Electric power conversion systems – Current conversion – Having plural converters for single conversion
Patent
1998-06-11
2000-02-29
Sterrett, Jeffrey
Electric power conversion systems
Current conversion
Having plural converters for single conversion
363 89, 363126, H02M 708
Patent
active
060317450
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains generally to electrical power supply circuitry, and more particularly to a method and apparatus for obtaining multiple, independent, variable voltage power supplies from a single secondary transformer winding.
2. Description of the Background Art
There exists situations wherein two or more independently variable voltage DC power supplies are required; for example, the operation of multiple direct current devices such as DC servo motors or DC stepper motors in motion control and robotic applications. While it is possible to link together multiple linear power supplies or multiple switching power supplies under a common control system, there are a number of problems with doing so, including: (i) it is difficult and expensive to link together, in a coordinated manner, the control of such power supply combinations; and (ii) both types of such power supplies require numerous components that take up a large amount of physical space and are costly to build. Since physical transformers are not ideal devices, an increase in current draw will cause a lowering of the output voltage on the secondary winding (and on any other secondaries that may be on the same transformer). The result is that the power supply output capacitors may not get the desired amount of current and voltage (i.e. there is excessive voltage sag on the transformer), and instabilities can arise as the various instances attempt to compensate by drawing even more current on subsequent cycles.
BRIEF SUMMARY OF THE INVENTION
The present invention overcomes such deficiencies by allowing multiple, independent, variable voltage power supplies to be connected in parallel to a single secondary transformer winding without simultaneously loading the transformer secondary. Each voltage supply circuit is controlled by a logic circuit that gates a power FET which, in turn, delivers current to a storage capacitor from a full wave rectifier on the transformer secondary winding. By controlling when the FET is "on"in relation to the AC waveform, the voltage to which the storage capacitor is charged can be regulated. This provides a controllable, variable voltage supply from the storage capacitor. By coordinating the timing of the FETs in several of these circuits, they can share a single transformer secondary winding without adversely affecting the regulation of the output of the other secondary voltage circuits. Moreover, the total amperage drawn on the transformer at a given point in time is substantially reduced. Consequently, the size of the transformer can be considerably smaller than if all the variable voltage supply circuits were drawing current simultaneously.
An object of the invention is to operate multiple, direct current, variable voltage power supplies independently from a single transformer secondary winding.
Another object of the invention is to operate multiple, direct current, variable voltage power supplies independently from a single transformer secondary winding without simultaneously loading the transformer secondary.
Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be more fully understood by reference to the following drawings which are for illustrative purposes only:
FIG. 1 is a diagram of a single variable voltage direct current power supply in accordance with the present invention connected to a transformer with a bridge rectifier.
FIG. 2 is a diagram of a plurality of variable voltage direct current power supplies as shown in FIG. 1 connected in parallel to the secondary of the transformer and to time multiplexing circuitry in accordance with the present invention.
FIG. 3 is a diagram of a zero crossing detector employed in the present invention.
FIG. 4 is a diagram of a variable voltage powe
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Dwyer Patrick H.
Southman Gordon R.
Aim Controls, Inc.
O'Banion John P.
Sterrett Jeffrey
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