Abstract:
The switching transistors in multiple switching regulators sharing the same input power source are coordinated to lower the peak current drain on the input power source. The turn on times of the transistors in each regulator are set so that each switching transistor turns on at a predetermined time in a cycle. The predetermined time for each regulator is chosen so that the maximum peak current drain on the input power source is minimized. The predetermined times may be changed on-the-fly by inputs to the system when information about current or projected output loads are known. The transistors in each regulator may also be turned on when the transistor in the previous regulator in a sequence turns off. Another embodiment lets the regulator with the largest change in input current over a cycle run independently. The other regulators then switch in a designated order, or at designated times after the first regulator turns its switch off.

Description:
CROSS REFERENCE 
     This application is a continuation of 09/437,669 filed on Nov. 10, 1999, now U.S. Pat. No. 6,265,855. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to switching power supplies and more particularly to systems with multiple switching regulators drawing current from the same input power source. 
     BACKGROUND OF THE INVENTION 
     Many electronic devices require multiple power supplies. For example, a device with both analog and digital circuits may require +5 volts for the digital logic, and +12 Volts, −12 volts for the analog circuitry. In battery powered devices, switching power supplies are a way to create these power supplies. 
     A switching power supply may function by having a controller switch a transistor at high frequency. This frequency is typically in the 20 kHz to 1 MHz range. This draws current from the input power source to produce a chopped intermediate voltage that is then filtered by an L-C (inductor-capacitor) circuit to produce a smoother output voltage. The output voltage is controlled by varying the on time to off-time ratio of the transistor. Unfortunately, if there are multiple regulators in the system, the switching transistors of these multiple regulators may switch on and off in phase. This switching in phase can causes multiple regulators to be drawing current at the same time, this increases the current drain on the input power source. In fact, with enough switching transistors switching in phase, the current drain on the input power source may increase to the point where regulation cannot be maintained. Due to the high series resistance of many types of batteries, battery powered devices are particularly susceptible to this condition. 
     Accordingly, there is a need in the art for a multiple voltage switching power supply controller that helps lower the peak current drain on the input power source. 
     SUMMARY OF THE INVENTION 
     The invention coordinates the current drawn by multiple switching regulators sharing a common input power source to lower the peak current drain on the input power source. Coordination of the current drawn can be implemented with simple logic, or can be adapted to a complicated algorithm that takes into account many different variables such as dynamic loading of different regulators or worst case scenarios. One embodiment sequences the turn-on, turn-off, or intermediate switching times of the switches in each regulator so that each regulator draws current at a predetermined time in a cycle. The predetermined time for each regulator is chosen so that the maximum peak current drain on the input power source is minimized. The predetermined times may be changed on-the-fly by inputs to the system when information about current or projected output loads are known. Another embodiment merely sequences the turn-on or turn-off times of the switches in each regulator so that each regulator starts drawing current when the previous regulator in the sequence stops drawing current. Another embodiment lets the regulator with the largest change in input current over a cycle run independently. The other regulators then draw current in a designated order or at designated times after the first regulator turn stops drawing current. 
     Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of multiple buck type switching regulators with the same input power source. 
     FIG. 2 is a schematic diagram of multiple boost type switching regulators with the same input power source. 
     FIG. 3A is plot of the typical input current waveform for a buck type switching regulator in continuous mode and discontinuous mode. 
     FIG. 3B is plot of the typical input current waveform for a boost type switching regulator in continuous mode and discontinuous mode. 
     FIG. 4A illustrates a sample set of control waveforms and input power source current for multiple buck switching regulators utilizing sequential switching of switching transistors. 
     FIG. 4B illustrates a sample set of control waveforms and input power source current for multiple boost switching regulators utilizing sequential switching of switching transistors. 
     FIG. 5 is a block diagram illustrating a control system that sequentially switches the switching transistors of multiple switching regulators. 
     FIG.  6 . illustrates a sample set of control waveforms for multiple switching regulators utilizing the simultaneous switching of two regulators sequentially after a first regulator. 
     FIG. 7 is a block diagram illustrating a control system that switches two switches sequentially after switching a first regulator. 
     FIG. 8 illustrates a sample set of control waveforms for multiple switching regulators switching transistors at predetermined times. 
