Patent Grant
7554309
The present invention is related to voltage regulators. More particularly, the present invention is related to circuits, systems and methods for maintaining voltage regulators at a desired loading condition.
A prior art regulated system 100 is depicted in
Overall load 140 includes a drive load 132 and a dummy load 136. Dummy load 136 is a resistive load, and is included to assure that voltage regulator 110 is always supplying at least some load. By maintaining at least some loading on voltage regulator 110, operational amplifier 112 is maintained in a desired range of operation and regulated voltage 120 is maintained relatively constant. However, maintaining minimum loading through use of dummy load 136 is wasteful. In particular, dummy load 136 is always drawing current from voltage regulator 110 which is dissipated as heat. Both the heat and the wasted current are undesirable.
Hence, for at least the aforementioned reasons, there exists a need in the art for advanced circuits, systems and methods for regulating voltages.
The present invention is related to voltage regulators. More particularly, the present invention is related to circuits, systems and methods for maintaining voltage regulators at a desired loading condition.
Various embodiments of the present invention provide circuits for regulator minimum load control. The circuits include a load control circuit and a switched load. The load control circuit includes a reference current, and a sense current representative of a load current. In addition, the load control circuit includes a comparator circuit that drives a control signal in response to a comparison between the reference current and the sense current. The switched load is electrically coupled to a load voltage signal and to the control signal from the load control circuit. The switched load is operable to switch between a first loading factor and a second loading factor in response to the control signal.
As just one of many examples, such a circuit may be used to selectively load a voltage regulator by asserting/de-asserting the control signal. In such a case, the circuit may further include a voltage regulator circuit that provides the load current and the load voltage signal to the switched load. The load current may include a drive load component and switched load component. The drive load component includes current provided to a drive load attached to the voltage regulator, and the switched load component includes current provided to the switched load.
In some instances of the embodiments, the switched load includes a transistor and a resistor. In such instances, the transistor is used to selectively control current flow to the resistor. Thus, the transistor may be used to modify the switched load between a resistive load approximately equal to the resistor and a no-load (i.e., open) condition. In one particular instance, the transistor is controlled by a substantially binary control signal that transitions between a logical ‘1’ state and a logical ‘0’ state. As an example, in the logical ‘1’ state the switched load has a load approximately equal to the resistor, and in the logical ‘0’ state the switched load looks like an open or no-load. In some cases, the resistor is selected to provide a minimum load. This “minimum load” is defined as a load drawing a current sufficient to maintain the regulator circuit in an operationally stable, or otherwise desirable state.
In various instance of the embodiments, the comparator circuit comprises a bipolar transistor. In such instances, the sense current may be electrically coupled to the base of the bipolar transistor, and the reference current may be electrically coupled to the collector of the bipolar transistor. The control signal provided by the comparator may also be electrically coupled to the collector of the bipolar transistor.
Other embodiments of the present invention provide methods for controlling voltage regulator loading. Such methods include providing a voltage regulator circuit, a reference current and a switched load. The voltage regulator circuit provides a load current and a load voltage signal, and the switched load is electrically coupled to the load voltage signal. The methods further include comparing a representation of the load current with the reference current. Based at least in part on comparing the representation of the load current with the reference current, a load control signal is activated (i.e., asserted). Upon activating the load control signal, the switched load is transitioned from a first loading factor to a second loading factor.
Yet other embodiments of the present invention provide systems for regulator minimum load control. The systems include a voltage regulator circuit that drives a load voltage signal and provides a load current. In addition, the systems include a switched load and a load control circuit. The switched load is electrically coupled to the load voltage signal. The load control circuit is operable to sense the load current, and based thereon, to modify and/or activate the switched load. In some instances of the embodiments, the switched load is a smooth switched load capable of switching between three or more load factors, while in other instances the switched load is a step switched load capable of switching between two load factors. In particular instances of the embodiments, modification of the switched load is performed via a load control signal. In such cases, the load control signal may be a substantially binary signal transitioning between an active state and an inactive state, or a substantially smooth signal transitioning between three or more distinct levels or states.
