Patent Publication Number: US-9899146-B2

Title: Signal transfer device

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This non-provisional application for a U.S. patent claims the benefit of priority of JP PA 2014-243529 Dec. 4, 2014, the entire contents of which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a signal transfer device for driving a semiconductor power switch such as an IGBT (Insulated Gate Bipolar Transistor) provided on a high side of a switching power supply, an inverter or any of various drive circuits including a semiconductor switching element. 
     2. Description of the Background Art 
       FIG. 11  is a view showing a configuration example of a typical switching power supply constituted by semiconductor power switches one of which includes a signal transfer device transferring a signal through an insulating transformer. For example, an IGBT, an MOSFET (Metal Oxide Field-Effect Transistor) etc. can be used as each of the semiconductor power switches. In a circuit for switching the semiconductor power switches, a high-side semiconductor power switch MH is driven to turn ON/OFF in accordance with an output from the signal transfer device through the insulating transformer. 
       FIG. 12  is a view showing the configuration of a background-art signal transfer device. In  FIG. 12 , the background-art signal transfer device is constituted by a transmitting circuit  200 , a receiving circuit  300 , and an insulating transformer  100  provided between the transmitting circuit  200  and the receiving circuit  300 . In addition, a driver  400  is connected to a rear end of the receiving circuit  300 . Further, the insulating transformer  100  has a configuration in which two transformer parts, i.e. a transformer part  1  and a transformer part  2 , are used so that a signal (set signal) indicating a turn-ON timing of the semiconductor power switch MH can be transmitted to an R 1  terminal of the receiving circuit  300  through the transformer part  1  and a signal (reset signal) indicating a turn-OFF timing of the semiconductor power switch MH can be transmitted to an R 2  terminal of the receiving circuit  300  through the transformer part  2 . As shown in  FIG. 12 , configuration is made so that output terminals of secondary-side windings of the transformer part  1  and the transformer part  2  can have the same magnetic polarity (voltages in the output terminals can change in the same direction when a magnetic flux changes in one and the same direction). The background-art signal transfer device in  FIG. 12  drives the semiconductor power switch MH on the high side of the switching circuit shown in  FIG. 11 , through the driver  400 . 
       FIG. 13  is a view showing an ideal operation waveform of the background-art signal transfer device shown in  FIG. 12 .  FIG. 14  is an operation waveform view for explaining a problem of the background-art signal transfer device shown in  FIG. 12 . Since  FIG. 14  partially overlaps with  FIG. 13 , operation of the background-art signal transfer device will be described with reference to  FIG. 11  and  FIG. 14 . 
     When the high-side power switch MH shown in  FIG. 11  is driven, a GND 2  potential in  FIG. 12  and  FIG. 14  fluctuates in accordance with ON/OFF operations of power switches MH and ML. When the power switch MH turns OFF and the power switch ML turns ON due to an output from the signal transfer device, the GND 2  potential drops from a high-side power supply voltage to GND 1 , as shown in  FIG. 14 . Due to the fluctuation of the GND 2 , plus common-mode noises (N 1   +  and N 2   + ) occur in the signal terminals R 1  and R 2  of the receiving circuit  300  side through parasitic capacitances (not shown). 
     On the other hand, when the power switch ML turns OFF and the power switch MH turns ON due to an output from the signal transfer device, the GND 2  potential rises from the GND 1  to the high-side power supply voltage. Due to the fluctuation of the GND 2 , minus common-mode noises (N 1   −  and N 2   − ) occur in the signal terminals R 1  and R 2  of the receiving circuit  300  side through the parasitic capacitances (not shown). 
     In some cases, the high-side power switch MH shown in  FIG. 11  may turn ON/OFF by mistake due to any of the aforementioned common-mode noises. 
     In the background art in order to prevent malfunction from being caused by common-mode noise, a circuit (not shown) for detecting the common-mode noise and suppressing generation of a false pulse is usually mounted inside the receiving circuit  300 . 
     JP-A-2013-51547 discloses a configuration in which a detection circuit for preventing malfunction from being caused by common-mode noise is mounted (see Paragraph [0058], FIG. 5). 
     JP-A-3-44507 discloses a circuit configuration for preventing malfunction from being caused by common-mode noise (see FIG. 1). 
     The aforementioned configuration described in JP-A-2013-51547 has a problem that a receiving circuit becomes complicated and a malfunction preventing effect deteriorates as the fluctuation width of GND 2  increases. 
