Patent Grant
8981736
Electric utilities have recently begun to monitor customer power usage using “smart” electrical meters. In addition to the overall amount of energy consumed at a location, the smart meters can monitor the quality of the energy and the particular time when the energy was used. The information can be used to more accurately bill a customer. In addition, the smart meters can transmit the energy information to a central location without the need for personnel to observe the meter. In certain examples, the smart meter may require 8 watts to transmit the energy information. When not transmitting, the smart meter may only use 0.25 watts of power. Typical power supply regulators can use 48 milliwatts (mW) or more of power. During non-transmission times, the regulator may use about 20% of the meter power. This is wasted energy. This wasted energy is characteristic of other devices that monitor conditions during standby, such as devices that can be used with a remote control. Significant energy savings can be realized with more efficient power supply regulators.
This overview is intended to provide an overview of subject matter of the present patent application. It is not intended to provide an exclusive or exhaustive explanation of the invention. The detailed description is included to provide further information about the present patent application.
This document refers to, among other things, apparatus for high-efficiency, thermally-compensated regulators. In an example, a regulator can include a zener diode having a first temperature coefficient, the zener diode configured couple to an output and to provide at least a portion of a reference voltage, a transistor having a second temperature coefficient, the transistor configured to receive the reference voltage, to receive a representation of the output, and to provide feedback information indicative of an error of the output using the representation of the output voltage and the reference voltage, and wherein the first temperature coefficient and the second temperature coefficient are configured to reduce at least a portion of a temperature drift effect of the zener diode and the transistor.
In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.
Power levels for smart meters can range between 1 watt (W) and 15 W. Non-smart meters can have power levels of around 1 W. In certain examples, smart meter specifications can allow continuous transmission of energy information so the power supplies need to be dimensioned for the high power levels used during transmission. In certain examples, a smart meter can use about 0.25 watts between transmissions for housekeeping. (˜99% of the time). Power that is used by a secondary power supply regulator can significantly impact the overall efficiency of the power supply during housekeeping intervals. Traditional regulators can require 1 mA worst-case keep-alive, plus 0.5 to 1 mA for the reference divider, plus any current needed for an optical isolator if the regulator is isolated. Overall, this can amount to 48 mW. In power supplies with low power outputs such as 250 mW output this can amount to ˜19.2% power loss.
The present inventor has recognized, among other things, example zener-based regulators including thermal compensation based upon a thermal gradient of a transistor junction such as the base-emitter thermal gradient of a BJT transistor, to provide a high quality, thermally stable, low-current references at low power and price. Example regulators can use only a few milliwatts in certain examples and are capable of significantly improving overall efficiency of power supplies used in low power applications.
In certain examples, a high-efficiency regulator can use less than 6.24 mW. (At 250 mW output ˜3% loss). If 10 million smart meters are installed using a high-efficiency regulator, the power saving can be around 500,000 watts.
In addition to providing a low power, high efficiency regulator, the example regulator 201 can also improve the temperature drift performance of a power supply. Performance of electrical components, in general, can vary as temperature of the power supply components change. The measure of the change can be represented by a temperature coefficient and the change in a device operating condition can be known as a temperature drift effect. In certain examples, the temperature coefficient of the zener diode 206 and the temperature coefficient of the base-emitter junction of the transistor 210 can be configured to reduce at least a portion of a temperature drift effect of the zener diode and the transistor as well as the combined temperature drift effect of the regulator. The example regulator of
In certain examples, the regulator 201 can recursively regulate the current that produces the voltage drop across the zener diode 206, thus, providing additional output voltage VOUT stability.
In certain examples, the output voltage VOUT can be selected, or the various values of the regulated can be selected, using the following general formula:
where VREF includes the voltage across the zener diode 306 and the base-emitter junction of the transistor 310, R1 includes the value of the first resistor 307, and R2 includes the value of the second resistor 308.
