United States Patent (19)
`Lu
`
`54) DUAL-OUTPUT DC-DC POWER SUPPLY
`75 Inventor: Qun Lu, Lexington, Mass.
`
`73 Assignee: International Power Devices, Inc.,
`Boston, Mass.
`
`*
`
`Notice:
`
`This patent issued on a continued pros-
`ecution application filed under 37 CFR
`1.53(d), and is subject to the twenty year
`patent term provisions of 35 U.S.C.
`154(a)(2).
`
`21 Appl. No.: 09/016,074
`22 Filed:
`Jan. 30, 1998
`Related U.S. Application Data
`
`62 Division of application No. 08/763,685, Dec. 11, 1996, Pat.
`No. 5,715,153.
`(51) Int. Cl. ............................................... Ho2M 0000
`52 U.S. CI
`363/65; 363/146
`-rr.
`s
`58 Field of Search ..................................... 323/266, 267,
`323/269,271, 272; 363/65, 146; 307/12,
`17, 33, 36, 37, 39
`
`US006067241A
`Patent Number:
`11
`(45) Date of Patent:
`
`6,067,241
`*May 23, 2000
`
`56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`... 321/47
`3,723,850 3/1973 Daniels et al...
`323/282
`3,760,256 9/1973 Rast, Jr. et al.
`... 363/21
`4,628,426 12/1986 Steigerwald ...
`363/174
`4,680,688 7/1987 Inou et al. ..........
`SE SN s al - - - - - - - - - - - - - - - - - - - 3.
`2Y------
`acDonala et al. ...................
`3:
`S. SE itynski
`... 363/21
`554.828 7/1996 Rozman.
`5,663,874 9/1997 Mader et al. ............................. 363/21
`Primary E.
`iner Matthew Nguy
`fill
`EX fille
`atthew Nguwen
`Attorney, Agent, or Firm Fish & Richardson P.C.
`57
`ABSTRACT
`A multi-output power Supply having half-brick dimensions
`includes a forward converter circuit which receives a DC
`input Voltage and in response to a first control Signal
`generates a first DC output Voltage at a first level; and a buck
`regulator circuit which receives the first DC output voltage
`from the forward converter circuit. In response to a Second
`control Signal, the buck regulator generates a Second DC
`output voltage at a Second level.
`11 Claims, 10 Drawing Sheets
`
`
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`W
`N
`48V
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`
`
`100
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`Forward
`Converter
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`BUCK
`Regulator
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`
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`
`Control &
`Housekeeping
`Functions
`
`"
`
`V
`OUT 1
`5W
`
`W
`OUT 2
`8a 3.3V
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`U.S. Patent
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`May 23, 2000
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`Sheet 1 of 10
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`6,067.241
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`U.S. Patent
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`May 23, 2000
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`Sheet 2 of 10
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`U.S. Patent
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`Sheet 3 of 10
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`|100A
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`U.S. Patent
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`Sheet 4 of 10
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`6,067.241
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`U.S. Patent
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`Sheet 5 of 10
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`U.S. Patent
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`Sheet 6 of 10
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`6,067.241
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`U.S. Patent
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`May 23, 2000
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`Sheet 10 of 10
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`6,067.241
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`FIG. 5B
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`FIG.5C
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`FIG.5D
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`1
`DUAL-OUTPUT DC-DC POWER SUPPLY
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`6,067.241
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`The present invention combines a pair of independently
`controlled Switching DC circuit topologies which can be
`disposed within a relatively compact housing having "half
`brick' dimensions. Independent control of the forward and
`buck converters ensures that the outputs of each converter
`are well-regulated. The topologies are interconnected in a
`way to allow available output power to be flexibly distrib
`uted to each of the pair of Voltage outputs.
`Preferred embodiments include the following features.
`The multi-output power Supply includes a Synchronization
`circuit which ensures that a Second control Signal from the
`Second control circuit is applied to the buck converter at
`Substantially the same time a first control signal from the
`first control circuit is applied to the forward converter. The
`multi-output power Supply also includes a Voltage regulator
`circuit disposed within the housing and connected to the
`forward converter and buck converter to maintain the dif
`ference between the first DC output voltage and the second
`DC output voltage below a predetermined threshold value.