     FIG. 9 is a block diagram illustrating a control system that switches on the switching transistors of multiple switching regulators at predetermined times. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a schematic diagram of multiple buck type switching regulators with the same input power source. FIG. 2 is a schematic diagram of multiple boost type switching regulators with the same input power source. These types of regulators were chosen for exemplary purposes only. It should be understood that this invention is applicable to other types of switching regulators known to those of ordinary skill in the art. Furthermore, the type of switch in these regulators is shown as an N-channel MOSFET. This is also only for exemplary purposes and other types of switching devices know to those skilled in the art could be used. 
     In FIG. 1, the input voltage to the multiple regulators  1010 ,  1020 , and  1030  is V i . The aggregate input current into the multiple regulators is I i . Input current into the first regulator  1010  is I i1 . The input current into the second regulator  1020  is I i2  and so on, such that the input current into the third regulator  1030  is I i3 . 
     In FIG. 1, first regulator  1010  is shown comprising switching transistor S 1 ,  1012 , diode  1014 , inductor L 1 ,  105 , and filter capacitor C 1   1016 . First regulator  1010  is shown as producing output voltage V 1  into load LOAD 1   1018 . Switching transistor S 1  is shown as an N-type enhancement MOSFET with its drain connected to V i , its body and source connected to the cathode of diode  1014 , and its gate connected to control voltage V g1 . The anode of diode  1014  is shown being connected to the reference node of V i , gnd. The cathode of diode  1014 , source and body of S 1 , are also connected a first terminal of inductor L 1 ,  1015 . The second terminal of L 1 ,  1015 , is connected to a first terminal of filter capacitor C 1 ,  1016 . The second terminal of filter capacitor C 1 ,  1016  is shown connected to gnd. The load on the first regulator LOAD  1 ,  1018  is shown connected in parallel with filter capacitor C 1   1016 . 
     Second regulator  1020  is shown with the same circuit design as first regulator  1010 . Second regulator  1020  is shown comprising switching transistor S 2 ,  1022 , diode  1024 , inductor L 2 ,  1025 , and filter capacitor C 2   1026 . Second regulator  1020  is shown as producing output voltage V 2  into load LOAD 2   1028 . Switching transistor S 2  is shown as an N-type enhancement MOSFET with its drain connected to V i , its body and source connected to the cathode of diode  1024 , and its gate connected to control voltage V g2 . The anode of diode  1024  is shown being connected to the reference node of V i , gnd. The cathode of diode  1024 , source and body of S 2 , are also connected a first terminal of inductor L 2 ,  1025 . The second terminal of L 2 ,  1025 , is connected to a first terminal of filter capacitor C 2 ,  1026 . The second terminal of filter capacitor C 2 ,  1026  is shown connected to gnd. The load on the first regulator LOAD 2 ,  1028  is shown connected in parallel with filter capacitor C 2   1026 . 
     Third regulator  1030  is shown with the same circuit design as first regulator  1010  and second regulator  1020 . Third regulator  1030  is shown comprising switching transistor S 3 ,  1032 , diode  1034 , inductor L 3 ,  1035 , and filter capacitor C 3   1036 . Second regulator  1030  is shown as producing output voltage V 3  into load LOAD 3   1038 . Switching transistor S 3  is shown as an N-type enhancement MOSFET with its drain connected to V i , its body and source connected to the cathode of diode  1034 , and its gate connected to control voltage V g3 . The anode of diode  1034  is shown being connected to the reference node of V i , gnd. The cathode of diode  1034 , source and body of S 3 , are also connected a first terminal of inductor L 3 ,  1035 . The second terminal of L 3 ,  1035 , is connected to a first terminal of filter capacitor C 3 ,  1036 . The second terminal of filter capacitor C 3 ,  1036  is shown connected to gnd. The load on the first regulator LOAD 3 ,  1038  is shown connected in parallel with filter capacitor C 3   1036 . 
     Although only three are shown, multiple regulators  1010 ,  1020 , and  1030  are intended to represent an arbitrary number of supply voltages generated from a single input power source. In addition, the basic design of these supplies is a buck regulator type design. However, it should be understood that the principles of this invention are not limited to this particular type of regulator and that the principles of this invention could also be used with boost type, or buck-boost type, or a combination of switching regulator types. 
