Electrical transmission or interconnection systems – Plural supply circuits or sources
Patent
1991-04-11
1992-12-08
Pellinen, A. D.
Electrical transmission or interconnection systems
Plural supply circuits or sources
307 64, H02J 906, H02M 3315
Patent
active
051700700
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to an improvement applicable to a switching power supply and to an adapter employable for a switching power supply. More specifically, this invention relates to an improvement brought out for an object to enable the switching power supply to continue supplying electric power for a certain period, despite supply of the input power is suspended and to an adapter to be adapted to a switching power supply available in the prior art to enable the switching power supply to continue supplying electric power for a certain period, despite supply of the input power is suspended.
A switching power supply which is employed for supplying electric power to some of the electronic equipment employable for industrial purposes is required to continue supplying electric power for a certain period, even after supply of the input power is suspended (Hereinafter referred to as a power failure.). Otherwise, some of the electronic equipment employable for industrial purposes such as numerical control equipment (Hereinafter referred to as NC equipment.) controlling a machine tool or the like has a possibility to erroneously work, potentially resulting in breakage of the machine tool or the like controlled thereby. For the purpose to avoid these accidents, it is required to promptly detect a power failure and to allow the NC equipment or the like to take a sequential procedure to stop the function thereof without being accompanied by any malfunction, within the period in which the switching power supply keeps supplying electric power. The voltage required for the switching power supply to keep supplying during the foregoing period, however, is not the normal voltage but the minimum voltage required to allow the NC equipment or the like to conduct the foregoing limited procedure to stop the function thereof.
In this specification, the interval between a power failure and the detection thereof is called a time length for detecting a power failure, and the interval between the detection of a power failure and the time at which the voltage of the switching power supply has decreased to the foregoing minimum voltage is called a time length wherein the DC output voltage V.sub.O is held.
Available in the prior art are two exemplary switching electric power supplies which are able to keep supplying electric power for a certain period, even after supply of the input electric power is suspended.
A first example of a prior art switching power supply having the ability to continue supplying electric power after a power failure will not be discussed.
This switching power supply includes a rectifier and a switching circuit to intermit the DC current, wherein a means for detecting a power failure is attached to the AC circuit.
Referring to FIG. 1 the switching power supply in accordance with the first example available in the prior art is provided with a rectifier 40 which rectifies an AC voltage V.sub.I into a DC voltage, a capacitor 1, a switching means 2, a transformer 3, a diode 4, a flywheel diode 5, an inductance 6, a smoothing capacitor 7, a first voltage comparator 8 which compares the DC output voltage V.sub.O and a reference voltage V.sub.R a pulse width modulation means 9, and a means for detecting a power failure 10.
The DC current flowing out of the rectifier 40 is charged into the capacitor 1. The switching means 2 is closed during a period .DELTA.T out of a predetermined clock period T. The ratio of the period .DELTA.T and the clock period T (Hereinafter referred to as a duty ratio .DELTA.T/T) is automatically determined by a pulse width modulation means 9 referred to later, to be suitable to maintain the DC output voltage V.sub.O at a predetermined value, regardless of variation in the AC input voltage V.sub.I and variation in a load of the switching power supply. In response to the intermittent current flowing in the primary winding 31 of the transformer 3, an intermittent voltage is induced in the secondary winding 32 of the transformer 3. This intermittent voltage supplies ele
Hattori Masayuki
Nakamura Shigeo
Sakurai Akihiro
Fanuc Ltd.
Krishnan Aditya
Pellinen A. D.
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