Voltage regulation and power switching system

A power switching and voltage regulation system utilizing a conventional switching element to provide distributed power switching and voltage regulation. The system utilizes a switching element to impose an impedance in a controlled manner to provide power to a load such as a plug-in module in an electronic apparatus. The power source supplying an input DC voltage is intentionally set to a higher voltage than the level required by the plug-in module. The voltage supplied is required to be sufficiently high such that the voltage delivered to the plug-in module, exceeds the maximum permitted voltage level of the voltage required by the particular plug-in module. Once the switching device is turned on, the switching element exerts an impedance which functions to drop the voltage supplied to the load to the required value. The impedance is generated in accordance with a feedback control signal. The drop in voltage is achieved in accordance with a reference signal input to a comparison circuit such as an operational amplifier. A first embodiment discloses a system wherein a plurality of DC output voltages are generated in which all the output voltage levels are the same. A second embodiment discloses a system wherein a plurality of DC output voltages are generated whereby the level of each output voltage is independent of the others.

FIELD OF THE INVENTION
 The present invention relates generally to electrical power systems and
 more particularly relates to the integration of voltage regulation and
 power switching systems.
 BACKGROUND OF THE INVENTION
 The power requirements for electrical and electronic systems being designed
 today are placing increasing demands upon power supply designs. The latest
 semiconductor devices call for lower and lower supply voltage levels. The
 typical 5 V supply has been reduced to 3.3 V for many components. Many
 semiconductor devices already available require an even lower supply
 voltage of 2.8 V such as memory devices.
 A high level block diagram illustrating an example of a prior art power
 supply distribution system in an electronic device is shown in FIG. 1. The
 power supply distribution system, generally referenced 200, comprises a
 power supply 202, power supply wires or cables 204, sense wires 206 for
 voltage feedback, distribution bus 208 and a plurality of printed circuit
 cards (PCBs) 210, 212.
 The power supply 202 receives an input voltage from a source of electrical
 power and functions to generate an output voltage which is distributed to
 the power distribution bus 208 via cables 204. Cables 206 comprise sense
 wires to provide voltage feedback to the power supply 202. The power
 supply 202 utilizes the feedback voltage in maintaining a stable output
 voltage.
 Typical systems comprise a plurality of PC boards that connect to a
 backplane via a modular connector. For example printed circuit board 210
 connects to the power distribution bus, i.e., the typically the backplane,
 via connector 220. Similarly, printed circuit board 212 connects to the
 power distribution bus via connector 222.
 On some printed circuit boards, also termed plug-in boards or modules,
 electrical power is delivered directly to the board once the board 210 is
 seated in the connector 220. The electrical load placed on the power
 supply 202 is represented by the load block 211 on printed circuit board
 210.
 On other printed circuit boards electrical power is switched on the board
 itself. Printed circuit board 212 is an example of such a type of board.
 After the board 212 is seated in the connector 222, electrical power flows
 to the load 213 only when switches 215 are closed. In this case,
 electrical power to the plug-in modules like module 213 is controlled by
 switching devices such as switches 215 on board 212. Typically, the unit
 housing the distribution system 200 comprises a central control unit (not
 shown) which functions to control electrical power to the modules. Once a
 new module is installed in the system, for example, a request is made to
 the central control unit to activate the new module. Upon receiving the
 request, the central control unit examines the functional parameters of
 the particular module and if the parameters are within predetermined
 tolerances, the central control unit switches on electrical power to the
 new plug-in module.
 The switching device 215 may comprise any suitable switch such as an
 electromechanical relay, solid sate relay, transistor or other
 controllable switching device.
 The prior art electrical power distribution scheme described above,
 however, fails to deliver electrical power with sufficient accuracy when
 the required voltage levels begins to drop, for example, to 3.3 V and
 less. This is a major disadvantage especially considering that, the
 current trend in electronic technology is to operate electronic components
 at lower and lower voltages, e.g., 3.3 V +/-5%, 2.8 V +/-5% or lower. At
 such low voltage values, the current needed to be supplied is fairly large
 while the permitted variability of the voltage supply is only a few tens
 of millivolts. Even a small modest impedance naturally existent in the
 copper traces and connectors making up the power distribution path will
 cause voltage drops much larger than tens of millivolts. To make matters
 worse, the impedance in the copper traces and the connectors is usually
 not a design parameter that can be adjusted arbitrarily. In actuality, the
 impedance in the copper trances and the connectors is typically
 unpredictable.