In addition to providing a low power, high efficiency regulator, the example regulator 301 can also improve the temperature drift performance of a power supply. The example regulator 301 of
In an example, such as for a 12 volt power supply, the current limit resistor 314 can be about 2.2 kohms, and the bias resistor 312 can be about 510 kohms. In such an example, the operating current of the regulator can be about 260 μA.
In an example, as the output voltage VOUT is pulled higher or lower by changes in the input voltage VIN, the voltage divider 605 can exert a corresponding change to VREF. In response to the exertion to change VREF, the transistor 610 can change voltage at the gate of the power transistor 630 to maintain the VOUT established by the equation above. For example, if the input voltage VIN rises, exerting an increase on VREF and VOUT, the power transformer 630 can increase shunt current resulting in more current through the limit resistor 631 thus creating a larger voltage drop across the limit resistor 631 to maintain the desired lower output voltage VOUT. If the input voltage VIN decreases, exerting a decrease on the reference voltage VREF and the output voltage VOUT, the power transistor 630 can reduce the shunt current resulting in less current through the current limit resistor 631 thus reducing the voltage drop across the limit resistor 631 and maintaining the desired higher output voltage VOUT.
In an example, the second resistor 608 can be adjustable such that the output voltage VOUT can be selected via the adjustment of the second resistor 608. In certain examples, the transistor 610 and the zener diode 606 can be selected to have complementary thermal coefficients such that the high-current shunt regulator is thermally compensated. In an example, an integrated circuit can include the transistor 610 and the zener diode 606.
where VREF can be the voltage across the zener diode and the junction of the transistor coupled to the zener diode. The input voltage VIN can disable the precision current source by not maintain a voltage high enough to maintain VREF. In an example, the sense resistor 740 can be adjustable such that the output current IOUT can be selected via the adjustment of the sense resistor 740. In certain examples, the transistor 710 and the zener diode 706 can be selected to have complementary thermal coefficients such that the precision current source is thermally compensated. In an example, an integrated circuit can include the transistor 710 and the zener diode 706.
In certain examples, a kit can include an integrated circuit and instructions for making examples circuits such as those illustrated in
In Example 1, a regulator can include a zener diode having a first temperature coefficient, the zener diode configured to couple to a power supply output and to provide at least a portion of a reference voltage, a transistor having a second temperature coefficient, the transistor configured to receive the reference voltage, to receive a representation of the power supply output, and to provide feedback information indicative of an error of the power supply output using the representation of the power supply output and the reference voltage, and wherein the first temperature coefficient and the second temperature coefficient are configured to reduce at least a portion of a temperature drift effect of the zener diode and the transistor.
In Example 2, the regulator of Example 1 optionally includes a first resistor coupled to the power supply output, a second resistor coupled to ground in series with the first resistor, and wherein a control node of the transistor is configured to receive the at least portion of the reference voltage from a node coupled to the first resistor and the second resistor.
In Example 3, the zener diode of any one or more of Examples 1-2 is optionally coupled between the transistor and ground.
In Example 4, the power supply output of any one or more of Examples 1-3 is optionally configured to provide an output current, such as a regulated output current.
In Example 5, the power supply output of any one or more of Examples 1-4 is optionally configured to provide an output voltage, such as a regulated output voltage.
In Example 6, the output voltage, VOUT, of any one or more of Examples 1-5 is optionally given by,
VOUT=VREF(1+R1/R2),
wherein VREF is the reference voltage, R1 is a resistance value of the first resistor, and R2 is a resistance value of the second resistor.
In Example 7, the zener diode of any one or more of Examples 1-2 is optionally coupled in series with the first resistor and the second resistor.
In Example 8, the power supply output of any one or more of Examples 1-7 is configured to provide an output current, such as a regulated output current.
In Example 9, the power supply output of any one or more of Examples 1-8 is optionally configured to provide an output voltage, such as a regulated output voltage.
In example 10, a ratio of the first thermal coefficient to the second thermal coefficient of any one or more of Examples 1-9 is optionally substantially equal to a ratio of a resistance of the first resistor to a resistance of the second resistor.
