Patent Application
20060220463
A computer system that has to be on all the time may have two redundant hot-pluggable power supplies to supply electrical power to the components of the computer system. Under normal operating conditions, both power supplies work together to supply the electrical power for the computer system. Thus, each power supply generates half of the total power required by the computer system. When one of the power supplies fails or is removed from the computer system, then the remaining power supply generates the entire amount of the power for the computer system. In this manner, the computer system is ensured to operate almost all the time, even if one of the power supplies should fail.
During normal operation, each power supply generates its share of the required electrical power at the same voltage level as the other power supply. Upon failure or removal of one of the power supplies, the remaining power supply quickly increases its power output. The sudden increase in the remaining power supply's power output causes a momentary drop in the output voltage level of the power supply. A number of filter capacitors is included across the output to prevent the output voltage level from dropping below a minimum required voltage level at which the components of the computer system can continue to operate without interruption. The filter capacitors take up valuable space within the computer system and add cost to the computer system.
A computer system 100 incorporating an embodiment of the present invention is shown in
The computer system 100 also includes within the housing 102 a printed circuit board (PCB) 112 and various peripheral devices 114. The PCB 112 includes various connectors (e.g. 116, 118 and 120) and electronic components (e.g. 122). Some of the connectors 116 and 118 connect the PCB 112 to the power supply modules 108 and 110 via wires or cables 124 and 126, respectively.
The power supply modules 108 and 110 receive AC power through power cables 128 and convert the AC power into appropriate electrical power for the components 122 and devices 114. The power supply modules 108 and 110 supply the electrical power to the various components 122 on the PCB 112 through the wires or cables 124 and 126, the connectors 116 and 118 and various electrical traces on the PCB 112. The power supply modules 108 and 110 also supply electrical power through additional wires or cables 130 to some of the devices 114 that are not mounted on the PCB 112. Additionally, others of the devices 114 may receive electrical power from the power supply modules 108 and 110 through the PCB 112, the connector 120 and additional wires or cables 132. Each power supply module 108 and 110 supplies half the power requirements of the computer system 100 when both of the power supply modules 108 and 110 are installed within the computer system 100 and operational. When either of the power supply modules 108 or 110 fails to operate or is removed from the housing 102, then the remaining power supply module 108 or 110 generates and supplies the total power requirements of the computer system 100, or of the components 122 and the devices 114.
The power supply modules 108 and 110 are mounted within the housing 102 by any appropriate means, such as by being attached to the rear wall of the housing 102 by mounting screws or other means. The power supply module 108 or 110 can be removed from the housing 102 by disconnecting its power cable 128, disconnecting the wires or cables 124 or 126, detaching the power supply module 108 or 110 from its mounting means and pulling the power supply module 108 or 110 out of the housing 102. Another power supply module 108 or 110 may be inserted into the housing 102 by reversing this procedure.
The power supply modules 108 and 110 are “hot-pluggable,” which means that either of the power supply modules 108 or 110 can be removed from and replaced into the housing 102 of the computer system 100 while the computer system 100 is operational. Removal and replacement of either power supply module 108 or 110, while the computer system 100 is operational, may be performed as long as the other power supply module 108 or 110 is functioning properly and can supply the computer system 100 with its entire power requirement. Therefore, when one of the power supply modules 108 or 110 fails or is removed during the operation of the computer system 100, the other of the power supply modules 108 or 110 quickly increases its power output to satisfy the entire power requirement of the computer system 100. This rapid power increase can cause the voltage output of the remaining power supply module 108 or 110 to momentarily decrease, but the voltage output soon returns to its prior value.
The components 122 and devices 114 typically have specified power, current and voltage requirements in order to operate properly. Typically, the components 122 and devices 114 have a specified nominal voltage at which they are intended to operate. Additionally, the components 122 and devices 114 also have a specified minimum voltage, below the nominal voltage, below which they are not intended to operate, even for the short duration of the momentary decrease of the voltage output of the remaining power supply 108 or 110. For ease of description, the following embodiments will be described with reference primarily only to the components 122.
One or more filter capacitors 134 (
The total capacitance of the filter capacitors 134 is dependent on, among other parameters, the difference between the minimum voltage below which the components 122 are not intended to operate and the output voltage of the power supply modules 108 and 110 immediately prior to the momentary decrease due to the failure or removal of one of the power supply modules 108 or 110. A larger difference in these voltages results in a lower required total capacitance of the filter capacitors 134. Therefore, a larger difference in these voltages results in the ability to use fewer and/or smaller filter capacitors 134 in order to prevent the output voltage of the power supply modules 108 and 110 from decreasing below the minimum voltage. The use of fewer and/or smaller filter capacitors 134 results in cost and space savings in the computer system 100.
According to an embodiment of the present intention, the output voltage of the remaining power supply module 108 or 110 is increased above the nominal voltage at which the components 122 are intended to operate following the failure or removal of the other power supply module 108 or 110. The increased voltage level of the output voltage is referred to herein as a maximum voltage. The increase in the voltage level of the output voltage of the remaining power supply module 108 or 110 results in there being a larger difference between the output voltage of the remaining power supply module 108 or 110 and the minimum voltage than there would be if the output voltage remained at the nominal voltage. Therefore, according to various embodiments, cost and space savings are realized with respect to the filter capacitors 134, since the required number and/or size of the filter capacitors 134 is lower than that required if the output voltage were not increased due to the greater difference between the maximum voltage and the minimum voltage.
