Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2000-06-30
2001-04-03
Bethane, Adolf Deneke (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S097000, C323S284000
Reexamination Certificate
active
06212079
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to power supplies and, more specifically, the present invention relates to a switching regulator.
2. Background Information
Electronic devices use power to operate. Switched mode power supplies are commonly used due to their high efficiency and good output regulation to power many of today's electronic devices. In a known switched mode power supply, a low frequency (e.g. 50 or 60 Hz mains frequency), high voltage alternating current (AC) is converted to high frequency (e.g. 30 to 300 kHz) AC, using a switched mode power supply control circuit. This high frequency, high voltage AC is applied to a transformer to transform the voltage, usually to a lower voltage, and to provide safety isolation. The output of the transformer is rectified to provide a regulated DC output, which may be used to power an electronic device. The switched mode power supply control circuit usually provides output regulation by sensing the output and controlling it in a closed loop.
A switched mode power supply may include an integrated circuit switching regulator, which may include an output transistor coupled in series with a primary winding of the transformer. Energy is transferred to a secondary winding of the transformer by turning on and off of the output transistor in a manner controlled by the switching regulator to provide a clean and steady source of power at the DC output. The transformer of a switched mode power supply may also include another winding called a bias or feedback winding. In some switched mode power supplies, the feedback or control signal can come through an opto-coupler from a sense circuit coupled to the DC output. The feedback control signal may be used to modulate a duty cycle of a switching waveform generated by the switching regulator. The duty cycle is defined as the ratio of the on time to the switching period of the output transistor. If there is a large load at the DC output of the power supply, the switching regulator responds to this situation by increasing the duty cycle and thereby delivering more power to the load. If the load becomes lighter, then the switching regulator senses this change through the feedback signal and reduces the duty cycle.
If the load is further reduced and if the power delivered to the DC output cannot be reduced indefinitely, then the DC output voltage increases, resulting in poor output regulation. This unfavorable situation becomes worse if the load is completely removed. To improve the output regulation, a constant load may be connected internal to the power supply. However, because the internal load is always connected, even when there is no load at the DC output, the power supply efficiency is decreased. The power supply efficiency loss is generally due to three components: (1) DC operating power that keeps the switching regulator circuitry operating, (2) the switching losses that are due to switching of the switching regulator output transistor and its drivers—switching losses are directly proportional to the operating frequency, and (3) the power that is consumed by the internal load.
In order to improve efficiency, a switching regulator may use a method called cycle skipping. Cycle skipping method involves reducing the duty cycle as the load decreases, and when the duty cycle is reduced down to a predetermined minimum duty cycle, it alternatively switches for some duration of time and stays idle for another duration of time depending on the load. During this mode, if the load increases very slightly, the output transistor will switch at minimum duty cycle for a short time until the power demanded by the load is delivered and then stop switching again. In theory, the cycle skipping mode decreases the switching losses at light loads since switching occurs as intermittent groups of pulses. Also, cycle skipping eliminates the need for the constant internal load. However, if the groups of pulses occur at a frequency that is within the audio range and the minimum duty cycle is larger than optimum, then the power supply may create an undesirable audio noise. In addition, cycle skipping degrades the output ripple since it typically occurs in groups of pulses and therefore the energy is delivered to the load intermittently.
SUMMARY OF THE INVENTION
Switching regulator methods and apparatuses are disclosed. In one embodiment, a switching regulator includes a power switch coupled between first and second terminals. The first terminal is to be coupled to an energy transfer element of a power supply and the second terminal is to be coupled to a supply rail of the power supply. A control circuit is coupled to a third terminal and the power switch. The third terminal is to be coupled to an output of the power supply. The control circuit is coupled to generate a feedback signal responsive to the output of the power supply. The control circuit is coupled to switch the power switch in response to the feedback signal. The control circuit is coupled to switch the power switch at a fixed switching frequency for a first range of feedback signal values and coupled to vary a switching frequency of the power switch without skipping cycles in response to the feedback signal for a second range of feedback signal values. Additional features and benefits of the present invention will become apparent from the detailed description, figures and claims set forth below.
REFERENCES:
patent: 3909695 (1975-09-01), Peck
patent: 4459651 (1984-07-01), Fenter
patent: 4460951 (1984-07-01), Fenter et al.
patent: 4849869 (1989-07-01), Tanuma et al.
patent: 5430633 (1995-07-01), Smith
patent: 5747977 (1998-05-01), Hwang
patent: 5912552 (1999-06-01), Tateishi
Balakrishnan Balu
Djenguerian Alex B.
Bethane Adolf Deneke
Blakely , Sokoloff, Taylor & Zafman LLP
Power Integrations, Inc.
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