Electric power conversion systems – Current conversion – With condition responsive means to control the output...
Patent
1997-12-29
1999-04-06
Sterrett, Jeffrey
Electric power conversion systems
Current conversion
With condition responsive means to control the output...
363 21, H02M 7539
Patent
active
058926720
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a voltage converter for producing a controlled output voltage from an input voltage.
Voltage converters are well known in the prior art, and are described in their various constructions as step-down transformers, step-up transformers, isolating transformers, etc., in Tietze, Schenk: "Halbleiterschaltungstechnik," 9th ed., 1990, pp. 561 to 576. In voltage converters of this sort, a switching element is connected with an inductive element, e.g. a coil or the primary winding of a transformer, in order to apply an input voltage, which can be a rectified alternating voltage, pulse-by-pulse to the inductive element. Dependent on a control circuitry, the switching element is clock-controlled in pulse-width-modulated fashion in such a way that an output voltage with a desired characteristic is present. The controlled output voltage is normally supposed to be a voltage that is as constant as possible and is present in load-independent fashion.
The control circuit required for controlling the switching element is normally realized as an integrated circuit with external wiring elements for signal production and preparation. The integrated control module TDA 4605 from Siemens is suited for use as a control IC for isolating-transformer switch-mode power supplies. The signal processing in the TDA 4605 is carried out with analog circuit technology. This circuit technology has the advantage that a relatively small number of transistors is required, but has the disadvantage of difficult dimensioning and high sensitivity to disturbances in relation to operational fluctuations and the influence of parasitic elements.
In the reference Patent Abstracts of Japan, 1991, vol. 15, no. 236, (E-1078), JP 3-70464, a switching controller with a digitally operating controlling is specified. The control circuit contains a counter driven by an oscillator a counter state of which is compared with a comparison value. A switching element provided in the switching controller is controlled dependent on the comparison result. The comparison value is provided by a bidirectional counter whose bidirectional counter input is driven by a comparator, by means of which the output voltage to be controlled is compared with a reference value.
In Patent Abstracts of Japan, 1992, vol. 16, no. 316 (E-1231), JP 4-87556, a free-wheeling switch-mode power supply with a digitally operating controlling is specified, in which an operational counter, clock-controlled by an oscillator, is reset by a feedback signal derived from a transformer winding. By this means, the turn-off time of the switching transistor is matched to the resonance frequency of the transformer.
In Patent Abstracts of Japan, 1990, vol. 14, no. 95 (E-892), JP 1-298958, a switch-mode power supply is described whose control circuit contains a CPU.
The previously known digitally operating power packs are operated with unaltered functioning for low load at the output side (standby), and provide no particular circuit means that take this operational state into account. A low power loss of the power pack is desirable in standby operation in particular.
SUMMARY OF THE INVENTION
An object of the invention is to provide a voltage converter of the type named above that has a lower power loss in low load operation.
According to the present invention, a voltage converter is provided for producing a controlled output voltage from an input voltage. An inductive element is connected between an input circuit and an output circuit. The inductive element is also connected with a switching element for pulse-by-pulse application of the input voltage to the inductive element. A control circuit is provided for driving the switching element for controlling the output voltage. The control circuit has a digital counter unit having an output signal which is compared with a digital comparison value derived from the output voltage so that, dependent on a comparison result, the switching element is turned off. The digital comparison value derived from the output vol
REFERENCES:
patent: 4984145 (1991-01-01), Daugschat et al.
patent: 5325282 (1994-06-01), Bansard
patent: 5684685 (1997-11-01), Komatsu et al.
U.Tietze-Ch. Schenk--Halbleiter-Schaltungstechnik--p. 561-576 Dec. 1990.
Patent Abstracts of Japan--E-1231 Jul. 10, 1992, vol. 16,/No. 316, 4-87556.
Patent Abstracts of Japan--E-892, Feb. 21, 1990 vol. 14/No. 95,1-298958.
Patent Abstracts of Japan--E-1078--Jun. 18, 1991 vol. 15/No. 236--3-70464.
Siemens Aktiengesellschaft
Sterrett Jeffrey
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