 The following example illustrates the problems associated with the prior
 art power distribution system. Consider a plug-in module that consumes 100
 W which at 3.3 V draws approximately 30 A. An impedance of 10 m.OMEGA.
 would generate a drop of approximately 300 mV. This voltage drop is
 already almost twice as large as the 5% tolerance of 165 mV. In another
 example, if one considers a power FET, the typical R.sub.DS (On) impedance
 is approximately 4 m.OMEGA.. A current of 40 A yields a voltage drop of
 160 mV which almost equals the 3.3 V 5% tolerance. Further, higher
 impedances, lower supply voltages and tighter tolerances only worsen the
 problem.
 SUMMARY OF THE INVENTION
 The present invention in a power switching and voltage regulation system
 that utilizes the conventional switching element is a new way. In prior
 art approaches, the switching element is configured to present a minimal
 impedance with zero impedance being ideal. The system of the present
 invention, in contrast, utilizes the switching element to impose an
 impedance in a controlled manner. The power source supplying an input DC
 voltage is intentionally set to a higher voltage than the level required
 by the plug-in module. The voltage supplied is required to be sufficiently
 high such that the voltage delivered to the plug-in module, i.e., the
 load, exceeds the maximum permitted voltage level of the voltage required
 by the particular plug-in module.
 Once the switching device is turned on, the switching element exerts an
 impedance which functions to drop the voltage supplied to the load to the
 required value. The impedance is generated in accordance with a feedback
 control signal. The drop in voltage is achieved in accordance with a
 reference signal input to a comparison circuit such as an operational
 amplifier.
 Two embodiments of the present invention are presented. The first
 embodiment discloses a system wherein a plurality of DC output voltages
 are generated in which all the output voltage levels are the same. The
 second embodiment also discloses a system wherein a plurality of DC output
 voltages are generated however the level of each output voltage is
 independent of the others.
 There is therefore provided in accordance with the present invention a
 power switching and voltage regulation system for providing regulated
 electrical power to at least one plug-in module, the system comprising a
 voltage regulator coupled to a source of electrical power, the voltage
 regulator for generating an intermediate supply voltage, an on/off control
 unit for receiving an on/off command from an external source, a reference
 voltage generator for generating a reference voltage, the reference
 voltage regulator responsive to an output signal produced by the on/off
 control unit and regulation means for providing a controlled impedance
 which functions to regulate the intermediate supply voltage so as to
 provide an output voltage at a predetermined level to the plug-in module.
 The system further comprises a fuse in series with the intermediate supply
 voltage output from the voltage regulator. In addition, the regulation
 means comprises an off state wherein electrical power to the plug-in
 module is turned off and an on state wherein a controlled impedance is
 placed in series with the intermediate supply voltage so as to generate
 the output voltage to the plug-in module.
 Further, the regulation means comprises on/off control means for either
 turning electrical power to the plug-in module off or for enabling a
 controlled impedance and a controlled impedance placed in series with the
 intermediate supply voltage, the controlled impedance responsive to the
 on/off control means so as to maintain the output voltage at a
 predetermined level.
 The controlled impedance may comprise a switching device, a semiconductor
 transistor or a semiconductor field effect transistor (FET). The
 regulation means comprises operational amplifier (op amp) means adapted to
 receive the reference voltage and a sample of the output voltage and a
 switching device responsive to the output of the op amp means, the
 switching device configured to function as a controlled impedance for
 generating the output voltage at a predetermined level from the
 intermediate voltage.
 There is also provided in accordance with the present invention a power
 switching and voltage regulation system for providing regulated electrical
 power to a plurality of plug-in modules, the system comprising a voltage
 regulator coupled to a source of electrical power, the voltage regulator
 for generating an intermediate supply voltage, an on/off control unit for
 receiving an on/off command from an external source, a reference voltage
 generator for generating a reference voltage, the reference voltage
 regulator responsive to an output signal produced by the on/off control
 unit and a plurality of regulation means, each regulation means for
 providing a controlled impedance which functions to regulate the
 intermediate supply voltage so as to provide an output voltage at a
 predetermined level to the plug-in module, each regulation means
 generating the same level of output voltage.
