IL89284A - Method and device for supplying electric power including a cycled transformer - Google Patents

Description

89284/2 ABSTRACT There is disclosed an improved method and apparatus for supplyinq electric power including a cycled transformer having a primary winding and a plurality of secondary windings, in a manner that includes the changing of the current permeability of a variable load component connected in parallel to one of the secondary windings for preventing the current flowing within the circuitry thereof from decreasing below a predetermined value during a no-load condition at the output terminal of such secondary winding, thus assuring that the widths of the direct current pulses admitted into the primary winding are maintained above a predetermined value and that the energy transfer to each of the secondary windings is sufficient. 8 8 The invention related to method and apparatus for supplying electric power ' including a cycled transformer to maintain output voltages at a plurality of output terminals.

Background Of The Invention The transformation of electric loads by the admittance of direct current pulses into the primary winding of a transformer is priorly known. Such transformers are commercially available, and are known as "cycled transformers". Such cycled transformers are often employed as power suppliers to consumer circuits, for example, telecommunications equipments. In various applications' of such cycled transformers, the voltage values provided on the secondary windings output terminals must be maintained within restricted tolerances or limits and, consequently, voltage regulation is indispensable. In known cycled transformers such regulation was usually provided to the secondary windings which were designed for handling the larger output terminal loads. More particularly, such regulation was provided by changing the width of the direct current pulses admitted into the primary windings of the cycled transformers in accord with the magnitude of the load connected to the output terminals of the regulated secondary windings. problem to the prior art in that during the no-load condition of the regulated secondary windings only very narrow direct current pulses were admitted into the primary windings which resulted in satisfying only minimum energy transfers to the secondary windings. This often caused a breakdown in the voltage at the output terminals of the regulated secondary windings, as well as a breakdown of voltage at the output terminals of the other secondary windings, or at a minimum caused such output voltages to decrease below acceptable levels. To limit the consequences of such prior art problem, use limitations were etated on the various prior art cycled transformers as to the minimum load required for the output terminals of the regulated secondary windings. In other cases, .'the cycled transformers were limited to only one secondary winding each with concomitant expense and space requirements.

Objects Of The Invention An object of the present invention is to provide a novel method and apparatus for supplying electric power including a cycled transformer with a plurality of secondary windings which may be operated independent of the load condition associated with the secondary winding that is regulated.

Another object of the present invention is to provide a novel method and apparatus for operating a windings are operational, notwithstanding a low-load or no-load condition as to the secondary winding of such plurality which determines the width of direct current pulses admitted into the primary winding.

Still another object of the present is to provide a novel method and apparatus for operating a cycled transformer having a plurality of secondary windings without being subject to restrictions as to low-load or no-load conditions on the output terminals of the secondary windings.

Summary Of The Invention These and other objects of the present invention are achieved by a method and apparatus for supplying electric power - ' including a cycled , direct current, voltage transformer by changing the current permeability of a variable load component connected in parallel to a regulated one of a plurality of secondary windings. More particularly, the current permeability of such variable load component is changed in dependency upon the current flowing in the circuitry of the regulated secondary winding in a manner that such current does not decrease below a predetermined value. As a consequence of such variable load component, a minimum internal load condition is achieved in the circuit of the regulated secondary winding during a no-load condition at the output terminal of such secondary winding, and the secondary windings 6, 7 and 8. The direct current potential on output terminal Al results from secondary winding 6, while the direct current potential on output terminal A2 results from secondary winding 7, and the direct current potential on output terminal A3 results from the secondary winding 8. Further, the transformer U includes a core 9. As only the direct current potential at output terminal Al is regulated, only the secondary winding 6 with its associated circuitry is illustrated, the circuitry associated with the secondary windings 7 and 8 are not shown for simplicity.

The circuitry associated with the secondary winding 6 includes a rectifier 10 connected between one side of the secondary winding 6 and an impedance element 11. Connected on each side of the impedance element 11, and to the other side of the secondary winding 6 are two capacitors 12 and 13. Connected in parallel to the capacitor 13 is a voltage divider formed by a pair of serially connected resistors 14 and 15. A connection point T between the resistors 14 and 15 is connected to a first input terminal of a comparison circuit 16, which preferably functions as an operational amplifier. To a second input terminal of the comparison circuit 16 there is applied a reference, direct current, potential designated UREF. An output terminal of the comparison circuit 16 is in turn connected to a control circuit 17 from which cycled, direct current pulses are generated.

The comparison circuit 16 drives the control circuit 17 in accord with the potential detected at the connection point T between the resistors 14 and 15/ thereby controlling the width of the direct current pulses generated by the control circuit 17. A switch 18 connected in the circuit to ground of the primary winding 5, is connected to the control circuit 17 so as to have the time duration of its "open" and "closed" conditions dependent upon the width or time duration of such generated, direct current pulses. The switch 18 may, for example, comprise a standard type transistor. Depending upon the variations in the magnitude of the load condition at output terminal Al, the potential at the connection point T varies, resulting in a change in the width of the direct current pulses generated by the control circuit 17, which in turn varies the duration of energization of the primary winding 5, which in turn is translated to the secondary winding 6, as well as the secondary windings 7 and 8.

