Abstract:
The invention relates to a vertical-type power switch disposed in a semi-conductor chip, comprising a winding ( 30 ) located on the periphery of at least one face of said chip. Said winding comprises two binding posts ( 31, 32 ) which supply a signal that is proportional to the current fluctuations in said switch.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to the switching of a load connected by a bidirectional switch to an A.C. network or by a one-way switch to an A.C. network rectified by a rectifying bridge. The present invention for example finds applications in the control of medium-power loads, for example, a vacuum cleaner motor, a temperature-controlled heating circuit, a dimmer lighting system, etc. 
   2. Discussion of the Related Art 
     FIG. 1  very schematically shows such a switching circuit. Load  1  is arranged between terminals A and B of an A.C. voltage or of a rectified A.C. voltage, in series with a power switch SW. Switch SW will be called a power switch, although it is, in the given examples, a medium-power switch intended for switching loads connected to the mains. Switch SW is controlled by a control circuit  2  receiving a control order, periodic or not, on a terminal  3 . The control circuit is, for example, intended for turning on the switch for a portion only of a halfwave of the A.C. voltage across terminals A and B, which corresponds to a so-called phase angle control. Then, when the switch turns on, a strong current surge occurs in the load. In other words, the current variation along time (di/dt) is abrupt and the current exhibits strong peaks upon each turning-on of the switch. 
   These current peaks are capable of being sent back by terminals A and B onto the A.C. supply network and to disturb this network and other circuits connected to this network. 
   Conventionally, to attenuate these disturbances, an inductance L of relatively high value is provided in series with the switching circuit, which, independently from the cost of this inductance, which is a discrete component of relatively large dimension, complicates the circuit design. 
   U.S. Pat. No. 6,127,746 discloses a relatively complex circuit for detecting current peaks and controlling a MOS transistor so as to dampen these current peaks. 
   Japanese patent application 07/131316 provides for detecting overcurrents on an output pad of a MOS transistor by surrounding this pad with a winding, whereby the surface area of the semiconductor chip containing the transistor is substantially increased. 
   SUMMARY OF THE INVENTION 
   Thus, the present invention aims at solving the problem of sending back noise onto a supply source and the elements connected to this source without adding any discrete element such as a high-value inductance, without providing a complex circuit, and without increasing the surface area of the chip. 
   To solve this and other problems, the present invention provides a vertical-type power switch formed in a semiconductor chip, including a winding formed at the periphery of at least one surface of said chip, this winding including two connection terminals providing a signal proportional to the current variations in said switch. 
   According to an embodiment of the present invention, the switch further includes a resistor of high value arranged in or on the semiconductor chip. 
   According to an embodiment of the present invention, the switch is of bipolar transistor, MOS transistor, or insulated-gate bipolar transistor type. 
   According to an embodiment of the present invention, the switch is associated with a circuit for controlling a control signal of this switch according to the signal across said winding. 
   The foregoing objects, features and advantages of the present invention, will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings, in which: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  schematically shows a switching circuit of a load according to prior art; 
       FIG. 2  schematically shows a load switching circuit associated with a current variation detector; 
       FIG. 3A  is a partial cross-section view of an example of a switch according to the present invention; 
       FIG. 3B  is a simplified top view of an example of a switch according to the present invention; 
       FIG. 4  shows a circuit for switching the current in a load according to the present invention. 
   

   DETAILED DESCRIPTION 
   In the various drawings, the same elements are designated with the same references. Further, as usual, the cross-section and top views of semiconductor components are not drawn to scale. 
   The present invention aims at forming in a simple way a circuit of the type illustrated in  FIG. 2 . In this circuit, a load I is connected between A.C. supply terminals A and B via a switch SW. Switch SW is controlled by a control circuit  12  receiving a turn-on signal  3  from a chosen time of each halfwave. The current variation di/dt in the charge circuit at the closing time is detected and a correction signal linked to the value of variation di/dt is applied to control circuit  12  so that this value di/dt does not exceed a determined threshold. The present invention provides forming the current variation detection circuit monolithically with power switch SW. 
   An embodiment of the present invention is illustrated in the partial cross-section view of  FIG. 3A  in the case where the vertical power component is a MOS transistor. 
