United States Patent
`Rossi et al.
`
`119
`
`{11] Patent Number:
`[45] Date of Patent:
`
`4,879,641
`Nov. 7, 1989
`
`[54] ANALOG MULTIPLEX FOR SENSING THE
`MAGNITUDE AND SENSE OF THE
`CURRENT THROUGH A H-BRIDGE STAGE
`UTILIZING A SINGLE SENSING
`RESISTANCE
`
`[75]
`
`Inventors: Domenico Rossi, Cilavegna; Andrea
`Cuomo, Milano, both of Italy
`
`[73] Assignee:
`
`SGS-Thomson Microelectronics
`S.RLL.,Italy
`
`[21] Appl. No.: 263,935
`
`[22] Filed:
`
`Oct. 28, 1988
`
`Fore‘gn Application Priority Data
`[30]
`Nov. 2, 1987 [IT]
`Ttaky ..cccssccccseseseessensseenece 8366 A/87
`
`[51] Unt, C04 ec ccsesseestestsscnectsesesenees HO02M 3/24
`[82] US. Che once eeeeeceeeeceeeeseeneeeee 363/98; 363/58;
`318/293; 318/599
`[58] Field of Search .................0 363/56, 58, 98, 132,
`363/17, 136; 318/281, 287, 288, 289, 291, 293,
`.
`294, 599
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`4,410,926 10/1983 Hofer ct al.
`scenes 363/58 X
`
`
`4,494,181
`1/1985 Ramlohretal
`318/293 KX
`
`4,654,568
`3/1987 Mansmanon ......
`ae 318/287 X
`we 318/293 X
`4,677,356 6/1987 Tsunedaetal.
`4,710,686 12/1987 Guzik oo.ceceeteeeeesees 363/98 X
`
`FOREIGN PATENT DOCUMENTS
`
`0135390 6/1986 Japath ......sssecseeseeresserseneenenes 318/293
`
`Primary Examiner—Patrick R. Salce
`Assistant Examiner—Kristine Peckman
`Attorney, Agent, or Firm—Pollock, Vande Sande &
`Priddy
`
`ABSTRACT
`[57]
`A circuit for sensing the magnitude and sense of a cur-
`rent flowing through the load of an H-bridge stage
`driving the load in a switching mode by means of a
`clocked, square-wave driving signal and the inverted
`signal thereof applied, respectively,
`to two pairs of
`analog switches arranged in a bridge ccenfiguration and
`functionally switching the load between a supply node
`and a virtual ground node is madebyutilizing a single
`sensing resistance connected between the virtual
`ground nodeandthe real ground nodeofthecircuit, the
`signal across the resistance and the inverted signal
`thereof are fed to two inputs of an analog multiplex
`whose outputsignal is fed to the input of a comparator
`in order to obtain at the outputofthelatter a signal with
`an amplitude proportionalto the intensity of the current
`and a polarity determined by the polarity of a reference
`voltage which is applied to another input of the com-
`parator. The PWM control loop may then be completed
`by meansofa flip-flop to the inputs of which the output
`signal of the comparator and a clock signal are applica-
`ble in order to generate at the outputof the flip-flop the
`clocked driving signal.
`
`5 Claims, 3 Drawing Sheets
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`MPX OUT
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`APPLE 1020
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`1
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`APPLE 1020
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`US. Patent—Nov. 7, 1989 Sheet1 of 3
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`4,879,641
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`IN4
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`|
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`V4
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`4v2
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`IN1*
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`V1
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`v2
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`A
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`Vout =(V1-V2)
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`Vout =(V1-V2)
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`2
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`US. Patent—Nov. 7, 1989 Sheet 2 of 3
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`4,879,641
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`MPX QUT = V1 - V2
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`3
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`US. Patent—Nov. 7, 1989 Sheet 3 of 3 4,879,641
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`MPX OUT
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`4
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`ANALOG MULTIPLEX FOR SENSING THE
`MAGNITUDE AND SENSE OF THE CURRENT
`THROUGHA H-BRIDGE STAGE UTILIZING A
`SINGLE SENSING RESISTANCE
`
`BACKGROUND OF THE INVENTION
`
`Thepresent invention relates to circuits for a switch-
`ing modedriving of a load andin particular to circuit
`arrangements for controlling the current being deliv-
`ered to the load.
