Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2000-06-19
2001-10-30
Nguyen, Matthew (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
Reexamination Certificate
active
06310469
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to switching DC-DC regulators, and more particularly, to a technique of detecting a light output loading condition of synchronous switching regulators.
2. Description of the Prior Art
Systems and methods to sense light loading of synchronous switching regulators are known. Known systems and methods generally detect light load conditions by adding a sense resistor in the conduction path, or by sensing a voltage rise in the regulator's output. A disadvantage of these standard systems and methods is the necessity to add costly components to detect light loads. Such known synchronous switching regulator light load detection techniques inefficiently detect light loads by failing to recognize that assets already employed in synchronous switching regulators can also serve to detect a light loading operating point. In view of the foregoing, a need exists in the synchronous switching DC-DC regulator art for a system and method to detect light load conditions by using assets already employed in the switching regulator thereby eliminating the need for additional components such as sense resistors or other components necessary to monitor a voltage rise in the regulator's output.
SUMMARY OF THE INVENTION
The present invention is directed to a buck and boost synchronous switching DC-DC regulator light load detection technique that provides a mechanism to determine a general light loading condition with out the necessity to add high precision components or detection systems. The present light load detection system includes a SWnode connected comparator and a pulse detector for generating a light load output signal LOW-I. The light load condition is characterized by the point where the switching losses dominate over DC conduction losses and is sensed by positive-going switch node voltages during the discontinuous operating phase of the switcher. Energy is supplied to the switching node via an inductor. The output load current is simply the average inductor current in which a constant amplitude triangular, switching, current waveform rides upon. Thus, the output load current directly shifts up and down this offset, triangular inductor current waveform. When the switching node voltage goes positive, for example, the inductor is devoid of current and is charging in the reverse direction. This crossover, or discontinuous operating point, is load dependent, as described above, and occurs when the average output current minus half the switching current goes negative. Thus, a desired range of light load trigger points can be implemented by choosing the inductor to accommodate a specified trip range over the supply voltage since the switching current amplitude, i.e., the above described triangular waveform, is a function of the supply voltage, frequency, duty cycle, and passive components, and is largely independent of loading. Known techniques incur significant costs and energy loss by failing to recognize that for most applications, light load detection could be achieved with existing assets as prescribed by this invention, instead of adding supplementary high precision components and/or high cost detection systems.
According to one aspect of the present invention, light load conditions for a buck and boost synchronous switching DC-DC regulator are sensed by a positive going switch node voltage during the discontinuous operating phase of the switcher.
REFERENCES:
patent: 3875493 (1975-04-01), Kunzinger et al.
patent: 4496897 (1985-01-01), Unnewehr et al.
patent: 5773966 (1998-06-01), Steigerwald
Bentolila Ariel S.
Shen Sisan
Brady III Wade James
Holmbo Dwight N.
Nguyen Matthew
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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