Vst.

[0038] In a period T13, assume that the electronic device 110 is turned on, and the first dummy load 113 is turned on, such that the power value PW1 of the DC output voltage Vdc exceeds the power detection level LPD. At this time, the power detector 141 controls the counter 143 to reset the count result CR1, and the power conversion control unit 123 controls the AC to DC converter 121 to output the DC output voltage Vdc having the normal voltage Vnr.

[0039] In a period T14, assume that the electronic device 110 is turned off, and the first dummy load 113 is not turned on. Therefore, the power value PW1 of the DC output voltage Vdc returns to be within the predetermined range (between 0 to the power detection level LPD). At this time, the power detector 141 controls the counter 143 to count the predetermined time TD. Moreover, during the predetermined time TD, the voltage level of the DC output voltage Vdc is still maintained at the normal voltage Vnr.

[0040] After the period T14, the counter 143 has counted the predetermined time TD, and therefore the count result CR1 of the counter 143 is maintained. Moreover, the power conversion control unit 123 controls the AC to DC converter 121 to output the DC output voltage Vdc having the standby voltage Vst. Since the electronic device 110 is turned off at this time, which means that the power value PW1 of the DC output voltage Vdc will not exceed the power detection level LPD, the voltage level of the DC output voltage Vdc is maintained at the standby voltage Vst.

[0041] FIG. 1C is a schematic view of a pulse modulation controller according to an embodiment of the invention. With reference to FIGS. 1A and 1C, in the present embodiment, a pulse modulation controller 149a includes a trigger circuit 151 and a logic circuit 153, for example. The trigger circuit 151 outputs a switch trigger signal Strs according to the voltage setting signal Svs2, and the logic circuit 153 generates the switch signal Ssw according to the switch trigger signal Strs, and the logic circuit 153 outputs the switch signal Ssw to the converter circuit 131 of the AC to DC converter 120. The trigger circuit 151 may obtain an adjustment requirement of the DC output voltage Vdc according to the voltage setting signal Svs2. Moreover, the trigger circuit 151 may regulate the voltage level of the switch signal Ssw generated by the logic circuit 153 through the switch trigger signal Strs, such that the AC to DC converter 120 correspondingly regulates the voltage level of the DC output voltage Vdc.

[0042] FIG. 2A is a block diagram of a power supply system according to another embodiment of the invention. With reference to FIGS. 1A and 2A, similar or same elements are labeled with similar or same reference numerals. In the present embodiment, a power supply system 200 includes an electronic device 210 and a power conversion apparatus 220. The electronic device 210 includes a controller 211, a first dummy load 213, a second dummy load 215, and a battery 217. The functions of the battery 217 is similar to the battery 115. The first dummy load 213 and the second dummy load 215 receive the DC output voltage Vdc to regulate the power value of the DC output voltage Vdc. The controller 211 may determine whether to turn on the first dummy load 213 and the second dummy load 215 according to a state of the electronic device 210. For example, when the electronic device 210 is turned off, the controller 211 may turn on the first load 213, such that the power value of the DC output voltage Vdc is increased. Thereafter, when the electronic device 110 is turned on, the controller 111 may turn on the first dummy load 213 and the second dummy load 215, and accordingly the power value of the DC output voltage Vdc is again increased.

[0043] The power conversion apparatus 220 includes the AC to DC converter 121 and a power conversion control unit 221. The power conversion control unit 221 includes a power detector 231, a counter 233, a voltage feedback circuit 235, an optical coupling circuit 237, and a pulse modulation controller 239. Since the functions and coupling relationships of the power detector 231, the counter 233, the voltage feedback circuit 235, the optical coupling circuit 237, and the pulse modulation controller 239 are similar to the power detector 141, the counter 143, the voltage feedback circuit 145, the optical coupling circuit 147, and the pulse modulation controller 149, further elaboration thereof is omitted hereafter.

