Power unit and power connecting method

Abstract: A switch is connected in series to a capacitor inserted in parallel into a direct-current output portion, and the switch is controlled to turn OFF when an AC input source is not connected to a power unit and turn ON when a constant time period is elapsed after the connection to the AC input source. The capacitor is charged when the switch is in the OFF state but not charged in response to the connection to the input source.

Description: The present invention relates generally to a power supply apparatus and a power connecting method, and more particularly to a power supply apparatus which, irrespective of a fault of a power source for a computer such as a fault-tolerant computer, continues to supply power to the computer and which allows exchange of the faulty power source as the hot line is kept to the energized state in terms of AC and DC. Fig. 5 of the accompanying drawings shows a circuit and arrangement of a basic portion of a conventional hot-line type power supply apparatus. In the illustration, numeral 1 represents a power unit making up the hot-line type power supply apparatus. In the internal circuit of the power unit 1, D1 to D4 respectively designate diodes, C1 and C2 respectively depict capacitors, L1 denotes an inductor, T1 indicates a pulse transformer, and TR1 is a switching transistor for converting into a pulse voltage a direct-current voltage developed across the capacitor C2. The diodes D2 and D3 make up a rectifier M, and the capacitor C1, the inductor L1 and others constitutes a smoothing circuit F. Operation of the apparatus thus arranged will be described hereinbelow. In the power unit 1, an input rectified by a full-wave rectifier and ON-OFF-controlled by the transistor TR1 is supplied to an input side of the transformer T1 to generate an output having a great amplitude, the output of the transformer T1 being rectified by the rectifier M and then smoothed by the smoothing circuit F so as to produce a direct current (DC) output whose voltage value is 5 [V], for example. In this case, an output line 30 for supplying the 5[V] DC voltage are coupled in common to the output sides of the respective power units. Thus, even if one power unit goes wrong, the other power unit can compensate for this power unit trouble. Similarly, the input sides of the respective power units are coupled in common to an input line 31. Here, the diode D3 is a flywheel diode to obtain a rectified electric power. Although in Fig. 5 there are illustrated three power units, the 5[V] DC output load can be covered by the total output capacity of two power units. Now, assuming that one of the power units 1 breaks down, difficulty is encountered to correctly generate the switching pulse at the secondary side 2 of the transformer T1 of the faulty power unit, whereby the voltage is lowered at the junction portion 3 between the inductor L1 and capacitor C1 making up the circuit F. Although the faulty power unit cannot output the 5[V] DC because of the lowering of the voltage at the junction portion 3, the other two power units supply the 5[V] DC therefor, thus allowing the continuous supply to the load. On the other hand, the faulty power unit detects the lowering the voltage at the junction portion 3 and gives information to the operator for exchange with a good new one. The removal of the faulty power unit does not affect the 5[V] output because current does not flow through an output terminal 4 line. Further, in inserting a new power unit in place of the faulty power unit, the voltage at the junction portion 3 is 0 [V] in the initial state and hence electric charge is not charged into the capacitor C1, while the reverse-current preventing diode D1 prevents the supply of current from the 5[V] DC line to the capacitor C1 and hence the insertion of the new power unit does not affect the 5[V] DC output. In response to the operation of this new power unit to restore the voltage at the junction portion 3, current passes through the diode D1 to the 5[V] DC line. In the conventional hot-line type power supply apparatus thus arranged, since the reverse-current preventing diode D1 is always connected in series to the output portion of the power supply, when the forward-direction voltage drop is taken to be V F , the power loss is taken as P and the output current of the power unit is I F , they take the following relation and there is a problem that the conversion efficiency of the power supply lowers and heat is generated. P = V F x I F For example, when I F = 100A and V F = 1V, the power loss P becomes 100W, thus resulting in a great problem. The present invention has been developed in order to eliminate the above-described problem, and it is object of the present invention to provide a power supply apparatus and power connecting method which is capable of preventing the lowering of the power conversion efficiency and increase in heating. According to the first aspect of the present invention, there is provided a power supply unit comprising: an input section for inputting a current from an input source; an output terminal for outputting a direct current on the basis of an output of said input section; and a capacitor connected in parallel with said output terminal, characterised in that: said capacitor is connected to a charging means and is connected in parallel with said output terminal via a