This summary provides only a general outline of some embodiments of the present invention. Many other objects, features, advantages and other embodiments of the present invention will become more fully apparent from the following detailed description, the appended claims and the accompanying drawings.
In the Figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label with a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.
The present invention is related to voltage regulators. More particularly, the present invention is related to circuits, systems and methods for maintaining voltage regulators at a desired loading condition.
Various embodiments of the present invention provide circuits, systems and methods for regulator load control. Such embodiments may include a load control circuit and a switched load. The load control circuit may include a reference current and a sense current representative of a load current. In addition, the load control circuit may include a comparator circuit that drives a load control signal in response to a comparison between the reference current and the sense current. The load control signal is operable to switch the switched load between various supported load factors. As used herein, the term “load factor” is used in its broadest sense to mean any circuit load. In some cases, the load is a purely resistive load. In other cases, the load is a purely capacitive or inductive load, while in other cases, the load is some combination of resistive, capacitive, and/or inductive loads.
As just one of many examples, such embodiments may be used to selectively load a voltage regulator by asserting/de-asserting the load control signal. In such a case, the circuit may further include a voltage regulator circuit that provides the load current and the load voltage signal to the switched load. The load current may include a drive load component and switched load component. The drive load component includes current provided to a drive load attached to the voltage regulator, and the switched load component includes current provided to the switched load. As used herein, the term “drive load” includes any load other than the switched load that is being driven by the voltage regulator.
In some cases, the sense current may be a representation of the load current. For the purposes of this document, the term “representation” is used in its broadest sense to mean any value mathematically related to any other value. Thus, as just some general examples, the sense current may be some percentage of the load current, the load current plus some offset current, and/or a combination of the aforementioned. Based on the disclosure provided herein, one of ordinary skill in the art will appreciate the myriad of relationships between a sense current and a load current that are considered a “representation of the load current”.
As used herein, the term “switched load” is used in its broadest sense to mean any load capable of being switched between two or more loading factors. There are generally two types of switched loads: a “step” switched load capable of switching between two loading factors, and a “smooth” switched load capable of switching between three or more loading factors. Thus, as will be appreciated by one of ordinary skill in the art, a smooth switched load may be switched between three discreet points across a continuum, between an upper limit (potentially a thousand or more) of points across the continuum, or between any number of points between three and the upper limit.
The load control signal may be a step signal capable of toggling between two detectable levels. In general, the two levels are a logical ‘1’ and a logical ‘0’ level. In one case, the logical ‘1’ level is associated with a supply voltage level and the logical ‘0’ level is associated with a ground level, however, one of ordinary skill in the art will appreciate a number of associations that can correspond with the logical ‘0’ and logical ‘1’ levels. Alternatively, the load control signal may be a “smooth” signal capable of transitioning between three or more detectable levels. Thus, as will be appreciated by one of ordinary skill in the art, a smooth load control signal may be switched between three discreet points across a continuum, between an upper limit (potentially a thousand or more) of points across the continuum, or between any number of points between three and the upper limit.
Also, as used herein, the term “electrically coupled” is used in its broadest sense to mean any type of coupling whereby an electrical connection is made between two endpoints. Thus, for example, two devices electrically connected via a wire or other conductive path are electrically coupled. Alternatively, two end devices separated by one or more electrically conductive devices are electrically coupled where there is a signal path capable of passing some electrical current originating at one end device to the other end device. It should be noted that not all current originating at one end device must be received at the other end device for the devices to be considered electrically coupled. Rather, only some portion of the current need pass from one end device to the other end device to be electrically coupled in accordance with the definition use herein.
Turning to
Voltage regulator circuit 210 includes an operational amplifier 212 receiving an input voltage (Vin) 204 and driving a gate 215 of a Field Effect Transistor (“FET”) 214. A drain 213 of FET 214 is connected to a voltage source 222, and a source 217 of FET 214 is connected to a node 230 exhibiting a regulated voltage (Vreg). A feedback loop 206 of operational amplifier 212 is connected to a node 229 exhibiting a Vreg as divided by resistors 216, 218. A relatively small feedback current (Ifb) flows through feedback loop 206.