[0044] FIG. 2B is a driving waveform diagram of a power supply system according to another embodiment of the invention. With reference to FIGS. 2A and 2B, similar or same elements are labeled with similar or same reference numerals. In a period T21, the AC to DC converter 121 receives the AC input voltage AC and outputs the DC output voltage Vdc, and the power conversion control unit 123 controls the AC to DC converter 121 to output the DC output voltage Vdc having the normal voltage Vnr. At this time, the power detector 231 detects the rise of a power value PW2 of the DC output voltage Vdc, and therefore the power detector 231 controls the counter 233 to count the predetermined time TD. Moreover, during the predetermined time TD, the voltage level of the DC output voltage Vdc is maintained at the normal voltage Vnr. Furthermore, assume that the electronic device 210 is electrically connected to the power conversion apparatus 220 at a time TB to provide the DC output voltage Vdc to the electronic device 210, such that the power value PW2 of the DC output voltage Vdc rises to be within a predetermined range (between the power detection level LPD and a system on level LSON) due to the first dummy load 213.

[0045] In a period T22, the counter 233 has counted the predetermined time TD, and the power value PW2 of the DC output voltage Vdc rises to be within the predetermined range (between the power detection level LPD and the system on level LSON). Therefore, the power detector 231 controls the counter 233 to maintain a count result CR2. At this time, since the count result CR2 remains fixed, this represents the electronic device 210 is electrically connected to the power conversion apparatus 220 and the electronic device 210 is turned off. Accordingly, the power conversion control unit 221 controls the AC to DC converter 121 to output the DC output voltage Vdc having the standby voltage Vst.

[0046] In a period T23, assume that the electronic device 210 is turned on. That is, the first dummy load 213 is not turned on and the second dummy load 215 is turned on, such that the power value PW2 of the DC output voltage Vdc exceeds the system on level LSON. At this time, the power detector 231 controls the counter 233 to reset the count result CR2. Moreover, the power conversion control unit 221 controls the AC to DC converter 121 to output the DC output voltage Vdc having the normal voltage Vnr, and then the second dummy load 215 may be turned off

[0047] In a period T24, assume that the electronic device 210 is turned off, and the second dummy load 215 has not been turned on. Therefore, the power value PW2 of the DC output voltage Vdc returns to the predetermined range (between the power detection level LPD and a system on level LSON). At this time, the power detector 231 controls the counter 233 to count the predetermined time TD. During the predetermined time TD, the voltage level of the DC output voltage Vdc is still maintained at the normal voltage Vnr. Moreover, assume that the electronic device 210 is cut off from the power conversion apparatus 220 at a time TC. Accordingly, the power value PW2 of the DC output voltage Vdc is reduced to be lower than the power detection level LPD.

[0048] After the period T24, the counter 233 has counted the predetermined time TD. However, the power value PW2 of the DC output voltage Vdc has reduced to be lower than the power detection level LPD. Therefore, the power detector 231 controls the counter 233 to reset the count result CR2, and the power conversion control unit 123 controls the AC to DC converter 121 to output the DC output voltage Vdc having a ground voltage (i.e. 0V).

[0049] Embodiments of the invention also provide a power control method of an electronic device. By having the power conversion apparatuses 120 and 220 obtain the power requirements of the connected electronic devices 110 and 210 through the power value of the DC output voltage Vdc, a suitable power source can be provided and a power saving effect can be achieved.

[0050] FIG. 3 is a flow diagram of a power control method of a power conversion apparatus according to an embodiment of the invention. With reference to FIG. 3, in Step S302, the power conversion apparatus detects the power value of the DC output voltage, in which the power value of the DC output voltage corresponds with state of the electronic device. In detail, the controller in the electronic device may turn on the dummy load according to the state of the electronic device, such that the power value of the DC output voltage changes in accordance with state of the electronic device.

[0051] In Step S304, the power conversion apparatus determines whether the electronic device is turned on. In specifics, the power detector in the power conversion apparatus may determine the state of the electronic device by the power value of the DC output voltage.

[0052] In Step S306, when the electronic device is determined to be turned on, the power conversion apparatus provides the DC output voltage having the normal voltage to the electronic device. In detail, when the power detector determines that the electronic device is turned on, the switch signal provided to the AC to DC converter may be regulated, such that the AC to DC converter provides the DC output voltage having the normal voltage to the power conversion apparatus.

[0053] In Step S308, when the electronic device is determined to be turned off, the power conversion apparatus provides the DC output voltage having the standby voltage to the electronic device. In specifics, when the power detector determines that the electronic device is turned off, the switch signal provided to the AC to DC converter may be regulated, such that the AC to DC converter provides the DC output voltage having the standby voltage to the power conversion apparatus.