switch; and said power supply unit further comprises switch control means which is arranged to leave said switch open as the power supply unit is connected to a load and to close said switch after said capacitor has been charged by said charging means subsequent to said power supply unit being connected to said load. Accordingly, the reverse-current preventing serial diode which causes the power loss may be removed from the output portion. In one embodiment of the present invention, a precharge circuit is provided and the switch is arranged to be closed after the completion of the precharge to the capacitor by the precharge circuit so as to eliminate the excessive current at the time of the insertion of the power unit to prevent the DC supply line from being instantaneously cut. In another embodiment of the present invention, a voltage from an output terminal is precharged through a resistor to the capacitor, and the switch is closed when a predetermined time period is elapsed. In a further embodiment of the present invention, a voltage from an output terminal is precharged through a resistor to the capacitor and the voltage across the capacitor is detected by a comparator for closing control of the switch. The power supply units according to the first aspect of the present invention may be coupled with their direct-current output lines in parallel to create a power supply apparatus. According to a second aspect of the present invention there is provided a power connecting method comprising the steps of: performing a load connecting process to couple a power source to a load circuit via a direct-current output terminal, the power source having a capacitor connected in parallel with said output terminal; and performing an input source connecting process to couple an input source to said power source, characterised in that: said capacitor is connected in parallel with said output terminal via a switch; and the method further comprises: performing a precharge process to charge said capacitor whilst leaving said switch open; and closing said switch to couple said capacitor in parallel with the output terminal after said capacitor has been charged. If the serial diode is not provided at the output portion, since a rapid charging current is supplied through the DC line to the capacitor at the output portion when inserting the power unit, the voltage on the DC supply line is instantaneously cut which can cause an error in an electronic circuit of a computer or the like which is the load. Thus, according to this invention, when inserting the power unit, the charging current is stopped by the switch and the capacitor is precharged so as to give electric charge to the capacitor, thereafter closing the switch. This pre-charging may be made by a dedicated pre-charging circuit, or made via a resistor provided between the capacitor and the output terminal. The resistor may be connected in parallel with the switch (and in series with the capacitor) to suppress the rapid charging current to the capacitor which occurs when inserting the power unit. The switch may be closed after a predetermined time period has elapsed due to a delay or after the fact that the pre-charging voltage becomes a predetermined voltage is detected. The invention will be further described by way of non-limitative example with reference to the accompanying drawings, in which:- Fig. 1 is an illustration of an arrangement including a circuit of a basic portion a hot-line type power supply apparatus according to a first embodiment; Fig. 2 is a timing chart for describing the operation of the Fig. 1 apparatus; Fig. 3 is an illustration of an arrangement of including a circuit of a basic portion of a hot-line type power supply apparatus according to a third embodiment; Fig. 4 is an illustration of an arrangement including a circuit of a basic portion of a hot-line type power supply apparatus according to a fourth embodiment; and Fig. 5 is an illustration of an arrangement of a circuit of a basic portion of a conventional hot-line type power supply apparatus. A first embodiment of the present invention will be described hereinbelow with reference to the drawings. In Fig. 1, numeral 10 represents each of power units constituting a hot-line type power supply apparatus which is one of power supply apparatus according to this invention. In the internal circuit of the power unit 10, D1 to D4 designate diodes, C2 denotes a capacitor, T1 depicts a pulse transformer for insulation, and Tr1 indicates a switching transistor for converting into a pulse voltage the direct-current voltage developed across the capacitor C2. These parts make up an input section for the current from an input source AC [100V]. Further, C1 is a capacitor, D5 represents a diode, 11 designates a delay for producing delay by a predetermined time period, RL is a switch the contact of which is controllable in accordance with a signal from the delay 11, R1 depicts a resistor for limiting current, and T2 is a transformer insulated from AC and converting a voltage. In addition, numeral 12 is a precharge circuit comprising the diode D5 and the transformer T2 and 13 is a direct current output line for outputting a direct current 5[V] DC. Here, although three power units are illustrated in Fig. 1, the 5[V] DC load can be covered by the total output capacity of two of the three power units. Assuming that one of the power units 