# Patent

## Title
Voltage regulator with internal controls for adjusting output based on feed-forward load information

## Abstract

Methods and apparatus for controlling a voltage supplied to a device based on an anticipated change in load current demanded by the device are provided. In response to detecting the anticipated change in load current, a load control signal may be generated that causes the voltage regulator to adjust the output voltage supplied to the device.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is related to co-pending U.S. patent application Ser. No. 10/189,223 entitled, “ADVANCED VOLTAGE REGULATION USING ANTICIPATORY LOAD INFORMATION”, filed herewith.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to computer systems and more specifically to an apparatus and method for adjusting operation of a voltage regulator in anticipation of a change in load.
2. Description of the Related Art
In a typical computer system, one or more voltage regulators provide supply voltages to various system components. For example, a first voltage regulator on a motherboard may provide a supply voltage to a central processing unit (CPU) while a second voltage regulator on a graphics card may provide a supply voltage to a graphics processing unit (GPU). Unfortunately, as operating frequencies increase, voltage regulators may struggle to supply enough current when such processing devices rapidly demand additional current.
This may be illustrated by considering the exemplary graphics processing subsystem shown in FIG. 1, in which a voltage regulator 100 provides a supply voltage (VOUT) to a GPU 110. The GPU 110 may utilize a number of high speed processing pipelines operating in parallel to produce high end (realistic) graphical output. When these pipelines are not being heavily used, the current demand of a GPU may be relatively stable. However, when several of these pipelines are loaded up for processing, the resultant switching (of potentially several hundred million transistors) may cause a current demand several times greater than what is demanded when the pipelines are not as heavily loaded.
As illustrated in FIG. 2, a sudden increase in current when the GPU pipelines are heavily loaded (at time T0) may result in a transient drop (spike) in supply voltage, as the current supplied by an output capacitor (or set of capacitors) CO is depleted. As illustrated in FIG. 1, voltage regulators may utilize some type of feedback mechanism, such as a feedback circuit 120 that samples the output voltage and provides a voltage or current feedback signal to the regulator 100. By monitoring this feedback signal and detecting the voltage drop, the regulator can compensate for the drop in voltage by increasing its output, for example, by generating an error signal and using it to increase the duty cycle of a pulse-width-modulated PWM signal used to drive a switching transistor. As a result, after a recovery time (labeled TR0) which may be several milliseconds, the output voltage may recover to at least approach the previous level.
Similarly, when the pipelines are unloaded (at time T1), a sudden decrease in current load may result in a upward transient spike. For some cases, the peak-to-peak magnitude of the transient may be even greater upon release of the load than when the load is increased. In any case, the feedback mechanism may ensure that after a recovery time (labeled TR1) the output voltage may recover to at least approach the previous level.
If these transient voltage spikes cause the supply voltage level to fall below a minimum threshold or exceed a maximum threshold, the GPU may fail, regardless of how quickly the previous voltage level is restored. Unfortunately, by the time the regulator 100 is able to detect the transient voltage changes based on the feedback signal, the output voltage may have changed too much to allow the regulator 100 to adequately compensate. In some cases, the peak-to-peak magnitude of the transient voltage spikes may be controlled with careful selection of components in the regulator circuit. For example, output capacitors CO (typically dominated by rather large “bulk” capacitors) used in the regulator circuit may be chosen with an effective series resistance (ESR) that minimizes peak-to-peak transient magnitudes, while still providing an adequate recovery time. Unfortunately, the size and/or cost penalty of such capacitors tends to be prohibitive.
Accordingly, what is needed is an improved method and apparatus for regulating voltage supplied to integrated circuit devices, such as processing devices (CPUs and GPUs) that exhibit large abrupt changes in current demand.
SUMMARY OF THE INVENTION
Embodiments of the present invention generally provide methods and apparatus for controlling a voltage supplied to a device based on an anticipated change of load current demanded by the device.
One embodiment provides a method of controlling an output voltage provided to a device by a voltage regulator. The method generally includes receiving, by the voltage regulator, a load control signal indicating an anticipated change in load current required by the device and directly controlling a driver circuit of the voltage regulator used to generate the output voltage based on the load control signal.
Another embodiment provides a voltage regulator including a drive circuit and a control circuit. The voltage regulator includes at least one input pad to receive a load control signal indicating an anticipated change in load current required by the device. The control circuit is generally configured to control the drive circuit to alter the output voltage based on the load control signal.
Another embodiment provides a computer system generally including a voltage regulator and a processor device that is supplied an output voltage by the voltage regulator. A control circuit is included, internal to the voltage regulator, to alter the output voltage based on a load control signal indicating an anticipated change in load current required by the processor device.



