Modular power supply system

0001This invention directs itself to modular power supply systems for use with computers and telecommunications equipment.

0002Power supply systems are well known in the art. Further, power supply systems having battery backup power sources are also well known in the art. Such existing systems, however, do not provide a positive indication of battery capability, and thus may produce a catastrophic failure when the primary power is lost.

0003Some prior art systems must be switched from the primary source to a battery backup source responsive to detection of a loss of the primary power source. Such switchover between sources of energy result in transients being generated and transmitted to the loads coupled to the power supply output. In other situations, the switching may be fast enough to avert the generation of such transients, but allows the voltage input to the output inverter circuits to droop sufficiently so as to disturb the regulation of the output voltage being supplied to the load.

0004In other prior art systems, the battery backup system can only be tested by removing the primary power source and allowing the changeover circuit to detect the loss of primary power and energize the backup system. Obviously, if there is a fault in the battery backup system, the output load will cease to be supported and such is unacceptable for critical computer and telecommunications applications.

0005Accordingly, the present invention has been developed to overcome the specific shortcomings of prior art systems, such as those described above, as well as achieve other benefits and improvements over prior art systems.

0006In accordance with the invention there is provided a modular power supply system, comprising: <ul id="ul0001" list-style="none"><li>a. a DC voltage bus;</li><li>b. boost converter means having an input coupled to a power source for generating a first DC voltage signal from an input line voltage supplied by said power source, said boost converter means having an output connected to said DC voltage bus for coupling said first DC voltage signal to said DC voltage bus;</li><li>c. at least one converter module having an input coupled to said DC voltage bus for converting said first DC voltage signal to a second DC voltage signal, said second DC voltage signal being of a different magnitude than a magnitude of said first DC voltage signal;</li><li>d. a battery backup module having an input and an output coupled to said DC voltage bus for generating a third DC voltage signal responsive to said magnitude of said first DC voltage signal decreasing in value below a predetermined first reference value; and</li><li>e. first control means for generating a control voltage signal and having (1) a first input coupled to said input of said boost converter means for monitoring said input line voltage, (2) a second input coupled to said DC voltage bus for monitoring said first DC voltage signal, and (3) first and second outputs respectively coupled to said at least one converter module and to said battery backup module for supplying said control voltage signal respectively thereto.</li></ul>

0007An embodiment of the invention thus provides a modular power supply system including a DC voltage bus and a boost converter circuit having an input coupled to a power source for generating a first DC voltage signal from an input line voltage supplied by the power source. The boost converter circuit has an output connected to the DC voltage bus for coupling the first DC voltage signal to the DC voltage bus. The modular power supply system also includes at least one converter module having an input coupled to the DC voltage bus for converting the first DC voltage signal to a second DC voltage signal. The second DC voltage signal may be of a lesser magnitude than the magnitude of the first DC voltage signal where such converter module is a down converter, or may be greater magnitude where an up converter is utilized. The modular power supply system further includes a battery backup module having an input and an output coupled to the DC voltage bus for generating a third DC voltage signal responsive to the magnitude of the first DC voltage signal decreasing in value below a predetermined first reference value. The modular power supply system also includes a first control circuit for generating a control voltage signal and having (1) a first input coupled to the input of the up converter circuit for monitoring the input line voltage, (2) a second input coupled to the DC voltage bus for monitoring the first DC voltage signal, and (3) first and second outputs respectively coupled to the at least one down converter module and to the battery backup module for supplying the control voltage signal respectively thereto.

0008Thus an embodiment of the invention provides a modular system wherein an input voltage is boosted to a high voltage level, the high voltage being utilized as the input for one or more output modules. Further, an embodiment of the invention provides a power supply system having a battery backup subsystem for maintaining the high voltage level input to the one or more output modules. Still further, an embodiment of the invention provides a power supply system having inverter circuits utilizing a transformer having a controlled leakage inductance.

0009An embodiment of the invention is described hereinafter by way of example, with reference to the accompanying drawings, in which: <ul id="ul0002" list-style="none"><li>Figure 1 is a block diagram of a modular power supply system in accordance with the present invention;</li><li>Figure 2 is a circuit diagram of a power factor corrected up converter circuit in accordance with the present invention;</li><li>Figure 3 is a circuit diagram of a battery backup module in accordance with the present invention;</li><li>Figure 4 is a circuit diagram of a central control circuit in accordance with the present invention; and</li><li>Figure 5 is a circuit diagram of a down converter circuit in accordance with the present invention.</li></ul>

0010Referring to the Figures, there is shown modular power supply system 10 for providing highly regulated voltages to computer and telecommunication systems. As will be seen in following paragraphs, modular power supply system 10 includes an input conversion circuit 20 which provides power factor correction, such that system 10 substantially represents a resistive load to the alternating current voltage source to which system 10 is connected. The input converter 20 provides power to a high voltage DC bus 22, from which a plurality of output modules 70a - 70n draw power and convert such to respective predetermined output voltages. Further, system 10 includes a battery backup module 40 for maintaining the high voltage DC bus power during an outage of the AC source, allowing the computer or telecommunications systems coupled to system 10 to be maintained in operation, or shut down in an orderly manner.