10 breaks down, the current supply from the faulty power unit to an output terminal 13 is stopped, while the remaining two power units continues to supply the 5[V] DC to the load. That is, the output terminals 13 of a plurality of power units 10 are coupled to each other and output terminals 14 of the precharge circuits 12 for respectively precharging the AC inputs are coupled to each other, thereby constituting a power supply apparatus in which the entire output is not reduced even if one power unit has broken down. The operation of the entire hot-line type power supply apparatus is similar to that of the conventional apparatus described above and hence omitted. Here, a description will be made hereinbelow in terms of operation when exchanging one power unit because of fault. In removing the faulty power unit, the current between the 5[V] DC lines (DC supply lines) is cut by means of the diode D2 so that it does not flow through the output terminal 13 line, thereby not affecting the 5[V] DC lines. Further, in the case of inserting a new power unit therefore, although the voltage VC across the capacitor C1 is 0V in the initial state, the switch RL is in the OFF state so that the charging current is not introduced from the 5[V] DC line, thereby not affecting the 5[V] DC line. Operation of this portion will hereinbelow be described in detail with reference to Fig. 2. When a power unit is inserted into an electric circuit of a computer or the like (load connecting process) and a 100[V] AC input is supplied to the power unit (input source connecting process), the AC voltage is applied through the transformer T2 of the precharge circuit 12 to the diode D5 and a direct-current voltage is developed at the output terminal 14 portion of the precharge circuit 12. Further, the direct-current voltage at this output terminal 14 portion causes the capacitor C1 to be charged with the current being limited by the resistor R1 (precharge process). On the other hand, a signal is generated from the delay 11 after a predetermined delay time so as to switch the switch RL from the OFF state to the ON state, and as a result the capacitor C1 is connected to the output terminal 13 line (switching process). If the charging of the capacitor C1 is designed to be completed when the switch RL turns ON, it is possible to prevent the charging current to the capacitor C1 from being introduced through the output terminal 13 line. Moreover, if the switching operation of the switching transistor TR1 is also arranged to be started through the delay 11, the capacitor C1 is always coupled to the output portion for the operation of the power source, thereby allowing stable operation. As described above, in the hot-line type power supply apparatus according to the embodiment, the direct-current outputs of a plurality of direct-current power units are coupled in parallel to each other so that the direct-current output can be applied to the load without stopping even if one of the plurality of the power units is broken down and so that the faulty power unit is exchangeable with a normal power unit as the hot-line state is kept. That is, a switch is connected in series to a capacitor, which is inserted in parallel to the direct-current output portion, without inserting a reverse current-limiting diode into the direct-current output line of the power unit in series, and the switch is controlled so as to take the OFF state when there is no AC input source to the power unit and take the ON state when a constant time period is elapsed after being coupled to the AC input source. In addition, the capacitor is charged before the constant time period by means of the precharge circuit which is arranged to generate a voltage from the AC input source side through the diode D5 and current-limiting resistor R1 coupled in series. Although in the above-described embodiment 1 the precharge circuit 12 is simply composed of the transformer and the diode, it is also possible in a second embodiment for the precharge circuit 12 further to include a regulator if required. Furthermore, a description will be made hereinbelow in terms of a power supply apparatus according to a third embodiment of this invention. As described in the first embodiment, the provision of the precharge circuit 12 provides a problem that the occupied volume of the apparatus increases. Accordingly, a power supply apparatus according to the third embodiment is for size-reduction of the apparatus. In Fig. 3, parts similar or corresponding to those in Fig. 1 are indicated with the same marks and the description thereof will be omitted. Different portions are a resistor R1, a resistor R2 and a light-emitting diode LED, R1 being connected in series to a capacitor C1 and disposed in parallel to a switch RL, R2 being disposed at the secondary side 15 of a transformer T1, and LED being acting as an indication lamp for indicating the fact that the power unit does not break down. In this embodiment, the faulty power unit is exchanged with a new power unit by the operator with the light-emitting diode LED turning OFF in response to lowering of the pulse voltage at the secondary side 15 of the transformer T1. When removing the faulty power unit, the current from the output terminal 13 does not flow into the inside of the faulty power unit due to a diode D2, thereby not affecting the 5[V] DC line. Further, when inserting the new power