Electricity: power supply or regulation systems – Output level responsive – Using a transformer or inductor as the final control device
Reexamination Certificate
2000-05-02
2001-02-20
Wong, Peter S. (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a transformer or inductor as the final control device
C323S283000, C323S263000
Reexamination Certificate
active
06191567
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a converter for converting an input voltage into an output voltage, having a switch for controlling the converter under control of a binary signal by means of adaptation of the duty cycle of the binary signal so as to obtain a desired value of the output voltage, which converter has at least two conversion modes and which converter in its operation condition is in one of at least two conversion modes, and selection means for the selection of at least one of the at least two conversion modes.
Such a converter is known from United States Patent Specification 5,475,296. Said Specification describes a switched-mode voltage converter which operates in a so-called buck mode or in a so-called boost mode. The known converter further has means for comparing the output voltage with the input voltage. The result of said comparison is used for determining whether the converter is to be switched from the buck mode to the boost mode or vice versa. If the input voltage is higher than the output voltage the converter is in the buck mode. If the input voltage is lower than the output voltage the converter is in the boost mode.
A drawback of the known converter is that the method of determining when the converter should change from the buck mode too the boost mode or vice versa is comparatively complex.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a converter which does not have this drawback.
To this end, according to the invention, the converter of the type defined in the opening paragraph is characterized in that the selection means include detection means for the detection of the duty cycle of the binary signal, and comparison means for comparing the duty cycle of the binary signal with a reference duty cycle and for supplying a mode control signal in response to the comparison in order to change over from one of the at least two conversion modes to another one of the at least two conversion modes.
As a result of this, in contradistinction to the known converter, no means are required for comparing the output voltage with the input voltage for the purpose of changing over from the one conversion mode to the other conversion mode.
The invention is based on the recognition of the fact that the duty cycle of the binary signal inherently contains information that can be used to indicate, by means of the mode control signal, when the converter should change over from the one conversion mode to another conversion mode. Let it be assumed, for example, that the converter has two conversion modes: an up-conversion mode, i.e. the converter functions as a so-called up-converter, and a down-conversion mode, i.e. the converter functions as a so-called down-converter. Let it further be assumed that the input voltage is 10 V, that the output voltage is 3 V, and that the desired output voltage is 12 V. (This situation can arise, for example, in that in a prior situation the input voltage was 10 V and the desired output voltage was 3 V, so that eventually the converter was permanently in the down-conversion mode in order to achieve the conversion from 10 V to 3 V, and subsequently the desired output voltage was changed to 12 V). It is then further likely (because the output voltage is much lower than the input voltage) that in spite of the fact that, in principle, it is also possible to realize a down-conversion by means of conventional up-converters, the converter will be dimensioned in such a manner that it is the down-conversion mode because the conversion is then more efficient. The duty cycle of the binary signal will adapt itself in order to end up at the desired output voltage of 12 V. When it is assumed that, in order to increase the output voltage of the converter (in the down-conversion mode) the duty cycle should be increased, the duty cycle of the binary signal will continually increase as long as the output voltage is lower than the desired output voltage. In the down-conversion mode the output voltage can never become greater than the input voltage. In the present example the output voltage can therefore not become higher than 10 V as long as the converter is in the down-conversion mode. In order to allow the desired output voltage to be reached in the end, the converter should duly change over from the down-conversion mode to the up-conversion mode. However, for reasons of efficiency the converter should preferably change over to the up-conversion mode when the output voltage is relatively close to 10 V, for example 9.7 V. It is important to recognize that the duty cycle (which, by definition, is always in the range from 0 to 1) of the binary signal is correlated with the output voltage. By comparison of the duty cycle of the binary signal with the reference duty cycle, it is therefore possible to determine when the converter should change over to the up-conversion mode. In the present example, as a result of said correlation, the reference duty cycle should have nearly its maximum value (for example 0.98) because an output voltage of 9.7 V lies comparatively close to the (theoretically) maximum attainable output voltage of 10 V. After the converter has changed over to the up-conversion mode the converter can raise the output voltage to the desired value of 12 V by adaptation of the duty cycle of the binary signal.
It is to be noted that the above example merely serves to clarify the invention and should not be interpreted as prerequisite for the implementation of the invention. Thus, the change-over from the one conversion mode to another conversion mode may, for example, be based on a reference duty cycle which is comparatively close to zero. It is also possible to use more than one binary signal, for example a binary signal for controlling the converter in the down-conversion mode and a further binary signal for controlling the converter in the up-conversion mode. It is also possible to use a plurality of reference duty cycles, for example in such a manner that each conversion mode has its own reference duty cycle. Furthermore, it is possible to have, for example, two up-conversion modes. Moreover, it is to be noted that in the known converter the change-over from an up-conversion mode to a down-conversion mode or vice versa is always effected at the instant that the output voltage equals the input voltage. This is in contradistinction to the converter in accordance with the invention, where the change-over point may be chosen freely.
An embodiment of a converter in accordance with the invention is further characterized in that the conversion modes include a first, a second and a third conversion mode, and in the operating condition the converter can change over from the first or from the third conversion mode to the second conversion mode under control of the mode control signal. To elucidate this, it is assumed by way of example that the first and third conversion mode is an up-conversion mode and a down-conversion mode, respectively, and that the second conversion mode is a so-called window conversion mode. The change-over from the up-conversion mode to the window conversion mode or from the down-conversion mode to the window conversion mode operates in a manner similar (i.e. by comparison of a duty cycle with a reference duty cycle) to that described in the previous example in which the converter changes over from a down-conversion mode to an up-conversion mode or vice versa. In the window conversion mode each of the switches in the converter is either permanently closed or permanently open. An advantage of this is that there are no switching losses and, as a result of this, the efficiency of the converter is higher. As long as the output voltage is within a so-called voltage window the converter remains in the window conversion mode. The voltage window defines a lower limit and an upper limit within which the output voltage may be situated.
Since in the window conversion mode each switch is either permanently closed or permanently open the change-over to the down-conversion mode or to the up-conversion mode
Biren Steven R.
U.S. Philips Corporation
Vu Bao Q.
Wong Peter S.
LandOfFree
DC-DC converter, with duty cycle comparison for a dual mode... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with DC-DC converter, with duty cycle comparison for a dual mode..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and DC-DC converter, with duty cycle comparison for a dual mode... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2613050