   The vertical MOS transistor is formed from an N-type substrate  21  including on its lower surface side a more heavily-doped N-type layer  22  covered with a drain metallization D. On the upper surface side are formed P-type wells  23 . In each well is formed an N-type ring  24 , the periphery of which extends close to the periphery of well  23 . The area of well  23  between the periphery of this well and the external periphery of P-type region  24  is covered with a gate metallization  26  formed on an insulating layer  27 . A source metallization is solid with the central portion of wells  23  and of rings  24 . Thus, when no voltage is applied to gate electrode G, the component is off. When a voltage is applied to electrode G, a current can flow from source metallization S to drain metallization D, through area  24 , a channel area formed in the external upper portion of well  23 , then vertically through substrate  21  to N+ region  22 . 
   A peripheral P-type region  28  deeper than wells  23  at the component periphery has also been shown. Area  28  or other peripheral means for ensuring that the breakdown of a vertical MOS transistor cannot occur at the periphery are known by those skilled in the art and are likely to have many alternatives. Such a periphery is necessary and corresponds to a lost, non active, surface area of the component. 
   A vertical MOS transistor has been shown hereabove as an example. The present invention could also be implemented with other vertical power switches such that the current flowing therethrough is linked to the voltage applied on their control electrode. Examples of such components are bipolar transistors, or insulated-gate bipolar transistors (IGBT) (it should be noted that the structure of an IGBT transistor only differs from the structure schematically shown in  FIG. 3A  by the fact that layer  22 , instead of being heavily doped of the same conductivity type as the substrate, is heavily doped of the opposite conductivity type). Such other components also comprise a peripheral region for having a sufficiently high breakdown voltage. 
   According to the present invention, the component periphery is coated with a metallization  30  wound in successive spirals around the power component. Metallization  30  is insulated from substrate  21  by an insulating layer  29 , for example made of silicon oxide. 
   Metallization  30  can be better seen in the top view of  FIG. 3B  where it extends between pads  31  and  32 . The contour of source metallization S and the contour of a gate contact recovery G are also shown in  FIG. 3B , in dotted lines. 
   When the component conducts a vertical current, variations of this current will generate across terminals  31 ,  32  of inductance  30  a signal proportional to the variation of this current. It should by the way be noted that this signal is detectable even if the current is not strictly vertical, provided that it does not remain in the spiral plane. A four-spiral winding has been shown in the drawing. Windings with more or less spirals could of course be provided according to the desired detection threshold. 
   To detect the signal between terminals  31  and  32 , a resistor of very high value could for example be connected between terminals  31  and  32 . This resistor may be arranged externally or may be formed monolithically on semiconductor chip  21  in the form of a polysilicon resistor or in any other way known of those skilled in the art. 
     FIG. 4  shows an example of use of a component according to the present invention in a circuit. In  FIG. 4 , this component has been generally designated with reference  40  and for example includes a power transistor T, a winding  30 , and a resistor R monolithically integrated. Terminal  32  of winding  30  and of resistor R is grounded. Terminal  31  is connected via a multiplier  41  by a coefficient K to the subtraction input of an adder  42 , the addition input of which receives the control signal from terminal  12 . Thus, when an order is applied on input  3  of circuit  12 , this order tends to turn transistor T on. A current variation then occurs in the circuit and signal di/dt is amplified/attenuated by amplifier  41  and combined with the control order to limit the turn-on speed of transistor T. 
   It should be understood that the control circuit of transistor T or another power switch is likely to have various alterations, modifications, and improvements which will readily occur to those skilled in the art. For example, to fulfil standards of sending back of noise on a supply network, a control circuit which performs different compensations according to the frequency of signal di/dt may be provided. 
   Further, the control circuit and the circuit for processing signal di/dt may be altogether integrated on the same semiconductor chip as that which contains the power component. Many other alternatives will occur to those skilled in the art, especially as concerns the component sizing. 
   According to an advantage of the present invention, the formation of winding  30  does not cause a loss in the surface area of the semiconductor chip as this winding is disposed above the periphery of the chip, which normally corresponds to a necessary, but non active, region. 
   Having thus described at least one illustrative embodiment of the invention, various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be within and scope of the invention. Accordingly, the foregoing description is by way of example only and is not as limiting. The invention is limited only as defined in the following claims and the equivalents thereto.