     In addition, the configuration described in JP-A-3-44507 also has a problem that a receiving circuit becomes complicated because a device such as a differential amplifier for canceling common-mode noise by subtraction of a common-mode voltage signal is required on the side of the receiving circuit. 
     Therefore, an object of the invention is to provide a signal transfer device for transferring a signal through an insulating transformer, in which occurrence of common-mode noise can be suppressed and a countermeasure circuit against the noise can be simplified. 
     SUMMARY OF THE INVENTION 
     In order to solve the foregoing problem, according to a first configuration of the invention, there is provided a signal transfer device which transfers a signal through a transformer, wherein: a secondary-side winding of one transformer part of the transformer connected to a set-side input terminal of a receiving circuit and a secondary-side winding of another transformer part of the transformer connected to a reset-side input terminal of the receiving circuit are magnetically coupled to each other so densely that a magnetic flux interlinking with one of the secondary-side windings can also interlink with the other; and the two secondary-side windings are connected to the receiving circuit so that the set-side input terminal and the reset-side input terminal of the receiving circuit can have magnetic polarities reverse to each other. 
     According to a second configuration of the invention, there is provided a signal transfer device according to the first configuration of the invention, wherein: the two secondary-side windings are wound in one and the same direction but signal terminals and ground terminals of the two secondary-side windings are reversed to each other so that the set-side input terminal and the reset-side input terminal of the receiving circuit can have magnetic polarities reverse to each other. 
     According to a third configuration of the invention, there is provided a signal transfer device according to the second configuration of the invention, wherein: the transformer is made up of rectangular, circular, elliptical or polygonal spiral coils. 
     According to a fourth configuration of the invention, there is provided a signal transfer device according to the second configuration of the invention, wherein: the transformer is made up of rectangular, circular, elliptical or polygonal solenoid coils. 
     According to a fifth configuration of the invention, there is provided a signal transfer device according to the second configuration of the invention, wherein: the transformer is made up of solenoid coils in which rectangular, circular, elliptical or polygonal spiral coils are laminated. 
     According to a sixth configuration of the invention, there is provided a signal transfer device according to the first configuration of the invention, wherein: the two secondary-side windings are wound in reverse directions so that the set-side input terminal and the reset-side input terminal of the receiving circuit can have magnetic polarities reverse to each other. 
     According to a seventh configuration of the invention, there is provided a signal transfer device according to the sixth configuration of the invention, wherein: the transformer is made up of rectangular, circular, elliptical or polygonal spiral coils. 
     According to an eighth configuration of the invention, there is provided a signal transfer device according to the sixth configuration of the invention, wherein: the transformer is made up of rectangular, circular, elliptical or polygonal solenoid coils. 
     According to a ninth configuration of the invention, there is provided a signal transfer device according to the sixth configuration of the invention, wherein: the transformer is made up of solenoid coils in which rectangular, circular, elliptical or polygonal spiral coils are laminated. 
     According to a tenth configuration of the invention, there is provided a signal transfer device according to the second or sixth configuration of the invention, wherein: a primary-side winding is formed out of a single coil or out of a plurality of coils connected in series or in parallel. 
     According to an eleventh configuration of the invention, there is provided a signal transfer device according to the tenth configuration of the invention, wherein: the transformer is made up of rectangular, circular, elliptical or polygonal spiral coils. 
     According to a twelfth configuration of the invention, there is provided a signal transfer device according to the tenth configuration of the invention, wherein: the transformer is made up of rectangular, circular, elliptical or polygonal solenoid coils. 
     According to a thirteenth configuration of the invention, there is provided a signal transfer device according to the tenth configuration of the invention, wherein: the transformer is made up of solenoid coils in which rectangular, circular, elliptical or polygonal spiral coils are laminated. 
     According to a fourteenth configuration of the invention, there is provided a signal transfer device according to the first configuration of the invention, wherein: a primary-side winding is formed out of one coil, and a signal transmitted to the set-side input terminal of the receiving circuit and a signal transmitted to the reset-side input terminal of the receiving circuit are inputted to opposite end terminals of the primary-side winding. 
     According to a fifteenth configuration of the invention, there is provided a signal transfer device according to the second or fourteenth configuration of the invention, wherein: an intermediate tap is provided at a connection point at which one ends of the two secondary-side windings are connected to each other, and the other ends of the two secondary-side windings are connected to the set-side input terminal and the reset-side input terminal of the receiving circuit respectively. 