`In another aspect of the invention, a multi-output power
`Supply which generates first and Second DC output voltages
`to respective loads includes a housing having half-brick
`dimensions and first and Second pairs of Voltage output
`terminals corresponding to the first and Second DC output
`Voltages, respectively. In a preferred embodiment, each of
`the Voltage terminals of the first and Second pair of Voltage
`output terminals are adjacent to each other.
`Because the terminal pins of each of the first and Second
`pairs of output terminal pins are adjacent to each other, lead
`lengths associated with the physical layout of the circuit
`asSociated with each pair are reduced.
`Other features and advantages of the invention will
`become apparent from the following description of the
`preferred embodiments and from the claims.
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1A is a plan View of the half-brick package enclosing
`the dual-output power Supply.
`FIG. 1B is a side view of the half-brick package enclosing
`the dual-output power supply of FIG. 1A.
`FIG. 2 is a functional block diagram of the dual-output
`power Supply of the present invention.
`FIGS. 3A and 3B are a detailed block diagram of the
`dual-output power Supply of FIG. 2.
`FIGS. 4A and 4B are a schematic representation of the
`forward converter and buck converter Sections of the dual
`output power supply of FIG. 3.
`FIGS. 5A-5C are a detailed schematic representation of
`the control sections of the dual-output power supply of FIG.
`3.
`FIG.5D is a diagram which displays the correct Sequence
`of FIGS 5A-5C.
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`This application is a Division of U.S. Ser. No. 08/763,
`685, now U.S. Pat. No. 5,715,153.
`BACKGROUND OF THE INVENTION
`The invention relates to Switching power Supplies, and
`more particularly to multi-output DC-DC Switching power
`Supplies.
`There are about fourteen basic topologies (basic block
`diagrams) commonly used to implement a Switching power
`Supply. Each topology has characteristics which make it a
`Suitable candidate for use in a particular application.
`One of the most fundamental Switching power Supply
`topologies is the “buck' converter or “step-down” Switching
`regulator. The buck converter includes a Switch, usually in
`the form of a transistor, whose “on” time is controlled so that
`a Series of rectangular voltage pulses of adjustable width can
`be appropriately filtered to provide a well-regulated average
`DC output.
`Other Switching power Supply topologies are better Suited
`for use as DC-DC converters. A DC-DC converter is a
`device which converts a DC voltage at one level to a DC
`Voltage at another level. The converter typically includes a
`25
`transformer, having primary and Secondary windings wound
`around a common magnetic core. By opening and closing
`the primary circuit for appropriate intervals, control over the
`energy transfer between the primary and Secondary wind
`ings is accomplished. The transformer provides an alternat
`ing Voltage whose amplitude can be adjusted by changing
`the number of turns of the primary and Secondary windings.
`Moreover, the transformer provides DC isolation between
`the input and the output of the converter.
`One of the most common DC-DC converter topologies
`is the forward converter. When the primary winding of the
`forward converter is energized by closing the primary
`circuit, energy is immediately transferred to the Secondary
`winding.
`Recently, in the field of Switching power Supplies, greater
`attention has been directed toward compactness, energy
`efficiency, and higher performance. AS integrated circuits
`pack more features in Smaller Volumes, it becomes increas
`ingly important that the size of the System's power Supply
`also decreases. Moreover, the complexity of many Systems
`have increased with different parts of the system's circuitry
`requiring different power Supply Voltages. Thus, power
`Supply designers are faced with the problem of providing
`Smaller power Supplies with multiple outputs and better
`performance.
`SUMMARY OF THE INVENTION
`The invention features a multi-output power Supply
`including independently-controlled forward and buck con
`verters disposed within a housing having half-brick dimen
`Sions.
`In one general aspect, the multi-output power Supply
`includes a forward converter which receives a DC input
`Voltage and generates a first DC output voltage, a first
`control circuit which controls the level of the first DC output
`voltage; a buck converter which receives the first DC output
`Voltage and generates the Second DC output voltage, a
`Second control circuit which controls the level of the second
`DC output voltage; and a housing having half-brick
`dimensions, with the forward converter, the buck converter,
`the first control circuit and the Second control circuit dis
`posed within the housing.
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`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`Referring to FIGS. 1A and 1B, a dual-output power
`Supply 10 is provided within a molded package 6 having
`dimensions consistent with a standard "half-brick' module.