`Apparatuses for controlling electric motors and more
`generally for delivering a current to inductive loads
`utilize the so-called Pulse Width Modulation technique
`(PWM). This technique is implemented by means of an
`“H-bridge”stageutilizing a square-wave driving signal,
`whose frequency and duty-cycle are controlled by
`meansof a clock signal, and the inverted signal thereof
`whichare applied, respectively, to two pairs of switches
`arranged in a bridge configuration and operatively
`switching the load between a supply and a ground or a
`virtual ground nodeofthe bridge stage. For implement-
`ing a system for monitoring and controlling the current
`being delivered to the load, sensing resistances, con-
`nected between the virtual ground nodes of the two
`branches of the H-bridge stage and the real ground of
`the circuit are frequently used. These sensing resistors
`must necessarily be power components, suitable to
`withstand the current which flows through the load,
`and for this reason are almost exclusively discrete com-
`ponents, connected externally to an integrated driver
`circuit and generally representing a remarkable cost
`factor of the apparatus also because they must often
`possess well determined precision and temperature co-
`efficient characteristics and be exempt of any apprecia-
`ble inductance.
`The circuit for sensing the magnitude and direction of
`the current according to the present invention deter-
`-mines the magnitude and direction of the current being
`delivered to a load of an H-bridge stage by utilizing a
`single sensing resistor connected between a common
`virtual ground node of the driving bridge circuit and a
`real ground node.
`Thedifferent aspects and advantages of the invention
`in relation to the knowntechnique will be moreeasily
`understood through the following description with
`reference to a series of drawings, wherein:
`BRIEF DESCRIPTION OF THE DRAWINGS
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`FIG.1 is a principal circuit diagram of an H-bridge
`stage provided with a circuit for sensing the magnitude —
`and sense of the electric current flowing through the
`load, according to a known technique;
`FIGS. 2 and 3 show two typical signal diagrams
`representative of the circuit of FIG.1;
`FIG. 4 shows a principal circuit diagram of an H-
`bridge stageutilizing a circuit for sensing the magnitude
`and direction of the electric current through the load in
`accordance with the present invention;
`FIG.5 is a signal diagram representative ofthe circuit
`of FIG.4;
`FIG.6 is a circuit diagram of an embodimentofthe
`circuit of FIG. 4 utilizing analog switches implemented
`by means of MOStransistors.
`An H-bridge stage for driving an inductive load L is
`shown in FIG.1 using conventional symbols. The stage
`is formed by four switches: SW1, SW4 and SW2, SW3;
`driven, repectively, by a driving signal IN1 and by the
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`4,879,641
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`inverted signal thereof IN1,the latter being obtained by
`meansof an inverter I. For completeness’s sake recircu-
`lation diodes D1, D4 and D2, D3 are also shown in
`FIG. 1. The two pairs of switches (namely SW1, SW4
`and SW2, SW3) arranged in a bridge configuration
`functionally switch the load L between the supply node
`Vs, and virtual ground nodes, (which in the case shown
`in FIG. 1 coincide with the nodes (V1) and (V2), in
`function of a certain “duty cycle”, whichis in turn
`determined by the relative duration of the driving sig-
`nals IN1 and INI (in accordance with a Pulse Width
`Modulation technique).
`The control of the driving of the load is based upon
`the sensing of the magnitude (modulus) and of the sense
`(direction) of the current flowing through the load L.