A formula for determining the number of a particular given type of filter capacitors 134 to be used in a given situation is as follows:
where N is the number of the given type of filter capacitors 134, ESRofthecapacitor is the equivalent series resistance of the given type of filter capacitors 134, currentloadchange is the change in the amount of current that the remaining power supply module 108 or 110 undergoes upon increasing its output power to satisfy the entire power requirement for the computer system 100, Vmax is the maximum voltage to which the output voltage is increased and Vmin is the minimum voltage below which the components 122 are not intended to operate. If this formula results in a number with a fraction, then the next higher whole number may be used. For this formula, an appropriate available capacitor, for which the equivalent series resistance and the capacitance are known, is chosen for the filter capacitors 134. The total capacitance of the filter capacitors 134 is, therefore, the known capacitance of one of the given type of filter capacitors 134 multiplied by the number N. The current load change and minimum voltage are determined by the components 122 and the design of the computer system 100. The maximum voltage is selected to be an appropriate amount above the nominal voltage and which will not adversely affect the operation of the components 122. Since the difference between the maximum and minimum voltages is in the denominator of the formula, a larger maximum voltage will result in a smaller number of the filter capacitors 134.
Each power supply module (A and B) 108 and 110 includes, among other signals in the wires or cables 124 and 126 (
The control signals 144 control the operation of the power supply modules 108 and 110. For example, when the module present signals 140 and 142 are asserted, the control signals 144 indicate to each power supply module 108 and 110 to supply half of the power requirements of the computer system 100. On the other hand, when one of the module present signals 140 or 142 is deasserted, indicating that its associated power supply module 108 or 110 has failed or been removed, the control signal 144 to the remaining power supply module 108 or 110 indicates to the remaining power supply module 108 or 110 to supply the entire power requirements of the computer system 100.
Each power supply module 108 and 110 generally includes, among other components, a voltage regulator 152 and a resistive/capacitive divider 154. (The resistive/capacitive divider 154 may be incorporated in the voltage regulator 152.) The voltage regulator 152 generates the output voltage at the output signal 138 from an appropriate power input at 156. The voltage regulator 152 receives feedback of the output voltage at 158. The voltage regulator 152 compares the output voltage feedback with a reference voltage (Vref) received at 160. The Vref is created by the resistive/capacitive divider 154 from an appropriate source voltage (Vs). Under normal operating conditions, the Vref is the nominal voltage for the power supply module 108 or 110.
The resistive/capacitive divider 154 receives the module present signal 140 or 142 in addition to the Vs. Under normal operating conditions, i.e. both power supply modules 108 and 110 are present and operational, the module present signals 140 and 142 are grounded. In this case, the ground on the module present signals 140 and 142 causes the resistive/capacitive dividers 154 to create the Vref at the nominal voltage, so the voltage regulators 152 generate the output voltage at the nominal voltage for powering the computer system 100.
When one of the power supply modules (e.g. 110) fails or is removed, the module present signal 142 received by the remaining power supply module 108 is driven to the voltage V supplied at input 148 of the PCB 112, as shown in
Since the output voltage of the remaining power supply module 108 is increased upon failure or removal of the other power supply module 110, the momentary decrease of the output voltage of the remaining power supply module 108 will occur from the maximum voltage, rather than from the nominal voltage. Therefore, the voltage difference in the denominator of the above formula is based on the maximum voltage, rather than on the nominal voltage, so the voltage difference is larger than it would be if the output voltage of the remaining power supply module 108 were not increased upon failure or removal of the other power supply module 110. Consequently, the required number of filter capacitors 134 is smaller than it would be if the output voltage of the remaining power supply module 108 were not increased.
The capacitive characteristics of the resistive/capacitive divider 154 form an RC time constant in the resistive/capacitive dividers 154 that causes the Vref to decay from the maximum voltage to the nominal voltage over a period of time. In this manner, the power supply modules 108 and 110 will generate the maximum voltage only temporarily, so the output voltage returns to the nominal voltage. The RC time constant is selected so that the decay of the Vref will not allow the momentary decrease of the output voltage to drop below the minimum voltage. Therefore, the changes in the output voltage due to both the Vref change and the momentary decrease are temporary, so the components 122 will be operated at the nominal voltage with only a temporary fluctuation upon failure or removal of one of the power supply modules 108 and 110.
According to an alternative embodiment, a resistor divider is used in place of the resistive/capacitive divider 154. In this case, when the Vref is increased to cause the voltage regulator 152 to generate the maximum voltage, the Vref does not decay back to the nominal value. Instead, the Vref remains at the increased value, causing the voltage regulator 152 to continue to generate the maximum voltage. When this situation occurs due to removal of one of the power supply modules 108 or 110, ordinarily a replacement power supply module 108 or 110 will be inserted into the computer system 100 within a matter of minutes. At this point, the module present signal 140 or 142 is reasserted, so the Vref and the output voltage return to the nominal value. Therefore, the components 122 will operate at the maximum voltage for only a few minutes.