`A half-brick module has a width, depth and height of 2.28,
`2.4 and 0.5 inches, respectively. As will be discussed in
`greater detail below, power Supply 10 includes an isolated
`DC-DC forward converter in combination with a regulated
`buck converter for generating a pair of Voltage outputs.
`Power Supply 10 is capable of generating as much as 60
`watts of output power to the pair of outputs.
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`Package 6 includes four input terminal pins 7a-7d includ
`ing +V, -V. GND and remote ON/OFF pins. A relatively
`broad input voltage range between 34 and 75 volts can be
`applied to the +V, and -V, pins. Package 6 also includes
`Six output pins 8a–8f including +V, -V., +V2,
`-V, Trim 1 and Trim 2 pins. The terminal pins are
`grouped So that the +V and -V pins are adjacent to
`each other to ensure a short AC loop. Similarly, the +V.
`and -V pins are positioned to be adjacent to each other.
`With this particular "pin out' arrangement, the physical
`layout of the circuits associated with each pair of outputs
`(described in greater detail below) are confined to a smaller
`area and lead lengths associated with each of the circuits are
`reduced. Minimizing the lead lengths reduces inductance
`asSociated with the physical layout of these lead lengths,
`thus, filtering at the pair of outputS is more efficient. Trim 1
`and trim2 pins allow the user to adjust the level of the output
`DC voltages from 90% to 110% of their factory settings.
`Referring to FIG. 2, power supply 10 receives the DC
`input voltage (e.g., 48 V) at input terminal pin 7d (+V) and
`generates the DC output voltages of 5 V and 3.3 V, at output
`terminal pins 8d and 8a, respectively. Connected between
`input terminal pin 7d and output terminal pin 8d is a forward
`converter 100 which receives the DC input voltage and
`generates the first DC output voltage of 5 V to a first load
`(not shown). The first DC output voltage (V) from
`forward converter 100 is also received by a buck converter
`200 where it is stepped down to the second DC output
`voltage (3.3 V) provided to a second load (not shown)
`through output terminal pin 8a. Power supply 10 also
`includes control and housekeeping circuitry 18 for generat
`ing the necessary power to a number of auxiliary circuits
`needed to ensure proper functioning of power Supply 10.
`Referring to FIG. 3, the basic functional blocks diagram
`of dual-output power Supply 10 are shown and will be
`described in greater detail below. Schematic representations
`of the circuitry used for each functional block of FIG. 3 are
`shown with like reference numerals in FIGS. 4 and 5 as
`dashed-line boxes.
`Forward converter 100 includes an LC input filter 102 for
`Smoothing the DC input voltage applied to input terminal
`pin 7a. The filtered voltage is received by a switched
`primary winding 104 of a transformer 106 with a secondary
`winding 108 of the transformer providing a series of AC
`pulses whose amplitudes are fixed by the ratio of the number
`of turns of the primary and Secondary windings. An example
`of a transformer well-suited for use in the forward converter
`is described in co-pending application, Ser. No. 08/693,878,
`assigned to the assignee of the invention, and hereby incor
`porated by reference. The Series of Square-wave pulses are
`converted back to a rectified DC voltage using rectifier 110
`and smoothed with an output filter 112.
`Referring to FIG. 4, more particularly, a MOSFET tran
`sistor Switch 114 is connected in series with the primary
`winding 104 of transformer 106. When Switch 114 is closed,
`energy in primary winding 104 is transferred through a
`secondary winding 108 via rectifier 110 and output filter 112
`to a load (not shown). Output filter 112 includes an inductive
`winding 116 of a transformer and a bank of capacitors 118.
`AS will be discussed below, output filter 112 generates a
`V DC voltage (5V) which is equal to the average of the
`duty-cycle-modulated raw DC input voltage. When Switch
`114 is opened, the forward energy transfer is stopped by a
`free-wheeling diode 116 which is connected in parallel with
`output filter 112 and allows the energy stored in inductive
`winding 116 of the filter to be released into capacitors 118.
`Connected in parallel with output filter 114 of forward
`converter 100 is a buck converter 200 having a MOSFET
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`transistor Switch 202 which receives the V DC voltage
`from forward converter 100. Switch 202 is controlled to
`generate an adjustable duty cycle output Voltage, V DC
`voltage (3.3 V), to an output filter 204 formed of an
`inductive winding 206 of a transformer 208 and a bank of
`capacitors 210.