0011Referring now to the block diagram of the modular power supply system 10, shown in FIG. 1, the AC power supplied on line 16 is converted to a high voltage DC level for distribution to a plurality of output modules 70a - 70n on a DC voltage bus 22. The output modules down convert the DC voltage supplied on bus 22 to particular predetermined DC or AC levels for output to respective loads on the output lines 72a - 72n. This two stage approach, boost converting the input voltage and down converting from the boost converted voltage improves the overall regulation of the system. As will be described in following paragraphs, the voltage output to bus 22 is maintained substantially constant for an input AC RMS voltage on line 16 within the range of 90 - 264 volts. With a substantially constant voltage supplied to the input of the down converter modules 70a - 70b, those modules are better able to regulate their respective outputs, with their input voltage being substantially invariant. The arrangement further provides for an efficient means to incorporate a battery backup function, the battery backup module 40 monitoring the voltage of bus 22 and maintaining such at a predetermined level without introducing any switching transients or time delay between loss of the AC input voltage and power being supplied from the battery source.

0012Thus, boost converter 20 functions to convert the AC power supplied on line 16 to a high voltage DC output supplied to the DC voltage bus 22, in a manner which makes system 10 appear as a substantially resistive load to the AC source.

0013As is conventional with large power supply systems, the system ground 14 is coupled to an external earth ground by a line 18. Although each of the modules coupled to the DC bus 22 include their own discrete control circuitry, system 10 includes a central control circuit 30 for coordinating the. operations of system 10, providing alarms to external devices, providing for start up of the system and emergency shut down thereof. Central control circuit 30 generates bias voltages and synchronization signals which are output to each of the down converter modules 70a - 70n on the output line 36 for respective coupling to each of the modules by the lines 36a - 36n. Central control circuit 30 also provides an output 32 which is coupled to the power factor corrected boost converter 20 to provide a synchronization signal and bias voltage thereto. The generation of the bias voltages which are supplied to each of the modules define the power source for the amplifiers and logic circuits therein, and thereby provide an efficient means for shutting the system down from a central point in the system, as will be further described. Central control circuit 30 monitors the thermal conditions of system 10 and also provides the operational voltage to a DC fan 60 by the coupling line 34. Additionally, control circuit 30 monitors the voltage level of bus 22 by means of the coupling line 24 in order to provide for start up of the system and properly generate the bias voltages supplied to each of the modules and the power factor corrected up converter 20.

0014System 10 may include at least one converter module, with additional modules added as required to meet the demands of a particular application. Although such converter modules are typically down converters, they may be up converter modules for applications requiring such. Each of the modules 70a - 70n derive their input power from the DC voltage bus 22, and are designed to provide a predetermined regulated output voltage on their respective output lines 72a - 72n. The down converter modules are designed to maintain a substantially constant output voltage, which may be AC or DC, depending upon the particular application, with a variation of input voltage within the range of 300 - 420 volts, with the voltage on bus 22 being maintained at substantially 390 volts by boost converter 20. Each of the down converter modules 70a - 70n also provides alarm and interface signals to the particular load to which they are connected, through a respective control and interface signal bus 74a - 74n. Such interface signals may include a shut down control signal transmitted from the load to the down converter module, to disable the output therefrom responsive to some external condition.

0015It is particularly important to the application of modular power supply system 10 in critical computer and telecommunications applications that it maintain the regulated output voltage from each of the respective down converter modules 70a - 70n during interruptions in the AC power supplied on line 16, which is accomplished by means of the battery backup module 40. The battery backup module is coupled to the bias and synchronization signal output of central controller circuit 30 by means of the coupling line 37, and is coupled to the DC voltage bus 22 for monitoring the magnitude of the voltage thereon. Battery backup module 40 provides an output 42 coupled to DC voltage bus 22 for supplying a DC voltage output, responsive to a drop in the bus voltage from the nominal 390 volts to a level approximating 360 volts. Thus, if the AC voltage on line 16 is interrupted, the power factor correcting boost converter 20 will cease to generate voltage, resulting in its output filter capacitors discharging. The bus voltage will thereby begin dropping, and as such reaches 360 volts, the battery backup module 40 will generate sufficient power to maintain the bus voltage at the 360 volt level, without generating any transience or glitches in the voltage on bus 22. As the change from 390 volts to 360 volts will not affect the regulated output of the down converter modules 70a - 70n, the respective output voltages on outputs 72a - 72n are unaffected by the transfer from AC power to the battery backup source 50. The battery backup module 40 is coupled to the battery source 50 by a DC bus 48 for carrying battery power to an up converter of module 40 and carries power to the battery from a battery charger circuit of the module 40. Module 40 further supplies battery charger alarm, logic and battery current monitoring signals to external systems through the coupling line 46, and receives control and interface signals from external systems on the bus 44.

