Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2000-09-07
2001-09-25
Riley, Shawn (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
C323S284000
Reexamination Certificate
active
06294904
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to multiple frequency switching power supplies and methods to operate a switching power supply.
BACKGROUND OF THE INVENTION
Switching power supplies are used in applications where power supply efficiency is a concern. Several different types of switching power supplies are known and commonly used. A first type is known as a “buck” power supply. Buck power supplies are DC-to-DC converters providing a stable output voltage from an input voltage that is larger than the output voltage. In other words, by bucking a portion of the electromotive force of the input voltage, the buck supply is able to provide a regulated, reduced output voltage. Ideally, the buck power supply is able to perform voltage step-down and regulation functions with very little power loss.
A second type of switching power supply is known as a “boosting” power supply. Boosting power supplies incorporate a transformer or coil and one or more switches coupled in series with a primary winding of the transformer or in series with the coil. Boosting power supplies are able to supply a DC output voltage from a DC input voltage that is lower than the output voltage. Examples of switching power supplies using both principles of operation are described in U.S. Pat. No. 5,691,632, entitled “Switching Power Supply,” issued to Otake and hereby incorporated herein by reference. These examples use a switching transistor as a synchronous rectifier. Efficiency of switching transistor operation is improved by reducing charge storage effects.
Other examples of switching power supplies are known. For example, U.S. Pat. No. 5,675,479, issued to Tani et al. and hereby incorporated herein by reference, discloses a switching power supply where efficiency is improved under light loading by lowering the switching speed of a switching element. Under heavy load, output ripple is reduced by increasing switching speed.
U.S. Pat. No. 5,390,101, issued to Brown and hereby incorporated herein by reference, discloses a switching power supply having a voltage controlled oscillator (VCO) to provide high efficiency operation throughout a wide range of input voltages and load conditions. VCO frequency is increased when output loading increases. U.S. Pat. No. 4,683,529, issued to Bucher II and hereby incorporated herein by reference, discloses a switching power supply that uses pulse-width modulation together with switching frequency modulation to maintain high efficiency.
All of these examples are concerned with maintaining efficiency over portions of a load curve where significant amounts of power are being drawn from the switching power supply. As a result, the range of frequencies over which they operate is relatively narrow. Additionally, power dissipation in switching power supplies (i.e., inefficiency) is composed of two principal components: (i) conduction losses, caused by parasitic resistance in power supply components and (ii) switching losses, caused by charge storage and other effects in the switching elements. Switching losses are proportional to switching speed.
When the amount of electrical power being drawn from the switching power supply is reduced to very low levels, the conduction losses become very small and the switching losses are the dominant source of switching power supply inefficiency. For example, switching power supplies that have efficiencies on the order of 95% under normal loading may have efficiencies of about 50% under standby conditions, due primarily to switching losses.
Moreover, increased concern over pollution caused by power generation and increasingly larger numbers of electrically-powered devices used in homes and industry combine to create new standards and guidelines for power consumption budgets for electrical appliances. Also, increasing numbers of electrical appliances are maintained in a “ready-to-operate” state twenty-four hours a day.
Further, the United States Government Environmental Protection Agency (EPA) has developed new guidelines for compliance with Energy Star power consumption limit guidelines for power budgets for such appliances. As a result, these appliances are being designed to incorporate power-saving “standby” modes whereby the appliance is both ready to be operated and is consuming as little electricity as possible whilst in the standby mode.
Additionally, as the number and the diversity of electrically-powered appliances has increased, especially data communications, data storage and data manipulation appliances, demand has grown for battery-powered electrical appliances. Consumer trends for such appliances place heavy emphasis on size and weight for the appliances. A particular emphasis on increased battery life, and hence on reduced consumption of electrical power, places a substantial premium on reduction of power consumption in such appliances.
What is needed is a new type of switching power supply capable of extremely low power consumption in a standby mode while still being capable of supporting all required functions in a host appliance and which is also capable of switching very rapidly to full power operation on demand.
SUMMARY OF THE INVENTION
In a first aspect, the invention provides a multiple frequency switching power supply. The power supply includes a pulse width modulation circuit having an output, having an input and having a clock signal input. The power supply also includes a switching transistor having first and second current-carrying electrodes and having a control electrode. The first current-carrying electrode is coupled to a voltage source, the control electrode is coupled to the output of the pulse width modulation circuit and the second current-carrying electrode is coupled to a power supply output configured to provide a regulated output voltage. The power supply additionally includes a voltage sensing circuit coupled to the power supply output and having an output coupled to the pulse width modulation circuit input and also includes a switch coupled to the clock input of the pulse width modulation circuit. The switch supplies a first clock signal having a first frequency to the pulse width modulation circuit when the power supply is in a normal mode of operation and supplies a second clock signal having a second frequency more than order of magnitude lower than the first frequency to the pulse width modulation circuit when the power supply is in a standby mode of operation.
In another aspect, the invention provides a method to operate a switching power supply. The method includes determining when an output current from the power supply falls below a threshold and switching from one switching frequency to another, discrete switching frequency when the output current falls below the threshold.
In another aspect, the invention provides a method to operate a switching power supply. The method includes determining when an output current from the power supply is above a threshold and supplying a first switching signal having a first frequency to a switching transistor in the power supply when the output current is above the threshold. The method also includes determining when the output current from the power supply is below the threshold and supplying a second switching signal having a second frequency to the switching transistor in the power supply when the output current is below the threshold. The second frequency is less than one tenth of the first frequency.
In another aspect, the invention includes provision of a control input on a multiple frequency switching power supply. Commands from a print engine controller select a first switching frequency for the power supply when the printer is in a normal mode of operation and select a second switching frequency for the power supply when the printer is in a standby mode of operation.
REFERENCES:
patent: 4030015 (1977-06-01), Herko et al.
patent: 5969515 (1999-10-01), Oglesbee
patent: 6127816 (2000-10-01), Hirst
Hewlett--Packard Company
Riley Shawn
LandOfFree
Multiple frequency switching power supply and methods to... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Multiple frequency switching power supply and methods to..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Multiple frequency switching power supply and methods to... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2509910