     In FIG. 2, the input voltage to the multiple regulators  2010 ,  2020 , and  2030  is V i . The aggregate input current into the multiple regulators is I i . Input current into the first regulator  2010  is I i1 . The input current into the second regulator  2020  is I i2  and so on, such that the input current into the third regulator  2030  is I i . 
     In FIG. 2, first regulator  2010  is shown comprising switching transistor S 1 ,  2014 , diode  2015 , inductor L 1 ,  2012 , and filter capacitor C 1   2016 . First regulator  2010  is shown as producing output voltage V 1  into load LOAD 1   2018 . Inductor L 1   2012  is shown connected between V i  and the drain of switching transistor S 1   2014 . Switching transistor S 1  is shown as an N-type enhancement MOSFET with its body and source connected to the reference node of V i , gnd, and its gate connected to control voltage V g1 . The anode of diode  2015  is connected to the drain of switching transistor S 1   2014 . The cathode of diode  2015  is connected a first terminal of filter capacitor C 1   2016 . The second terminal of C 1   2016  is connected to gnd. The load on the first regulator LOAD  1 ,  2018  is shown connected in parallel with filter capacitor C 1   2016 . 
     In FIG. 2, second regulator  2020  is shown comprising switching transistor S 2 ,  2024 , diode  2025 , inductor L 2 ,  2022 , and filter capacitor C 2   2026 . Second regulator  2020  is shown as producing output voltage V 2  into load LOAD 2   2028 . Inductor L 2   2022  is shown connected between V i  and the drain of switching transistor S 2   2024 . Switching transistor S 2  is shown as an N-type enhancement MOSFET with its body and source connected to the reference node of V i , gnd, and its gate connected to control voltage V g2 . The anode of diode  2025  is connected to the drain of switching transistor S 2   2024 . The cathode of diode  2025  is connected a first terminal of filter capacitor C 2   2026 . The second terminal of C 2   2026  is connected to gnd. The load on the first regulator LOAD 2 ,  2028  is shown connected in parallel with filter capacitor C 2   2026 . 
     In FIG. 3, third regulator  2030  is shown comprising switching transistor S 3 ,  2034 , diode  2035 , inductor L 3 ,  2032 , and filter capacitor C 3   2036 . Second regulator  2030  is shown as producing output voltage V 3  into load LOAD 3   2038 . Inductor L 3   2032  is shown connected between V i  and the drain of switching transistor S 3   2034 . Switching transistor S 3  is shown as an N-type enhancement MOSFET with its body and source connected to the reference node of V i , gnd, and its gate connected to control voltage V g3 . The anode of diode  2035  is connected to the drain of switching transistor S 3   2034 . The cathode of diode  2035  is connected a first terminal of filter capacitor C 3   2036 . The second terminal of C 3   2036  is connected to gnd. The load on the first regulator LOAD 3 ,  2038  is shown connected in parallel with filter capacitor C 3   2036 . 
     FIG. 3A is a plot of the typical input current waveforms for a buck type switching regulator in continuous mode and discontinuous mode. FIG. 3B is plot of the typical input current waveforms for a boost type switching regulator in continuous mode and discontinuous mode. Note that these current waveforms come to a peak before declining. When the current peaks of multiple regulators drawing from the same input power source coincide roughly in time a large input current peak occurs. This invention helps prevent that condition so that the overall peak input current is reduced. 
     FIG. 4A illustrates an example set of control signals and current waveforms for sequential switching of transistors in multiple buck regulators. Signal CLOCK is a periodic waveform that sets triggers the switching of the first regulator in the sequence. That regulator is controlled by V g1 . Note that V g1  rises turning on the switching transistor in the first regulator when CLOCK falls. When V g1  falls switching off the switching transistor in the first regulator, Vg 2  rises turning on the switching transistor in the second regulator in the sequence. Then when V g2  falls switching off the switching transistor in the second regulator, V g3  rises turning on the switching transistor in the third regulator in the sequence. After that, V g3  falls turning off the switching transistor in the third regulator. The falling edge of signal CLOCK starts the sequence again. 