0016Referring now to FIG. 2, there is shown a circuit diagram for the power factor correcting boost converter 20. AC voltage from the source 12 is supplied by the lines 16 to the electromagnetic interference filter 100 which prevents high frequency noise generated by the inverter circuits of system 10 from being fed back into the AC lines. The output of EMI filter 100 is supplied to the AC input terminals 106, 108 of the rectification circuit 110. The output of rectifier circuit 110 is coupled to an in-rush current limit circuit 120, which limits the starting current flowing from rectifier 110 during an initial start up time period. Rectifier circuit 110 includes a negative voltage output terminal 114 which is coupled to the system ground 116, and a positive voltage output terminal which is coupled to one end of a current limiting resistor 118. After the initial start up time period has lapsed, a pair of switching devices 122 and 124 of the in-rush current limit circuit 120 bypass resistor 118 to permit a maximum current to pass to the high voltage DC bus 22.

0017Switching devices 122 and 124 may be silicon controlled rectifiers (SCRs) each having its anode coupled to a respective AC input terminal 106, 108 of rectifier 110. The gate voltage supplied on line 123 is referenced to the line 127, also part of bus 32, and coupled to the cathodes of the SCRs 122 and 124. A node 121 disposed between the series coupling of current limiting resistor 118 and diode 126 is coupled to the positive voltage line 22a of DC voltage bus 22 through the bypass diode 128. Thus, on initial start up, the rectified voltage from rectifier output terminal 112 is coupled to the positive voltage line 22a of DC high voltage bus 22 by the series circuit comprising resistor 118 and diode 128, which provides current limiting by virtue of the impedance of resistor 118.

0018The generation of the gate drive voltage for SCRs 122 and 124 will be described in following paragraphs, however, subsequent to such being generated and supplied to the respective gates of SCRs 122 and 124 by line 123, resistor 118 is effectively removed from the circuit. When SCRs 122 and 124 are turned on, alternating half cycles of the AC voltage supplied to the respective anodes thereof is supplied to the node 125 for coupling to the positive voltage line 22a through the boost circuit 129.

0019The inverter boost circuit 129 includes a current transformer 142 having a primary winding 144 through which an oscillation or pulsating current flows responsive to the repetitive switching on and off of the switch 148. Current transformer 142 provides feedback of the current flowing through switch 148. Switch 148 may be any solid state switching device such as a MOSFET switching device, or alternately a plurality of MOSFET switching devices coupled in parallel. Switch 148 is turned on and off responsive to a switching control signal supplied from the DRIVE output terminal of the pulse width modulator/power factor correction circuit 150 by the coupling line 152. Thus, DC voltage supplied to node 131 passes through an inductor 130, for coupling to one end of the primary winding 144 of current transformer 142, and from the opposing end of primary winding 144 through the switching MOSFET 148 to the system ground 116. When the MOSFET 148 is switched from a conductive to a nonconductive condition, a high voltage is induced in the inductor 130 to boost the voltage supplied to the node 131, by flyback voltage inducted in the inductor.

0020The voltage supplied to node 131 is coupled to the positive voltage line 22a of the DC high voltage bus 22 through the current monitoring transformer primary winding 134 and at least one series coupled blocking diode 138. The reference voltage line 22b of the voltage bus 22 is coupled to the system ground 116, and a storage capacitor 140 is coupled across the bus voltage lines 22a and 22b for providing low frequency filtering and charge storage. Capacitor 140 may be one or more capacitors combined to have a value within the range of 1400 - 1500 microfarads.

0021The voltage on the positive voltage bus line 22a is fed back to the voltage feedback input terminal V_F of pulse width modulator/power factor correction circuit 150 by means of the coupling line 162, the resistor 160 and the coupling line 164. The pulse width modulator/power factor correcting circuit 150 controls the switching of MOSFET 148 so as to regulate the voltage generated in inductor 130, and maintain a regulated voltage of 390 volts impressed between the DC voltage bus lines 22a and 22b. The switching of MOSFET 148 is controlled so as to generate a current in inductor 130 which is reflected at the input 16 as a current whose phase is maintained in close relation to the phase of the voltage from the AC source.