BRIEF DESCRIPTION OF THE DRAWINGS
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
FIG. 1 illustrates an exemplary graphics subsystem with a voltage regulator providing a supply voltage to a graphics processing unit (GPU) in accordance with the prior art;
FIG. 2 illustrates an exemplary current load induced transient voltage response of the voltage regulator of FIG. 1 in accordance with the prior art;
FIG. 3 illustrates an exemplary graphics subsystem with a voltage regulator providing a supply voltage to a graphics processing unit (GPU) in accordance with embodiments of the present invention;
FIG. 4 illustrates an exemplary current load induced transient voltage response of the voltage regulator of FIG. 1 utilizing a load line feature of a voltage regulator in accordance with embodiments of the present invention;
FIG. 5 is a flowchart of exemplary operations for controlling a voltage regulator in accordance with one embodiment of the present invention;
FIG. 6 illustrates an exemplary circuit arrangement for controlling a voltage regulator by artificially adjusting a feedback voltage based on a load control signal;
FIG. 7 illustrates an exemplary circuit arrangement for controlling a voltage regulator by artificially adjusting a feedback current based on a load control signal;
FIG. 8 illustrates an exemplary graphics subsystem with a voltage regulator with internal controls to receive a load control signal from a graphics processing unit (GPU) in accordance with embodiments of the present invention;
FIGS. 9A-9B illustrate an exemplary voltage regulators with internal controls to directly effect a voltage adjust circuit based on a load control signal; and
FIGS. 10A-10B illustrate exemplary voltage regulators with internal controls to directly effect a voltage adjust circuit based on a conditioned and/or scaled load control signal.



