Patent Publication Number: US-2003223253-A1

Title: Stable voltage converter with multiple pulse width modulated channels

Description:
FIELD OF THE INVENTION  
       [0001] The present invention relates to a power converter and especially to a stable voltage converter with multiple pulse width modulated channels.  
       [0002] BACKGROUND OF THE INVENTION  
       [0003] Since the power consumption of the central processing unit (CPU) of computers is increasing, direct current (DC) converters need to supply more than 60 amps of current for computer operation. Consequently, a multi-channel structure converter provides a more economical performance than a single channel converter. Among the multi-channel converters, the multi-channel pulse width modulated (PWM) converter having a current ripple scattering effect may choose the smaller and cheaper filter capacitor. Therefore, most of the paralleled multi-channel converters employ the structure of the multiple PWM converter channels.  
       [0004] A multi-channel converter connects in parallel a plurality of pulse width modulated channels with the same output voltage for providing a higher output current. There is often a voltage difference between the channels supplying the same load. The difference between the channels may occur one or some channels providing a comparatively higher current. In particular, some types of converters, synchronous rectified converters, have the ability to sink as well as source output current. In these converters, a great current may flow from one channel to another. This phenomenon can lead to excessive power dissipation, at which point these channels bear the highest power load. Thereafter, the supplying ability of working components in every channel must be increased and the load that the converter supplies must be limited below the combined full load capability of the individual channel. Therefor, the converter cost may increase and the working life thereof may be reduced for only a few channels working in the high temperature. Hence, a converter with the capability to share and balance the load current may be the better choice. Every channel provides the same current, that is to say, every channel bears the same load and has almost the same working life. The working life and cost problems are solved by sharing and balancing the load current.  
       [0005] As shown in FIG. 1, there is one kind of converter called the passive droop converter. This converter utilizes a plurality of independent PWM channels coupled with a plurality of resists respectively located on the output sides of the channels. The output current of every channel is reduced as the output current increases, whereupon every channel shares the output current equally. The passive droop converter with a simple control circuit increases additional power consumption and the total output voltage is reduced as the total output current increases. As the drawing depicts, error amplifier (E/A)  201   a ,  201   b ,  201   c  compares the V REF  and the voltage of position  205   a ,  205   b ,  205   c  and then outputs control signal to the pulse width modulator  202   a ,  202   b ,  202   c.  The pulse width modulator  202   a ,  202   b ,  202   c  controls the duty cycle of the power switch  203   a ,  203   b ,  203   c  to output pulse power output. The inductor  204   a ,  204   b ,  204   c  and the capacitor  208  filter the pulse power output to form a direct current output. The direct current output reduces the output voltage be proportional to the direct current output by the devoltage resister  206   a ,  206   b ,  206   c , and then outputs to the load  207 . The output voltage is more reduced if the output current is more increased, whereupon every channel shares the output current equally. The converter may balance every channel&#39;s output current but problems of additional power consumption and total output voltage reducing as the total output current increases still exist.  
       [0006] Another kind of converter is shown in the FIG. 2. The converter, called an active droop converter, is an improvement on the passive droop converter of FIG. 1. The converter senses the channel current signals of the converter channels and then adjusts a modified reference signal according to the deviation between the channel current signal and the reference voltage, V REF . Every channel may reduce the channel power output proportional to the channel current output, and therefore every channel may share the total output current equally. The active droop converter improves upon the passive droop converter to reduce the power consumption problem but the total output voltage still is reduced as the total output current increases. As the drawing depicts, the active droop converter with multiple converter channels utilizes the current sensors  306   a ,  306   b ,  306   c  to sense channel current signals of the channels and the subtraction circuits  301   a ,  301   b ,  301   c  compare the V REF  and the channel current signals to output modified reference signals to the E/As  302   a ,  302   b ,  302   c.  The E/As  302   a ,  302   b ,  302   c  compare the modified reference signals and the voltage output of the channel to form signals, V E/A . The pulse width modulators  303   a ,  303   b ,  303   c  adjust the duty cycle of the power switches  304   a ,  304   b ,  304   c  based on the signals V E/A  and a ramp input. Finally, the inductor  305   a ,  305   b ,  305   c  and the capacitor  309  filter the pulse power output to form the direct current output to the load  308 .  
       [0007] According to the above description, the multi-channel PWM converter in parallel reduces the total output voltage as the total output current increasing because of the reference signals be reduced. Therefore, a method for simplifying the control circuits of the converter with a stable total output voltage is needed in the paralleled multi-channel PWM converter.  
       SUMMARY OF THE INVENTION  
       [0008] The present invention provides a stable voltage and balanced current converter with multiple pulse width modulated channels.  