     According to the invention, it is possible to suppress occurrence of common-mode noise and simplify a countermeasure circuit against the noise in the signal transfer device transferring a signal through the insulating transformer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view showing the configuration of a signal transfer device according to a first embodiment of the invention; 
         FIG. 2  is a view showing a basic operation waveform of the signal transfer device according to the first embodiment of the invention shown in  FIG. 1 ; 
         FIG. 3  is a view showing the configuration of a signal transfer device according to a second embodiment of the invention; 
         FIG. 4  is a view showing a configuration example (Example 1) in which a transformer in the first embodiment shown in  FIG. 1  is made up of spiral coils; 
         FIG. 5  is a view showing a configuration example (Example 2) in which a transformer in the first embodiment shown in  FIG. 1  is made up of spiral coils; 
         FIG. 6  is a view showing a configuration example (Example 3) in which a transformer in the second embodiment shown in  FIG. 3  is made up of spiral coils; 
         FIG. 7  is a view showing a configuration example (Example 4) in which a transformer in the second embodiment shown in  FIG. 3  is made up of spiral coils; 
         FIG. 8  is a view showing a configuration example (Example 5) in which a transformer in the second embodiment shown in  FIG. 3  is made up of spiral coils; 
         FIG. 9  is a view showing a configuration example (Example 6) in which a transformer in the first embodiment shown in  FIG. 1  is made up of solenoid coils; 
         FIG. 10  is a view showing a configuration example (Example 7) in which a transformer in the second embodiment shown in  FIG. 3  is made up of solenoid coils; 
         FIG. 11  is a view showing a configuration example of a typical switching power supply constituted by semiconductor power switches one of which includes a signal transfer device transferring a signal through an insulating transformer; 
         FIG. 12  is a view showing the configuration of a background-art signal transfer device; 
         FIG. 13  is a view showing an ideal operation waveform of the background-art signal transfer device shown in  FIG. 12 ; and 
         FIG. 14  is an operation waveform diagram for explaining a problem of the background-art signal transfer device shown in  FIG. 12 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the invention will be described below in detail. 
     Embodiments 
     A signal transfer device according to each of embodiments of the invention has a basic configuration in which a secondary-side set winding and a secondary-side reset winding are magnetically coupled to thereby cancel in-phase changes in set and reset signals. When the configuration is made thus, a common mode which could occur in signal terminals R 1  and R 2  of a receiving circuit in the signal transfer device having the background-art configuration can be suppressed. Accordingly, it is possible to attain a function or an effect that a common-mode rejection unit (not shown) in a subsequent stage which was required in the background-art configuration can be dispensed with or the configuration of the common-mode rejection unit (not shown) can be simplified. 
     Embodiment 1 
       FIG. 1  is a view showing the configuration of a signal transfer device according to a first embodiment of the invention. The signal transfer device according to the first embodiment shown in  FIG. 1  serves for driving a high-side semiconductor power switch (not shown) of a switching power supply, an inverter, any of various driving circuits, etc. In order to transfer a signal for driving the high-side semiconductor power switch, the signal transfer device according to the first embodiment is configured to include a transmitting circuit  20 , a receiving circuit  30 , and an insulating transformer  10  provided between the transmitting circuit  20  and the receiving circuit  30 . 
     As shown in  FIG. 1 , the insulating transformer  10  provided between the transmitting circuit  20  and the receiving circuit  30  has two transformer parts (a transformer part  1  and a transformer part  2 ) so that the insulating transformer  10  can operate to transmit a signal (set signal) indicating a turn-ON timing through the transformer part  1  and transmit a signal (reset signal) indicating a turn-OFF timing through the transformer part  2 . 
     In the insulating transformer  10  in  FIG. 1 , a secondary side (S 1 ) of the set transformer part  1  and a secondary side (S 2 ) of the reset transformer part  2  are magnetically coupled. The magnetic coupling direction is formed so that a secondary-side terminal (pinS 1 ) of the transformer part  1  and a secondary-side terminal (pinS 2 ) of the transformer part  2  can have reverse polarities (voltages in the output terminals can change in opposite directions to each other when a magnetic flux changes). Specifically, a secondary-side set winding (S 1 ) and a secondary-side reset winding (S 2 ) are wound densely to share a core (including an air-core) so that a magnetic flux interlinking with one of the secondary-side set winding (S 1 ) and the secondary-side reset winding (S 2 ) can also interlink with the other of the secondary-side set winding (S 1 ) and the secondary-side reset winding (S 2 ). The winding direction of the secondary-side winding (S 1 ) of the set-side transformer part  1  and the winding direction of the secondary-side winding (S 2 ) of the reset-side transformer part  2  are made one and the same. 
