Power supply apparatus to selectively output one of a plurality of input powers

A power supplying apparatus supplying power to a predetermined system unit is provided with a power selecting unit which is directly connected to the system part, to select one of a plurality of inputs of power and output a selected power to the system unit; and a controller which is provided outside a power supplying path between the power selecting unit and the system unit, to control the power selecting unit to selectively output the power selected by the power selecting unit to the system unit according to a power switching signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. §119 from Korean Patent Application No. 2006-84872, filed on Sep. 4, 2006, in the Korean Intellectual Property Office the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power supply apparatus, and more particularly, to a power supply apparatus capable of selecting and supplying power from one of a plurality of inputs.

2. Related Art

An electric apparatus, such as a mobile printer, a notebook personal computer (PC) or other mobile device, may include a power supply apparatus comprising an adapter to convert an external power and a battery provided inside thereof, and a device to properly select or control between the power provided from the adapter (hereinafter, referred to as “adapter power”) and the power provided from the battery (hereinafter, referred to as “battery power”) based on a current state of the electric apparatus.

FIG. 1illustrates a typical electric apparatus. As shown inFIG. 1, such an electric apparatus10comprises a power selecting unit11, a power switching unit12and a system unit13. The system unit13comprises actual components of every configuration, except for a configuration connected to power, for example, a printing engine (not shown), a user interface (not shown) and so on. The power selecting unit11selects between the adapter power Va and the battery power Vb according to the condition, and supplies the selected power to the power switching unit12. The power switching unit12then transmits the selected power Vx from the power selecting unit11to the system unit13according to a system power on/off signal (hereinafter, referred to as “power switching signal”) which is inputted by a user. Herein, the power selecting unit11and the power switching unit12can be referred to as a power supplying apparatus.

In the conventional power supplying apparatus, the power switching unit12is provided at an output terminal of the power selecting unit11to directly control a system power Vin which is the main power. In addition, multiple high-cost field-effect transistors (FETs) and a separated control device are required for a high-power application. As a result, the conventional power supplying apparatus can be large and expensive.

Specifically, FETs are incorporated into the power selecting unit11as well as the power switching unit12. In the situation where the power selecting unit11and the power switching unit12are combined, a plurality of FETs are connected in series so that a value of voltage can be dropped by each circuit element. Therefore, a voltage value of the system power Vin (hereinafter, referred to as “input voltage level”) may not be in the range which is needed in the system unit13because of the voltage drop. However, if the FETs having a low resistance value are used for a high-power application to ensure that the input voltage level is at a level needed in the system unit13, the production cost can be very high. Furthermore, if the input voltage level is at the level needed in the system unit13, the range of usable voltage in the battery power Vb (for example, generally it is between 3V and 4.2V) becomes more narrow such that the battery power Vb cannot be sufficiently used. As a result, the life of the battery can be shortened.

SUMMARY OF THE INVENTION

Several aspects and example embodiments of the present invention provide a power supply apparatus which is capable of reducing a cost and a size thereof when selecting and supplying a selected power from of a plurality of power sources, and which makes a voltage drop by a circuit element minimal.

In accordance with an example embodiment of the present invention, a power supplying apparatus for supplying power to a predetermined system unit is provided with a power selecting unit which is directly connected to the system part, to select one of a plurality of inputs of power and output a selected power to the system unit; and a controller which is provided outside a power supplying path between the power selecting unit and the system unit, to control the power selecting unit to selectively output the selected power to the system unit according to a power switching signal.

According to an aspect of the present invention, the plurality of inputs of power comprises an adapter power and a battery power.

According to an aspect of the present invention, the power selecting unit selects one which has a higher input voltage between the adapter power and the battery power.

According to another aspect of the present invention, the power selecting unit further comprises a first comparator and a second comparator which compare voltages of the adapter power and voltage of the battery power, respectively, and output signals having opposite logic states each other according to the comparing result, respectively; and a first switching part and a second switching part which selectively output the adapter power and the battery power according to the outputs of the first and the second comparators to the system part.

According to an aspect of the present invention, the outputs of the first and the second comparators are open-collector inputs, and the controller comprises at least one switching transistor selectively supplying a pull-up voltage to output terminals of the first and the second comparators according to the power switching signal.

According to an aspect of the present invention, the power selecting unit further comprises a division resistor dividing voltage of at least one of the adapter power and the battery power.

According to an aspect of the present invention, the first and the second switching parts respectively comprise an MOSFET.

According to an aspect of the present invention, the power selecting unit comprises a first transistor and a second transistor respectively operating the first switching part and the second switching part according to the outputs of the first comparator and the second comparator.

