Patent Application
20120119814
1. Technical Field
The disclosed embodiments relate to power off circuits, and more particularly to a power off circuit and an electronic device using the power off circuit.
2. Description of Related Art
Power off circuits are widely used in electronic devices, such as digital versatile disc (DVD) player, notebook computers, etc. Generally, an electronic device includes a power source, a power off circuit, and functional modules. The power off circuit includes a control unit and a power management unit. The power management unit receives a supply voltage from the power source and provides a working voltage to the functional modules. When the electronic device receives a power off command input by a user, the control unit signals the functional modules to be ready for being powered off, for example, the functional modules need to store data in time before the electronic device is powered off.
When the functional modules have stored data completely, the control unit executes software programs to disable the power management unit. However, when a glitch occurs in the software programs, the control unit may malfunction, thus the power management unit cannot be disabled, and the electronic device will not be powered off.
What is needed, therefore, is a power off circuit and an electronic device to overcome the above described limitations.
Many aspects of the embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout two views.
Referring to
The power off circuit 300 includes a power management unit 12, a control unit 14, a switching unit 16, a detecting unit 18, and a delay unit 20. The power management unit 12 is used for receiving the supply voltage from the power source 200 and providing an operating voltage to the control unit 14 and the at least one functional module 400, therefore the control unit 14 is enabled and the at least one functional module 400 performs a predetermined function.
The detecting unit 18 is connected to the power source 200 through the switching unit 16, and the delay unit 20 is connected to the power source 200 through the switching unit 16. When the switching unit 16 is turned on, the power source 200 provides the supply voltage to the detecting unit 18 and the delay unit 20. When the switching unit 16 is turned off, the power source 200 stops providing the supply voltage to the detecting unit 18 and the delay unit 20. The detecting unit 18 is used for detecting whether the switching unit 16 is turned off and generating a detecting signal when detecting that the switching unit 16 is turned off. The control unit 14 signals the at least one functional module 400 to be ready for being powered off according to the detecting signal, for example, the at least one functional module 400 needs to store data in time before the electronic device 100 is powered off.
The delay unit 20 is connected to the power management unit 12 and the switching unit 16. The delay unit 20 generates a control signal after a predetermined time period from a time point when the switching unit 16 is turned off, the power management unit 12 stops providing the operating voltage to the control unit 14 and the at least one functional module 400 according to the control signal. Therefore, the control unit 14 and the at least one functional module 400 are disabled, and the electronic device 100 is powered off. During the predetermined time period, the at least one functional module 400 stores data in time, thus the data loss is effectively prevented.
Referring to
The delay unit 20 includes a capacitor C1, a fifth resistor R5, a sixth resistor R6, and a diode D1. One end of the fifth resistor R5 is connected to the power management unit 12, an anode of the diode D1 is connected to the switching unit 16, a cathode of the diode D1 is connected to the other end of the fifth resistor R5. One end of the sixth resistor R6 is connected between the fifth resistor R5 and the power management unit 12, the other end of the sixth resistor R6 is grounded. One end of the capacitor C1 is connected between the cathode of the diode D1 and the fifth resistor R5, the other end of the capacitor C1 is grounded. In this embodiment, the capacitance of the capacitor C1 is adjustable.
The principle of the electronic device 100 is illustrated as follows:
The power management unit 12 receives the supply voltage from the power source 200 and provides the operating voltage to the emitter of the transistor Q1. When the switching unit 16 is turned on, the supply voltage from the power source 200 is transmitted to the base of the transistor Q1 through the resistor R2, thus the transistor Q1 is cut off; at the same time, the supply voltage from the power source 200 charges up the capacitor C1 through the diode D1, and capacitor C1 stores energy. When the switching unit 16 is turned off, the base of the transistor Q1 is pulled low, thus the transistor Q1 conducts; then the operating voltage from the power management unit 12 is transmitted to the control unit 14 through the emitter and the collector of the transistor Q1 and the resistor R4; thus the detecting unit 18 generate the high voltage level detecting signal to the control unit 14. The control unit 14 signals the at least one functional module 400 to store data in time before being powered off according to the detecting signal.
At the same time, when the switching unit 16 is turned off, the capacitor C1 discharges through the fifth resistor R5 and the sixth resistor R6. After the predetermined time period T, T is calculated by the following formula: T=C1*(R5+R6), from the time point when the switching unit 16 is turned off, the capacitor C1 has been discharged completely, thus the delay unit 20 generates the low voltage level control signal to the power management unit 12. The power management unit 12 stops providing the operating voltage to the control unit 14, the delay unit 18, and the at least one functional module 400 according to the control signal, so that the electronic device 100 is powered off with no glitches or less likely chance of glitches.
In this embodiment, the delay unit 20 controls the power management unit 12 to stop providing the operating voltage to the control unit 14 and the at least one functional module 400, and the delay unit 20 includes the capacitor C1, the resistors R5, R6, and the diode D1. Because the delay unit 20 generates the low voltage level control signal to disable the power management unit 12, but does not execute software programs to disable the power management unit 12; the error of the software programs is effectively prevented, and the electronic device 100 is powered off.
Alternative embodiments will become apparent to those skilled in the art without departing from the spirit and scope of what is claimed. Accordingly, the present invention should be deemed not to be limited to the above detailed description, but rather only by the claims that follow and equivalents thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201010542476.X | Nov 2010 | CN | national |
