Patent Application
20060255779
The present invention relates to the field of power supplies, and particularly to a linear voltage regulator for providing a regulated voltage to electronic devices.
DC-to-DC power converters are widely used to supply power to electronic devices, such as computers, printers, etc. Such linear voltage regulators are available in a wide variety of configurations for many different applications.
Referring to
However, the typical linear voltage regulator is without current sink capabilities. When there is a voltage delta appears, a back-drive current created by the voltage delta cannot be consumed. For example, when the typical linear voltage regulator provides voltage to a front side bus (FSB), there is possibility a voltage delta appears due to a difference in a processor and a memory controller hub (MCH). When the FSB is inactive, the voltage delta creates a condition where a higher processor voltage creates a back-drive current in the MCH termination. Since a MCH leakage current or the typical linear voltage regulator cannot consume the back-drive current, the processor voltage will increase beyond the regulation limits. As a result, an impedance calibration of the active MCH front side bus termination transistors will be impacted. And the heightened processor voltage may also reduce a life span of the MCH.
What is desired, therefore, is a linear voltage regulator which has current sink capabilities.
In one preferred embodiment, a linear voltage regulator comprises an error amplifier receiving an operational voltage and provided a control signal, a pass device controlled by the control signal and providing a load voltage from a power supply, and a leakage circuit controlled by the control signal and consuming a drive-back current. Since the linear voltage regulator includes the leakage circuit, a drive-back current created can be grounded via the switch transistor of the leakage circuit. Thereby an impedance calibration of termination transistors will be normal, and a life span of electronic components will be protected.
Other advantages and novel features will become more apparent from the following detailed description of preferred embodiments when taken in conjunction with the accompanying drawings, in which:
As shown in
An operational voltage Vcc is fed to the error amplifier 10 to make the error amplifier 10 function. A non-inverting of the error amplifier 10 receives a voltage reference Vref. An inverting of the error amplifier 10 is connected to the pass device 20 for sensing a load voltage of a load 50. A control signal from the output of the error amplifier 10 is fed to the pass device 20 for controlling the pass device 20. An N-channel metal-oxide-semiconductor field-effect transistor (MOSFER) Q1 is used as the pass device 20. A gate of the MODFET Q1 acts as a control terminal 201 of the pass device 20 for receiving the control signal. A source of the MODFET Q1 acts as an input terminal 202 of the pass device 20 for receiving an input voltage V1 provided by a power supply. A drain of the MODFET Q1 acts as an output terminal 203 of the pass device 20 for providing the load voltage of the load 50. The leakage circuit 30 includes a limiting resistor R1 and a switch transistor. An NPN bipolar transistor Q2 is employed as the switch transistor. A base of the bipolar transistor Q2 acts as a control end 301 for receiving the control signal via the limiting resistor R1. A collector of the bipolar transistor Q2 acts as an input end 302 for receiving the load voltage. An emitter of the bipolar transistor Q2 acts as an output end 303 for grounding.
As shown in
When the linear voltage regulator operates normally, the control signal from the output of the error amplifier 10 controls the pass device 20 to provide current from a power supply to the load 50. The pass device 20 maintains a desired output voltage despite fluctuations in the load 50. The leakage circuit 30 does not function. When the linear voltage regulator operates abnormally, that is, when a back-drive current appears, the switch transistor Q2 of the leakage circuit 30 turns on. The back-drive current is grounded via the switch transistor Q2.
In the illustrated embodiment, because that the linear voltage regulator includes the leakage circuit 30, a drive-back current created can be grounded via the switch transistor of the leakage circuit 30 when the voltage delta appears, that is, the drive-back current can be consumed. For example, when the linear voltage regulator provides voltage to a front side bus (FSB), there is possibility a voltage delta appears due to a difference in a processor and a memory controller hub (MCH). When the FSB is inactive, the voltage delta creates a condition where a higher processor voltage creates a back-drive current in the MCH termination. The switch transistor of the leakage circuit 30 can consume the drive-back current. As a result, an impedance calibration of the active MCH front side bus termination transistors will be normal. And a life span of the MCH will be protected.
It is believed that the present embodiment and its advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the example hereinbefore described merely being a preferred or exemplary embodiment.
| Number | Date | Country | Kind |
|---|---|---|---|
| 200510034681.4 | May 2005 | CN | national |
