News Column

Patent Issued for Low Noise Voltage Regulator

August 20, 2014

By a News Reporter-Staff News Editor at Journal of Engineering -- According to news reporting originating from Alexandria, Virginia, by VerticalNews journalists, a patent by the inventors Thomas, Teddy D. (Bedford, NH); Waterfall, Gregory Stewart (Tucson, AZ), filed on June 30, 2011, was published online on August 5, 2014.

The assignee for this patent, patent number 8797772, is Texas Instruments Incorporated (Dallas, TX).

Reporters obtained the following quote from the background information supplied by the inventors: "A voltage regulator power supply is typically used to ensure that the electrical power supplied to an electronic device is maintained at a relatively constant voltage while providing the (variable) current needed for the proper functioning of the electronic device. There are several types, or topologies, of voltage regulators, each with different advantages and disadvantages. Design considerations for selecting the type of voltage regulator to use in a given situation often involve tradeoffs between parameters such as conversion efficiency and output voltage noise. The efficiency generally refers to the amount of power that can be provided by the regulator with a given input power. The noise generally refers to any fluctuation, including 'ripple', exhibited by the output voltage, usually during steady state operating conditions, but also when changes occur in either the available input line voltage or the output load current draw.

"A linear regulator is a type of voltage regulator that provides an output voltage with relatively low noise. A low-dropout (LDO) linear regulator, for instance, may be capable of as little as a 500 microvolt ripple in a 5-Volt output, i.e. about 0.01% noise. The efficiency of such regulators, however, is typically relatively low, since they ineffectively convert input power to output power, the wasted energy being dissipated as heat. For instance, a linear regulator with a high input voltage (e.g. Vin about 12 Volts) and a low output voltage (e.g. Vout about 5 Volts) is typically less than 50% efficient.

"A switching power supply (e.g. a buck converter, a step-down DC to DC converter, a switched-mode power supply, etc.), on the other hand, is typically very efficient, usually 90-95% (or higher) efficient. The noise, however, can be quite significant. A switching power supply that produces 5 Volts, for example, may exhibit a total peak-to-peak ripple of anywhere from 5 to 200 millivolts, i.e. 0.1 to 4% noise.

"FIG. 1 shows a simple example of a prior art switching power supply (buck converter 100) that converts a given input voltage Vin to an appropriate output voltage Vout for an output load 101. The buck converter 100 generally includes a switch 102, a diode 103, an inductor 104 and a capacitor 105 configured as shown. An appropriate control component (not shown) typically controls the switch 102, based on feedback of the output voltage Vout. When the switch 102 is closed, the input power (at voltage Vin) provides current to the inductor 104, so the current in the inductor 104 increases. When the switch 102 is open, the current to the inductor 104 (provided through the diode 103) decreases. A graph 106 illustrating this increasing and decreasing (ripple) of the current in the inductor 104 is shown in FIG. 2. In this example, the current in the inductor 104 fluctuates about 200 milliamps around 1.5 Amps. As a consequence of the current ripple in the inductor 104, the output voltage Vout ripples accordingly, as shown in a graph 107 in FIG. 3. The output voltage Vout fluctuates about 8 millivolts around about 3.29 Volts, which calculates to about 0.24% noise.

"A more complicated intermediary solution to improve both efficiency and noise reduction involves a combination of a switching power supply and an LDO regulator. The switching power supply generally takes an input voltage down to a lower intermediate voltage with a relatively high efficiency, but with an undesirably high noise level. The LDO regulator then takes the lower intermediate voltage and produces the desired low noise output voltage. Since the LDO regulator starts with a lower voltage, the loss in the LDO regulator is smaller than in solutions that use only the LDO regulator. Thus, the end result of this combination has a greater efficiency (about 75% or less) than an LDO regulator alone and a lower noise level than a switching power supply alone. A disadvantage is, however, that a device manufacturer often must use two components (the switching power supply and the LDO regulator) instead of one, thus increasing the size, complexity and cost of the resulting device.

"A continuing trend in the electronics industry is the need for ever greater conversion efficiency combined with ever lower operating voltage noise levels in addition to ever smaller device/component sizes and costs. Current technology is reaching the limits of the efficiency and noise capabilities of the available power supply topologies. A new topology is needed.

"It is with respect to these and other background considerations that the present invention has evolved."

In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "The present invention introduces a new power supply topology with a conversion efficiency approaching that of a switching power supply and an output voltage noise level equivalent to, or approaching, that of a linear regulator. The present invention is embodied in an electronic device that generally includes an output switching stage and an amplifier, both of which contribute current to produce an output voltage at a substantially constant level. The amplifier produces a current that is based on a difference between a reference voltage and a feedback of the output voltage. The current from the amplifier counterbalances the current from the output switching stage to maintain the output voltage at the substantially constant level. The output switching stage is controlled in response to a level of the counterbalancing current.

"Some embodiments include a current ramp generator connected to the amplifier and the output switching stage. The current ramp generator is preferably activated and deactivated in response to the output switching stage being deactivated and activated, respectively. A current from the current ramp generator preferably forms the counterbalancing current in combination with the current from the amplifier.

"In some embodiments, the output switching stage includes a step down Buck regulator. In other embodiments, the output switching stage includes an isolated forward converter regulator. Still other embodiments may incorporate other appropriate types of switching stages.

"In some embodiments, the output voltage exhibits less than about 0.002% (or about 0.001% to 0.0015%, or less than 50 microvolts) of voltage ripple around a desired voltage level. Additionally, in some embodiments, the output voltage is produced with an efficiency of greater than about 80% (or about 80% to 85% or even greater). Furthermore, in some embodiments, when the output current is below a light load threshold level, the output switching stage is not switched on.

"A more complete appreciation of the present disclosure and its scope, and the manner in which it achieves the above noted improvements, can be obtained by reference to the following detailed description of presently preferred embodiments taken in connection with the accompanying drawings, which are briefly summarized below, and the appended claims."

For more information, see this patent: Thomas, Teddy D.; Waterfall, Gregory Stewart. Low Noise Voltage Regulator. U.S. Patent Number 8797772, filed June 30, 2011, and published online on August 5, 2014. Patent URL:

Keywords for this news article include: Texas Instruments Incorporated.

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Source: Journal of Engineering

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