0022In addition to regulating the voltage of bus 22, pulse width modulator/power factor correction circuit 150 controls the current supplied to the bus as well as regulating the voltage, the current feedback information being supplied by the secondary winding 136 of current monitoring transformer 132 and secondary winding 146 of current monitoring transformer 142, which are coupled in parallel relation. Secondary winding 146 provides feedback of the current flowing through the switching device 148. The two secondary windings 136 and 146 are each coupled in series with a respective diode 156 and 154, the cathode of both diodes being coupled together to the system ground 116. The opposing end of each of the windings 136 and 146 are coupled together for providing an output to the feedback current input terminal I_F of the pulse width modulator circuit 150, through the coupling line 158. Resistor 141 and capacitor 143 are coupled in parallel relation between the feedback coupling line 158 and ground 116 to provide filtering thereof. The windings 136 and 146 are phased such that each provides a signal on alternate half cycles of the switching signal supplied on line 152, thereby time division multiplexing the respective current feedback signals. Thus, the pulse width modulator circuit 150 may vary the duty cycle of the control signal which drives MOSFET 148 in order to control the current which flows through the switching device as well as the current which is supplied to bus 22, and vary the duty cycle of the control signal in order to regulate the voltage induced in inductor 130.

0023The pulse width modulator/power factor correction circuit 150, in order to maintain an input current which is in phase with the AC input voltage, monitors the input signals supplied to the system. The input signals are represented by the rectified voltage supplied to node 125 and a current drawn therefrom. A representation of the AC voltage is supplied to the AC input voltage terminal V_AC through a voltage divider defined by resistors 153 and 155, the center tap therebetween being coupled to the V_AC terminal by the coupling line 157. The series combination of resistors 153 and 155 are coupled between the node 125 and the system ground 116. A representative current is supplied to the AC current input terminal I_AC of pulse width modulator 150 from node 125 through the resistor 151 and coupling line 159. Pulse width modulator circuit 150 utilizes the waveform of the current passing through resistor 151 as a reference for generating a full wave sinusoidal current in inductor 130 to derive substantially unity power factor at the input.

0024Two of the control signals provided from the central control circuit 30 are the bias supply voltage, supplied to the voltage supply terminal V_CC of pulse width modulator 150 by means of the coupling line 196, an a synchronization signal supplied by line 198 and coupled to the SYNC input terminal of circuit 150. Pulse width modulator circuit 150 also includes an enable/inhibit input terminal INH for inhibiting the output from the drive terminal responsive to a signal supplied to the INH input. Several logic functions are coupled to the INH input terminal for inhibiting generation of the boost voltage responsive to particular predetermined conditions.

0025One such condition for inhibiting generation of the boost voltage is an input undervoltage condition. After the system has completed the start up cycle, if the input voltage subsequently drops below 80 volts, the boost voltage generation is shut down. If the battery backup module is not available when the input voltage drops below 80 volts, then the whole system is shut down. The positive output voltage terminal 112 of rectifier 110 is monitored to provide a representation of the input AC voltage. Thus, a current limiting resistor 184 is coupled to terminal 112 to provide the input voltage representation to the comparator 186 via the coupling line 195. Comparator 186 compares the voltage supplied on coupling line 195 with a first reference voltage V_REF1. The output of comparator 186 is coupled to an inverter 190 by the coupling line 188, the output 192 of inverter 190 is coupled to the inhibit input terminal pulse width modulator circuit 150 by coupling line 172. The output of comparator 186 is also coupled to an input of the logic circuit 180 by the coupling line 174. Logic circuit 180 provides a system shut down output on line 175 responsive to the signal on line 174 indicating that the input voltage has dropped below 80 volts and an input signal supplied from an interlock switch 183 on line 182 indicating that the battery backup module is either present or not.

0026The bus voltage supplied on line 22A, supplied through resistor 160 is also coupled to the comparator 168, by the coupling line 166. Comparator 168 compares the voltage on the bus with a second reference voltage V_REF2, supplied to the comparator 168 by the coupling line 178. The output 170 of comparator 168 is coupled to the inhibit input terminal INH by the coupling line 172. The second reference voltage V_REF2 is selected such that the boost voltage is limited to a maximum value of approximately 450 volts, which will protect the battery backup module and the output converter modules from an overvoltage condition.

0027Referring now to FIG. 3, there is shown, the battery backup module 40 which comprises two major components, a charger 200 and a battery up converter 250. The charger circuit 200 is basically a down converting inverter circuit for converting the 390 volts DC supplied on bus 22 to a 56 volt DC level for charging the backup battery 50. This inverter circuit includes a controlled leakage inductance transformer 202 having a primary winding 204 coupled in series with a switching device 212 across the voltage bus 22. The leakage inductance of this and other transformers of system 10 are controlled by virtue of their construction using flat conductors formed on a flexible insulator which is wound on a bobbin. Switching device 212 may be a single MOSFET device, or a parallel arrangement of such devices controlled by a pulse width modulator circuit (PWM) 216. For simplification, the feedback connections to pulse width modulator 216 have not been shown, as such may be derived in a similar manner to that which has been described for the power factor correction of converter circuit 20, and such feedback connections for pulse width modulators are well known in the art. PWM 216 has an output drive signal supplied to the gate of the MOSFET switching device 212 through the coupling line 216. The high frequency switching of current through the primary winding 204 induces a voltage in the secondary winding 206 which is rectified by diode 208 and filtered by capacitor 210, to provide a voltage on the battery supply bus 48 for charging battery 50. The negative supply line 48b of bus 48 is coupled to the battery system ground 116' to provide a reference for the positive battery voltage supplied on line 48a. The battery voltage is supplied to the battery up converter 250 through the coupling line 222, which is monitored by the interface circuit 232.