According to another aspect of the present invention, a first diode and a second diode are further provided to supply one of the adapter power and the battery power to the first comparator and the second comparator.

According to an aspect of the present invention, the power selecting unit further comprises a division resistor dividing voltage of at least one of the adapter power and the battery power.

According to another aspect of the present invention, the power selecting unit further comprises a first transistor and a second transistor respectively operating the first switching part and the second switching part according to the outputs of the first comparator and the second comparator.

In addition to the example embodiments and aspects as described above, further aspects and embodiments will be apparent by reference to the drawings and by study of the following descriptions.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 2is a block diagram illustrating an electric apparatus100according to an embodiment of the present invention. Such an electric apparatus100can be a mobile printer, a notebook PC, and other portable devices. The electric apparatus100is also provided with an adapter (not shown) to convert power from an external power source, such as AC power, into DC power serving as usable system power, and a battery (not shown) provided inside to supply battery power.

As shown inFIG. 2, the electric apparatus100comprises a system unit110including on one or more system components arranged to receive an operating power and to perform a main operation, such as printing driven by such an operating power. The electric apparatus100further comprises a power supply apparatus200including a power selecting unit120and a controller130arranged to supply a system power Vin as an operating power to the system unit110. The power supplying apparatus200can be provided inside of the electric apparatus100or can be detachably provided outside of the electric apparatus100. The system unit110has an input voltage terminal provided with the system power Vin having the input voltage level, so as to operate one or more system components included therein. Herein, the input voltage level has a predetermined permissible range. As a result, if a voltage drop in the power selecting unit120is within the predetermined permissible range, the system unit110can be operated without any problem.

The power selecting unit120is directly connected to an input voltage terminal of the system unit110in order to supply the system power Vin to the system unit110. The power selecting unit120selects between an adapter power Va and a battery power Vb, and outputs a selected power as the system power Vin. According to an example embodiment of the present invention, the power selecting unit120selects between the adapter power Va and the battery power Vb according to a condition; however, such a condition is not necessary. In addition, the voltage drop of the circuit element in the power selecting unit120should be minimized so that the voltage level of the system power Vin can be within a predetermined permissible range of the input voltage level.

The controller130controls the power selecting unit120to selectively supply the system power Vin to the system unit110according to an external power switching signal. The controller130is provided outside a power supply path of the system power Vin between the power selecting unit120and the system unit110, to generate a control signal Vc and supply the control signal Vc to the power selecting unit120. Herein, the control signal Vc is used to determine whether the system power Vin is supplied to the system unit110. This way, the controller130does not switch the system power Vin ON/OFF directly such that simple circuitry can be utilized in place of high-power FETs for power switching operations. As a result, the cost and the size of the electric apparatus100can be advantageously reduced.

Turning now toFIG. 3, a detailed circuit diagram of a power supply apparatus according to an example embodiment of the present invention is illustrated. Referring toFIG. 3, the power selecting unit120outputs one, which has a higher voltage value between the adapter power Va and the battery power Vb, as the system power Vin. For example, if one of the adapter power Va and the battery power Vb is inputted to the power selecting unit120, the power selecting unit120outputs an input power as the system power Vin. However, if both of the adapter power Va and the battery power Vb are inputted to the power selecting unit120, the power selecting unit120outputs one, which has a higher voltage value between the adapter power Va and the battery power Vb, as the system power Vin. For example, if a voltage value of the adapter power Va is 5 volts (5V), and a voltage value of the battery power Vb is 4.2 volts (4.2V), and if both of the adapter power Va and the battery power Vb are inputted to the power selecting unit120, the adapter power Va of 5 volts is selected for output. Accordingly, power consumption of the battery is minimized.

As shown inFIG. 3, the power selecting unit120comprises a first switching part112a, a second switching part112b, a first comparator121aand a second comparator121b. If the adapter power Va is inputted to the first switching part112a, the first switching part112aselectively outputs the adapter power Va as the system power Vin according to an output of the first comparator121a. However, if the battery power Vb is inputted to the second switching part112b, the second switching part112bselectively outputs the battery power Vb as the system power Vin according to an output of the second comparator121b.

The first switching part112aand the second switching part112brespectively comprise metal-oxide-semiconductor field-effect transistors (MOSFETs). Generally, the voltage drop of the MOSFET is characteristically very little though the value of current of the MOSFET is high, when the MOSFET is turned ON so that the voltage drop of the first switching part112aand the second switching part112bis within a predetermined permissible range of the input voltage level of the system unit110. Accordingly, the voltage drop of the adapter power Va and the battery power Vb can be advantageously minimized. According to an example embodiment of the present invention, the first switching part112aand the second switching part112bare P-type MOSFETs. The first switching part112aand the second switching part112brespectively comprise sources (S) through which the adapter power Va or the battery power Vb is inputted and drains (D) which are output terminals of the system power Vin.

