Power supply with re-configurable outputs for different output voltages and method of operation thereof

For use with a DC power supply having first and second output rectifying circuits couplable in alternative configurations to provide dual voltages at an output of the DC power supply, an adaptive voltage controller and a method of adaptively controlling the output voltage. In one embodiment, the adaptive voltage controller includes: (1) a configuration determination circuit, coupled to the output, that generates a configuration signal that is a function of a configuration of the first and second output rectifying circuits, (2) a voltage feedback circuit, coupled to the configuration determination circuit, that develops a voltage feedback signal based on the configuration signal and (3) a voltage control circuit, coupled to the voltage feedback circuit, that receives the voltage feedback signal and controls an output voltage of the DC power supply as a function thereof.

TECHNICAL FIELD OF THE INVENTION 
The present invention is directed, in general, to power conversion and, 
more specifically, to a DC power supply that may be configured to provide 
alternative output voltages and a method of operating a DC power supply to 
provide alternative output voltages. 
BACKGROUND OF THE INVENTION 
The traditional reliability of telecommunications systems that users have 
come to rely upon is due largely to the systems' operation on highly 
reliable and redundant power systems. Power systems used in 
telecommunications applications typically consist of a DC power supply 
that converts commercial alternating current (AC) power into direct 
current (DC) power for use by the telecommunications system. To be 
suitable for use in many different countries, the DC power supply must be 
compatible with a wide range of voltages and frequencies. Commercial power 
in Europe, for example, is supplied at 220 VAC, 50 Hz. In the United 
States, however, a standard voltage is 120 VAC at 60 Hz. In addition, 
brownouts may significantly reduce line voltages and, conversely, lighter 
loads, particularly at night, may cause the line voltages to increase. 
Accordingly, power supplies are typically designed to operate with 
frequencies between 47 and 65 Hz, and with voltages ranging from 85 VAC to 
as high as 265 VAC (commonly known as "universal input"). 
The DC power supply converts this AC voltage to a DC voltage required by 
telecommunications equipment contained in a particular telecommunications 
system. The DC power supply generally includes an electromagnetic 
interference (EMI) filter, a power factor correction circuit and a DC/DC 
converter. The EMI filter is employed to ensure compliance with EMI 
standards. The power factor correction circuit converts commercial AC 
power to a DC voltage, for instance, 400 VDC. The DC/DC converter then 
scales the high DC voltage down to a lower voltage as required by a 
board-mounted power supply (BMP) within the telecommunications equipment. 
Telecommunications equipment typically operate on one of two voltages: +24 
VDC or -48 VDC. Wireless equipment, for instance, often require +24 VDC. 
Central office equipment, however, typically require -48 VDC. 
Telecommunications power supplies are, therefore, designed for either +24 
VDC or -48 VDC operation. 
To maintain high availability of the telecommunications system, the power 
supplies are used in the power systems in a redundant configuration. 
Seamless operations of the telecommunications system is assured, even if 
one DC power supply fails. The failed DC power supply must immediately be 
replaced, however, to maintain redundancy and avoid future loss of 
service. Service providers, therefore, must have an inventory of power 
supplies available for immediate placement in the system. Because of the 
different voltage requirements of the telecommunications equipment, 
service providers are currently forced to maintain in reserve both types 
of power supplies. It would be advantageous, for multiple reasons, to 
inventory only one type of DC power supply. 
Accordingly, what is needed in the art is a DC power supply capable of 
providing multiple output voltages (e.g., +24 VDC or -48 VDC), as required 
by the system it powers. 
SUMMARY OF THE INVENTION 
One way to provide reconfigurable outputs is to have multiple output 
rectifying circuits. The output rectifying circuits can be configured 
serially or in parallel to provide the necessary output voltage. 
The multiple output rectifying circuits can derive power from a single, 
common transformer and deliver power to a common load. The output current 
of each output rectifying circuit, however, may vary due to component 
tolerances. Though the output power from each rectifying circuit is the 
same, the output voltages and currents may still vary. Protective 
functions such as over-voltage and under-voltage shutdown and output 
current limit must, therefore, be scaled according to the current drawn 
from each output. If current-sharing can be guaranteed, current sensing 
may be performed at one output. Under these circumstances, the protective 
functions need not be individually calibrated for each rectifying circuit. 
One way to facilitate current sharing is to match the components of the 
output rectifying circuits to ensure that current is evenly shared. 