 Each regulation means comprises an on state wherein a controlled impedance
 is placed in series with the intermediate supply voltage so as to generate
 the output voltage to the plug-in module corresponding thereto.
 Further, each regulation means comprises on/off control means for either
 turning electrical power to the plug-in module off corresponding thereto
 or for enabling a controlled impedance and a controlled impedance placed
 in series with the intermediate supply voltage, the controlled impedance
 responsive to the on/off control means so as to maintain the output
 voltage at a predetermined level.
 Each regulation means comprises operational amplifier (op amp) means
 adapted to receive the reference voltage and a sample of the output
 voltage and a switching device responsive to the output of the op amp
 means, the switching device configured to function as a controlled
 impedance for generating the output voltage at a predetermined level from
 the intermediate voltage.
 There is further provided in accordance with the present invention a power
 switching and voltage regulation system for providing regulated electrical
 power to a plurality of plug-in modules wherein the voltage level
 generated for one plug-in module is independent from that generated for
 other plug-in modules, the system comprising a plurality of voltage
 regulators, each voltage coupled to a source of electrical power, each
 voltage regulator for generating an intermediate supply voltage wherein
 the intermediate supply voltage generated for one plug-in module is
 independent of that generated for other plug-in modules, a plurality of
 on/off control units, each on/off control unit for receiving an on/off
 command from an external source, a plurality of reference voltage
 generators, each reference voltage generator for generating a reference
 voltage, each reference voltage regulator responsive to an output signal
 produced by its respective on/off control unit, wherein the reference
 voltage generated by one reference voltage generate is independent of
 reference voltages generated by other reference voltage generators and a
 plurality of regulation means, each regulation means for providing a
 controlled impedance which functions to regulate the intermediate supply
 voltage corresponding thereto so as to provide an output voltage at a
 predetermined level to its associated plug-in module.

DETAILED DESCRIPTION OF THE INVENTION
 The present invention provides a system for integrating voltage regulation
 and power switching control functions. A high level block diagram
 illustrating a power supply distribution and regulation system constructed
 in accordance with a first embodiment of the present invention is shown in
 FIG. 2. The power supply system, generally referenced 10, comprises a
 voltage regulator 12, fuse 14, on/off control 16 and reference voltage
 generator 18. The power supply system also comprises operational
 amplifiers (op amps) 20, 22, 24 and transistors 26, 28, 30.
 The principle of the present invention is to shift the location of the
 final regulation of the voltage used by the plug-in modules to the plug-in
 modules themselves. Rather than have a centralized power supply generate
 precise voltages which are then distributed to the various plug-in modules
 with consequent IR drops along the way, as described in the Background of
 the Invention section of this document, the present invention develops a
 precise output voltage directly on the plug-in module itself. This avoids
 the disadvantages of the prior art, i.e., the intolerable IR drops due to
 the copper traces and connectors.
 An input DC voltage, either regulated or unregulated is input to the
 voltage regulator 12. The output voltage of the voltage regulator is set
 to a level slightly larger than that required by the plug-in modules. The
 voltage regulator thus outputs an intermediate voltage level. The output
 of the voltage regulator passes through a current protection fuse 14
 before being routed to the plug-in modules 32, 34, 36. Note that although
 only three plug-in modules are represented in FIG. 2, one skilled in the
 electrical arts could easily adapt the present invention to any number of
 plug-in modules having various configurations.
 Each plug-in module comprises voltage regulation and power switching
 circuitry adapted to receive two inputs. The first input is a reference
 voltage signal and the second is the regulated output voltage from the
 voltage regulator 12. The reference voltage is generated by the reference
 voltage generator 18. An on/off control unit 16 controls the operation of
 the reference voltage generator 18 via an output signal generated
 therefrom. An on/off command is applied to the on/off control unit 16
 which functions to turn the voltage off to each of the plug-in modules.
 In operation, the voltage regulator 12 supplies voltage to transistors 26,
 28, 30 in plug-in modules 32, 34, 36, respectively. Optionally, the output
 of the voltage regulator can be routed through a switch (not shown) to
 further control power to the plug-in modules. An `on` command input to the
 on/off control unit 16, causes the reference voltage generator 18 to be
 enabled. Conversely, an `off` command to the on/off control unit 16
 disables the reference voltage generator 18. The reference voltage is
 distributed to each of the plug-in modules that are to be supplied with
 the level of voltage associated with that particular reference voltage.