In order to prevent a breakdown of the voltage on the secondary windings 7 and 8 during a no-load condition at the output terminal Al, one side of a variable load device 19 is connected to output terminal Al, and the other side to a first side of a resistor 20. The second side of the resistor 20 is connected to the second side of the secondary winding 6. The current permeability of the variable load device 19 is dependent upon a current flow J through, and associated voltage drop across, the resistor 20. Upon current J passing through resistor 20 falling below a predetermined minimum value, the variable load device 19 becomes current permeable, resulting in a minimum load condition at the output terminal Al, and a current flow through the secondary winding 6, notwithstanding a no-load condition exists as to the plurality of consumer circuits V connectable to the .output terminal Al. Such minimum load condition assures adequate energization of the transformer U, so that the secondary windings 7 and 8 are energized and the direct current potentials on the output terminals A2 and A3 are respectively maintained.

Referring to Figure 3, the variable load device 19 schematically represented in Figure 2 comprises a bipolar transistor 2,1 having one side of its current path connected to the output terminal Al and the other side of such path connected to the first side of the resistor 20; a comparison circuit 22 having its output terminal connected to a base control electrode of the bipolar transistor 21 and its first input terminal El connected to the first side of the resistor 20; and a voltage divider comprising a serially connected Zener diode 23 and a resistor 24 connected between the output terminal Al and the second side of the resistor 20, the Zener diode 23 having one side thereof connected to an input terminal E2 of the comparison circuit 22, whereby a vo age rop across e res s or s app e o e input terminal El, and the Zener diode 23 applies a reference potential to the input terminal E2.

The operation of the circuit depicted in Figure 3 is as follows: As long as a sufficient load is provided to at least one of the plurality of consumer circuits V connected to the output terminal Al, a current of sufficient magnitude passes through the resistor 20 so that the voltage drop thereacross, which is applied to the input terminal El of the comparison circuit 22, causes the bipolar transistor 21 to retain an impermeable condition. Upon a decrease in the load connected to the output terminal Al, the current passing through the resistor 20 decreases, and the voltage drop across such resistor applied to input terminal El of comparison circuit 22 decreases. Consequently, the output potential of the comparison circuit 22 applied to the base control electrode of the bipolar transistor 21 increases, rendering such transistor permeable. Such potential is so adjusted that the current that passes through the current path of bipolar transistor 21 cannot decrease beyond a predetermined value. In the "no-load condition" (i.e., no consumer circuit V connected to the output terminal Al) , the current path of the bipolar transistor 21 conducts the total minimum current through the resistor 20. The minimum value of such current is e erm ne y e res s ance va ue o e res s or so as to cause a corresponding voltage drop for properly influencing the comparison circuit 22. Such minimum current corresponds to a minimum load condition at the output terminal Al that assures adequate energization of the transformer U, so that the secondary windings 7 and 8 are energized and the direct current potentials on the output terminals A2 and A3 are maintained.

While the invention has been described in connection with an exemplary embodiment thereof, it will be understood that many modifications will be apparent to those of ordinary skill in the art and that this application is intended to cover any adaptations or variations thereof. For example, though a bipolar transistor 21 is described with respect to the circuit of Figure 3, a ^field effect transistor, in particular, a MOSFET transistor may be used. Therefore, it is manifestly intended that the invention be only limited by the claims and equivalents thereof.

Claims (3)

89284/2, WHAT IS CLAIMED:

1. Method for supplyi ng electrics power T including a cycled, direct current, voltage transformer having a primary winding with an input terminal, and at least a first secondary winding with* a first output terminal and a second secondary winding with a second output terminal, comprising the steps of: applying a direct current potential to said input terminal; admitting direct current pulses to said primary winding from a direct current source; sensing the voltage across said first output terminal ; regulating the width of said direct current pulses in dependency upon said sensed voltage for regulating the voltage at said first output terminal; and changing the current permeability of a variable load component connected parallel to said first output terminal , in dependency upon the current flowing in the circuitry of said first secondary winding in a manner that such current does not decrease below a predetermined value independent from the load condition at said first output terminal. ' , Instal l ati on for.

2. Method-of suppl ying el ectric power Includi ng, a cycl ed directed current, voltage transformer having a primary winding with an input terminal, and at least a first secondary winding with a first output terminal and a second secondary winding with a second output terminal, comprising means for applying a direct current potential to said input terminal; means for admitting direct current pulses to said primary winding from a direct current source; means for sensing the voltage across said first output terminal; means for regulating the width of said direct current pulses in dependency upon said sensed voltage for regulating the voltage at said first output terminal; and means for changing the current permeability of a variable load component connected parallel to said first output terminal, in dependency upon the current flowing in the circuitry of said first secondary winding in a manner that such current does not decrease below a predetermined value Independent from the load condition at said first output terminal. Installation for'1 (>■

3 . Me-fcbed-ef suppl ing power . in accordance with claim 2 , wherein said first secondary winding is designed for handling the larger or largest of the output terminal loads.