0028The battery voltage is coupled to interface circuit 232 by the input coupling line 234, wherein the battery voltage is compared with a third reference voltage V_REF3 supplied to the circuit on line 228. The output of interface circuit 232, indicating an overvoltage condition, as when the battery is electrically removed, is supplied on coupling line 46, which provides logic level alarm signals to an external system, such as the computer or telecommunications system which is being powered by system 10. The presence of the battery is also monitored by the comparator 240, which receives the battery voltage through the input coupling line 238, providing an output on line 242 to the optical coupler 218 through the coupling line 246, responsive to the voltage on line 238 being less than the third reference voltage which is supplied to the comparator 240.

0029Other connections, not shown, to interface circuit 232 may provide such information as charging current, battery load current, a low battery voltage indication, a battery open indication and various temperature measurements. An output from the battery up converter, provided on line 296, is coupled to the node 244, disposed between the output of comparator 240 and the input of optical coupler 218, for inhibiting the operation of the charger when the up converter 250 is enabled. Thus, the pulse width modulator is inhibited responsive to a signal on line 248 from the optical coupler which in turn is generated responsive to either an output from comparator 240 indicating the battery voltage is less than the third reference voltage, or an output from the interface logic circuit 290 of the up converter 250 indicating that the voltage bus 22 is being supplied power from the up converter 250. The pulse width modulator 216 is supplied with a synchronization signal on line 220, and provided with a DC operating voltage by the line 298.

0030The battery up converter 250 includes an up converter circuit utilizing a controlled leakage inductance transformer 251 for generating a 360 volt DC output from the 48 volt battery source. The battery voltage is supplied from the positive bus line 48a to the center tap 254 of inverter transformer primary winding 252 by the coupling line 222. Each of the opposing ends of the primary winding 252 of transformer 251 are respectively coupled to a switching device 278, 282 for alternately drawing current through a respective half of winding 252. By this arrangement, one end of winding 252 is coupled to the drain 284 of the MOSFET switching device 282, with the source 286 of device 282 being coupled to the battery system ground 116', to thereby complete a current path from the positive lead of battery 50, through the center tap of winding 252 through one half of the primary winding 252 to the battery ground reference 116'. Similarly, the opposing end of winding 252 is coupled to the drain 279 of the MOSFET switch 278, its source 280 being coupled to the battery system ground 116'.

0031A pulse width modulator circuit 70 provides respective drive outputs 274, 276 which are coupled to the respective gates of MOSFETs 278, 282, switching each on in alternate half cycles. Responsive to the alternating current driven through the respective portions of primary winding 252, a voltage is induced in the secondary winding 256 of controlled leakage inductance transformer 251 which is coupled to the rectifier and filter circuit 260. Here again, the feedback signals for maintaining regulation of the induced voltage is not shown for simplicity.

0032When the high voltage DC bus 22 is above a predetermined level, the operation of pulse width modulator 270 is inhibited, the output drive signals being inhibited while the remainder of the circuit is operational, such as the high frequency oscillator and feedback monitoring circuits, such that the drive signals can be properly supplied to the MOSFET switches when the inhibit signal is removed. The voltage on the positive bus line 22a is coupled to the up converter output line 42a and from there to the logic circuit 264 by the coupling line 262. Control circuit 264 compares the voltage on the bus line 22a with a reference voltage so as to provide an output error signal on line 266 responsive to the voltage on bus line 22a for regulating the bus at 360 volts, and thereby inhibit voltage generation when the bus voltage is greater than 360 volts.

0033The output from control circuit 264 on line 266 is coupled to an optical coupler circuit 268, for providing isolation. The output of optical coupler circuit 268 is supplied to the pulse width modulator 270 by coupling line 272. Thus, when the voltage is properly generated by the power factor corrected boost converter circuit 20, the voltage on bus line 22a will be approximately 390 volts, which will in turn result in an output signal from control circuit 264 which inhibits the operation of pulse width modulator 270. If however the AC voltage input to the power factor corrected up converter 20 is lost for any reason, capacitor 140, shown in FIG. 2, will begin to discharge, and as the discharge voltage drops to 360 volts, control circuit 264 will generate an error signal which will allow pulse width modulator 270 to control the MOSFET switches 278 and 282. Responsive to the operation of the MOSFET switches, the secondary winding 256 will provide an induced voltage to the rectifier filter circuit 260, for supplying the DC voltage bus 22 with a 360 volt voltage, and thereby maintain power to the various other modules 70a - 70n coupled to the bus 22.