 The reference voltage is input to the non-inverting input of an op amp
 while the inverting input of each op amp is the sampled output voltage
 generated by the transistor for use by the components on the plug-in
 module. In particular, the voltage output of transistor 26 is fed back to
 the inverting input of op amp 20. Similarly, the voltage output of
 transistor 28 is fed back to the inverting input of op amp 22. Likewise,
 the voltage output of transistor 30 is fed back to the inverting input of
 op amp 24.
 The output of each op amp is used to control each respective switching
 device. In the case of the switch comprising a MOSFET transistor, the
 output of each op amp is input to the gate of each transistor. In
 particular, the output of op amp 20 is input to the gate of transistor 26,
 the output of op amp 22 is input to the gate of transistor 28, the output
 of op amp 24 is input to the gate of transistor 30. The output of the
 transistor which is fed back to the inverting input of each op amp also
 constitutes the DC output voltage supplied to the plug-in module. Thus,
 the combination of an op amp and switching element, i.e., transistor, form
 a regulation circuit to provide a controlled impedance to the input DC
 voltage. Note that the switching element is able to be placed in an off
 state whereby electrical power to the plug-in module is turned off. When
 the switching element is placed in the on state, the controlled impedance
 is applied.
 The switching devices 26, 28, 30 may comprise any suitable switch such as
 an electromechanical relay, solid sate relay, transistor or other
 controllable switching device. Suitable transistors include, but are not
 limited to FETs, JFETs and IGBTs.
 An important principle of the present invention is that the function of the
 switching element is changed from that of the prior art. In the prior art
 approach, the switching element is required to present a minimal
 impedance, with the ideal impedance being zero. In the present invention,
 in contrast, the switching element intentionally imposes an impedance in a
 controlled manner. The input DC voltage in combination with the voltage
 regulator 12 is adapted to intentionally supply a voltage higher than that
 required by the plug-in module. The voltage supplied is required to be
 sufficiently high such that the voltage delivered to the plug-in module,
 i.e., to the switching devices 26, 28, 30, exceeds the maximum permitted
 voltage level of the voltage required by the plug-in module.
 After the switching device is turned on via the on/off control unit 16 in
 combination with the reference voltage generator 18, each switching device
 exerts an impedance, in accordance with the feedback control via its
 associated op amp, which functions to drop the voltage supplied to the
 plug-in module to the required value. The drop in voltage is achieved in
 accordance with the reference signal input to the non-inverting input of
 each op amp.
 A schematic diagram illustrating the power supply distribution and
 regulation system constructed in accordance with the first embodiment in
 more detail is shown in FIG. 3. Similar to that shown in FIG. 2, the power
 supply distribution and regulation system of FIG. 3, generally referenced
 50, comprises a voltage regulator 52 which generates an output voltage
 from an input DC voltage. The voltage is input to a plurality of switching
 devices via current limiting fuse 54. Fuse 54 may also comprise a thermal
 cutoff device. The output of the fuse is input to one of the terminals of
 transistors 86, 88, 90 which function as switching devices. The on/off
 control and reference voltage regulation functions are performed by
 circuit block 60 which is adapted to receive an on/off command. Circuit
 block 60 comprises PNP transistors 68, 70, NPN transistor 74 and resistors
 62, 64, 66, 72, 78.
 The emitter of transistor 68 is connected to V.sub.CC and the base is
 connected to biasing resisters 62 and 64. The collector of transistor 68
 is connected in totem pole fashion to the emitter of transistor 70. The
 collector of transistor 70 is connected to ground via resistor 72. The
 base of transistor 70 is connected to the on/off command via resistor 66.
 The emitter of NPN transistor 74 is connected to the non-inverting input of
 each op amp via resistor 78. A zener diode 79 provides a stable reference
 voltage for each of the op amps. When the on/off command is high,
 transistors 68, 70 are off and there is insufficient drive to turn
 transistor 74 on. Consequently, switching devices, i.e., transistors 86,
 88, 90, are all off, since op amps 80, 82, 84 cannot supply sufficient
 gate drive to turn the transistors on. The supply input of op amps 80, 82,
 84 are all connected to V.sub.CC.