unit therefore, although the voltage Vc across the capacitor C1 is 0V in the initial state, since the switch is in the OFF state, the charging current from the 5[V] DC line is limited by the resistor R1. Thus, if determining the value of the resistor R1 to an adequate value, it is possible to prevent the effect to the 5[V] DC line. Operation of this portion will again be described with reference to Fig. 2. When a power unit is inserted into a power supply apparatus housing for encasing it, the 5[V] DC line is connected to the load circuit (load connecting process) and the 100[V] AC input is connected to the power unit (input source connecting process), the charging current which is limited through the resistor R1 flows to the capacitor C1 so that the voltage across the capacitor C1 gradually increases (precharge process). On the other hand, a delay 11 generates a signal for switching the switch RL from OFF to ON after elapse of a delay time which is a constant time period from the input of the 100[V] AC, whereby as a result the capacitor C1 is connected to the output terminal 13 line (switching process). Here, if the capacitor C1 is arranged to be completely charged when the switch RL turns ON, it is possible to prevent the charging current from being rapidly supplied to the capacitor C1 to transitionally lower the voltage of the 5[V] DC line, thereby avoiding the bad influence. Further, if the switching operation of the switching transistor TR1 is arranged to be started through the delay 11, the capacitor C1 results in being always coupled to the output portion for the operation of the power unit, thereby allowing stable operation. A description will be made hereinbelow in terms of a fourth embodiment of this invention. Although in the above-described embodiment 3 the delay 11 is used for controlling the switch RL inserted in series to the capacitor C1, it is also appropriate that the voltage across the capacitor C1 is detected so that the switch RL is closed when the detected voltage becomes above a predetermined voltage. For example, in Fig. 4, IC1 is a comparator which generates an output signal when exceeding a reference voltage VTH, 16 represents a drive for operating a switching transistor TR1 with the switch RL turning ON. Since the operation of the Fig. 4 embodiment 4 is the same as the Fig. 3 embodiment 3 except for the control operation for switching the switch RL to ON, a description will here be made only in terms of the operation of the switch RL. In the case of inserting a new power unit in place of the faulty power unit, the voltage Vc across the capacitor C1 is 0V in the initial state and the current from the 5[V] DC line is limited by the resistor R1 as the switch RL is in the OFF state, thereby not giving an influence to the 5[V] DC line. Further, the charging current flows from the resistor R1 to the capacitor C1 so as to gradually increase the voltage across the capacitor C1 so that the comparator IC1 generates an output when exceeding the reference voltage VTH. With this output, the drive 16 drives the switch RL to turn it ON, and the switching drive is started so as to start the function of the power source. At this time, since the capacitor C1 is coupled to the 5[V] DC output line 13, the operation of the power source can become stable. As described above, according to the third embodiment, for realizing the insertion and removal of the power unit as the hot line is kept, the serial diode is not used at the output portion, the switch is provided in series to the capacitor inserted in parallel to the output terminal, and the resistor is disposed in parallel to the switch, whereby the switch turns ON when a predetermined time delay is elapsed after the AC input. Thus, it is possible to realize a high-efficiency power source which is capable of being size-reduced, which is capable of reducing the heat quantity. In addition, even if as described in the fourth embodiment the timing for the turning-ON of the switch is determined with the voltage across the capacitor inserted in parallel to the output terminal being detected to check the completion of the charging to the capacitor, it is possible to obtain the similar effect. Although in the above-described embodiments 3 and 4 the trouble of the power unit is detected by means of the resistor R1 and the light-emitting diode LED, it is also possible in a fifth embodiment that the direct-current voltage due to a diode is detected by a comparator or the like so as to give an alarm through a means such as indicator and relay contact output. Although in the above-described embodiments 1 to 4 the description is made with respect to the three power units, this invention is applicable to the case that the number of the power units is 2 or 4 or more. Further, although in the above-described embodiments the circuit of the switching regulator portion is represented by the single inverter type circuit, it is possible to obtain the same effect even if using a different type of power unit. As described above, according to this invention, the switch is provided in series to the capacitor disposed at the output portion of the power unit and the timing for the turning-ON of the switch is delayed by a constant time period from the AC supply. Accordingly, it is possible to provide the effects that the efficiency of the power source can be improved and the heat can be suppressed.