The first and the second comparators121aand121brespectively output a first voltage signal V1showing which has a higher voltage level between the adapter power Va and the battery power Vb, and a second voltage signal V2having an opposite logic state to the first voltage signal V1. The circuits of the first and the second comparators121aand121bare respectively simple, and power consumption can be minimized because these simple circuits consume little power.

The first comparator121aoutputs the first voltage signal V1whose logic state is “high” if the voltage value of the adapter power Va is higher than the voltage value of the battery power Vb, and whose logic state is “low” if the voltage value of the adapter power Va is lower than the voltage value of the battery power Vb. Likewise, the second comparator121boutputs the second voltage signal V2whose logic state is “high” if the voltage value of the battery power Vb is higher than the voltage value of the adapter power Va, and whose logic state is “low” if the voltage value of the battery power Vb is lower than the voltage value of the adapter power Va. In any case, the logic state of the first voltage signal V1and the second voltage signal V2are always opposite.

The outputs of the first comparator121aand the second comparator121bare preferably open-collector outputs. In other words, the first comparator121aand the second comparator121boutput the first voltage signal V1and the second voltage signal V2only when a predetermined pull-up voltage is input to an output terminals (referring to V1and V2) thereof. If the pull-up voltage is not input to the first comparator121aand the second comparator121b, the first comparator121aand the second comparator121bdo not output signals. The pull-up voltage may be input as a control signal Vc by the controller130.

The power selecting unit120may further comprise first division resistors122aand123aand second division resistors122band123bwhich divide the voltage of the adapter power Va and the battery power Vb, and output the divided voltage to the first comparator121aand the second comparator121b. The value of the first division resistors122aand123aand the value of the second division resistors122band123bmay be equal. According to another embodiment of the present invention, the value of the first division resistors122aand123aand the value of the second division resistors122band123bcan be properly set so that the differences of the voltages across the first division resistors122aand123aand the second division resistors122band123b, respectively become large. Accordingly, the battery power Vb can be prevented from being selected unintentionally because the battery power Vb gets higher than the adapter power Va according to an error. Specifically, the value of the first division resistor123ais large or the value of the second division resistor123bis small. However, the values of these division resistors are not limited thereto.

The first comparator121aand the second comparator121breceive an operating power Vd which is supplied through a first diode141aand a second diode141b. The first diode141aand the second diode141bhave anodes which are respectively connected to the adapter power Va and the battery power Vb. The cathodes of the first diode141aand the second diode141bare connected to each other and the operating power Vd is outputted from the cathodes thereof. In other words, the input one of the adapter power Va and the battery power Vb is outputted as the operating power Vd. Because a voltage drop occurs in the first diode141aand the second diode141b, the first comparator121aand the second comparator121bpreferably have an input voltage level range which is capable of sufficiently compensating for the voltage drop. For example, a predetermined permissible range of the input voltage level of the first comparator121aand the second comparator121bmay be between 2 volts (2V) and 18 volts (18V).

The power selecting unit120may further comprise a first transistor113aand a second transistor113bwhich operate the first switching part112aand the second switching part112baccording to the output of the first comparator121aand the second comparator121b. The first transistor113aand the second transistor113bare preferred to respectively comprise bipolar transistors of NPN types. Also, the power selecting unit120may further comprise third division resistors125aand126aand fourth division resistors125band126bwhich properly divide the voltage of the first controlling signal V1and the second controlling signal V2for a base current of the first transistor113aand the second transistor113b.

Furthermore, the power selecting unit120may comprise protecting resistors114aand114bwhich respectively connect the respective sources (S) of the first and the second switching parts112aand112bto the respective gates (G) thereof so as to prevent the first and the second switching parts112aand112bfrom making an error due to noise.

The power selecting unit120operates as follows. First of all, at least one of the adapter (or external power) and the battery is first connected to the power selecting unit120, the operating power Vd is supplied to the first comparator121aand the second comparator121b, and the first comparator121aand the second comparator121bstart to operate. If the adapter power Va is input and the battery power Vb is not input thereto, the voltage value of the adapter power Va is higher than the voltage value of the battery power Vb. Accordingly, if the pull-up voltage (referring to Vc) is supplied, the first comparator121aoutputs the first voltage signal V1having a “high” logic state, and the second comparator121boutputs the second voltage signal V2having a “low” logic state which is opposite to the first comparator121a.