       [0009] The invention comprises a stable voltage converter including an error amplifier and a plurality of converter channels. The error amplifier has a reference voltage input and an average output voltage input. It compares the reference voltage and the average output voltage to generate an error signal. The plurality of converter channels couple with the error amplifier. Each converter channel includes a subtraction circuit, a pulse width modulator, a power switch, a filter and a current sensor. The subtraction circuit coupled with the error amplifier inputs the error signal and a channel current signal proportional to the direct current power output of the channel. Therefore, the subtraction circuit subtracts the channel current signal from the error signal and outputs a modified error signal. The pulse width modulator, having a ramp input and the modified error signal input and then to form a pulse width modulator signal output, couples with the subtraction circuit. The ramp input is coupled with a ramp voltage source. The power switch couples with the pulse width modulator, inputs the pulse width modulator signal and then outputs a pulse power output. The filter having an inductor and a capacitor couples with the power switch and filters the pulse power to generate the direct current power output. The current sensor detects the direct current power output of the channel and generates the channel current signal to the subtraction circuit. Therefore, each of the plurality of converter channels may automatically reduces the direct current power output thereof through a proportion of the direct current power output, and then the converter channels may balanced output current equally. The total output voltage may adjust according to the comparison result of the reference voltage and the total output voltage. Hence, the converter according to the invention may be a stable voltage and balanced current converter with multiple pulse width modulated channels. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0010] The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:  
     [0011]FIG. 1 is a circuit diagram of a passive droop converter with three PWM channels;  
     [0012]FIG. 2 is a circuit diagram of an active droop converter with three PWM channels; and  
     [0013]FIG. 3 is a circuit diagram of a converter with three PWM channels according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0014] The invention discloses a stable voltage converter with multiple pulse width modulated channels. The converter supplies a higher output current and simplifies and equally shares the current to every channel with a stable voltage output in different amounts of current output.  
     [0015]FIG. 3 is a circuit diagram of a converter with three PWM channels according to the invention. As the drawing depicts, the E/A  401  compares the V REF  and the output voltage of the converter and then outputs an error signal, V E/A . The V REF  is a reference voltage of the converter and is proportional to the requirement of output voltage of the converter. The error signal V E/A  increases while the output voltage of the converter is lower than the V REF . Conversely, the error signal V E/A  decreases while the output voltage of the converter is higher than the V REF . Then the V E/A  is an input of each converter channel to increase or decrease the duty cycle of the pulse width modulated channels  402   a ,  402   b ,  402   c.  Hence, the converter may adjust the output voltage getting higher as V REF  is higher than the output voltage and the converter may adjust the output voltage getting lower as V REF  is lower than the output voltage. Finally, the converter combines all the power outputs of the PWM channels  402   a ,  402   b  and  402   c  together and supplies them to the load  403 .  
     [0016] As the PWM channel  402   a  illustrates, each converter channel according to the invention includes a subtraction circuit  405 , a pulse width modulator  406 , a power switch  407 , an inductor  408  and a current sensor  409 . The subtraction circuit  405  compares the V E/A  and the channel current signal from the current sensor  409  and then generates a modified error signal, one input of the pulse width modulators  406 . The other input of the pulse width modulators  406  is a ramp input from a ramp voltage source. The pulse width modulators  406  compares the two input signal and adjusts the duty cycle thereof to control the duty cycle of the power switch  407 . Thereafter, the power switch  407  supplies a pulse power output and the filter circuit, the inductor  408  and the capacitor  410 , filters the pulse power output to a DC power output. In practice, the current sensor  409  may use a precision resistor or a turn-on resistor of the power switch  407 , a MOSFET switch, and a differential amplifier to measure the voltage drop of the two ends of the resistor. The voltage drop is proportional to the output current of the channel. One of ordinary skill in the art will realize various other implementations and applications with which such an inventive stable voltage converter may be employed.  
     [0017] The stable voltage converter with multiple pulse width modulated channels according to the invention utilizes a negative feedback loop to adjust the total output voltage to generate a stable output voltage in the converter with multiple pulse width modulated channels. The invention is an improvement upon the problem that the total output voltage is reduced as the total output current increases. Furthermore, the invention may turn on or turn off the converter channel dependent on the output current need because the invention utilizes a plurality of independent PWM converter channels without any correlative signal base on the channel quantity. That is to say, the invention may simply change the quantities of practical working channels and no circuit needs to be changed.  
     [0018] As is understood by a person skilled in the art, the foregoing preferred embodiments of the present invention are illustrative of the present invention rather than limiting of the present invention. It is intended that various modifications and similar arrangements be included within the spirit and scope of the appended claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structures.