Claims: A power supply unit (10) comprising: an input section (P) for inputting a current from an input source; an output terminal (13) for outputting a direct current on the basis of an output of said input section; and a capacitor (C1) connected in parallel with said output terminal (13), characterised in that: said capacitor (C1) is connected to a charging means (12, R1) and is connected in parallel with said output terminal (13) via a switch (RL); and said power supply unit (10) further comprises switch control means (11, 16) which is arranged to leave said switch (RL) open as the power supply unit (10) is connected to a load and to close said switch (RL) after said capacitor (C1) has been charged by said charging means (12, R1) subsequent to said power supply unit (10) being connected to said load. A power supply unit (10) as claimed in claim 1, wherein said capacitor (C1) is a smoothing capacitor. A power supply unit (10) as claimed in claim 1 or 2, further comprising alarm means for indicating whether power is supplied to said output terminal (13). A power supply unit according to claim 3, wherein said alarm means is a light-emitting diode (LED) connected in parallel with said output terminal (13). A power supply unit (10) according to any one of the preceding claims, wherein: said charging means comprises a recharge circuit (12) for charging said capacitor (C1) after said input section (31, P) is connected to said input source to provide said charging; and said switch control means (11) is arranged to close said switch (RL) after said capacitor (C1) is charged by said recharge circuit (12). A power supply unit (10) according to any one of claims 1 to 4, wherein: said charging means comprises a resistor (R1) connected in parallel with said switch (RL); and said switch control means comprises a delay circuit (11) for closing said switch (RL) when a delay time has elapsed after said input section (31, P) is connected to said input source. A power supply unit (10) according to any one of claims 1 to 4, wherein: said charging means comprising a resistor (R1) connected in parallel to said switch (RL); and said switch control means comprises: a comparator (IC1) for detecting a voltage across said capacitor (C1) so as to generate an output signal when the detected voltage exceeds a predetermined reference voltage; and a drive circuit (16) for closing said switch (RL) in response to the generation of said output signal of said comparator. A power supply apparatus comprising a plurality of power supply units (10), each being constructed and arranged as claimed in any one of the preceding claims, the output terminals (13) of said power supply units (10) being connected in parallel. A power connecting method comprising the steps of: performing a load connecting process to couple a power source to a load circuit via a direct-current output terminal (13), the power source having a capacitor connected in parallel with said output terminal (13); and performing an input source connecting process to couple an input source to said power source, characterised in that: said capacitor is connected in parallel with said output terminal via a switch (RL); and the method further comprises performing a precharge process to charge said capacitor (C1) whilst leaving said switch (RL) open; and closing said switch (RL) to couple said capacitor (C1) in parallel with the output terminal (13) after said capacitor (C1) has been charged.

Inventors: SAITO SEIICHI, SAITO, SEIICHI, Saito, Seiichi, c/o Mitsubishi Denki K. K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1992
Main classification: G06F1
IPC codes: H02J1, H02H7, H02M3, G06F1, H02M7, G05F1