Operational amplifier outputs a control voltage 211 depending on a difference between input voltage 204 and the voltage exhibited on feedback loop 206. FET 214 allows Iload to pass from drain 213 to source 217 depending upon control voltage 211. When voltage regulator 210 is maintained in a defined operational range, operational amplifier 212 acts to force the voltage exhibited on feedback loop 206 to be the same as input voltage 204. This process results in the desired condition of a stable Vreg at node 230 across a reasonably wide range of loads. However, when voltage regulator 210 is unloaded (i.e., no load is coupled to node 230), operational amplifier 212 can become unstable. The instability of operational amplifier 212 results in undesired instability of Vreg.
The combination of switched load 250 and load control circuit 260 operate to reduce or eliminate the possibility that operational amplifier 212 will become unstable by assuring that voltage regulator 210 is always driving at least a minimum load. To do this, load control circuit 260 monitors the operation of voltage regulator 210 to determine when drive load 232 is either removed, or does not present a load factor to voltage regulator 210 that is sufficient to maintain voltage regulator 212 in an operational range. Where this situation is detected, load control circuit 260 activates switched load 250 such that voltage regulator 210 is maintained in a minimum loading situation.
Load control circuit 260 includes a current source 268 that provides a reference current (Iref) to a comparator 266. In addition, load control circuit 260 includes a FET 262 with a gate 261, a drain 213, and a source 264. Drain 213 of FET 262 is connected to voltage source 222, and source 264 of FET 262 drives a sense current (Isense). As gate 261 of FET 262 is connected to gate 215 of FET 214, Isense provided from FET 262 is representative of the load current provided by FET 214. Based on the disclosure provided herein, one of ordinary skill in the art will appreciate a variety of components and/or designs that may be adopted to create a sense current that tracks or otherwise represents a load current. As just some examples, the circuit may be designed such that Isense is approximately equal to Iload, or another circuit may be designed such that Isense is proportional to, but much less than Iload. Isense is provided to comparator 266 that compares Isense with Iref. In response to the comparison, comparator 266 asserts/de-asserts a control signal 242. The following equations describe the operation of comparator 266:
Control Signal=Asserted, where Isense<=Iref; and
Control Signal=De-asserted, wherein Isense>Iref.
Based on the forgoing equations, it will be recognized that control signal 242 is a substantially binary signal transitioning between a logical ‘1’ and a logical ‘0’ state. As used herein, the term “substantially binary” refers to a signal that is intended for detection at two different states: asserted and de-asserted. Such a substantially binary signal may be a square wave, or a sinusoidal wave passing through distinct thresholds defining the active and inactive states. Such a signal is useful in switching a step switched load.
Switched load 250 includes a resistor 246 connected between drain 245 of a FET 244 and node 230. Control signal 242 is connected to a gate 241 of FET 244. Thus, when control signal 242 is asserted, resistor 246 is added as a load to node 230. In this condition a switch current (Iswitch) passes through resistor 246 and FET 244. Conversely, when control signal 242 is de-asserted FET 244 does not allow current to flow through resistor 246, and resistor 246 is effectively removed as a load from node 230. The following equations describe the operation of switched load 250:
Switched Load=Resistor, where Control Signal is asserted; and
Switched Load=Open, where Control Signal is de-asserted.
Based on the forgoing equations, it will be recognized that switched load 250 is a step switched load. In this particular case, the load values or factors of switched load 250 are finite and open.
Turning now to
Vcollector=Iref*R2; and
Vbase=Isense*R1, which is proportional to Iload*R1.
As Iref is substantially constant, Vcollector is also substantially constant. In contrast, Vbase varies in proportion to the changes in Iload as represented by Isense. Thus, where Iload becomes very low due to a disconnect or other change in drive load 232, Vbase decreases to a point that bipolar transistor turns off, and control signal 242 is asserted, which in this case is at the level of Vcollector. Alternatively, where Iload increases as governed by drive load 232, Vbase increases and bipolar transistor 211 turns on, and control signal 242 is de-asserted, which in this case is approximately ground. Based on the disclosure provided herein, one of ordinary skill in the art will recognize a variety of other comparator circuits that maybe used to perform the functions of comparator 266.