     Also shown on FIG. 4A are example input currents (I i1 , I i2 , I i3 ) for each of the three power supplies when controlled by sequenced control signals described above and shown in FIG.  4 A. The sum of these input currents is the total input current load on the input power source, I i . Note that the sequenced switching of the transistors in the three supplies in this example reduces the total current load when compared to the situation where all three switching transistors are switched so that all three supplies reach their peak current at about the same time. 
     In FIG. 4A, the control signals of all the power supplies are shown to switch off the transistors in all those power supplies before a new cycle starts with the falling edge of CLOCK. However, this is not required. For supplies that have dynamic loads, the length of time that each switching transistor of each regulator may be set according to an error signal derived from the output voltage of that regulator. The system may not operate with optimally low peak input current depending on the dynamic loading, but regulation should be maintained as long as the signal to switch off the transistor in a particular regulator occurs before or nearly the same time as the signal to switch on that particular transistor occurs again. Furthermore, arranging the sequence that supplies from the largest input anticipated current load to the smallest will help reduce the peak input current even when there are two or more switching transistors in different supplies on at the same time. 
     FIG. 4B illustrates an example set of control signals and current waveforms for sequential switching of transistors in multiple boost regulators. Signal CLOCK is a periodic waveform that sets triggers the switching of the first regulator in the sequence. That regulator is controlled by V g1 . Note that V g1  rises turning on the switching transistor in the first regulator when CLOCK falls. When V g1  falls switching off the switching transistor in the first regulator, Vg 2  rises turning on the switching transistor in the second regulator in the sequence. Then when V g2  falls switching off the switching transistor in the second regulator, V g3  rises turning on the switching transistor in the third regulator in the sequence. After that, V g3  falls turning off the switching transistor in the third regulator. The falling edge of signal CLOCK starts the sequence again. 
     Also shown on FIG. 4B are example input currents (I i1 , I i2 , I i3 ) for each of the three power supplies when controlled by sequenced control signals described above and shown in FIG.  4 B. The sum of these input currents is the total input current load on the input power source, I i . Note that the sequenced switching of the transistors in the three supplies in this example reduces the total current load when compared to the situation where all three switching transistors are switched so that all three supplies reach their peak current at about the same time. 
     In FIG. 4B, the control signals of all the power supplies are shown to switch off the transistors in all those power supplies before a new cycle starts with the falling edge of CLOCK. However, this is not required. For supplies that have dynamic loads, the length of time that each switching transistor of each regulator may be set according to an error signal derived from the output voltage of that regulator. The system may not operate with optimally low peak input current depending on the dynamic loading, but regulation should be maintained as long as the signal to switch off the transistor in a particular regulator occurs before or nearly the same time as the signal to switch on that particular transistor occurs again. Furthermore, arranging the sequence that supplies from the largest input anticipated current load to the smallest will help reduce the peak input current even when there are two or more switching transistors in different supplies on at the same time. 
     FIG. 5 illustrates a block diagram of a system that sequentially switches the transistors in multiple supplies. Clock generator  5002  sends a signal (CLOCK) to pulse width modulation (PWM) generator  5004  that turns on the switching transistor of the first regulator in the sequence via signal V g1 . The length of time that V g1  remains active keeping the switching transistor of the first regulator in the sequence on depends on a signal from error generator  5010 . The signal from error generator  5010  depends on the output voltage of the first regulator in the sequence. When this control system is used with three supplies as shown in FIG. 1, this would be V 1  for regulator  1010 . When this control system is used with three supplies as shown in FIG. 2, this would be V 1  for regulator  2010 . When the switching transistor of the first regulator in the sequence is turned off via signal V g1 , PWM generator  5006  turns on the switching transistor of the second regulator in the sequence via signal V g2 . The length of time that V g2  remains active keeping the switching transistor of the second regulator in the sequence on depends on a signal from error generator  5012 . The signal from error generator  5012  depends on the output voltage of the second regulator in the sequence. When this control system is used with three supplies as shown in FIG. 1, this would be V 2  for regulator  1020 . When this control system is used with three supplies as shown in FIG. 2, this would be V 2  for regulator  2020 . When the switching transistor of the second regulator in the sequence is turned off via signal V g2 , PWM generator  5008  turns on the switching transistor of the third regulator in the sequence via signal V g3 . The length of time that V g3  remains active keeping the switching transistor of the third regulator in the sequence on depends on a signal from error generator  5014 . The signal from error generator  5014  depends on the output voltage of the third regulator in the sequence. When this control system is used with three supplies as shown in FIG. 1, this would be V 3  for regulator  1030 . When this control system is used with three supplies as shown in FIG. 2, this would be V 3  for regulator  2030 . 
