Patent Application
20130241295
1. Technical Field
The disclosed embodiments relate to a power management circuit and an electronic device.
2. Description of Related Art
The power management circuit is widely used in electronic devices. The power management circuit is connected between a power source and a load, the power management circuit receives a supply voltage from the power source and provides an operation voltage to the load in response to an external control signal. The power management circuit has a feedback terminal, a sampling circuit samples the operation voltage to generate a sampling voltage and outputs the sampling voltage to the feedback terminal. The power management circuit adjusts the operation voltage according to the sampling voltage.
However, the adjustment of the power management circuit is limited, when the supply voltage is suddenly reduced, the operation voltage is also reduced. Therefore, the reduced operation voltage may not be enough to power the load.
Therefore, there is room for improvement in the art.
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
Firstly, we describe a first situation when the first power terminal 101 outputs the first supply voltage and the second power terminal 102 stops outputting the second supply voltage. The power management circuit 200 includes a first switch unit 22, a pulse width modulation (PWM) unit 24 having an input power terminal 240 and an output terminal 242, a storage unit 25, and a first sampling unit 26. The first switch unit 22 is capable of being turned on to establish a first electrical connection between the first power terminal 101 and the input power terminal 240 or being turned off to cut off the first electrical connection. In this embodiment, the first switch unit 22 is turned on or turned off in response to an external control signal.
The input power terminal 240 receives the first supply voltage from the first power terminal 101 when the first switch unit 22 is turned on, thus the pulse width modulation unit 24 is powered by the first supply voltage to generate a pulse voltage at the output terminal 242. The storage unit 25 is connected between the input power terminal 240 and the output terminal 242. The storage unit 25 receives the first supply voltage to store energy when the pulse voltage is in a first level, and releases energy to generate an operating voltage at the output terminal 242 when the pulse voltage is in a second level; the operating voltage powers the load 300.
In this embodiment, the first level is a low level, the second level is a high level; furthermore, when the pulse voltage is in the first level, the pulse voltage is zero volts, when the pulse voltage is in the second level, the pulse voltage is equal to the first supply voltage and the operating voltage is equal to two times the first supply voltage.
The first sampling unit 26 samples the operating voltage to generate a sampling voltage, the pulse width modulation unit 24 adjusts a duty cycle of the pulse voltage according to the sampling voltage. In detail, when the sampling voltage is larger than a threshold voltage, the pulse width modulation unit 24 decreases the duty cycle; when the sampling voltage is smaller than the threshold voltage, the pulse width modulation unit 24 increases the duty cycle. Therefore, the operating voltage keeps stable.
Secondly, we describe a second situation when the second power terminal 102 outputs the second supply voltage, the first power terminal 101 stops outputting the first supply voltage. The power management circuit 200 further includes a second switch unit 28, a voltage reduction unit 30, and a second sampling unit 32.
The second switch unit 28 is connected between the second power terminal 102 and the voltage reduction unit 30. The second switch unit 28 is capable of being turned on to establish a second electrical connection between the second power terminal 102 and the voltage reduction unit 30 or being turned off to cut off the second electrical connection. In this embodiment, the first switch unit 22 and second switch unit 28 are simultaneously turned on or turned off in response to the external control signal.
The voltage reduction unit 30 receives the second supply voltage from the second power terminal 102 through the second switch unit 28 when the second switch unit 28 is turned on, reduces the second supply voltage, and provides the reduced second supply voltage to the input power terminal 240 of the pulse width modulation unit 24 through the first switch unit 22 when the first switch unit 22 is turned on. The pulse width modulation unit 24 is powered by the reduced second supply voltage to generate the pulse voltage at the output terminal 242. Therefore, the storage unit 25 receives the reduced second supply voltage to store energy when the pulse voltage is in the first level, and releases energy to generate the operating voltage at the output terminal 242 when the pulse voltage is in the second level.
Second sampling unit 32 samples the reduced second supply voltage to generate a sampling signal, the voltage reduction unit 30 adjusts the reduced second supply voltage according to the sampling signal, therefore keeping the reduced second supply voltage stable.
Referring to
The source of the transistor Q1 receives the reduced second supply voltage from the voltage reduction unit 30 when the second switch unit 28 is turned on, the reduced second supply voltage is larger than the first supply voltage, thus the transistor Q1 is turned off and the first diode D1 is reverse-biased; therefore, the first power terminal 101 stops outputting the first supply voltage and the second power terminal 102 outputs the second supply voltage. When the second power supply 12 stops outputting the second supply voltage, the transistor Q1 is turned on and the first diode D1 is forward-biased, therefore the first power terminal 101 outputs the first supply voltage and the second power terminal 102 stops outputting the second supply voltage.
In this embodiment, the first power supply 10 is a battery, the second power supply 12 is an adaptor for converting an AC voltage (for example, 220 volts) to a DC voltage, the DC voltage is equal to the second supply voltage.
The storage unit 25 comprises an inductor L1, one end of the inductor L1 is connected to the input power terminal 240, and the other end of the inductor L1 is connected to the output terminal 242. In other embodiments, the storage unit 25 comprises a capacitor, one end of the capacitor is connected to the input power terminal 240, and the other end of the capacitor is connected to the output terminal 242.
In the electronic device 900, when the first supply voltage or the second supply voltage is suddenly increased, because the storage unit 25 stores energy when the pulse voltage is in the low level and release energy when the pulse voltage is in the high level, the operation voltage will still power the load 300.
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 disclosure should not be deemed to be limited to the above detailed description, but rather only by the claims that follow and the equivalents thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201210064645.2 | Mar 2012 | CN | national |