`Referring again to FIG. 3, dual-output supply 10 includes
`a control circuit 120 which controls the duty cycle of the
`pulse train applied to the gate of Switching transistor 114,
`thereby controlling the level of the V DC voltage. When
`control circuit 120 is used in a constant frequency operation,
`the “chopping period is kept constant and the “on” time is
`varied. Because the width of the pulse is being varied, this
`type of control is known as pulse width modulation (PWM)
`control. Alternatively, control circuit can be used in a
`variable frequency operation where the chopping frequency
`is varied with the “on” or “off time being held constant.
`This type of control is called frequency modulation.
`Buck converter 200 includes its own independent control
`circuit 212 which operates in the Same way as control circuit
`120 to control the duty cycle of the pulse train applied to the
`gate of Switching transistor 202, thereby controlling the
`level of the V DC voltage.
`A Synchronization circuit 29 receives a timing Signal from
`control circuit 120 which indicates when forward converter
`100 is being Switched. In response to the timing Signal,
`Synchronization circuit 29 generates a Sync Signal to control
`circuit 212 to ensure that the pulse trains for forward
`converter 100 and buck converter 200 are Switched simul
`taneously. Switching the converters at the same time, mini
`mizes the overall noise of the power Supply by limiting any
`Switching noise to the transition periods.
`Because buck converter 200 is in a cascade arrangement
`with forward converter 100, two separate power trains are
`not required, thereby minimizing the Space required for the
`two converters. Thus, both converters can be accommodated
`within the relatively small half-brick package 6 (FIGS. 1A
`and 1B). Moreover, the cascade arrangement of the buck and
`forward converters allows for greater flexibility in the dis
`tribution of the 60 watts of available power form the
`dual-output power Supply. For example, in one application,
`the 5 V DC voltage (V) generates 6A of current and the
`3.3 V DC voltage (V) generates 9A of current. However,
`in another application, the 60 watts of available power could
`be distributed so that the 5 V DC voltage generates about 8A
`of current and the 3.3 V DC voltage (V) generates 6A of
`Current.
`Control and housekeeping circuitry 18 (FIG. 2) includes
`an IC Voltage Supply 20 for powering the components (e.g.,
`MOSFET switch transistors) of the power train, as well as
`the control circuits and other auxiliary circuitry. A Start
`circuit 22 is used at initial Start-up of power Supply 10 to
`generate power to IC Voltage Supply 20, thereafter all power
`requirements are generated by IC Voltage Supply 20. A Soft
`Start circuit 23 is used in conjunction with Start circuit 22 to
`provide a gradual increase of the power provided to IC
`Voltage Supply 20 at initial Startup.
`Because Synchronization circuit 29 maintains precise con
`trol of the Switching of the pulse trains for forward converter
`100 and buck converter 200, the difference in voltage
`between the 5 V DC voltage (V) and the 3.3 V DC
`voltage (V) is relatively constant (i.e., about 1.7 V).
`However, at initial Startup of the power Supply, the differ
`ence between V and V can be greater than 1.7 due to
`the time required for V to reach its steady State. In Some
`applications, a difference greater than 4.0 V can, damage the
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`circuit driven by the power Supply. Thus, a linear regulator
`34 is connected between the output terminal 8d and the input
`to buck converter 200 to maintain the difference between the
`outputs below 2.0 V. Linear regulator 34 generally includes
`a simple resistor divider network which generates dissipated
`heat loSS during operation, but only for the short period
`needed for V.
`to reach its steady state value of 3.3 V.
`Linear regulator 34 includes a variable resistor (not shown)
`to allow adjustment of the desired regulation Voltage.
`Control and housekeeping circuitry 18 also includes an
`under voltage lockout (UVL) circuit 24 which senses the
`voltage level of the DC input voltage. If the voltage level is
`below a preselected threshold level, UVL circuit 24 gener
`ates a signal to IC Supply Voltage 20 to shutdown operation
`of the dual-output power supply 10. Similarly, an over
`voltage lockout (OVL) circuit 26 senses the voltage level of
`the V DC voltage. If the Voltage level is greater than a
`predetermined maximum threshold, OVL circuit 26 deter
`mines that a fault exists in forward converter 100 or its
`control circuitry and generates a Signal to IC Supply Voltage
`20 to shutdown operation of the dual-output power Supply
`10. Trim/compensation circuits 28, 31 are connected to
`forward converter 100 and buck converter 200 to allow for
`adjustment of the amplitude levels of the V and V DC
`voltages via terminal pins 8f and 8c (FIG. 1A), respectively.