0034Particular operating parameters of the battery up converter 250 are supplied to the interface logic circuit 290 by the coupling line 292 for output to external systems on the interface bus 44. Further, an output from interface circuit 290 is provided to the charger through the coupling line 296 to inhibit the charger's operation during operation of the up converter. A synchronization signal from the central control circuit 30 is provided to the pulse width modulator 270 by means of the coupling line 288. Further, the DC voltage for powering the logic circuits, the bias voltage, is supplied on line 298 to the interface logic circuit 290, pulse width modulator 270 and control circuit 264 of the up converter 250, as well as to the pulse width modulator 216 and interface circuit 232 of the charger 200.

0035Periodically, it may be desirable to test the battery backup module 40 to insure that such is operational and performs to specification. However, where the modular power supply system 10 is coupled to a live load, one which must be maintained operational, it would be imprudent to simply remove the AC power source as the means of testing the battery backup function. It is therefore desirable to provide a means for testing the operation of the battery up converter 250 without the danger of losing the ability to maintain the voltage of bus 22. Such a battery backup test function has been incorporated into the system 10. An external signal supplied to the battery test input terminal is coupled to the control circuit 264 by the coupling line 299. This logic signal is coupled to the pulse width modulator 270 through an optical channel of the optical coupler circuit 268, such coupling being represented by the coupling line 272. The function of this signal is to shift the voltage regulating operating point of pulse width modulator 270 from 360 volts to 415 volts.

0036Responsive to this test signal, the pulse width modulator 270 is enabled with the bus voltage at the 390 volt level, and is raised to 415 volts by the up converter circuit 250. The internal error amplifier of the PWM 150 of the power factor correction boost converter circuit 20 senses the bus voltage is above 390 volts, and thus shuts down the output drive signal to the MOSFET 148, while maintaining its other circuit functions in an operational state. Obviously, if there is a problem in the battery backup module 40 which does not permit the generation of the DC output voltage on the output lines 42, the DC voltage bus 22 will be maintained at the 390 volt level, the load will remain undisturbed, and an alarm signal will be output from interface logic circuit 290.

0037If the battery backup module 40 operates properly when in the battery test mode, the voltage on the bus will be raised to the 415 volt level, the power factor correction up converter circuit 20 will be shifted to a standby mode and the regulation of the output modules 70a - 70n will be unaffected by the small increase in bus voltage. Subsequent to removal of the battery test signal, the operation of pulse width modulator 270 will be inhibited, since its operating point will be returned to 360 volts and the bus voltage will be above 360 volts. The voltage on the DC voltage bus 22 will bleed off, and such will be sensed by the error amplifier of the PWM 150, which will reactivate the output drive signal of the pulse width modulator 150 once the bus drops to approximately 390 volts.

0038Referring now to FIG. 4, there is shown the central control circuit 30 which supplies synchronization and bias voltages to the various modules of the system 10. When system 10 is initially energized, the voltage supplied to the DC bus 22 begins to rise from a zero value, the voltage initially being supplied through the in-rush current limiting resistor 118 and bypass diode 128. During this initial time period the pulse width modulator 150 of the power factor correction boost converter circuit is not operational, as there is not yet sufficient voltage on line 196 to properly power pulse width modulator 150. The DC voltage initially supplied to the voltage bus line 22a is coupled to a voltage source 370, formed by a constant current source supplying a capacitor, through the coupling line 376 for providing an operating voltage (V_CC) to pulse width modulator 340. The voltage on bus line 22a is also supplied to one end of the primary winding 302 of the transformer 300, which may also be a controlled leakage inductance transformer. The opposing end of primary winding 302 is coupled in series relation with the switching device 344, which may be one or more MOSFET switching devices having a drain connection 346 coupled to primary winding 302 and a source connection 348 coupled to the system ground 116. Thus, as the voltage on the bus line 22a begins to rise, the pulse width modulator 340 operates to switch current through the primary winding 302. Responsive to the switching current in primary winding 302, the multiplicity of secondary windings of transformer 300 generate induced voltages therein. As the voltage increases on bus line 22a, the respective voltages generated in the secondary windings of transformer 300 also increase.

0039The voltage induced in secondary winding 304 is rectified by diode 380 and filtered by capacitor 382. The anode of diode 380 is coupled to one end of winding 304 through the current limiting resistor 378, the opposing end of winding 304 being coupled to the reference voltage line 127. The rectified voltage from diode 380 is coupled to the gate drive line 123 which is in turn coupled to the gates of SCRs 122 and 124, shown in FIG. 2 and the reference line 127 is coupled to the cathodes of SCRs 122 and 124 to provide a reference for the gate voltage. Thus, when the voltage generated on line 123 is sufficient to turn on SCRs 122 and 124, the in-rush current limiting resistor 118 is thereby bypassed.