According to the first voltage signal V1having the “high” logic state, the first transistor113ais turned ON and the gate (G) of the first switching part112ais grounded. The voltage difference between the gate (G) and the source (S) of the first switching part112asatisfies a turn ON condition of the MOSFET (for example, the voltage difference between the gate (G) and the source (S) is larger than 3V so that the first switching part112ais turned ON. In this case, the system power Vin has an almost equal voltage value to the adapter power Va.

If the second voltage signal V2has a “low” logic state, the second transistor113bis turned OFF. In this case, the voltage difference between the gate (G) and the source (S) of the second switching part112bdo not satisfy the turn ON condition of the MOSFET so that the second switching part112bis turned OFF.

If the adapter power Va is not input and the battery power Vb is input thereto, the system power Vin has an almost equal value to the battery power Vb. If both of the adapter power Va and the battery power Vb are input thereto, the adapter power Va is higher than the battery power Vb so that the system power Vin has an almost equal voltage value to the adapter power Va.

Meanwhile, referring back toFIG. 3, the controller130is provided with a first switching transistor131and a second switching transistor132which selectively supply the pull-up voltage (referring to Vc) to the output terminals (referring to V1and V2) of the first comparator121aand the second comparator121baccording to a power switching signal input from the outside. In addition, the controller130is further provided with first to fourth resistors133to136, a first pull-up resistor128a, and a second pull-up resistor128b.

The first switching transistor131is preferably an NPN-type bipolar transistor, and the second switching transistor132is preferably a PNP-type bipolar transistor. The power switching signal is input to a base of the first switching transistor131through the first resistor133, and an emitter of the first switching transistor131is grounded. One terminal of the second resistor134is connected to the base of the first switching transistor131and the other terminal of the second resistor134is grounded. The collector of the first switching transistor131is connected to a base of the second switching transistor132through the third resistor135. An emitter of the second switching transistor132is connected to the cathodes of the first diode141aand the second diode141b, and a collector of the second switching transistor132is connected to one terminal of the first pull-up resistor128aand one terminal of the second pull-up resistor128b. One terminal of the fourth resistor136is connected to the base of the second switching transistor132and the other terminal thereof is connected to the emitter of the second switching transistor132. The other terminals of the first pull-up resistor128aand the second pull-up resistor128bare respectively connected to the output terminals (referring to V1and V2) of the first comparator121aand the second comparator121b.

The controller130operates as follows. Referring toFIGS. 2 and 3, the electric apparatus100preferably comprises a power switch150which a user uses to turn power ON and OFF, and a detecting circuit140to generate a power switching signal after detecting the state of the power switch150. First of all, when the power switch150is turned OFF by a user, the power switching signal having a “low” logic state is input to the controller130so that the first switching transistor131and the second switching transistor132are turned OFF. Accordingly, the control signal Vc becomes low and the pull-up voltage is not input to the first comparator121aand the second comparator121b. Therefore, the first comparator121aand the second comparator121bare not able to output signals. Consequently, the system power Vin is not supplied to the system unit110even if at least one of the adapter power Va and the battery power Vb is input.

If the power switch150is turned ON by a user, the controller130receives the power switching signal having a “high” logic state. In this case, if at least one of the adapter power Va and the battery power Vb is input, the first switching transistor131and the second switching transistor132are turned ON. Accordingly, the control signal Vc becomes high and the pull-up voltage are input to the first comparator121aand the second comparator121b. Therefore, the first comparator121aand the second comparator121boutput signals and one of the input adapter power Va and battery power Vb is supplied to the system unit110as the system power Vin.

As described above, the present invention provides a power supply apparatus which can be cost-effective (i.e., lower production cost), smaller in size, and effective for enabling a user to select and output a selected one of a plurality of power sources. In other words, when the power supply apparatus selects and outputs one among the power, the controlling circuit does not directly switch the system power Vin, and switches output of the power selecting unit120. Therefore, the power supply apparatus200is capable of reducing the cost and size thereof. Furthermore, because the controller is provided outside a power supplying path of the system power Vin, the voltage drop and power consumption of circuit elements can be minimized, and the life of the battery can be extended as usable voltage when sufficiently used.

While there have been illustrated and described what are considered to be example embodiments of the present invention, it will be understood by those skilled in the art and as technology develops that various changes and modifications, may be made, and equivalents may be substituted for elements thereof without departing from the true scope of the present invention. Many modifications, permutations, additions and sub-combinations may be made to adapt the teachings of the present invention to a particular situation without departing from the scope thereof. For example, the controller130and the power selecting unit120, as shown inFIG. 3, can be constructed using different circuit elements, including simple transistors, diodes and resistors. Accordingly, it is intended, therefore, that the present invention not be limited to the various example embodiments disclosed, but that the present invention includes all embodiments falling within the scope of the appended claims.