Patent Application
20090085543
The present disclosure relates to variable output voltage power converters.
This section provides background information related to the present disclosure which is not necessarily prior art.
Power supplies generally provide an output voltage with different characteristics than the voltage input to the power supply. Numerous types of power supplies exist with different characteristics, benefits, efficiencies and deficiencies. Variable output voltage power supplies are operable to provide at least two different output voltages from a single power supply unit. Various methods of achieving this variable output voltage are known.
The full bridge converter 104 is operated with a fixed duty ratio close to 50 percent and a fixed frequency. Each switch Q1-Q4 receives a pulse width modulation (PWM) signal having a substantially constant duty cycle and a substantially constant frequency. The turns ratio of a transformer 108 is fixed. Because of the fixed duty cycle and fixed transformer turns ratio of the full bridge converter, the output voltage will have a fixed relationship with the intermediate voltage Vint. The output voltage Vout is varied, therefore, by changing the value of the intermediate voltage Vint that is output from the pre-regulator circuit 102 and input to the full bridge converter 104, such as from 300 volts to 150 volts.
Variable voltage power supplies such as the one illustrated in
The losses in the pre-regulator 102 are largely based on the output current. When the current in the pre-regulator 102 and the full bridge 104 remains the same regardless of the output voltage, the magnitude of the losses remains roughly the same. For example, a typical buck converter may have an efficiency of 98.5%. For a 1200 watt converter, i.e. 12 volts at 100 amps, the current in the pre-regulator 102 is about 4 amps and the losses are about 18 watts. When 6 volt output is desired, the intermediate voltage Vint from the pre-regulator 102 is about 150 volts at 4 amps. The power output is decreased significantly, from 1200 watts to 600 watts. This constant power loss combined with reduced power output results in decreased efficiency. Thus, at 600 watts, the constant 18 watt losses result in an efficiency of about 97%.
This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
According to one embodiment of the present disclosure, a variable output voltage DC-DC power supply includes a DC-DC converter selectively configurable as a full bridge converter for outputting a first DC voltage from the DC-DC converter and as a half bridge converter for outputting a second DC voltage from the DC-DC converter.
According to another aspect, a method of generating at least a first voltage and a second voltage in a power converter including at least one DC-DC converter is disclosed. The method includes operating the DC-DC converter as a full-bridge converter to generate the first voltage and operating the DC-DC converter as a half-bridge converter to generate the second voltage.
According to yet another aspect, a variable output voltage power supply includes a resonant converter having a plurality of switches selectively configurable as a full bridge converter for providing a first output voltage to a load and as a half bridge converter for providing a second output voltage to a load. The power supply also includes a pre-regulator circuit for providing a regulated voltage to the resonant converter. The pre-regulator circuit includes at least one switch. The power supply further includes a controller for controlling a duty cycle of the at least one switch according to the output voltage of the resonant converter.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.
Example embodiments will now be described more fully with reference to the accompanying drawings.
Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.
The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a”, “an” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.
When an element or layer is referred to as being “on”, “engaged to”, “connected to” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to”, “directly connected to” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
According to one aspect of the present disclosure, a method of generating at least a first voltage and a second voltage in a power converter having at least one DC-DC converter is disclosed. The method includes operating the DC-DC converter as a full-bridge converter to generate the first voltage and operating the DC-DC converter as a half-bridge converter to generate the second voltage.
In some embodiments, the DC-DC converter is operated with a substantially constant duty cycle when operated as a full bridge and as a half bridge converter. If the input voltage to the DC-DC converter is held substantially constant, the DC-DC converter, when configured as a half bridge converter, will generate a voltage approximately half the voltage generated when configured as a full bridge converter.
Example power converters capable of performing the method above will be discussed in further detail below. It should be understood, however, that other power converters can be employed without departing from the scope of this disclosure.
A variable voltage power supply 200 according to one example of the present disclosure is illustrated in
The output voltage Vout of the power supply 200 can be varied by selectively configuring the converter 204 as either a full bridge converter or a half bridge converter. The converter 204 includes four switches, Q1-Q4. In the full bridge configuration, all four switches Q1-Q4 operate in the manner of full bridge converters as known to those skilled in the art. The power supply 200 is illustrated in
While the switches in the various figures of this disclosure are illustrated as MOSFETs, it should be understood that other types of switches can be used without departing from the scope of this disclosure.
When the converter 204 is configured to operate as a full bridge converter, the output voltage Vout is the intermediate voltage Vint divided by the turns ratio of the transformer 212. When the converter is configured to operate as a half bridge converter, the output voltage Vout is the intermediate voltage Vint divided by twice the turns ratio of the transformer 212. If the intermediate voltage Vint and the turns ratio are substantially constant, the output voltage Vout in the half bridge configuration is approximately half the full bridge configuration output voltage Vout.
Although the intermediate voltage Vint is held substantially constant in the full bridge configuration and the half bridge configuration, the current output from the pre-regulator 202 is not. In the half bridge configuration, the current output from the pre-regulator 202 is approximately half of the full bridge configuration pre-regulator current. Because the losses in the pre-regulator 202 are largely determined by, and proportional to, the pre-regulator output current 202, the pre-regulator 202 operates with smaller losses when the converter 204 is configured as a half bridge converter. This, therefore, results in increased efficiency over other variable output voltage converters.
An example power converter 200 may provide a 12 volt and a 6 volt converter output both at 100 amps. The turns ratio of the transformer 212 is 25:1. The intermediate voltage Vint is 300 volts. As mentioned above, a typical buck converter may have an efficiency of 98.5%. Thus when the converter 204 is set to operate as a full bridge converter, the current in the pre-regulator 202 is about 4 amps and the losses are about 18 watts. When 6 volt output is desired, the converter 204 is configured as a half bridge. The pre-regulator 202 continues to output a 300 volt intermediate voltage Vint. The output current of the pre-regulator, however, is 2 amps. Thus, the pre-regulator 202 is operating at half the current load as it is when the converter 204 is configured as a full bridge converter. Typical buck converter efficiency at half load can be about 99%.
When the output voltage selection switch 426 is connected to the second voltage position 428, the control circuit 424 configures the converter 204 as a half bridge power converter. Placing the voltage selection switch 426 in the second voltage position 428 enables switches Q5-Q7. The relay contact 432 is moved to a second position 436. As a result, switch Q3 will be continuously enabled, i.e. a continuously closed, while switch Q4 will be continuously held open. This results in the converter 204 being configured as a half bridge converter as illustrated in
When the output voltage selection switch 526 is connected to the second voltage position 528, the control circuit 524 configures the power converter 304 as a half bridge power converter. Placing the voltage selection switch in the second voltage position enables switches Q5-Q7. This causes the relay 522 to close, while switch Q4 is held continuously held open. Closing the relay 522 creates a short circuit around the switch Q3. This results in the converter 304 being configured as a half bridge converter.
When the output voltage selection switch 1026 is connected to the second voltage position 1028, the control circuit 1024 configures the power converter 804 or 904 as a half bridge power converter. Placing the voltage selection switch in the second voltage position enables switches Q5-Q7. This causes the relay 1022 to move to position B. This results in the converter 804 or 904 being configured as a half bridge converter.
Although the pre-regulator circuit illustrated in the previous embodiments is a buck converter, this disclosure is equally applicable to different converter topologies.
The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the invention, and all such modifications are intended to be included within the scope of the invention.
This application claims the benefit of U.S. Provisional Application No. 60/976,154, filed on Sep. 28, 2007. The entire disclosure of the above application is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60976154 | Sep 2007 | US |