In Example 11, the first temperature coefficient of any one or more of Examples 1-10 optionally includes a positive voltage change with increasing temperature and the second temperature coefficient of any one or more of Examples 1-10 optionally includes a negative voltage change with increasing temperature.
In Example 12, the first temperature coefficient of any one or more of Examples 1-10 optionally includes a negative voltage change with increasing temperature and the second temperature coefficient of any one or more of Examples 1-10 optionally includes a positive voltage change with increasing temperature.
In Example 13, an integrated circuit of any one or more of Examples 1-12 optionally includes the transistor and the zener diode.
In Example 14, a power supply can include a power supply controller, power electronics configured to receive an input voltage and to provide an output using command signals from the power supply controller, and a regulator configured receive the output and to provide feedback information to the power supply controller. the regulator can include a zener diode having a first temperature coefficient, the zener diode configured to couple to the output and to provide at least a portion of a reference voltage, a transistor having a second temperature coefficient, the transistor configured to receive the reference voltage, to receive a representation of the output, and to provide the feedback information using the representation of the output and the reference voltage, the feedback information indicative of an error of the output, and wherein the first temperature coefficient and the second temperature coefficient are configured to reduce at least a portion of a temperature drift effect of the zener diode and the transistor.
In Example 15, the power supply controller of any one or more of Examples 1-14 optionally includes a pulse width modulated controller and the power electronics include a power transistor.
In Example 16, the power supply controller of any one or more of Examples 1-5 optionally includes a flyback power supply controller.
In Example 17, the power supply controller of any one or more of Examples 1-16 optionally includes a half bridge driver.
In Example 18, the power supply controller of any one or more of Examples 1-17 optionally includes a full bridge driver.
In Example 19, a method for regulating an output can include providing at least a portion of a reference voltage using an power supply output coupled to a zener diode, the zener diode having a first thermal coefficient, receiving the reference voltage at a transistor coupled to the zener diode, receiving a representation of the power supply output at the transistor, providing feedback information indicative of an error of the power supply output using the representation of the power supply output and the reference voltage, and reducing at least a portion of a temperature drift effect of the zener diode and the transistor using the first temperature coefficient and the second temperature coefficient.
The above detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention can be practiced. These embodiments are also referred to herein as “examples.” All publications, patents, and patent documents referred to in this document are incorporated by reference herein in their entirety, as though individually incorporated by reference. In the event of inconsistent usages between this document and those documents so incorporated by reference, the usage in the incorporated reference(s) should be considered supplementary to that of this document; for irreconcilable inconsistencies, the usage in this document controls.
In this document, the terms “a” or “an” are used, as is common in patent documents, to include one or more than one, independent of any other instances or usages of “at least one” or “one or more.” In this document, the term “or” is used to refer to a nonexclusive or, such that “A or B” includes “A but not B,” “B but not A,” and “A and B,” unless otherwise indicated. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Also, in the following claims, the terms “including” and “comprising” are open-ended, that is, a system, device, article, or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects.
The above description is intended to be illustrative, and not restrictive. For example, although the examples above may have been described relating to NPN devices, one or more examples can be applicable to PNP devices or MOSFET devices in some application. In other examples, the above-described examples (or one or more aspects thereof) may be used in combination with each other. Other embodiments can be used, such as by one of ordinary skill in the art upon reviewing the above description. The Abstract is provided to comply with 37 C.F.R. §1.72(b), to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Also, in the above Detailed Description, various features may be grouped together to streamline the disclosure. This should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may lie in less than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.
This patent application claims the benefit of priority, under 35 U.S.C. Section 119(e), to Dunipace, U.S. Provisional Patent Application Ser. No. 61/408,879, entitled “HIGH EFFICIENCY, THERMALLY STABLE REGULATORS AND ADJUSTABLE ZENER DIODES,” filed on Nov. 1, 2010, which is hereby incorporated by reference herein in its entirety.
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