BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a power supply apparatus according to the first embodiment of the present invention.
FIG. 2 illustrates the relation between the load current and the output voltage.
FIG. 3 illustrates a power supply apparatus according to the second embodiment of the present invention.
DETAILED DESCRIPTION
Certain terms are used throughout the description and following claims to refer to particular components. As one skilled in the art will appreciate, electronic equipment manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following description and in the claims, the terms “include” and “comprise” are used in an open-ended fashion, and thus should be interpreted to mean “include, but not limited to . . . ”. Also, the term “couple” is intended to mean either an indirect or direct electrical connection. Accordingly, if one device is coupled to another device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections.
Please refer to FIG. 1. FIG. 1 illustrates a power supply apparatus according to the first embodiment of the present invention. The power supply apparatus 100 includes a current modulation unit 110, a voltage converting unit 120, a current detector 130 and a control unit 140. The current modulation unit 110 receives the input voltage Vin and the control signal Sc from the control unit 140, and the current modulation unit 110 is controlled by the control signal Sc to adjust the amount of the current Ib. Practically, the control unit 140 generates a digital signal according to a clock signal, and the value of the digital signal increases gradually according to the frequency of the clock signal. The higher the frequency of the clock signal, the faster the value of the digital signal increases. The digital signal is converted into an analog current signal by a digital to analog converter (ADC). The analog current signal is the control signal Sc which controls the current modulation unit 110 to adjust the amount of the current Ib. The current modulation unit 110 increases the amount of the current Ib in accordance with the increase of the value of the digital signal. The voltage converting unit 120, which is coupled to the current modulation unit 110, is used for converting the output current Ib into an output voltage Vout. Practically, the voltage converting unit 120 is composed of at least one operation amplifier and at least one transistor. The output voltage Vout is transmitted to the output terminal of the power supply apparatus 100 via the current detector 130. The output terminal can be coupled to a load (not illustrated) to provide the desired voltage for the load, and the control unit 140 receives the output voltage Vout as well to monitor the value of the output voltage Vout. The current detector 130 detects the value of the current, which the power supply apparatus 100 provides to the load, and generates a current detection result Vs, which is a voltage signal, corresponding to the load current. As described above, since the output current Ib of the current modulation unit 110 keeps increasing, the output voltage Vout converted by the voltage converting unit 120 keeps increasing as well. In addition, when the load receives an increasing voltage, the load current increases accordingly, which results in an increase in the detection result Vs. The load current tends to be stable and does not increase when the load receives enough voltage and operates in a stable state. The control unit 140 determines when to stop increasing the value of the digital signal according to the detection result Vs and the output voltage Vout. More specifically, when the control unit 140 determines that the detection result Vs becomes stable and the output voltage Vout keeps increasing, the control unit 140 locks the value of the digital signal such that the current modulation unit 110 stops increasing the output current Ib, and thereby the voltage value of output voltage Vout is fixed.
The current detector 130 further has another function. The power supply apparatus 100 initially outputs a small voltage before any load is connected. Meanwhile, the current detector 130 detects the variation of the load current, and the control unit 140 compares the detection result Vs with a threshold value. When a load is connected to the power supply apparatus 100, there will be a change in the detection result Vs. Therefore, when the detection result Vs becomes larger than the threshold value, the control unit 140 resets the value of the digital signal and regenerates the digital signal. In brief, the power supply apparatus 100 starts to gradually increase the output voltage Vout provided to the load after the load is connected to the power supply apparatus 100. The increasing rate of the output voltage Vout can be determined according to the frequency of the clock signal of the control unit 140. The current detector 130 detects the load current flowing through the load when the output voltage Vout increases. The power supply apparatus 100 stops increasing the output voltage Vout and utilizes the present output voltage Vout as the output voltage when the load current stops increasing. Thereby the load can operate in a stable state. Please refer to FIG. 2, which shows the relation between the load current and the output voltage Vout. Vset is the stable output value of the power supply apparatus 100.
Please refer to FIG. 3. FIG. 3 illustrates a power supply apparatus according to a second embodiment of the present invention. The power supply apparatus 300 includes a current modulation unit 310, a voltage converting unit 320, a current detector 330, a determination circuit 340, a digital to analog converter (DAC) 350 and a digital control unit 360. The digital control unit 360 generates a multi-bit digital signal D (for example, 8-bit) according to a clock signal, and gradually increases the value of the digital signal D corresponding to the frequency of the clock signal. The digital to analog converter 350 converts the digital signal D into a control signal Sc, which can be an analog current signal. The current modulation unit 310 receives an input voltage Vin and is controlled by the control signal Sc to adjust the amount of the output current Ib. The larger the value of the digital signal D, the larger the output current Ib is. Next, the voltage converting unit 320 converts the output current Ib into the output voltage Vout, and the output voltage Vout is transmitted to the output terminal of the power supply apparatus 300 through the current detector 330. The output terminal can be coupled to a load (not illustrated), which is provided with the output voltage, and the output voltage Vout is transmitted to the determination circuit 340 as well. The current detector 330 is used for detecting the current flowing through the load and converting the load current into a current detection result Vs, which is a voltage signal and transmitted to the determination circuit 340. As described above, since the output current Ib increases in response to the increase of the value of the digital signal D, the output voltage Vout also increases in response to the increase of the value of the digital signal D. The load current increases when the load receives an increasing voltage, and the load current would stop increasing when the load operates in a stable state, in which the detection result Vs tends to be constant. The relation between the load current and the output voltage Vout is shown in FIG. 2. The determination circuit 340 determines the output voltage Vout and the detection result Vs. The determination circuit 340 generates a digital holding signal “hold” to inform the digital unit 360 to stop increasing the value of the digital signal D when the determination circuit 340 determines that the detection result Vs stop increasing and the voltage Vout keeps increasing. As a result, the value of the output voltage Vout can be fixed, which is the Vset shown in FIG. 2. In addition, the power supply apparatus 300 initially outputs a small voltage before any load is connected. Meanwhile, the current detector 330 detects the variation of the load current and the determination circuit 340 compares the detection result Vs with a threshold value. When a load is connected to the power supply apparatus 100, there will be a change in the detection result Vs. Therefore, when the detection result Vs becomes larger than the threshold value, the determination circuit 340 generates a digital starting signal “start” to indicate the digital control unit 360 to reset and then regenerate the digital signal D. In brief, the power supply apparatus 300 gradually and automatically increases the output voltage Vout provided to the load after the load is connected to the power supply apparatus 300. The current detector 330 detects the load current flowing through the load when the output voltage Vout is increasing. The power supply apparatus 300 stops increasing the output voltage Vout and utilizes the output voltage Vout at that time as the output value when the load current stops increasing. As a result, the load can operate in a stable state.
The present invention provides a power supply apparatus and a method for automatically providing a suitable voltage to a load. The apparatus and method can automatically generate suitable voltage corresponding to the load, and thereby only a single power supply apparatus is required for various kinds of loadings. There will be no need to manually switch the value of the output voltage; therefore, the problems in the prior art can be solved.
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.
Patent Application
20080001584