0040The pulse width modulator circuit 150, shown in FIG. 2, receives its power from a bootstrap voltage generating circuit 368. Bootstrap voltage generating circuit 368 generates sufficient voltage for operating the pulse width modulator 150 during the initial start up phase, then subsequently provides a change in transformation ratio to prevent the supply voltage from exceeding predetermined limits. By providing such a transformation ratio change, limiting the voltage generated by the bootstrap voltage generating circuit, allows the use of Shottkey type rectifying diodes, which are more efficient. When the output of the bootstrap voltage generating circuit 368 is sufficient to power the pulse width modulators 150 and 340, an output signal supplied on line 372 shuts down the voltage source circuit 370, thereby allowing the.bootstrap voltage generator circuit to supply power to the pulse width modulator 340 through the coupling line 374.

0041The output drive signal of pulse width modulator 340, supplied to the MOSFET 344 on line 342 is coupled to the power factor correction and charger sync circuit 356 through the coupling line 354. The synchronization circuit 356 utilizes the oscillation signal from the pulse width modulator to provide synchronization signals to pulse width modulator 150 through the coupling line 198 and to pulse width modulator 216 of charger circuit 200 through the coupling line 220. The secondary winding 306 is coupled to a voltage sense circuit 336, which provides an output to the bootstrap voltage generator circuit through the coupling line 338 when the induced voltage of winding 306 exceeds a predetermined value.

0042The signal from voltage sense circuit 336 is utilized to change the transformation ratio which provides the input thereto. The voltage generated by bootstrap voltage generator circuit 368 is derived from the output of the secondary winding 308, which is the combination of voltages induced in the tapped winding portions 310 and 312. Responsive to the signal output from voltage sense circuit 336, the winding 310 is preferably opened, thereby reducing the magnitude of the input voltage to the voltage generating circuit 368.

0043Transformer 300 includes a plurality of secondary windings 314a - 314n for providing bias voltage to the various modules of system 10. Each of the windings 314a - 314n is coupled to a respective bias rectifier and filter circuit 318a - 318n for supplying bias voltage and synchronization signals to the respective modules. The bias rectification and filter circuits may include a pair of diodes 322 and 324, each having an anode thereof coupled to an opposing end of the secondary winding 314a. the cathodes of each diode are respectively coupled to the sync signal line 402 for coupling to a respective down converter module circuit 70. The common cathode connection of diodes 322 and 324 is also coupled to one end of a choke 326, the opposing end of choke 326 being coupled in series relation with the parallel RC circuit formed by capacitor 326 and resistor 327, and the DC output line 404 which supplies the power supply voltage, with respect to a module ground 116'', to the logic and pulse width modulator circuits of the respective down converter module, to which it is coupled.

0044Such a rectification and filter circuit is provided for each of the down converter modules 70a - 70n of system 10. One of the rectification and filter circuits 318n supplies synchronization signals, output on line 288, to the pulse width modulator 270 of the battery up converter 250, shown in FIG. 3. The DC voltage supplied on line 298 provides the operating voltage for the pulse width modulators and logic circuits of the battery backup module 40. An additional secondary winding 316 is coupled to a logic power supply circuit 320 for powering the DC cooling fan 60 of system 10 and the logic circuits of the central control circuit 30. A DC output voltage supplied on line 34 powers the fan 60, and on line 358 for powering the control and interface logic circuit 330, and the logic circuit 360. Line 196, in addition to supplying PWM 150 also provides power for the comparators 168, 186 and 190 of boost converter 20, delaying their energization and that of PWM 150 relative to pulse width modulator 340, such that the low voltage inhibit function does not interfere with initial start up of system 10. The control and interface logic circuit 330 monitors the operation of the DC fan, through the fan fail monitoring line 332, receives a status from the output modules on line 36, and outputs alarm and status signals on the interface bus 38.

0045The generation of the bias voltages for powering the logic circuits of all of the modules in system 10 provides a unique and efficient means for providing a shut down of the entire system. When conditions indicate that the whole system should be shut down, such as when the input voltage drops below 80 volts and the battery backup module is not present, logic circuit 180, shown in FIG. 2, outputs a shut down signal on line 175. That signal is coupled to the logic circuit 360 of the central control circuit 30. Logic circuit 360 provides an output signal of appropriate polarity to the optical coupler 364 by means of the output coupling line 362. Optical coupler 364 provides an optically isolated signal output on line 366 for inhibiting the output of pulse width modulator 340. Thus, the switching device 344 is maintained in an off state to thereby cease the induction of voltage in the plurality of secondary windings of transformer 300. Hence, the DC voltages that were supplied to the logic circuits and pulse width modulators of each of the output modules, the battery backup module and the power factor corrected boost converter are substantially simultaneously cut off, quickly shutting down the entire system from a central point. As shown in the representative bias rectifier and filter circuit 318a, each of the bias supplies is provided with a bleed resistor 327, such that the bias voltage is quickly brought down when the induced voltage supplying the rectifier circuit is cut off.