Unfortunately, component-matching increases the overall time and expense 
required to manufacture the DC power supply. An alternative way to 
guarantee current-sharing is to provide separate, series-coupled 
transformers for each of the output rectifying circuits. By 
series-coupling the primary windings of the separate transformers, the 
same current is forced to flow through each transformer and therefore 
through each corresponding output rectifying circuit. 
Once current-sharing is guaranteed (by either of the above-described 
techniques) the current in one of the output rectifying circuits can be 
directly controlled, and the other output rectifying circuits are 
controlled indirectly. 
Having ensured that current is shared and correctly controlled, it next 
becomes necessary to control the output voltage. However, since the DC 
power supply is capable of selectively providing multiple output voltages, 
a voltage control technique that adapts to multiple output voltages must 
be developed. 
To address the need for an adaptive voltage control technique, the present 
invention provides, for use with a DC power supply having first and second 
output rectifying circuits couplable in alternative configurations to 
provide dual voltages at an output of the DC power supply, an adaptive 
voltage controller and a method of adaptively controlling the output 
voltage. In one embodiment, the adaptive voltage controller includes: (1) 
a configuration determination circuit, coupled to the output, that 
generates a configuration signal that is a function of a configuration of 
the first and second output rectifying circuits, (2) a voltage feedback 
circuit, coupled to the configuration determination circuit, that develops 
a voltage feedback signal based on the configuration signal and (3) a 
voltage control circuit, coupled to the voltage feedback circuit, that 
receives the voltage feedback signal and controls an output voltage of the 
DC power supply as a function thereof. 
The present invention therefore introduces the broad concept of adapting 
the voltage feedback signal in a voltage controller to accommodate 
different output voltages. This allows a single voltage controller to 
regulate a reconfigurable DC power supply at its output voltages. While a 
dual-voltage DC power supply will hereinafter be illustrated and 
described, the scope of the present invention is not so limited. The 
present invention generally provides an adaptive voltage control technique 
that is capable of accommodating two or more alternative voltages at an 
output of a power supply employing the same. 
The foregoing has outlined, rather broadly, features of the present 
invention so that those skilled in the art may better understand the 
detailed description of the invention that follows. Additional features of 
the invention will be described hereinafter that form the subject of the 
claims of the invention. Those skilled in the art should appreciate that 
they can readily use the disclosed conception and specific embodiment as a 
basis for designing or modifying other structures for carrying out the 
same purposes of the present invention. Those skilled in the art should 
also realize that such equivalent constructions do not depart from the 
spirit and scope of the invention in its broadest form.

DETAILED DESCRIPTION 
Referring initially to FIG. 1, illustrated is one embodiment of a DC power 
supply 100 constructed according to the principles of the present 
invention. The DC power supply 100 includes a first and second isolation 
transformer 110, 120 (each having a primary and a secondary winding) 
coupled to a first and second output rectifying circuit 130, 140, 
respectively. In the illustrated embodiment, the first and second 
transformers 110, 120 have the same turns ratio. The first and second 
transformers 110, 120 are series-coupled, thereby evenly dividing an 
output current of the DC power supply 100 between the first and second 
output rectifying circuits 130, 140. Those skilled in the art should 
understand, however, that a single transformer may also be used. The DC 
power supply 100 further includes an adaptive voltage controller 150 for 
controlling an output of the DC power supply 100. 
In one embodiment of the present invention, the first and second output 
rectifying circuits 130, 140 each include a rectifier diode and a filter 
capacitor. In a preferred embodiment, the first and second output 
rectifying circuits 130, 140 each include a pair of rectifier diodes, an 
output inductor, and a filter capacitor. The first and second output 
rectifying circuits 130, 140 are couplable in alternative parallel and 
series configurations to provide dual voltages at the output of the DC 
power supply 100. In the illustrated embodiment, the dual voltages are +24 
VDC and -48 VDC. Of course, the DC power supply 100 may be configured to 
supply other voltages and more than two voltages. The first and second 
output rectifying circuits 130, 140 are couplable as follows. In the 
parallel configuration, a first and second terminal 1, 2 are coupled to a 
third and fourth terminal 3, 4 respectively. In the series configuration, 
the second and third terminals 2, 3 are coupled together and the output 
voltage is provided across the first and fourth terminals 1, 4. 