     FIG.  6 . illustrates the control waveforms for multiple switching regulators utilizing the simultaneous switching of two regulators sequentially after a first regulator. In FIG. 6, signal CLOCK is a periodic waveform that sets triggers the switching of the first regulator in the sequence. That regulator is controlled by V g1 . Note that V g1  rises turning on the switching transistor in the first regulator when CLOCK falls. When V g1  falls switching off the switching transistor in the first regulator, Vg 2  and V g3  rise turning on the switching transistors in the second and third power supplies. V g2  and V g3  then fall independent of each other switching off the switching transistors in the second and third power supplies. The falling edge of signal CLOCK starts the sequence again. 
     Simultaneous turning on the switching transistors in two or more regulators allows a faster cycle time for signal CLOCK. This is particularly useful when two of the regulators are known, or expected, to have low input power source current when compared to other supplies. These two regulators may then be switched on at the same time to allow for a faster cycle time for signal CLOCK without greatly affecting the peak total input power source current. In addition, in another embodiment, instead of switching two supplies on simultaneously, a fixed delay may be introduced from the switching on of the transistor in one regulator, to the switching on of the transistor in another. This may be useful when the input current to two regulators are thought to roughly track each other, but one is expected to mostly be larger than the other. 
     FIG. 7 is a block diagram illustrating a control system that switches two switches sequentially after switching a first regulator. Clock generator  7002  sends a signal (CLOCK) to pulse width modulation (PWM) generator  7004  that turns on the switching transistor of the first regulator in the sequence via signal V g1 . The length of time that V g1  remains active keeping the switching transistor of the first regulator in the sequence on depends on a signal from error generator  7010 . The signal from error generator  7010  depends on the output voltage of the first regulator in the sequence. When this control system is used with three regulators as shown in FIG. 1, this would be V 1  for regulator  1010 . When this control system is used with three regulators as shown in FIG. 2, this would be V 1  for regulator  2010 . When the switching transistor of the first regulator in the sequence is turned off via signal V g1 , PWM generator  7006  turns on the switching transistor of the second regulator in the sequence via signal V g2 . The length of time that V g2  remains active keeping the switching transistor of the second regulator in the sequence on depends on a signal from error generator  7012 . The signal from error generator  7012  depends on the output voltage of the second regulator in the sequence. When this control system is used with three regulators as shown in FIG. 1, this would be V 2  for regulator  1020 . When this control system is used with three regulators as shown in FIG. 2, this would be V 2  for regulator  2020 . Also when the switching transistor of the first regulator in the sequence is turned off via signal V g1 , PWM generator  7008  turns on the switching transistor of the third regulator in the sequence via signal V g3  after an optional time delay  7016 . If no time delay is wanted, PWM generator  7008  turns on the switching transistor of the third regulator in the sequence via signal V g3  at the same time that PWM generator  7006  turns on the switching transistor of the second regulator via signal V g2 . The length of time that V g3  remains active keeping the switching transistor of the third regulator in the sequence on depends on a signal from error generator  7014 . The signal from error generator  7014  depends on the output voltage of the third regulator in the sequence. When this control system is used with three regulators as shown in FIG. 1, this would be V 3  for regulator  1030 . When this control system is used with three regulators as shown in FIG. 2, this would be V 3  for regulator  2030 . 
     FIG. 8 illustrates control waveforms for multiple switching regulators that turn on switching transistors at predetermined times. Signal CLOCK is a periodic waveform that is used as the timebase for turning on the switching transistors in the multiple supplies. Signal FIRST is a signal that when active shows which cycle of CLOCK marks the beginning of a new switching cycle. In FIG. 8, the switching transistor in the first regulator is turned on via V g1  rising during the first cycle of CLOCK. The switching transistor in the second regulator is turned on via V g2  rising during the second cycle of CLOCK. The switching transistor in the third regulator is turned on via V g3  rising during the forth cycle of CLOCK. Each of the control signals V g1 , V g2 , and V g3  fall independently. The falling edge of signal CLOCK starts the sequence again. The activation of signal FIRST starts a new switching cycle. 
