Switching power supply having a low power burst mode

Details Switching power supply having a low power burst mode Switching power supply having a low power burst mode

2000-04-10

2001-06-26

Han, Jessica (Department: 2838)

Electric power conversion systems

Current conversion

Including d.c.-a.c.-d.c. converter

C363S097000

Reexamination Certificate

active

06252783

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to switching power supplies and, more particularly, the invention relates to a switching power supply having a low power burst mode.
2. Description of Related Technology
Generally speaking, a switching power supply (SPS) provides a cost-effective and energy-efficient device for converting energy from a single direct current (TC) supply voltage into one or more DC output voltages that have a greater or lesser magnitude than the supply voltage. SPSs are commonly used to power electronic devices, particularly battery powered devices such as portable cellular telephones, laptop computers, etc., that have a normal operating mode, in which the devices consume a relatively large amount of power, and a standby operating mode (e.g., a sleep mode), in which the devices consume relatively little power. Typically, these electronic devices automatically reenter the standby operating mode when a user has not interacted with the device for a predetermined amount of time and automatically enter the normal operating mode when the user interacts in some manner with a control button, mouse, etc. of the device.
In conventional electronic devices, a standby operating mode is accomplished by either reducing the output voltage of the power supply within the devices or, alternatively, establishing a source of auxiliary power for the devices. However, both of these conventional approaches are undesirable because they require additional components, which results in higher production costs, and because there is an output voltage below which the device will not function, thereby limiting the amount that the power consumption of the device can be decreased. Additionally, when using a conventional SPS in a standby operating mode, a substantial switching loss occurs within the SPS despite any reduction in power consumption due to a reduced output voltage. More specifically, a conventional SPS varies the duty cycle of a power switch (e.g., a transistor) to compensate for changes in power requirements at the output of the supply and operates at a predetermined frequency regardless of the amount of power supplied. As a result, the power switch within a conventional SPS operating in a standby mode changes states (i-e., turns on and off) at the same rate as when the SPS is operating in a normal mode. In the standby operating mode, these switching transitions consume a significant amount of power, which significantly increases the lower limit of power consumption in the standby mode.
SUMMARY OF THE INVENTION
It In accordance with one aspect of the invention, a switching power supply includes a mode controller that provides a first mode control signal and a second. mode control signal. The power supply may further include a feedback circuit coupled to the mode controller that provides a first feedback signal based on the first mode control signal and a second feedback signal based on the second mode control signal. A switching controller coupled to the feedback circuit may generate a continuous fixed frequency signal in response to the first feedback signal and a series of fixed frequency burst signals in response to the second feedback signal.
In accordance with another aspect of the invention, a switching power supply includes a power switch and a mode controller that provides a mode control signal having a first level associated with a normal mode of operation of the switching power supply and a second level associated with a standby mode of operation of the switching power supply. The switching power supply may further include a feedback circuit coupled to the mode controller having a voltage controlled current source that provides a feedback current which varies in response to the mode control signal and a switching controller coupled to the feedback circuit and the power switch. The switching controller may switch the power switch in response to the feedback current so that in the normal mode of operation the power switch switches continuously at a predetermined frequency and in the standby mode of operation the power switch may be switched on and off in bursts having a predetermined frequency.
The invention itself, together with further objectives and attendant advantages, will best be understood by reference to the following detailed description, taken in conjunction with the accompanying drawings and the appended claims.


REFERENCES:
patent: 5453921 (1995-09-01), Shutts
patent: 6118675 (2000-09-01), Lionetto et al.

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