     That is, of two pairs of secondary-side terminals (two GND 2  and two signal terminals (set and reset terminals)), the placement of one GND 2  and one signal terminal (set or reset terminal) is made reverse to the placement of the secondary-side terminals (the other GND 2  and the other signal terminal (reset or set terminal)) of the other transformer part so that the secondary-side terminal (pinS 1 ) of the set-side transformer part  1  connected to the set terminal (R 1 ) of the receiving circuit  30  and the secondary-side terminal (pinS 2 ) of the reset-side transformer part  2  connected to the reset terminal (R 2 ) of the receiving circuit  30  are magnetically coupled reversely. Alternatively, the placements of the secondary-side terminals (pinS 1  and pinS 2 ) of the two transformer parts (the set transformer part  1  and the reset transformer part  2 ) are not reversed but the winding direction of the set-side secondary-side winding (S 1 ) and the winding direction of the reset-side secondary-side winding (S 2 ) are reserved so that the terminals can be magnetically coupled with reverse polarities. 
       FIG. 2  is a view showing an operation waveform of the signal transfer device according to the first embodiment of the invention shown in  FIG. 1 . A basic operation of the signal transfer device according to the first embodiment of the invention will be described with reference to  FIG. 2 . The operation waveform of the background-art signal transfer device shown in  FIG. 14  will be referred to here for suitable comparison. 
     Description about  FIG. 1  and  FIG. 2  will be made in detail as follows. That is, a signal for turning ON/OFF the semiconductor power switch (not shown) such as an IGBT (Insulated Gate Bipolar Transistor) is inputted to an IN terminal of the transmitting circuit  20  in  FIG. 1 . When the transmitting circuit  20  outputs a set signal (T 1 ) at a time t 1  in  FIG. 2  which is a leading edge timing of the signal of the IN terminal, a set signal (R 1 ) is received by the receiving circuit  30  through the transformer part  1  at the time t 1  in  FIG. 2 . 
     When the transmitting circuit  20  in  FIG. 1  outputs a reset signal (T 2 ) at a time t 2  in  FIG. 2  which is a trailing edge timing of the signal of the IN terminal, a reset signal (R 2 ) is received by the receiving circuit  30  through the transformer part  2  at the time t 2  in  FIG. 2 . 
     The receiving circuit  30  in  FIG. 1  generates pulses OUT changing over between H (High) and L (Low) at receiving timings of the set signal (R 1 ) and the reset signal (R 2 ), and supplies the generated pulses OUT to a driver  40  in  FIG. 1 . The driver  40  outputs the pulses for driving the semiconductor power switch (not shown) to a gate of the semiconductor power switch (not shown). 
     In the signal transfer device according to the first embodiment of the invention, the transformer parts are magnetically coupled with reverse polarities. Occurrence of common-mode noises which would occur in the secondary-side windings as in the background art can be therefore suppressed. That is, even when common-mode noises occur due to sudden changes in the GND 2  potentials and the potentials of the signal terminals R 1  and R 2  tend to change in the same direction, magnetic fluxes occurring in the secondary-side windings act to cancel the changes of the potentials of the mated terminals respectively. Accordingly, occurrence of common-mode noises can be suppressed. Therefore, a common-mode rejection unit (not shown) in a subsequent stage can be dispensed with or the configuration of the common-mode rejection unit (not shown) can be simplified. 
     Embodiment 2 
       FIG. 3  is a view showing the configuration of a signal transfer device according to a second embodiment of the invention. The signal transfer device according to the second embodiment shown in  FIG. 3  serves for driving a high-side semiconductor power switch (not shown) of a switching power supply, an inverter, any of various driving circuits, etc. in the same manner as the signal transfer device shown in  FIG. 1 . In order to transfer a signal for driving the high-side semiconductor power switch, the signal transfer device according to the second embodiment is configured to include a transmitting circuit  20 , a receiving circuit  30  and an insulating transformer  50  provided between the transmitting circuit  20  and the receiving circuit  30 . 