     FIG. 9 is a block diagram illustrating a control system that can switch on switching transistors of multiple switching regulators at predetermined times. Clock generator  9002  produces signal CLOCK that provides a periodic waveform that is used as the timebase for the system. CLOCK is input to rollover counter  9004 . Rollover counter  9004  takes the input pulses of clock and produces a digital output that is a count of those pulses. At a predetermined count, the rollover counter resets its output to a first count number and activates signal FIRST until another pulse is received on CLOCK. This produces a cyclic sequence on the outputs of rollover counter  9004 . In FIG. 8, this would be 1,2,3,4,5,1,2 . . . with FIRST being produced during the “1” part of the sequence. 
     The count output of rollover counter is input to comparators  9006 ,  9008 , and  9010 . Each of these comparators produces a signal when its input matches a predetermined number. If FIG. 8 is used as an example, then comparator  9006  would produce a signal when its input was 1, comparator  9008  would produce a signal when its input was 2, and comparator  9010  would produce a signal when its inputs was 4. 
     The signal generated by comparator  9006  triggers pulse width modulation (PWM) generator  9006  to turn on the switching transistor of a first regulator via signal V g1 . The length of time that V g1  remains active keeping the switching transistor of that regulator on depends on a signal from error generator  9014 . The signal from error generator  9014  depends on the output voltage of that regulator. When this control system is used with three supplies as shown in FIG. 1, this output voltage would be V 1  for regulator  1010 . When this control system is used with three supplies as shown in FIG. 2, this output voltage would be V 1  for regulator  2010 . 
     The signal generated by comparator  9008  triggers pulse width modulation (PWM) generator  9016  to turn on the switching transistor of a second regulator via signal V g2 . The length of time that V g2  remains active keeping the switching transistor of that regulator on depends on a signal from error generator  9018 . The signal from error generator  9018  depends on the output voltage of that regulator. When this control system is used with three regulators as shown in FIG. 1, this output voltage would be V 2  for regulator  1020 . When this control system is used with three regulators as shown in FIG. 2, this output voltage would be V 2  for regulator  2020 . 
     The signal generated by comparator  9010  triggers pulse width modulation (PWM) generator  9020  to turn on the switching transistor of a third regulator via signal V g3 . The length of time that V g3  remains active keeping the switching transistor of that regulator on depends on a signal from error generator  9022 . The signal from error generator  9022  depends on the output voltage of that regulator. When this control system is used with three regulators as shown in FIG. 1, this output voltage would be V 2  for regulator  1020 . When this control system is used with three regulators as shown in FIG. 2, this output voltage would be V 2  for regulator  2020 . 
     One way to choose the predetermined times to switch on the switching transistors of the multiple supplies is to choose the times that will result in the minimum peak input power source current. If the maximum input currents to each regulator for each load situation are known or estimated, the length of each control (V g1 , V g2 , etc.) pulse can be determined. This information, the input voltage, and the design of each regulator give enough data to determine the input current waveform for each regulator in a given load situation. These input current waveforms can then be used to determine when to start each control pulse so that the peak input power source current is minimized. 
     In FIGS. 4-9, the CLOCK signal is shown as having a constant period. However, a variable period clock may be used in any of these. This variable period (or frequency) clock may be derived in response to changing loads on the multiple power supplies, or some other control system variables. In addition, these systems have been shown as block diagrams of discrete blocks, it should be understood that any of these systems could be implemented using a microcontroller, other processor, or custom integrated circuit. Any of these systems may also take into account more variables than is shown when arranging, or timing, control pulses. For example, a microcontroller may know that it is about to perform a number of functions that require a great deal of power on a certain voltage supply. Before performing those operations, the microcontroller may rearrange, or change the timing of, the control pulses so that when these functions are performed, the peak input power source current will be minimized when that regulator begins to pull greater input current. 
     Although several specific embodiments of the invention have been described and illustrated, the invention is not to be limited to the specific forms or arrangements of parts so described and illustrated. The invention is limited only by the claims.