0046Referring now to FIG. 5, there is shown a typical output module 70a for converting the high voltage supplied on the DC bus 22 to a predetermined output voltage on the output lines 72a for use by a predetermined load. The DC voltage bus 22 is coupled to a high frequency inverter 400 whose output is coupled to a rectifier and filter circuit 434 to supply the required DC voltage on the output lines 72a. Inverter 400 is a bridge type switching circuit, sometimes referred to as an H-switch circuit, wherein the output is taken from the coupling between the central portion of each leg thereof. Each leg comprises a pair of switching devices coupled in series relation which are operated alternately. Each of the respective four MOSFETs 406, 408, 410 and 412 have their respective gates coupled to the output drive terminals O₁, O₂, O₃ and O₄ of the phase shift pulse width modulator 436 by the respective coupling lines 438, 440, 444 and 442.

0047Phase shift pulse width modulator 436 controls the operation of each of the four MOSFET switching devices such that the MOSFETs 406 and 412 are turned on during one portion of an AC cycle and MOSFETs 408 and 410 are operated during an alternate half cycle, to provide bi-directional current flow through the primary winding 426 of the controlled leakage inductance transformer 424. In order to provide the minimum stress on the circuit components and minimize the generation of harmonic signals, the switching of current through primary winding 426 is best accomplished when the voltage across each MOSFET is 0 volts. To accomplish this 0 voltage switching, the energy which is stored in primary winding 426 and the leakage inductance 422 of transformer 424 must induce a voltage equal the bus voltage. It is for this reason that it is important that the leakage inductance of transformer 424 be predictable and consistent from one transformer 424 to another, and since the leakage inductance is additive, it is equally important that its value be similarly known and controlled.

0048Each of the MOSFET switching devices has an intrinsic capacitance 414, 416, 418 and 420 between the respective source and drain terminals thereof. This intrinsic capacitance is a known value which is very consistent from one device to another. The capacitance value for each of the devices 406, 408, 410 and 412 is a relatively low value, in the picofarad range. Therefore, it is desirable to have a suitable inductance coupled therewith to form a resonant circuit, such that the stored energy can be efficiently transferred. Since the leakage inductance 422 effectively appears as an inductance value which is in series with the mutual inductance reflected in the primary winding 426, such is shown as a separate element coupled in series with the primary winding 426 between the output nodes 407 and 411.

0049The alternation of current through primary winding 426 induces a voltage in secondary winding 428, the opposing ends of which are coupled to the rectifier and filter circuit 434 through the coupling lines 432 and 430. Obviously, if an AC voltage is desired for supply to a particular load, the rectifier filter circuit 434 may be eliminated and the output from the secondary winding 428 provided thereto. Feedback from the output voltage line 72a is supplied to the "Sens" input of pulse width modulator 436 by the coupling line 452, feedback logic circuit 454, and coupling line 448, allowing the phase shift pulse width modulator 436 to control the switching of the respective MOSFETs 406, 408, 410 and 412 to maintain the output voltage or current at a predetermined level. Here again, conventional connections for feedforward, and current feedback have not been shown for purposes of clarity.

0050Thus, the feedback line 452 may represent voltage or current feedback, for discussion purposes. The feedback signal from line 452 is applied to the output line 448 of feedback logic circuit 454, unmodified, if no control signal is input on line 456 from control and interface logic circuit 446. The output module 70a further includes a control and interface logic circuit 446, for providing the inhibit signal to the phase shift pulse width modulator 436, by means of coupling line 450, as well as providing an interface for alarm and other signals which are exchanged between the module 70a and the particular load to which it supplies power. Control and interface logic 446 also provides a status output on line 36 to the control and interface logic circuit 330 (FIG. 4), indicating whether the output module is operating properly or not. A synchronization signal is supplied on line 402 to the SYNC input of pulse width modulator 436 and the bias supply voltage form the circuit 318a is supplied on line 404 to the V_CC input of pulse width modulator 436 and the voltage supply input of the control and interface logic 446, which permits the system to be shut down, as was previously described.

0051Multiple output converter modules 70 may be coupled in parallel to a load with the load current being equally divided among the paralleled modules. When this option is utilized, a control signal is input on the respective interface bus 74. Thus, if module 70a is being paralleled with module 70b, or a module 70a of another power supply system, then the power sharing control signals will be respectively on the buses 74a and 74b. This control signal, as shown in FIG. 5, is input to the control and interface logic circuit 446 of each module. The control and interface logic circuit 446 outputs a control signal to the feedback logic circuit 454. In response to the input from signal line 456, feedback logic circuit 454 modifies the feedback signal provided from feedback line 452 to generate a signal on line 448 which maintains a load current value substantially equal to that of the other paralleled module 70b.

0052Although this invention has been described in connection with specific forms and embodiments thereof, it will be appreciated that various modifications other than those discussed above may be resorted to without departing from the scope of the invention. For example, equivalent elements may be substituted for those specifically shown and described, certain features may be used independently of other features, and in certain cases, particular locations of elements may be reversed or interposed, all without departing from the scope of the invention.