DETAILED DESCRIPTION
Embodiments of the present invention provide a mechanism allowing a voltage regulator to adjust its output voltage in anticipation of a change in load. The voltage regulator provides a supply voltage to a device which, therefore, represents a load driven by the voltage regulator. The device, in turn, provides a load signal in anticipation of a change in load (e.g., caused by the utilization of a greater or lesser number of components on the device). In other words, the load signal may provide an “early warning signal” of sorts, causing the voltage regulator to adjust the supply voltage provided to the device to minimize the impact of transient voltage spikes caused by the change in load. As a result, the effective transient voltage response of the voltage regulator may improved, while the size and cost of components in the regulator circuitry (e.g., load capacitors) may be reduced.
As a specific, but not limiting example, one embodiment of the present invention provides a graphics processing unit (GPU) that adjusts a load signal in anticipation of a change in load, for example, based on an expected change in utilization of a number of parallel processing pipelines. However, those skilled in the art will recognize that the concepts described herein may be used to similar advantage in a variety of different devices, such as central processing units (CPUs) digital signal processors (DSPs), and the like, to reduce the impact of voltage transients caused by abrupt changes in load.
An Exemplary System
FIG. 3 illustrates an exemplary voltage regulator 300 that provides a supply voltage (VOUT) to a GPU 320 that generates an anticipatory load signal 312. As illustrated, for some embodiments, the load signal 312 may be used to control feedback circuitry 320 that generates a feedback signal monitored by the voltage regulator 300 and used to adjust the voltage regulator output power to maintain a desired output voltage VOUT.
As previously described, the GPU 310 may utilize a number of high speed processing pipelines operating in parallel. When several of these pipelines are loaded up for processing, after being idle, the resultant load increase may cause current demand several times greater than what is demanded when the pipelines are not as heavily loaded. With several hundred million transistors in the pipelines, the increase in current may be well over 100%. As previously described, with reference to FIGS. 1 and 2, in conventional systems, such an abrupt change in load may result in transient voltage spikes that might cause operational failures if the supply voltage levels fall outside operational limits. In addition, voltage overshoots caused when current demand is abruptly reduced may lead to reduced reliability.
As explained in greater detail herein, by generating the load signal in anticipation of such a change in load, the GPU 310 may provide an early warning signal of sorts, causing the voltage regulator 300 to adjust the supply voltage to compensate. For example, as illustrated in FIG. 4, at time T0′, prior to an expected sudden increase in current when the GPU pipelines are heavily loaded (at time T0), the load signal may cause VOUT to be adjusted upward (by ΔVU). As a result, when the load current increases, at time T0, the transient dip in voltage does cause the voltage to drop as low as it would have without the shift up. The anticipatory increase in voltage may result in additional current being available from the output capacitor, allowing it to better handle the increase in load. Similarly, prior to unloading the pipelines, at time T1′, the load signal may be changed, causing VOUT to be adjusted downward (by ΔVD). As a result, when the load current decreases, at time T1, the transient increase in voltage is not as great as it would have been absent the anticipatory shift down in the regulator output voltage.
For comparison, in FIG. 4 the transient swings in supply voltage signal without the anticipatory shifts before loading and unloading, are shown as dashed lines. In some cases, the peak-to-peak magnitude of the transients may be the same with and without use of the load signal. However, the absolute minimum voltage level reached is shifted up by increasing the supply voltage in anticipation of the loading, while the absolute maximum voltage level reached is shifted down by decreasing the supply voltage in anticipation of the unloading. In addition to providing a safety margin from the minimum and maximum values, by decreasing the total deviation from the nominal operating voltage, the response times required to recover from the loading and unloading (TR0′ and TR1′, respectively) are decreased. While this technique works with regulators that utilize load line (or droop) functionality, other regulators may utilize different circuitry responsive to a load signal. Further, even if the load signal is generated with little or no advanced warning relative to an increase in demand current, the load signal may result in faster regulator response time than the output voltage propagating through all the capacitors. In some cases, the load signal could even come after a load change and there may still be an advantage in quicker regulator response time.
FIG. 5 is a flowchart of exemplary operations for controlling a voltage regulator in accordance with one embodiment of the present invention. For example, these operations may be performed, for example, by the GPU 310 in order to adjust the load signal 312 to provide an early warning to the voltage regulator 300 of expected changes in load current. For some embodiments, an external device, such as a CPU that sends instructions or data to a GPU via a software driver, may detect an anticipated change in load current demanded by the GPU and may generate the load control signal instead of the GPU.
The operations begin, at step 502, by detecting an expected change in load current. As an example, the GPU 310 may monitor a number of idle cycles for a sample set of pipelines as an indication that the pipelines are being loaded. As another example, a set of instructions (e.g., a shader program), executed by the GPU 310 may contain markers that provide an indication to the GPU 310 that heavy pipeline activity, or a reduction in pipeline activity, is likely.
In any case, if a change in load is not expected, as determined at step 504, the operations are repeated without adjusting the load signal. On the other hand, if a change is load is expected, the load signal is adjusted, at step 506, thereby causing the a corresponding anticipatory change in the voltage supplied by the voltage regulator. As will be described in greater detail below, the load signal may be a single bit (e.g., driven on a singly output pin) or multiple bits. A single bit output signal will allow a device to indicate more or less current is to be required. Multiple bits, on the other hand, may allow quantification of the additional current expected (e.g., 25%, 50%, etc.), allowing the anticipatory increases or decreases in voltage supplied by the regulator to be adjusted accordingly.
Exemplary Mechanisms for Adjusting Output Voltage Based on a Load Signal
For some embodiments, feedback circuitry external to the voltage regulator may be configured to allow adjustment of a feedback signal provided to the voltage regulator in response to a change in an anticipatory load signal provided by a processing device. The exact circuitry may vary depending on the exact type of feedback signal utilized by the voltage regulator.
As an example, FIG. 6 illustrates a feedback circuit 620 configured to vary a feedback voltage (VFB) provided to a voltage regulator 600. As illustrated, the load signal is used to switch a transistor NL in order to vary the resistance of a voltage divider circuit (formed by RA, RB, and RL, depending on the load signal) used to generate the feedback voltage. When the load signal is not asserted (logic low or ‘0’), the transistor NL is switched off and the feedback voltage is defined by the following equation based on the voltage divider:

VFB=VOUT*[RB/(RA+RB)]

Once the load signal is asserted (logic high or ‘1’), indicating an expected increase in current demand, the transistor NL is switched on and the bottom portion of the voltage divider network becomes RL in parallel with RB (RB∥RL). As a result, the feedback voltage is defined by the following equation based on the voltage divider:

VFB=VOUT*[RB∥RL/(RA+RB∥RL)]

Because the parallel combination of RB and RL is less than RB alone, the feedback voltage is reduced which should cause the voltage regulator 600 to increase its output and raise VOUT. As illustrated, the regulator 600 may include an error amplifier 602 that generates an offset or “error” voltage VERROR indicating a difference between the feedback voltage and a reference voltage. The error voltage may be fed back to a voltage adjust circuit 604 that increases the output voltage if the feedback voltage is less than the reference or decreases the output voltage if the feedback voltage is greater than the reference voltage.

For embodiments where a multi-bit load signal is generated, multiple load resistors may be selectively placed in parallel to incrementally adjust the feedback voltage, as necessary. For some embodiments, the load signal may be used to adjust the reference voltage in a similar manner, which may have a similar effect. For example, increasing VREF when the load signal is asserted would also result in an increase in VERROR and a corresponding increase in VOUT.
As another example of how the load signal may be used to adjust the output voltage of a regulator, FIG. 7 illustrates a feedback circuit 720 configured to vary a feedback current (IFB) provided to a voltage regulator 700. As illustrated, the load signal may be used to control a current boost circuit 722. For example, the boost circuit 722 may be configured to generate an additional current IL that is used to increase the feedback current IFB when the load signal is asserted. In response, a load line adjust circuit 702 of the regulator 700 may generate a signal to a voltage adjust circuit 704 to increase the output voltage based on a comparison of the feedback current to a reference current (IREF). When the load signal is not asserted, the additional current may be removed (IL=0), causing a corresponding reduction in VOUT.
Those skilled in the art will recognize that various other types of feedback mechanisms may also be used and such mechanisms may be configured to allow the feedback signal provided thereby to be varied in any manner appropriate based on a load signal generated by a processor device.
Exemplary Voltage Regulators with Internal Controls for Adjusting Output Based on an Anticipatory Load Signal
For some embodiments, a voltage regulator may be provided with internal control circuitry to vary the regulator output in response to a change in an anticipatory load signal provided by a processing device. In some cases, such internal control circuitry may provide faster response times than conventional feedback mechanisms manipulated by the load control signal, as discussed above. In other words, while the embodiments described above may be used to achieve substantial improvement in performance of conventional voltage regulators, regulators with internal controls that allow a more direct path to adjust regulator output based on the load control signal may provide even greater improvements.
For example, FIG. 8 illustrates an exemplary voltage regulator 800 with internal controls 802 configured to control a driver circuit 806 of a voltage adjust circuit 804. As illustrated, the voltage adjust circuit 804 may still receive a feedback voltage signal (VFB) indicating the actual output voltage, and adjust the output accordingly. For some applications, the response time of changes due to such feedback may not be fast enough, particularly applications with rapidly changing load current demands. The response time of conventional feedback paths may be affected by bandwidth limitations of components in the feedback path, such as error amplifiers, comparators, and the like.
However, the internal controls 802 may, in effect bypass the conventional feedback path and provide a much faster response time by directly affecting the driver circuit 806. For some embodiments, internal controls 802 may work in conjunction with a conventional feedback mechanism. For example, the normal feedback mechanism may serve to and provide stability in situations with relatively normal changes in load current demands, while the internal controls 802 allows regulator output to be rapidly adjusted when a large change in load current demand is anticipated. Exactly how the internal controls 802 control the driver circuit 806 will depend on the mechanism used by the driver circuit 806.
For example, as illustrated in FIG. 9A, for some embodiments, a voltage regulator may provide direct external access to a relatively late stage in the conventional feedback path. In such cases, the internal controls 902 may scale and condition the load control signal (as described in greater detail below) to generate a supplemental error signal. This supplemental error signal may be superimposed onto a conventional error signal generated based on the feedback voltage (VFB) to generate an adjusted error signal (VERROR′) provided to the drive circuit 906. By effectively bypassing the error amplifier 911, the adjusted error signal may be rapidly manipulated, thereby achieving a faster overall response time.
