Patent Grant
7161393
The present invention relates to current regulation, and, in particular, to a current regulation circuit that provides a regulated output current that is substantially stabilized with respect to a load voltage, a load current, and a circuit temperature.
Certain electronic devices require regulated inputs, either regulated voltage or regulated current, to ensure they are stable and provide proper operation. Current regulators are often employed to provide a desired, regulated current to such devices including portable devices, cellular phones, battery chargers, and the like. For example, switching or linear regulators are often used to provide suitable power.
In applications in which a power supply provides a current to drive a load, it is desirable to control the amount of provided current at various cycles of operation to protect a load and optimize efficiency. Current regulators generally include a power pass device for regulating the current from a power source with a feedback mechanism. Commonly, the feedback is provided after the power pass device following the current regulation.
Thus, it is with respect to these considerations and others that the present invention has been made.
Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following drawings. In the drawings, like reference numerals refer to like parts throughout the various figures unless otherwise specified.
For a better understanding of the present invention, reference will be made to the following Detailed Description of the Invention, which is to be read in association with the accompanying drawings, wherein:
The present invention now will be described more fully hereinafter with reference to the accompanying drawings, which form a part hereof, and which show, by way of illustration, specific exemplary embodiments by which the invention may be practiced. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Among other things, the present invention may be embodied as methods or devices. Accordingly, the present invention may take the form of an entirely hardware embodiment or an embodiment combining software and hardware aspects. The following detailed description is, therefore, not to be taken in a limiting sense.
Briefly stated, the present invention is related to a current regulation circuit that provides a regulated output current with limited maximum output voltage and maximum internal power dissipation. The present invention is further aimed at providing a stable output current to a load by controlling conditions in the regulator circuit such as voltage, current, temperature, and the like, and addresses instability in conventional current regulators due to overshoot and oscillation at switch-over point between a constant current mode and a constant voltage mode. The oscillation may also be caused by over-temperature of the charging circuit. According to the invention, a load current and a load voltage may be sensed and amplified to provide a first and a second input signal to a current control device. A temperature sense device may provide a third input signal, and a reference device a fourth input signal. The current control device may be arranged to select a minimum of the last three input signals and combine it with the first input signal. Then the current control device may provide a control signal to a power pass device based on the combination. Providing a feedback based on the load voltage and the temperature to an input of the current control device, as opposed to a providing a similar feedback at a later stage, enables the circuit to substantially stabilize the regulated load current. While a preferred embodiment of the present invention may be implemented as a core in a battery charging circuit, the invention is not so limited. For example, the described circuit may be employed as a general-purpose current source. Thus, the current regulator circuit may be implemented in virtually any regulation circuit known to those skilled in the art.
Power pass 104 may perform a function of receiving an input voltage from an external power source such as power source 102 and providing a regulated current to load 106. In one embodiment power source 102, load 106, or both may be implemented on a chip with circuit 120. Current sense 108 may be performed on the regulated current provided to load 106. The regulated current may be sensed and a current sense signal provided to combination function 126 of current control 122. Voltage sense amplification 116 may sense a load voltage based on the regulated current provided to load 106. Voltage sense amplification 116 may amplify the sensed load voltage and provide a first signal to minority selection function 124 of current control 122. Temperature sensing 112 may provide a second signal to minority selection function 124 of current control 122. Temperature sensing 112 may be implemented as any device, known to those skilled in the art, that may detect a temperature of circuit 120 and provide a signal based on the temperature. In one embodiment, the second signal may decrease when the temperature of circuit 120 increases. Reference 114 may provide a third signal to minority selection function 124 of current control 122. Reference 114 may be implemented as an external reference voltage source, an internal reference voltage source, and the like.
Current control 122 may be arranged to include minority selection function 124, differential combination function 126, and amplification 110. Current control 122 may provide a control signal to power pass 104 based on the current sense, first, second, and third signals and enable a substantial stabilization of the load current with respect to load current, load voltage, and circuit temperature. Minority selection function 124 may be arranged to determine a minimum signal based on the first, second, and third signals received from voltage sense amplification 116, temperature sensing 112, and reference 114. The minimum signal may then be differentially combined with the current sense signal from current sense 108 at differential combination function 126. Differential combination function 126 may provide the resulting signal to amplification 110. Amplification 110 may amplify the differentially combined signal and provide the control signal to power pass 104.
In addition to the load voltage, load current, and the temperature of the circuit, an external signal may be provided to the minority selection function in one embodiment. Such external signal may be based, in part, on a load temperature, a power source temperature, an elapsed charging time, and the like.
Power transistor M204 is arranged to provide a regulated output current in response to input voltage VIN and a control signal Vcnt. The input voltage is provided to a source of power transistor M204. The control signal Vcnt is provided to a gate of power transistor M204 from an output of current control device 222.
Current control device 222 may perform the functions of current control 122 of
Current sense device 208 includes transistor M232 and resistor R21. A gate and a source of transistor M232 is coupled to a gate and source of power transistor M204. A drain of transistor M232 is coupled to an input of differential amplifier A224 and to resistor R21, which is coupled to ground at its other terminal. By sharing a source and gate voltage power transistor M204 and transistor M232 essentially form a current mirror. A current sense ratio of the circuit may be determined by a ratio of gate areas (width/length) between power transistor M204 and transistor M232. In one embodiment, power transistor M204 and transistor M232 may be selected such that the ratio of their gate areas is between about 500 and about 5000. A selection in this range may minimize sensing current and increase an efficiency of the circuit with respect to the load current.