`25
`A current Sensing circuit 30 is provided for Sensing the
`current flowing through primary winding 104 on an ongoing
`basis. When the current exceeds a predetermined threshold
`value current Sensing circuit 30 generates a control Signal to
`control circuit 120 (via a second current limiting circuit 32)
`to SuppreSS the generation of one of the Square-wave pulses
`by transformer 106. If the value of the current is greater than
`the threshold for an extended period of time (e.g., a short
`circuit condition), Second current limiting circuit 32 gener
`ates a Signal to Suppress the generation of a Series of the
`Square-wave pulses for a predetermined time period. At the
`end of the predetermined time period, the current is remea
`Sured and, if below the threshold, the Square-wave pulses
`from transformer 106 are reinitiated.
`Other embodiments are within the claims. For example,
`the dual-output power Supply 10 described above generates
`output voltages of 5V and 3.3 V. The invention, however, is
`applicable to dual-output power Supplies of other Voltage
`combinations such as 3.3 V/2.5 V or 2.5 V/ 2.1 V supplies.
`What is claimed is:
`1. A multi-output power Supply for generating first and
`Second DC output Voltages to respective loads, Said power
`Supply comprising:
`a first converter which receives a DC input Voltage and
`generates the first DC output voltage;
`a first control circuit which controls the level of the first
`DC output Voltage;
`a second converter which receives the first DC output
`Voltage from the first converter circuit and generates
`the Second DC output voltage;
`a second control circuit which controls the level of the
`Second DC output voltage.
`2. The multi-output power Supply of claim 1 further
`comprising a housing within which the first converter, the
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`Second converter, the first control circuit and the Second
`control circuit are disposed.
`3. The multi-output power supply of claim 1 further
`comprising a Synchronization circuit which applies the Sec
`ond control Signal to the Second converter at Substantially
`the same time the first control Signal is applied to the first
`COnVerter.
`4. The multi-output power Supply of claim 1 further
`comprising circuitry connected to the first converter and
`Second converter to maintain the difference between the first
`DC output voltage and the second DC output voltage below
`a predetermined threshold value.
`5. The multi-output power supply of claim 4 wherein the
`circuitry includes a voltage regulator.
`6. The multi-output power supply of claim 1 wherein the
`first converter is a forward converter and the Second con
`verter is a buck converter.
`7. A multi-output power Supply for generating first and
`Second DC output voltages to respective ones of the loads at
`a predetermined total output current level, Said power Supply
`comprising:
`a first converter which receives a DC input Voltage and
`generates the first DC output voltage, the first
`converter, in operation, providing a first variable output
`current level in a range between Zero and the prede
`termined total current level of the multi-output power
`Supply,
`a first control circuit which controls the level of the first
`DC output voltage and the first variable output current
`level;
`a second converter which receives the first DC output
`Voltage from the first converter circuit and generates
`the second DC output voltage, the second converter, in
`operation, providing a Second variable output current
`level in a range between Zero and the difference
`between the total current level of the multi-output
`power Supply and the first variable current level; and
`a second control circuit which controls the level of the
`Second DC output voltage and the Second variable
`output current level.
`8. The multi-output power Supply of claim 7 further
`comprising a housing within which the first converter, the
`Second converter, the first control circuit and the Second
`control circuit are disposed.
`9. The multi-output power Supply of claim 7 further
`comprising a Synchronization circuit disposed within the
`housing to ensure that the Second control Signal is applied to
`the Second converter at Substantially the same time the first
`control Signal is applied to the first converter.
`10. The multi-output power Supply of claim 7 further
`comprising a Voltage regulator circuit disposed within the
`housing and connected to the first converter and Second
`converter to maintain the difference between the first DC
`output voltage and the Second DC output Voltage below a
`predetermined threshold value.
`11. The multi-output power supply of claim 7 wherein the
`first converter is a forward converter and the Second con
`verter is a buck converter.
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