Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Patent
1998-01-08
1999-08-17
Wong, Peter S.
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
363 56, 363 97, H02M 3335, H02M 324, H02H 7122
Patent
active
059402814
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND INFORMATION
In the related art, the output current or the output voltage in a switched-mode power supply is regulated in the current mode or in the voltage mode.
In the current mode, the switched-mode regulator operates according to the following principle: a peak current setpoint that is to be reached in the transformer is selected. Then a certain pulse width is established in the transformer, depending on the setpoint, as illustrated in FIG. 1. This shows the current I in the transformer, the setpoint of the peak current I.sub.s and the resulting pulse width p.
It can easily be seen that the pulse width p can very rapidly assume large values in transient processes, so the transformer runs into saturation after only a few cycles because it is no longer completely demagnetized at large pulse widths. One could of course limit the pulse width p to a fixed value, but this has the disadvantage that long-range power supply units can hardly be implemented.
In the voltage mode, the selected setpoint is not a peak current but instead it is the pulse width p directly (FIG. 2). This is generated by comparison of a delta voltage or a saw-tooth voltage with the setpoint. However, here again there is the same problem that the pulse width p can vary too much in transient processes, and then the transformer no longer demagnetizes. FIG. 2 shows the three signals in the voltage mode: delta voltage U.sub.D, setpoint U.sub.s and pulse width p.
The object of the present invention is to find a possibility of limiting the pulse width according to the single-ended flux converter principle in a switched-mode power supply so that saturation phenomena in the transformer and the associated overvoltages are prevented.
SUMMARY OF THE INVENTION
By stipulating or limiting the maximum flux density in the transformer, instead of the peak current or the pulse width directly (current or voltage mode), it is possible to optimally utilize the transformer as well as the power components and expose them to the least thermal stress (due to the resulting overvoltages).
In addition, there are advantages in start-up of the switched-mode power supply because the pulse width never exceeds inadmissible values, and a "smooth start" is automatically achieved due to a favorable arrangement of the required components.
An advantageous secondary effect is achieved for the output controller. Although the system tends to instability in the current mode in particular (at least in the extreme ranges: rated load with line undervoltage, no-load operation and short-circuit of the output), the switching controller principle according to the present invention yields increased stability properties.
And finally, the switching controller can be designed very simply with existing integrated circuits (IC) for the current mode. The primary shunt resistor is eliminated, which permits a greater efficiency of the power supply unit.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows current and voltage diagrams of a known controller in the current mode.
FIG. 2 shows two voltage diagrams of a known switching controller in the voltage mode.
FIG. 3 shows an exemplary embodiment according to the present invention.
FIG. 4 shows two voltage diagrams for an operation of a switching controller illustrated in FIG. 3.
DETAILED DESCRIPTION
FIG. 3 shows a transformer with two magnetically coupled coils 19, 20, which are supplied by another coupled coil 18. Coil 20 is connected in parallel with an output capacitor 24 across a series-connected rectifier 21 and a shunt resistor 23. In parallel with output capacitor 24 there is an output terminal 37, 38 and a position voltage U can be picked up. Coil 19 has one end connected to ground and its second end connected to a power supply 14 across a diode 15. An integrator 11 is connected at node 1 between the second end of coil 19 and diode 15. At the input end, integrator 11 has a resistor R1 and a capacitor C1 whose second end is connected to a reference voltage V.sub.ref. Reference voltage V.sub.ref is connected across another
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Robert & Bosch GmbH
Vu Bao Q.
Wong Peter S.
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