For other embodiments, the driver circuit 806 may include a pulse width modulation (PWM) circuit 908 configured to vary the duty cycle of one or more pulse width modulated signals used to switch an output field effect transistor (FET) 909, as illustrated in FIG. 9B. In such an embodiment, internal controls 902 may be configured to generate control signals to directly affect the PWM circuit 908 based on the anticipatory load control signal.
For example, if the anticipatory load control signal received by the internal controls 902 indicates a sudden increase in load current demand is anticipated, the internal controls 902 may generate PWM control signals to cause the PWM circuit 908 to immediately increase the duty cycle of the PWM output signals to increase the regulator output. The PWM control signals may include a set of clock or “phase” signals that are out of phase with respect to one another. To compensate for an anticipated increase in load current demand, all phases may be “turned on” (e.g., full duty cycle) to temporarily increase regulator output. Conversely, if the load control signal indicates a sudden decrease in load current demand is anticipated, the internal controls 902 may generate PWM control signals to cause the PWM circuit 908 to immediately decrease the duty cycle of the PWM output signals to decrease the regulator output.
As described above, a single bit load control signal may allow the voltage regulator to simply increase or decrease regulator output, while multiple bits may allow quantification of the additional current expected (e.g., 25%, 50%, etc.), allowing the anticipatory increases or decreases in voltage supplied by the regulator to be adjusted accordingly. In either case, the internal controls may include signal conditioning designed to receive the load control signal and generate the necessary type control signals (e.g., PWM phase signals) to cause the drive circuit to adjust the regulator output as accordingly.
In some cases, an even greater degree of flexibility in regulator may be achieved by providing a scaling mechanism, wherein the magnitude of the changes in regulator output caused by the load control signal may be controlled. In other words, such scaling may allow the same regulator to be configured to increase/decrease the regulator output voltage over a relatively wide range (e.g., 1.5V to 3.3 V), with the particular range selected depending on the needs of a particular application. This may provide an advantage from an inventory perspective, as a single such regulator may be stocked rather than multiple regulators. Further, increases in volume may also be achieved, which may lead to reduced cost.
As illustrated in FIG. 10A, for some embodiments, a scale/adjust signal may be externally controlled. For example, a scaling resistor 1005 may be connected across external pads 1007 of a regulator 1000. The value of the scaling resistor 1005 may determine the value of the scale/adjust signal. Signal conditioning circuitry 1003 may receive this scale/adjust signal and condition the load control signal accordingly. For example, to attain a maximum scale, the resistor 1005 may be selected such that changes in the load control signal result in the maximum allowable changes in regulator output. As an example, a minimum value for resistor 1005 may be selected such that incremental changes in the load control signal result in a 5% change in regulator output, while a maximum value for resistor 1005 may be selected such that incremental changes in the load control signal result in a 25% change in regulator output.
As illustrated in FIG. 10B, for some embodiments, a programmable scale/adjust register 1009 may be provided for similar scalability. In other words, the signal conditioning circuit 1003 may read one or more bits in the scale/adjust register 1009 to determine how to condition the load control signal, as described above. The register may be programmable by an external device (e.g., a CPU or GPU) via any suitable type serial or parallel interface. For some embodiments, a CPU or GPU may program this register during a start up (e.g., boot) routine.
For some embodiments, such a register 1009 may also be used to enable/disable use of the internal controls 1002 to alter regulator output based on the load control signal. For example, single bit may be set to enable/disable the effect of the load control signal. A default setting of the bit may be to disable the effect of the load control signal, for example, until a processor device writes to the register 1009 to enable use of the internal controls 1002. For some embodiments, similar scalability may be provided by non-volatile storage means, such as one or more electrically programmable fuses that may be blown under external control.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

## Claims

1. A method of controlling an output voltage provided to a processing device that includes multiple processing pipelines by a voltage regulator, comprising:
receiving, by the voltage regulator, a feedback error signal for controlling the output voltage of the voltage regulator;
receiving a load control signal indicating an anticipated change in load current required by the device; and
directly controlling a driver circuit of the voltage regulator used to generate the output voltage based on the load control signal by modifying the feedback error signal to provide an anticipatory change in the voltage to the device, whereby an absolute minimum voltage level is shifted up in anticipation of an increased load on the processing pipelines and an absolute maximum voltage level is shifted down in anticipation of an unloading of one or more of the multiple processing pipelines, thereby minimizing a total deviation of the output voltage from a nominal output voltage.