Turning to
Following graph 251, at time T0 drive load 232 is disconnected from node 230. In this condition, control signal 242 is asserted (shown as dashed line 253a) causing FET 244 to turn on and load node 230 with resistor 246. As suggested above, FET 244 is turned on to apply a minimum load factor to node 230 and assure that voltage regulator 210 is maintained in an operationally stable region. With FET 244 turned on and drive load 232 disconnected from node 230, Iload is equal to Iswitch where Ifb is assumed to be insignificant. This continues until time T1 when drive load 232 is coupled to node 230 with a load that is linearly decreasing from time T1 to time T3. As shown by line 263a, Idrive increases as the load presented by drive load 232 decreases. This increasing Idrive is added to Iswitch resulting in Iload depicted as line 273b. At time T2, Iload has increased to the extent that comparator 266 de-asserts control signal 242. With control signal 242 de-asserted (shown as dashed line 253b), FET 244 turns off effectively detaching the load of resistor 246 from node 230. At this point, Iload is equal to Idrive where Ifb is assumed to be insignificant (shown as line 273c).
Beginning at time T3, the load presented to node 230 by drive load 232 is continually increased until time T5 where drive load 232 is effectively disconnected from node 230. From time T3 until time T4, the load presented to node 230 increases resulting in a corresponding decrease in Iload (shown as line 273d), but is sufficient to maintain voltage regulator 210 in a stable operational region. At time T4, the load presented at node 230 by drive load 232 becomes insufficient to maintain voltage regulator 210 in an operationally stable condition. At this point, Iload has decreased to the extent that load control circuit 260 asserts control signal 242 (shown as dashed line 253c). Assertion of control signal 242 causes FET 244 to turn on, whereby node 230 is loaded with resistor 246. At this point, Iload (shown as line 273e) is equal to Idrive (shown as dashed line 263b) plus Iswitch. At time T5, drive load 232 appears essentially disconnected from node 230 and Iload is equal to Iswitch where Ifb is assumed to be insignificant (shown as line 273f).
Graph 251 is contrived to show the effect of transitioning switched load 250 on switched load system 200. It should be noted that Iload may assume a number of different wave forms depending upon the operation of drive load 232 and the transition levels selected for switching switched load 250. Further, it should be noted at this juncture that while switched load system 200 is illustrated with particular components including FETs and operational amplifiers, one of ordinary skill in the art upon reading this disclosure will appreciate a variety of other components may be used to create circuitry capable of performing the functions of switched load system 200. Thus, for example, where n-channel FETs are shown it should be recognized that p-channel FETs or bipolar transistors may be used to create similar functionality. Also, one of ordinary skill in the art will recognize that voltage regulator 210 is exemplary of many different types of voltage regulators known in the art. Based on the disclosure provided herein, one of ordinary skill in the art will appreciate that load control circuit 260 and/or switched load 250 may be applied to other types of voltage regulators in accordance with one or more embodiments of the invention. Yet further, one of ordinary skill in the art will appreciate functional equivalents of load control circuit 260 and switched load 250 that may be used in accordance with various embodiments of the present invention.
Turning now to
The smoothly varying load is produced by an amplifier loop circuit 366. Amplifier loop circuit 366 receives Iref and Isense. As discussed above, Isense decreases as drive load 232 increases. In this case, where Isense decreases to equal Iref, amplifier loop circuit 366 begins applying a load to node 230. This load is varied such that Isense holds at a constant level. Based on the disclosure provided herein, one of ordinary skill in the art will be capable of designing an amplifier loop circuit capable of providing the desired loading condition.