The voltage controller 150 includes a configuration determination circuit 
160, coupled to the output of the DC power supply 100, that generates a 
configuration signal 167 that is a function of a configuration of the 
first and second output rectifying circuits 130, 140. In this embodiment 
of the present invention, the configuration determination circuit 160 
consists of a comparator 165 and its associated components (i.e., 
resistors R4, R5, reference voltage source Vref). The voltage controller 
150 further includes a voltage feedback circuit 170, coupled to the 
configuration determination circuit 160, that develops output voltage 
feedback signals 175, 177 based on the configuration signal 167. The 
voltage feedback circuit 170 consists, in this embodiment, of two 
circuits, each having a resistor ladder formed from a first, second, and 
third resistor R1, R2, R3, coupled to a resistor bypass switch Q1. Those 
skilled in the art should realize that the voltage feedback circuit 170 
may, in alternative embodiments, consist of one or more circuits, 
developing one or more voltage feedback signals. The voltage feedback 
signals 175, 177 of the two circuits represent, respectively, the output 
voltage sensed at the output of the DC power supply 100 and at a load (not 
shown). The voltage feedback signals 175, 177 may operate alternatively as 
required by the DC power supply 100. The voltage controller 150 still 
further includes a voltage control circuit 180, coupled to the voltage 
feedback circuit 170. The voltage control circuit 180 consists of, in this 
embodiment, a set of comparison circuits 185, 187 that receives the 
voltage feedback signals 175, 177. Of course, the use of any number of 
comparison circuits is within the broad scope of the present invention. 
The voltage control circuit 180 uses the voltage feedback signals 175, 177 
to control the output voltage of the DC power supply 100 as a function 
thereof. Those skilled in the art are familiar with closed loop feedback 
circuits, and, as a result, an operation of the voltage control circuit 
180 will not be described in detail. Additionally, the voltage control 
circuit 180 may use the voltage feedback signals 175, 177 to initiate 
under-voltage and overvoltage shutdown. 
The present invention therefore introduces the broad concept of adapting 
the voltage feedback signals 175, 177 in the voltage controller 150 to 
accommodate different output voltages. This allows the single voltage 
controller 150 to control a dual-voltage DC power supply at either of its 
output voltages. While the power supply 100 is a dual-voltage power 
supply, the scope of the present invention is not so limited. 
The operation of conventional DC power supplies should already be familiar 
to those skilled in the art, and, as a result, the operation thereof will 
not be described in detail. The voltage controller 150 operates as 
follows. The configuration determination circuit 160 senses the output 
voltage of an output terminal of one of the output rectifying circuits 
130, 140. In the illustrated embodiment, the configuration determination 
circuit 160 senses the output voltage of the second terminal 2. The output 
voltage of the second terminal 2 is either +24 VDC or ground, indicating 
the configuration of the first and second output rectifying circuits 130, 
140. If, for instance, the first and second output rectifying circuits 
130, 140 are configured in series to provide -48 VDC, the second and third 
terminals 2,3 will be coupled together. The output voltage of the second 
terminal 2 will, therefore, be +24 VDC. If, however, the first and second 
output rectifying circuits 130, 140 are configure in parallel to provide 
+24 VDC, the output voltage of the second terminal 2 will be ground (0 
VDC). The comparator 165 of the configuration determination circuit 160 
thus generates the configuration signal 167 from the output voltage of the 
second terminal 2. 
In the illustrated embodiment of the present invention, the configuration 
signal 167 assumes a discrete value (e.g., a logic zero or logic one) as a 
function of the configuration. Alternatively, the configuration signal 167 
may be continuously variable or of another function. The present invention 
is not limited to a particular form of configuration signal 167. 
The configuration signal 167 is used by the voltage feedback circuit 170 to 
generate the voltage feedback signals 175, 177. In the illustrated 
embodiment, the resistance of the resistor ladder is a function of the 
configuration signal 167. The configuration signal 167 either enables or 
disables a resistor bypass switch Q1, altering the overall resistance of 
the resistor ladder, and thereby producing the voltage feedback signals 
175, 177. 
The comparison circuits 185, 187 of the voltage control circuit 180 then 
compare the voltage feedback signals 175, 177 to reference voltages to 
control the output voltage. Additionally, the comparison circuits 185, 187 
may initiate under-voltage and over-voltage shutdown of the power supply 
100. Those skilled in the art are familiar with conventional control 
techniques based on feedback and development of error signals. 