`According to a widely used technique embodied in
`the circuit of FIG. 1, the sensing circuit employs two
`distinct sensing resistors R1 and R2 connected, respec-
`tively, between the two virtual ground nodes (V1) and
`(V2) of the H-bridge circuit and a real ground node of
`the circuit. The voltage signals across these two sensing
`resistors Ri and R2 (i.e. the potentials V1 and V2) are
`fed to the inputs of a differential sensing amplifier (As).
`The representative signal diagrams of the circuit are
`shown in FIGS. 2 and 3. By supposing to operate with
`a “duty-cycle” of the input signal different from 50%
`and therefore to adjust the current through the load L
`(which is presumed inductive) to an average value dif-
`ferent from the operating situation may be depicted by
`‘meansof the time diagrams of FIG. 2 which represent a
`drive signal IN1 (having a certain duty-cycle), the voit-
`ages of the two virtual ground nodes, V1 and V2, and
`the output voltage of the differential amplifier As. In the
`case illustrated, the output signal of the amplifier will
`have a positive polarity and the amplitudeofthissignal
`(Vout) will be proportional to the magnitude of the
`current flowing through the load L.
`Vice versa, by supposing to apply a driving signal
`IN1*, complementary to the driving signal IN1 of the
`situation depicted in the diagrams of FIG. 1, the corre-
`sponding signals will take the form depicted in the dia-
`grams of FIG.3. Basically the output signal of the am-
`plifier A, will have the same amplitude but an inverted,
`negative polarity.
`As easily recognized, according to such a sensing
`circuit ofthe prior art, the sensing of the direction of the
`current flowing through the load could not take placeif
`only one sensing resistor is used.
`This is what is made possible by the sensing circuit of
`the present invention which is schematically depicted in
`FIG.4. In this figure as well as in the others, the same
`symbols and numeralsare utilized for identifying recur-
`ring or equivalent components, commonto the circuits
`shownin the differentfigures.
`As may be observed, the circuit of the invention
`utilizes a single sensing resistor R connected between a
`single common virtual ground node (V1) and a real
`ground node ofthe circuit. The necessary reconstruc-
`tion of the complete information of the current deliv-
`ered to the load L of the bridge stage takes place by
`meansof an analog multiplex (MPX) having twoinputs,
`formed by two switches SWA and SWB) which are
`respectively driven by the clocked driving signal IN1
`and byits inverted signal IN1, to the inputs of which are
`applied,
`respectively,
`the common virtual ground
`node’s voltage signal (V1 during a first phase) and an
`inverted signal thereof (V2 during a second phase)
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`which is obtained by means of an inverting analog
`between a supply node and a virtual ground nodeof the
`buffer BIN. The output signal of the multiplex (MPX
`stage, said circuit comprising:
`OUT)is then fed to the non inverting input (+) of a
`a single sensing resistor connected between a virtual
`comparator,to the other (inverting) input (—) of which
`ground node and a real ground nodeofthe circuit;
`a control voltage (Vref) is suitably applied.
`an analog,
`two input, multiplex including two
`As may be easily observed, once a certain control
`switches driven, respectively, by the driving signal
`voltage Vrefis set, the output signal of the comparator
`and bythe inverted driving signal, the input corre-
`C will contain the desired information on the magnitude
`sponding to the switch driven by the driving signal
`and direction of the electric current flowing through
`being connected to the virtual ground node and the
`the load L of the H-bridge stage. The amplitude of the
`input corresponding to the switch driven by the
`output signal of the comparator is proportional to the
`inverted driving signal being connected to the out-
`magnitude of the current while the polarity thereof(in
`put of an inverting analog buffer having an input
`respect to the polarity of the reference or control volt-
`connected to said virtual ground node; and
`age Vref) is indicative of the direction of the current.
`a comparator having two input terminals and an out-
`This is figuratively shown in FIG. 5 by means of the
`put terminal, the output of said analog multiplex
`time diagramsof the different signals representative of
`being connected to a first input terminal of said
`the circuit of FIG. 4, as will later be described in more
`comparator and a reference voltage being applied
`detail.
`to a second input terminal of said comparator.