[0054] Moreover, when the power conversion apparatus receives the AC input voltage, the AC input voltage may be converted into the DC output voltage having the normal voltage and provided to the electronic device. However, when the electronic device is still turned off during the predetermined period, the power conversion apparatus provides the DC output voltage having the standby voltage to the electronic device. Furthermore, when the power conversion apparatus is cutoff from the electronic device, the output of the DC output voltage may be terminated. That is, the DC output voltage having the ground voltage may be outputted.

[0055] To sum up, according to the embodiments of the invention, the power supply system has at least one dummy load configured in the electronic device, such that the power value of the DC output voltage is adjusted according to the state of the electronic device. Therefore, the power conversion control unit in the power conversion apparatus may determine the state of the electronic device according to the power value of the DC output voltage. Moreover, the power conversion control unit may dynamically regulate the voltage level of the DC output voltage according to the power requirement of the electronic device, and thereby save power by preventing unnecessary power consumption.

[0056] It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.

Claims

1. An electronic device, comprising: a controller; and a first dummy load connected to the controller, wherein the controller turns on the first dummy load according to a state of the electronic device, wherein when the controller turns on the first dummy load, the first dummy load regulates a direct current (DC) output voltage outputted to the electronic device by a power conversion apparatus connected to the electronic device.

2. The electronic device according to claim 1, wherein the power conversion apparatus comprises: an alternating current to direct current (AC to DC) converter coupled to the electronic device, converting an AC input voltage to the DC output voltage according to a switch signal and providing the DC output voltage to the electronic device; and a power conversion control unit coupled to the AC to DC converter, detecting the DC output voltage to determine the state of the electronic device, wherein when the electronic device is turned off, the power conversion control unit sets the DC output voltage as a standby voltage through the switch signal.

3. The electronic device according to claim 2, wherein when the electronic device is turned on, the controller turns on the first dummy load, and the power conversion control unit sets the DC output voltage as a normal voltage through the switch signal, wherein the normal voltage is higher than the standby voltage.

4. The electronic device according to claim 2, wherein the electronic device further comprises a second dummy load, the first dummy load and the second dummy being used for regulating the DC output voltage.

5. The electronic device according to claim 4, wherein when the electronic device is turned off, the controller turns on the first dummy load, and the power conversion control unit sets the DC output voltage as the standby voltage through the switch signal.

6. The electronic device according to claim 5, wherein when the electronic device is turned on, the controller turns on the second dummy load, and the power conversion control unit sets the DC output voltage as a normal voltage through the switch signal, wherein the normal voltage is higher than the standby voltage.

7. The electronic device according to claim 4, wherein when the electronic device is cut off from the power conversion apparatus, the power conversion control unit sets the DC output voltage as a ground voltage through the switch signal.

8. The electronic device according to claim 2, wherein the AC to DC converter comprises: a converter circuit converting the AC input voltage into a first power voltage according to the switch signal; a transformer converting the first power voltage into a second power voltage; a rectifier circuit converting the second power voltage into the DC output voltage.

9. The electronic device according to claim 2, wherein the power conversion control unit comprises: a power detector detecting the power value of the DC output voltage; a counter counting a predetermined period when the power value of the DC output voltage is within a predetermined range; a voltage feedback circuit detecting a voltage level of the DC output voltage, the voltage feedback circuit outputting a voltage setting signal according to the voltage level of the DC output voltage and a count result of the counter; and a pulse modulation controller outputting the switch signal according to the voltage setting signal.

10. The electronic device according to claim 9, wherein the pulse modulation controller comprises: a trigger circuit outputting a switch trigger signal according to the voltage setting signal; and a logic circuit outputting the switch signal to the AC to DC converter according to the switch trigger signal.

11. The electronic device according to claim 9, wherein the power conversion control unit further comprises: an optical coupling circuit transmitting the voltage setting signal to the pulse modulation controller.

12. The electronic device according to claim 2, wherein when the AC to DC converter receives the AC input voltage, the power conversion control unit controls the AC to DC converter to output the DC output voltage having a normal voltage to the electronic device within a predetermined period, wherein the normal voltage is higher than the standby voltage.