     The configuration of the insulating transformer  50  of the signal transfer device according to the second embodiment in  FIG. 3  is different from the configuration of the insulating transformer  10  of the signal transfer device according to the first embodiment in  FIG. 1  as follows. That is, in the configuration of the insulating transformer  50  shown in  FIG. 3 , the number of primary-side windings formed in a transformer  3  is one, and an intermediate tap is provided between secondary-side windings and connected to GND 2 . Here, opposite ends of the primary-side winding serve as terminals to which a set signal and a reset signal are inputted from the transmitting circuit  20  respectively. In addition, the secondary-side windings may be regarded as a single secondary-side winding in which the two GND-side terminals of the secondary-side windings shown in  FIG. 1  are connected to each other and an intermediate tap is provided in the connection point. Since the remaining configuration is the same as the configuration of the insulating transformer  10  of the signal transfer device according to the first embodiment shown in  FIG. 1 , its description will be omitted here. 
     Transformer Coil Patterns 
       FIG. 4  is a view showing a configuration example 1 in which the transformer according to the first embodiment shown in  FIG. 1  is made up of spiral coils. Although each coil shown in  FIG. 4  has a rectangular coil pattern, it may have a circular, elliptical or polygonal coil pattern. The winding directions of the primary-side and secondary-side windings of the coils are made common but the terminals disposed on the set side are made reverse to the terminals disposed on the reset side. 
       FIG. 5  is a view showing a configuration example 2 in which the transformer according to the first embodiment shown in  FIG. 1  is made up of spiral coils. Although each coil shown in  FIG. 5  has a rectangular coil pattern, it may have a circular, elliptical or polygonal coil pattern. The winding directions of the primary-side and secondary-side windings of the coils are made reverse but the terminals disposed on the set side are made common to the terminals disposed on the reset side. 
       FIG. 6  and  FIG. 7  are views showing a configuration example 3 and a configuration example 4 in each of which the transformer according to the second embodiment shown in  FIG. 3  is made up of spiral coils. Although each coil shown in each of  FIGS. 6 and 7  has a rectangular coil pattern, it may have a circular, elliptical or polygonal coil pattern. 
     When the transformer made up of the coil patterns shown in each of  FIGS. 4 to 7  is manufactured by a semiconductor technique, for example, the transformer can be formed in such a manner that the coil patterns are formed in three layers or four layers with interposition of an insulating layer between adjacent ones of the coil patterns. 
       FIG. 8  is a view showing a configuration example 5 in which the transformer according to the second embodiment shown in  FIG. 3  is made up of spiral coils. Although each coil shown in  FIG. 8  has a rectangular coil pattern, it may have a circular, elliptical or polygonal coil pattern. In addition, in  FIG. 8 , the sequence of the primary-side winding (pinP 1 , pinP 2 ), the set-side secondary winding (pinS 1 , GND 2 ), and the reset-side secondary winding (GND 2 , pinS 2 ) may be changed. Further, the number of primary windings may be set as two or more. In this case, the primary windings, the set-side secondary winding and the reset-side secondary winding may be disposed alternately. 
     When the transformer made up of the coil patterns shown in  FIG. 8  is manufactured by a semiconductor technique, for example, the transformer can be manufactured in such a manner that all the coil patterns are formed in the same layer. In this case, connection to pinS 1 , pinP 1  and GND 2  may be made by multilayer wiring. That is, the connection can be formed in such a manner that the coil patterns in  FIG. 8  are covered with an insulating film, opening portions (also referred to as through holes) are formed in the insulating film immediately above pinS 1 , pinP 1  and GND 2 , and pinS 1 , pinP 1  and GND 2  are connected to wiring of an upper layer through the opening portions. In addition, the connection to pinS 1 , pinP 1  and GND 2  may be made by bonding wires. Moreover, the connection to pinS 1 , pinP 1  and GND 2  may be made by external wiring of a printed circuit etc. Further, a not-shown connection portion connecting GND 2  in two places (in the lower left and the center portions) in  FIG. 8  corresponds to the intermediate tap in  FIG. 3 . 
       FIG. 9  is a view showing a configuration example 6 in which the transformer according to the first embodiment shown in  FIG. 1  is made up of solenoid coils. Although each coil shown in  FIG. 9  has a rectangular coil pattern, it may have a circular, elliptical or polygonal coil pattern. 
       FIG. 10  is a view showing a configuration example 7 in which the transformer according to the second embodiment shown in  FIG. 3  is made up of solenoid coils. Although each coil shown in  FIG. 10  has a rectangular coil pattern, it may have a circular, elliptical or polygonal coil pattern.