`The PWM control and adjustment loop may be com-
`2. The sensing circuit according to claim 1, wherein
`pleted in a conventional manner as shown in FIG.4 by
`said multiplex is formed by a pair of analog switches
`feeding the output signal of the comparator C to an
`made with MOStransistors.
`input (R) ofa flip-flop Q, to the other input (S) of which
`3. In a combination, H-bridge stage for driving a load
`a timing clock signal is applied. This allows for invert-
`in a switching mode by meansof a clocked square-wave
`ing or not inverting the sense signal of the monitored
`driving signal and an inverted signal thereof, and circuit
`current syncronously with the driving signal IN1.
`meansfor sensing the magnitude and directions of the
`The clock signal, the driving signal 11, the two “pha-
`electric current flowing throughthe load, said H-bridge
`ses” of the potential of the common virtual node
`comprising:
`namely: V1 whichis fed directly to one input multiplex
`twopairs of switches arranged in a bridge configura-
`MPX and V2 which is inverted by the inverter BIN
`tion for receiving the driving and the inverted
`before being fed to the other input of the multiplex
`signals, respectively, and functionally switching
`MPX,and the output signal MPX OUTofthe multiplex
`the load between a supply node andavirtual
`MPXare depicted in the time diagram of FIG.5.
`ground node ofthe bridge stage, and recirculation
`The amplitude of the MPX OUTsignal will be pro-
`diodes connected across said switches;
`portional to the magnitude of the current which flows
`said sensing circuit means including:
`through the load L ofthe bridge stage, while the polar-
`a single sensing resistor connected between the vir-
`ity of the corresponding output signal of the compara-
`tual ground node and a real ground node ofthe
`tor C will be determined by the polarity of the voltage
`circuit;
`Vref which is applied to the other input (—) of the
`an analog, two input, multiplex having two switches
`comparatorC.
`Therefore the inversion of the direction of the cur-
`driven, respectively, by the driving signal and by
`the inverted driving signal, the input correspond-
`rent flowing through the loadis easily implemented by
`ing to the switch driven by the driving signal being
`simply inverting the polarity of Vref.
`connected to the virtual ground nodeandthe input
`The circuit of the invention is particularly advanta-
`corresponding to the switch driven by the inverted
`geousin those applications which contemplate the inte-
`driving signal being connected to the output of an
`gration of the H-bridge stage either by meansofinte-
`inverting analog buffer having an input connected
`grated powerbipolar transistors or MOStransistors In
`to the virtual ground node; and
`these embodiments, the multiplex will be conveniently
`a comparator having two input terminals and an out-
`made by means of two integrated analog switches. Such
`put terminal, an output of said analog multiplex
`an integrated circuit is shown in FIG. 6, wherein the
`being connected to a first input terminal of said
`power switches of the bridge stage (SW1, SW4 and
`comparator and a reference voltage being applied
`SW3, SW2) are made with as many power MOStransis-
`to a second input terminal of said comparator.
`tors, while the multiplex MPX is formed by two analog
`4. The combination according to claim 3, wherein
`switches each being formed by a pair of complementary
`MOStransistors one with a N-channel and the other
`said multiplex is formed by a pair of analog switches
`made with MOStransistors.
`with a P-channel), i.e. in CMOStechnology.
`What weclaim is:
`5. The combination according to claim 3, character-
`1. A circuit for sensing the magnitude and direction
`ized in that the output terminal of said comparatoris
`of an electric current flowing through a load driven in
`connected to an input terminal ofa flip-flop, to another
`a switching maode by an H-bridge stage by meansof a
`input terminal of which a clock signal is applied;
`clocked square-wave driving signal and an inverted
`an output signal of said flip-flop constituting said
`driving signal which are applied, respectively, to two
`driving signal and the polarity of said reference
`pairs of analog switches arranged in an H-bridge config-
`voltage determining the direction of the current
`uration and having recirculation diodes connected
`flowing through the load of the bridge stage.
`*
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`££
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`across said switches, said switches switching the load
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