Turning now to FIG. 2, illustrated is another embodiment of a DC power 
supply 200 constructed according to the principles of the present 
invention. The DC power supply 200 includes a first and second isolation 
transformer 210, 220 coupled to a first and second output rectifying 
circuit 230, 240, respectively. In the illustrated embodiment, a first 
output of the first rectifying circuit 230 is provided across first and 
second terminals 1, 2. A second output of the second rectifying circuit 
240 is provided across third and fourth terminals 3, 4. The DC power 
supply 200 further includes an adaptive voltage controller 250 for 
controlling an output of the DC power supply 200. 
The first and second output rectifying circuits 230, 240, each include a 
first and second rectifier diode, an output inductor, and a filter 
capacitor. Alternatively, the first and second output rectifying circuits 
230, 240 may each include a rectifier diode and a filter capacitor. Those 
skilled in the art should realize that the output inductor and second 
rectifier diode are not an integral part of the first and second output 
rectifying circuits 230, 240. The first output rectifying circuit 230 
further includes a first output diode 235. The second output rectifying 
circuit 240 further includes a second output diode 245. The first and 
second output rectifying circuits 230, 240 are, of course, couplable in 
alternative parallel and series configurations. 
The voltage controller 250 includes a configuration determination circuit 
260, coupled to the output of the DC power supply 200, that generates a 
configuration signal 267 that is a function of a configuration of the 
first and second output rectifying circuits 230, 240. The voltage 
controller 250 further includes a voltage feedback circuit 270, coupled to 
the configuration determination circuit 260, that develops voltage 
feedback signals 275, 277 based on the configuration signal. 
The voltage controller 250 further includes a voltage control circuit 280, 
coupled to the voltage feedback circuit 270. The voltage control circuit 
280 consists of, in this embodiment, a set of comparison circuits 285, 287 
that receives the voltage feedback signals 275, 277 and controls the 
output voltage of the DC power supply 200 as a function thereof. In the 
illustrated embodiment, the voltage control circuit 280 is a conventional 
closed loop feedback circuit, familiar to those skilled in the art. The 
comparison circuits 285, 287 compare the voltage feedback signals 275, 277 
to a reference voltage and produce therefrom pulse width modulated drive 
signals to control switches in a power stage of the DC power supply 200. 
The voltage controller 250 still further includes a diode bypass circuit 
290, coupled to the second output diode 245, that receives the 
configuration signal from the configuration determination circuit 260 and 
bypasses the output diode as a function thereof. In the illustrated 
embodiment, the diode bypass circuit 290 consists of a relay. Of course, 
any type of bypass circuit may be used. 
The operation of the DC power supply 200 is substantially similar to the 
operation of the DC power supply 100 of FIG. 1 and will not be described 
in detail. In the illustrated embodiment, the second and third terminals 
2, 3, are coupled together, configuring the first and second output 
rectifying circuits 230, 240 in series to provide -48 VDC. The 
configuration determination circuit 260, coupled to the second terminal 2, 
thus senses +24 VDC. Alternatively, the first and second output rectifying 
circuits 230, 240 may be configured in parallel to provide +24 VDC. The 
configuration determination circuit 260 would then sense 0 VDC (ground). 
The first and second output diodes 235, 245 protect the first and second 
output rectifying circuits 230, 240, respectively, when the first and 
second output rectifying circuits 230, 240 are coupled in a parallel 
configuration. The second output diode 245 is not required, however, when 
the first and second output rectifying circuits 230, 240 are 
series-configured. The diode bypass circuit 290, therefore, bypasses the 
second output diode 245 as a function of the configuration signal. By 
bypassing the second output diode 245, any inefficiency associated 
therewith is eliminated. Of course, the number of diode bypass circuits 
may vary depending on the number of output rectifying circuits. 
In the illustrated embodiment, the first and second output rectifying 
circuits 230, 240 are in series. The +24 VDC sensed by the configuration 
determination circuit 260 may thus be used to drive the diode bypass 
circuit 290 to bypass the second output diode 245. Alternatively, if the 
first and second output rectifying circuits 230, 240 are in parallel, the 
0 VDC (ground) sensed by the configuration determination circuit 260 may 
be used to turn off the diode bypass circuit 290, thereby leaving the 
second output diode 245 in the circuit. 
Although the present invention has been described in detail, those skilled 
in the art should understand that they can make various changes, 
substitutions and alterations herein without departing from the spirit and 
scope of the invention in its broadest form.