Turning to
Following graph 351, at time T0 drive load 232 is disconnected from node 230. In this condition, amplifier loop circuit 366 provides a constant load to node 230. This results in a constant Iload (shown as line 363a) which continues until time T1. At this time, Idrive is zero, and Iload is equal to Iswitch (shown as line 393a offset from zero for clarity). At time T1, drive load 232 is coupled to node 230 and presents a linearly decreasing load from time T1 to time T3, and a lineraly increasing load from time T3 to time T5. As shown by line 383a, Idrive increases as the load presented by drive load 232 decreases. Between time T1 and time T2, Iload is approximately equal to Idrive plus Iswitch. To maintain Iload constant, Iswitch (shown as line 393b) is decreasing at a rate complementary to the increase in Idrive (shown as line 383a). Thus, between time T1 and T2, the load presented by amplifier loop circuit 366 is increasing. At time T2, the load presented by amplifier loop control 366 appears as an open circuit at node 230, and Iswitch is zero (shown as line 393c). Thus, from time T2 to T4, Iload is equal to Idrive (shown as lines 363b and 363c).
From time T4 to time T5, the load presented to node 230 drops below a defined load value, yet Iload remains constant (shown as line 363d). During this time, Idrive (shown as dashed line 383b) is decreasing in relation to the change in drive load 232, and the load presented by amplifier loop circuit 366 is changing to negate the change in drive load 232. Said another way, Iswitch (shown as line 393d) is increasing at a rate complementary to the decrease in Idrive (shown as dashed line 383b). At time T5, drive load 232 is disconnected from node 230 and Idrive equals zero. At this time, Iload (shown as line 363d) equals Iswitch (shown as line 393e).
Turning to
Operation of circuit 367 is described in relation to switched load system 300 where circuit 367 takes place of amplifier loop control 366. In operation, circuit 367 forces Idrive+Iswitch to be greater than or equal to nIref. To do this, FET 310 and FET 320 are switched based on the current differential across the inputs 331, 332 of current input operational amplifier 330. Where Isense is not substantially less than Iref, FETs 310, 320 are not switched and Iswitch is approximately equal to zero. In this situation, Iload is approximately equal to Idrive where the current through resistor 218 and the feedback loop to operational amplifier 212 is insignificant relative to Idrive. This operation is depicted as line 363b and line 363c of graph 351.
In contrast, where Isense becomes substantially lower than Iref as would occur where drive load 232 is removed, a voltage sufficient to swith FET 310 and FET 320 will exist at output 333 of current input operational amplifier 330. In this condition, the following equations approximately describe the various currents in switched load system 300 where FET 214 is “n” times larger than FET 262, and FET 320 is “n” times larger than FET 310:
Iload=nIsense; and
Iref=Isense+(1/n+1)Iswitch
From these two equations, the current supplied (Iload) when drive load 232 is either disconnected or becomes very large can be derived by solving for Iload as follows: Solving the preceding equations for Iload yields:
Iload=nIref−(n/n+1)Iswitch
This current is depicted as line 363a and line 363d of graph 351. Where n is large, the following equation provides a reasonable approximation for Iload:
Iload=nIref
This establishes an approximate minimum current supplied by switched load system 300 when drive load 232 is removed. As previously stated, one of ordinary skill in the art will appreciate other circuits that may be used to perform the functionality of amplifier loop control 366. Such alternative circuits may provide different minimum load currents and/or characteristics from those described above and shown in relation to graph 351.
The invention has now been described in detail for purposes of clarity and understanding. However, it will be appreciated that certain changes and modifications may be practiced within the scope of the appended claims. Thus, although the invention is described with reference to specific embodiments and figures thereof, the embodiments and figures are merely illustrative, and not limiting of the invention. Rather, the scope of the invention is to be determined solely by the appended claims.
| Number | Name | Date | Kind |
|---|---|---|---|
| 5481178 | Wilcox et al. | Jan 1996 | A |
| 5864227 | Borden et al. | Jan 1999 | A |
| 6201375 | Larson et al. | Mar 2001 | B1 |
| 6580258 | Wilcox et al. | Jun 2003 | B2 |
| RE38940 | Isham et al. | Jan 2006 | E |
| Number | Date | Country | |
|---|---|---|---|
| 20060261793 A1 | Nov 2006 | US |