 When the on/off command is low, transistors 68, 70 are on and sufficient
 current flows through the base of transistor 74 to turn it on. Op amps 80,
 82, 84 are supplied with sufficient voltage to operate and a reference
 voltage appears at the non-inverting input of op amps 80, 82, 84 so as to
 generate a stable DC output voltage from switches 86, 88, 90. As described
 in connection with system 10 of FIG. 2, the switching elements
 intentionally impose an impedance in a controlled manner. The circuit
 block 60 is adapted to intentionally supply a voltage higher than that
 required by the plug-in module. The voltage supplied is required to be
 sufficiently high such that the voltage delivered to the plug-in module,
 i.e., to the switching devices 86, 88, 90, exceeds the maximum permitted
 voltage level of the voltage required by the plug-in module.
 After the switching device is turned on, each switching device exerts an
 impedance, in accordance with the feedback control via its associated op
 amp, which functions to drop the voltage supplied to the plug-in module to
 the required value. The drop in voltage is achieved in accordance with the
 reference signal input to the non-inverting input of each op amp.
 A block diagram illustrating a power supply distribution and regulation
 system constructed in accordance with a second embodiment of the present
 invention is shown in FIG. 4. The power supply distribution and regulation
 systems of FIGS. 2 and 3 can be adapted to supply a plurality of
 individual DC voltage levels rather than a plurality of the same DC
 voltage. For illustration purposes, only three independent circuits are
 shown. The present invention, however, can be utilized to provide an
 arbitrary number of independent output DC voltages, limited only by space
 and cost.
 Circuit #1 101 comprises a voltage regulator 102 adapted to receive an
 input DC voltage #1, fuse 104, on/off control unit 110, reference voltage
 source #1 112, op amp 106 and switching device 108. Similarly, circuit #2
 121 comprises a voltage regulator 122 adapted to receive an input DC
 voltage #2, fuse 124, on/off control unit 130, reference voltage source #2
 132, op amp 126 and switching device 128. Likewise, circuit #3 141
 comprises a voltage regulator 142 adapted to receive an input DC voltage
 #3, fuse 144, on/off control unit 150, reference voltage source #3 152, op
 amp 146 and switching device 148.
 In the power supply distribution and regulation system, generally
 referenced 100, of FIG. 4 each op amp is supplied with its own reference
 voltage input to its non-inverting terminal. However, for each circuit,
 the voltage regulator functions to supply a voltage higher than that
 required by corresponding plug-in module. The voltage supplied is required
 to be sufficiently high such that the voltage delivered to the plug-in
 module, i.e., to the switching devices 108, 128, 148, exceeds the maximum
 permitted voltage level of the voltage required by the particular plug-in
 module.
 After the switching device is turned on each switching device exerts an
 impedance, in accordance with the feedback control via its associated op
 amp, which functions to drop the voltage supplied to the plug-in module to
 the required value. The drop in voltage is achieved in accordance with the
 reference signal input to the non-inverting input of each op amp. Each
 reference voltage generated by each reference voltage source is
 independent of the other reference voltage sources.
 Thus, the power switching and voltage regulation system of the present
 invention permits the input DC voltage to be generated in a central
 location with somewhat relaxed restrictions on the accuracy of the output
 voltage generated by the centralized power supply. This is because the
 final regulation of the voltage is performed directly on the plug-in
 module and thus the IR drops due to the copper traces and connectors have
 little effect on the output DC voltage supplied to the plug-in module.
 In accordance with the present invention, it is preferable that the level
 of the voltage supplied to the switching device in each circuit be as
 close to the permitted maximum as possible so as to reduce the power
 dissipation. For example, a circuit configured to drop the input DC
 voltage by 250 mV which supplies 40 A to its plug-in module, must be able
 to dissipate 10 W of power. Thus, sufficient heat sinking and/or cooling
 must be provided in order to maintain reasonably normal operating
 temperatures.
 Note that in both the first and second embodiment, even when an `off`
 command is issued and the power to the plug-in modules is cut off, a small
 portion of the circuitry is still powered waiting for the issuance of an
 `on` command. Upon receipt of an `on` command, power is applied to the
 plug-in module circuitry.
 While the invention has been described with respect to a limited number of
 embodiments, it will be appreciated that many variations, modifications
 and other applications of the invention may be made.