Voltage sense amplification device 216 is arranged to sense an output voltage provided to load 106 and to provide Vsns based on an amplification of the sensed output voltage. Voltage sense amplification device 216 may include a voltage divider that comprises resistors R22 and R23 serially coupled between a drain of power transistor M204 and a ground. Voltage sense amplification device 216 may further include amplifier A234, one input of which is coupled to node N235 between R22 and R23. The reference voltage Vref may be provided to another input of amplifier A234. In one embodiment, amplifier A234 may be implemented as a differential amplifier.
Temperature sense device 212 is arranged to detect a temperature of circuit 220 and to provide Vtemp based on the temperature. In one embodiment, Vtemp may decrease when the temperature of circuit 220 increases. Reference device 214 may provide Vref to amplifier 244. Reference device 214 may be implemented as an external reference voltage source, an internal reference voltage source, and the like.
In an exemplary operation, the output voltage and the temperature of the circuit may be below their respective, predetermined limits before the circuit is turned on. When the circuit is first turned on, a current flowing through power transistor M204 may be about zero. Because transistor M232 shares a common gate voltage with power transistor M204, a current flowing through transistor M232 will also be about zero. Consequently, there will not be a current flowing through resistor R21 resulting in a voltage difference between differential amplifier A224's inputs. This voltage differential, in turn, may result in a change of the output voltage of differential amplifier A224, which provides the gate voltages to power transistor M204 and transistor M232. An increase in the gate voltages of power transistor M204 and transistor M232 may lead to an increased conductivity of the transistors and an increased current flow to load 106 as well as through resistor R21. Increased current through resistor R21 may lead to an increase of the voltage VIsns at the input of differential amplifier A224 such that the circuit may reach a balanced operation condition when the load current may be expressed by:
where K is a ratio of gate area width/length of power transistor M204 and transistor M232.
In one embodiment, Vsns may decrease as the load voltage approaches a predetermined limit, and Vtemp may decrease as the temperature of the circuit increases. When the load voltage or the circuit temperature approach their respective limits, the value of Vsns or Vtemp may drop below a predetermined reference voltage Vref. In this condition, the load current may be regulated by:
where K is as described above.
If at least one of the load voltage and the circuit temperature exceeds its respective limit, corresponding voltage Vsns or Vtemp, may drop to about zero resulting in a drop of the output current of differential amplifier A224 dropping to about zero and power transistor M204 being turned off.
Minority selection circuit 326 is arranged to receive three signals: Vsns, Vtemp, and Vref. Minority selection circuit 326 is further arranged to provide a first signal to another stage of an operational amplifier such as differential amplifier A224 based on a selection of the smallest value of Vsns, Vtemp, and Vref. Minority selection circuit 326 comprises transistors M344, M346, and M348. Sources of all three transistors are coupled to an output providing the selected minority signal as the first signal to the other stage. Drains of M344, M346, and M348 are coupled to current source I328. M344 is arranged to receive Vref at its gate. M346 is arranged to receive Vsns at its gate. Finally, M348 is arranged to receive Vtemp at its gate.
As described in the example above, Vsns and Vtemp may be arranged to decrease when the load voltage and the circuit temperature increase and approach Vref as the load voltage and the circuit temperature approach their respective predetermined limits. Transistors M344, M346, and M348 may comprise p-channel MOSFET type transistors. When both Vsns and Vtemp are greater than about Vref, transistor M344 conducts providing a path for a current from current source I328 to the output. In this case transistors M342 and M344 operate as a differential pair providing a combination of VIsns and Vref to the other stage.
If Vsns drops below Vref, while Vtemp is still above Vref, M346 will begin to conduct and transistors M342 and M346 will act as differential pair providing a combination of VIsns and Vsns to the next stage of operational amplifier A224. Similarly, if Vtemp drops below Vref, while Vsns is still above Vref, transistor M348 will conduct and transistors M342 and M348 will act as differential pair providing a combination of VIsns and Vtemp to the following stage.
Transistor M342 is arranged to provide a second signal that is based on VIsns to the following stage for differential combination with the first signal. Transistor M342 is further arranged such that a source of the transistor provides an output for the following stage. A drain of transistor M342 is coupled to current source I328 along with other transistors in the circuit. A supply voltage VDD is provided to body terminals of all four transistors.
Current source I328 is arranged to provide current to transistors M342, M344, M346, and M348 in response to the supply voltage VDD.
An order of transistors M344, M346, and M348 is not significant for the operation of the circuit. The transistors may be laid out in a different order and still perform their intended function.
The above specification, examples and data provide a description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention also resides in the claims hereinafter appended.
| Number | Name | Date | Kind |
|---|---|---|---|
| 5696435 | Koenck | Dec 1997 | A |
| 5796278 | Osborn et al. | Aug 1998 | A |
| 6233128 | Spencer et al. | May 2001 | B1 |
