Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Patent
1995-08-04
1997-09-23
Krishnan, Aditya
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
H02J 710
Patent
active
056711298
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an electronic switched-mode power supply for supplying power to an accumulator from an input voltage source, comprising a self-oscillating flyback converter having a transformer whose primary winding, in series arrangement with the collector-emitter circuit of a switching transistor and a resistor, is connected in parallel with the input voltage source, and whose secondary winding is connected in series with the accumulator and a diode, with the base of the switching transistor being connected to the secondary winding through a feedback circuit in addition to being coupled to a control circuit inhibiting conduction of the switching transistor when the switching voltage at the accumulator has reached a predetermined upper level, and rendering it conducting again when the switching voltage has dropped below this level.
A switched-mode power supply of this type is known, for example, from EP 0 162 341 B1. After a specified (adjustable) upper switching voltage is reached, the charging current is controlled by the pulsed mode of the switched-mode power supply, that is, by means of the ratio of the duration of oscillation pauses to the duration of oscillation bursts of the converter. FIG. 5 is a graph showing the typical curve of the cell voltage during charging of an accumulator, plotted as a function of the stored charge. When it is desired to recharge a depleted accumulator as rapidly as possible, it is necessary for the switching voltage to be as high as possible. However, in such a switched-mode power supply, this switching voltage cannot reside at any desired point close to the top (hump) of the charging curve, because then the trickle-charging current flowing after the accumulator is charged to full capacity would be too high which would be detrimental to the accumulator.
It is an object of the present invention to configure a switched-mode power supply of the type initially referred to such as to permit a high charge in a minimum possible time, without the trickle-charging current rising in an inadmissible way.
This object is accomplished in that a switching arrangement is provided which operates on the control circuit such that the upper switching voltage is lowered to a lower switching voltage when, with the switched-mode power supply in the pulsed mode, the ratio of the duration of oscillation pauses to the duration of oscillation bursts exceeds a specified magnitude.
This has the advantage that the upper switching voltage of the switched-mode power supply can be increased to a level enabling the accumulator to be charged to at least about 80% of its rated capacity within a relatively short period of time. By evaluating the ratio of pulse spaces to pulse duration, an adjustment of the upper and lower switching voltage is only necessary in a greatly expanded tolerance field. After the switching voltage is lowered, setting an end to the high-current charge, the switched-mode power supply is deactivated until the accumulator voltage has reached the level of the lower switching voltage. At the end of this high-current charge, the charge acceptance response of the accumulator is rather poor as a result of the temperature increase. After the accumulator has cooled down, the lower switching voltage is reached, and recharging of the accumulator is continued until it is fully charged, yet starting with a lower charging current than before.
Advantageously, the switching arrangement is comprised of an evaluating circuit with a capacitor which is charged during the occurrence of oscillation pauses and is discharged during the occurrence of oscillation bursts, and a trigger circuit which passes to the other condition after the voltage across the capacitor has reached a specified level and drives an adjusting device reducing the switching voltage of the control device.
By evaluating the ratio of the duration of oscillation pauses to the duration of oscillation bursts, it is possible to annunciate a defined state of charge of the accumulator.
Further advantageous embodiments will become app
REFERENCES:
patent: 3585482 (1971-06-01), Zelina
patent: 4965506 (1990-10-01), Algra et al.
Braun Aktiengesellschaft
Krishnan Aditya
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