2. The method of claim 1, wherein directly controlling the driver circuit comprises:
changing the duty cycle of a pulse width modulated (PWM) output signal used to control a switching transistor based on the load control signal and the feedback error signal, thereby changing the output current available from an output capacitor of the voltage regulator and allowing the voltage regulator to better handle a change in load in the multiple processing pipelines.

3. The method of claim 1, further comprising:
receiving the load control signal including a scaling signal that is adjustable externally to the voltage regulator; and
wherein the load control signal is conditioned based on the scaling signal.

4. The method of claim 3, wherein the scaling signal is adjustable via a plurality of external resistors placed in parallel and selectively utilized to modify the feedback error signal to provide the anticipatory voltage change.

5. The method of claim 3, wherein the scaling signal is adjustable via a writable register of the voltage regulator.

6. The method of claim 5, wherein the load control signal comprises a plurality of bits loaded into the writeable register.

7. A voltage regulator configured to provide an output voltage to a multi-pipeline processing device, comprising:
a drive circuit to alter the output voltage provided to a device;
a first input pad to receive a feedback error signal for controlling the output voltage;
the first input pad receiving a load control signal indicating an anticipated change in load current required by the multiprocessing device due to a change in loading one or more of the pipelines; and
a control circuit configured to control the drive circuit to alter the output voltage based on a modification of the feedback error signal by the load control signal, whereby an absolute minimum voltage level is shifted up in anticipation of an increased load on the processing pipelines and an absolute maximum voltage level is shifted down in anticipation of an unloading of one or more of the multiple processing pipelines, thereby minimizing a total deviation of the output voltage from a nominal output voltage.

8. The voltage regulator of claim 7, wherein:
the drive circuit comprises a switching transistor controlled by a pulse width modulated signal; and
the control circuit is configured to vary the duty cycle of the pulse width modulated signal in response to the feedback error signal and the load control signal, thereby changing the output current available from an output capacitor of the voltage regulator and allowing the voltage regulator to better handle a change in load in the multiple processing pipelines.

9. The voltage regulator of claim 7, further comprising:
a signal conditioning circuit for generating a conditioned control signal based on the load control signal; and
wherein drive circuit is controlled by the conditioned control signal based on the load control signal and the feedback error signal.

10. The voltage regulator of claim 9, wherein the signal conditioning circuit receives a scaling signal that determines a magnitude of the conditioned control signal.

11. The voltage regulator of claim 10, wherein the signal conditioning circuit includes an input for receiving the scaling signal.

12. A computer system, comprising:
a voltage regulator including a drive circuit configured to alter an output voltage produced by the voltage regulator based on a feedback error signal generated in response to a feedback voltage indicative of the output voltage;
a processor device that includes multiple pipelines operating in parallel that is supplied the output voltage by the voltage regulator; and
internal to the voltage regulator, a control circuit configured to control the output voltage, based on a load control signal indicating an anticipated change in load current required by the processor device, by superimposing the load control signal onto the feedback error signal prior to the anticipated change in load current, whereby an absolute minimum voltage level is shifted up in anticipation of an increased load on the processing pipelines and an absolute maximum voltage level is shifted down in anticipation of an unloading of one or more of the multiple processing pipelines, thereby minimizing a total deviation of the output voltage from a nominal output voltage.

13. The system of claim 12, wherein the processor device is a graphics processing unit (GPU).

14. The system of claim 12, wherein:
the voltage regulator comprises a configuration register; and
the processor device is configured to write to the configuration register to configure use of the control circuit.

15. The system of claim 12, wherein:
the drive circuit comprises a switching transistor controlled by a pulse width modulated signal; and
the control circuit is configured to vary the duty cycle of the pulse width modulated signal based on the load control signal.