Abstract:
Time-sharing technique is used for power conversion to improve the thermal dissipation thereof. In a power supply arrangement to provide a supply voltage to a load, a plurality of linear regulators are so switched that each time only one of them is enabled to convert an input voltage to the supply voltage, thereby each of them suffering less thermal dissipation.

Description:
FIELD OF THE INVENTION 
     The present invention is related generally to power conversion arrangement and method and, more particularly, to thermal dissipation improvement in an arrangement for power conversion. 
     BACKGROUND OF THE INVENTION 
       FIG. 1  shows a low dropout (LDO) regulator  10 , which is a linear regulator and is capable of converting an input voltage VIN to be a supply voltage VOUT if it is enabled by an enable signal ENABLE.  FIG. 2  shows a circuit diagram of a typical LDO regulator  10 , which comprises a transistor  14  connected between an input voltage VIN and the regulator output VOUT, two resistors R 1  and R 2  connected between the regulator output VOUT and ground GND to serve as a voltage divider to divide the supply voltage VOUT to generate a feedback voltage VFB, and an amplifier  12  to control the transistor  14  in response to the difference between the feedback voltage VFB and a reference voltage Vref, so as to maintain the supply voltage VOUT at a desired value. However, when the LDO regulator  10  operates in high current condition, due to its poor thermal dissipation, the LDO regulator  10  is usually operated with degraded performance, and even damaged. 
     To improve the over thermal condition,  FIG. 3  shows an ideal solution, which uses two common-output LDO regulators  20  and  22  to equally share the loading current I. Since each of the LDO regulators  20  and  22  operates with only half of the loading current I, the power dissipation is shared to them, and the thermal dissipation in each of them is reduced. In practice, however, even if the LDO regulators  20  and  22  are produced by the same manufacturing process or produced in the same batch, they may generate different output voltages. For example, 3V is the supply voltage VOUT the designer desires each of the LDO regulators  20  and  22  to generate, while actually, the LDO regulator  20  may generate a deviated one, for example 3V+1% or 3.03V, and the LDO regulator  22  may generate another one, for example 3V−1% or 2.97V. In this case, because the regulated voltage provided by the LDO regulator  22  is lower than that by the LDO regulator  20 , the LDO regulator  22  will not work when the power supply arrangement of  FIG. 3  operates, and as a result, the loading current I will be supplied by the LDO regulator  20  alone. Therefore, this approach will not really improve the thermal dissipation and the performance. 
     Therefore, it is desired a power supply arrangement and a control method thereof which really share the thermal dissipation by multiple linear regulators. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is directed to the thermal dissipation improvement of a power supply arrangement having multiple linear regulators. 
     According to the present invention, time-sharing technique is used for power conversion to improve the thermal dissipation thereof. Preferably, a power supply arrangement comprises a plurality of common-output linear regulators, and a time-sharing control scheme is employed in serial or parallel manner to enable the linear regulators in turn to convert an input voltage to a supply voltage. Preferably, a clock is used for the time-sharing control to enable the linear regulators. Since each time only one of the linear regulators is enabled for generate the regulated output voltage, the whole thermal dissipation for the power conversion is shared to the linear regulators, and each of the linear regulators suffers only a less thermal dissipation. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       These and other objects, features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  shows a LDO regulator; 
         FIG. 2  shows a circuit diagram of a typical LDO regulator; 
         FIG. 3  shows an ideal solution for thermal dissipation issue by using multiple LDO regulators; 
         FIG. 4  shows a first embodiment according to the present invention; 
         FIG. 5  shows a second embodiment according to the present invention; and 
         FIG. 6  shows a third embodiment according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in  FIG. 4 , a power supply arrangement  30  comprises two common-output LDO regulators  32  and  34 , each of which can individually convert the input voltage VIN to a supply voltage VOUT. However, a switch circuit  36  is further provided to enable the LDO regulators  32  and  34  with a clock CLK. The clock CLK is connected to the enable input EN of the LDO regulator  32  directly, and to the enable input EN of the LDO regulator  34  through an inverter  38 . When the clock CLK is logical high, the LDO regulator  32  is enabled by the clock CLK, and thus it converts the input voltage VIN to the supply voltage VOUT. In this phase, the LDO regulator  34  is disabled because of the inverter  38 . When the clock CLK changes to logical low, the low LDO regulator  32  is disenabled, and the LDO regulator  34  is enabled instead, to convert the input voltage VIN to the supply voltage VOUT. As such, each time only one of the LDO regulators  32  and  34  is enabled, and the LDO regulators  32  and  34  are switched by turns, the heat generated in the power supply arrangement  30  is shared by the LDO regulators  32  and  34 . Further, at any time only one of the LDO regulators  32  and  34  operates to supply the regulated voltage VOUT, so that there is no need to worry about the voltage generated by one of the LDO regulators  32  and  34  will be higher than that by the other one. 
       FIG. 5  shows a second embodiment according to the present invention. In a power supply arrangement  40 , a plurality of common-output LDO regulators  42  are alternatively switched by a switch circuit  44 . All the enable pins EN of the LDO regulators  42  are parallel connected to the switch circuit  44 , and the switch circuit  44  uses a time-sharing multiplexer  46  to switch between the LDO regulators  42  by turns. Each time only one of the LDO regulators  42  will be enabled to convert the input voltage VIN to the supply voltage VOUT, and therefore the heat generated in the power supply arrangement  40  is shared by the LDO regulators  42 , without causing any output deviation issue. 
     In a power supply arrangement  50  shown in  FIG. 6 , common-output LDO regulators  52 ,  54 ,  56  and  58  are connected in a ring, in such a manner that each of the LDO regulator  52 ,  54 ,  56  and  58  provides the enable signal for the next stage. When the first LDO regulator  52  is enabled, it converts the input voltage VIN to the supply voltage VOUT, and the other LDO regulators  54 ,  56  and  58  are disabled. After operating for a time period, the first LDO regulator  52  disables itself and provides an enable signal EN 1  to enable the second LDO regulator  54 . Similarly, after operating for a time period, the second LDO regulator  54  disables itself and provides an enable signal EN 2  to enable the third LDO regulator  56 , and then after operating for a time period, the third LDO regulator  56  disables itself and provides an enable signal EN 3  to enable the fourth LDO regulator  58 , and then after operating for a time period, the fourth LDO regulator  58  disables itself and provides an enable signal EN 4  to enable the first LDO regulator  52 . As such, each time only one of the LDO regulators  52 ,  54 ,  56  and  58  is enabled to convert the input voltage VIN to the supply voltage VOUT. In other embodiments, the switching between the LDO regulators  52 ,  54 ,  56  and  58  may be triggered by other parameters, such as temperature. For example, any of the LDO regulators  52 ,  54 ,  56  or  58  operates until it detects its temperature reaches a certain value, even though its operating time not so long to reach the threshold, it will disable itself and provide the enable signal to enable the next LDO regulator. 
     While the present invention has been described in conjunction with preferred embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and scope thereof as set forth in the appended claims.