Patent Publication Number: US-2002001213-A1

Title: Integrated circuit (ic) switching power converter

Description:
BACKGROUND OF THE INVENTION  
       [0001] The invention is in the field of integrated circuit (IC) switching power converters, and relates more particularly to switching power converters of the type having a main power supply and an auxiliary power supply.  
       [0002] Switching power converters, used in switched-mode power supplies, and the circuits used therein, are generally well known in the art. They are typically used to obtain good regulation as well as efficient and economical filtering, since smaller-value filtering components can be used because of the typically high switching frequency used.  
       [0003] In addition to the main power supply in the switching power converter, an auxiliary (typically lower-voltage) power supply is often required to power the control circuitry of the converter, and possibly also other circuits of the switched-mode power supply. Ideally, such an auxiliary supply should create a low voltage with a relatively low power requirement, and should operate efficiently and use low-cost componentry.  
       [0004] Presently, various techniques exist for meeting these requirements to varying degrees, but none are fully satisfactory in all respects. Thus, for example, an auxiliary power supply can be simply created by providing a resistor or linear regulator operating off the main voltage supply. Such a solution is inexpensive, but not efficient, particularly when the main voltage is high. Alternatively, an auxiliary supply can be created by providing an extra winding on an existing switched inductor or transformer, which is an efficient but costly solution. Additionally, output relation of the auxiliary supply will be less than optimum, since voltage regulation will be affected by operating point changes in the main power converter operating off the same transformer or inductor. Finally, an auxiliary supply can be created by using a small self-oscillating converter, formed of either discrete transistors and a transformer or a partiallyintegrated control and switching circuit. Although such solutions are efficient and do not suffer from regulation problems, they can be costly.  
       [0005] Several different power supply configurations, using various prior-art techniques for generating an auxiliary power supply and employing partial integration, are disclosed in A TRIPLE LOW-SIDE DRIVER POWER IC WITH REGULATION AND MICROPROCESSOR INTERFACE CONTROL, Thiel and Hach, IEEPESC, pp. 806-811, 1991; FUTURE DEVELOPMENT IN ELECTRONIC SYSTEMS IS IMPACTED BOTH BY SEMICONDUCTOR TECHNOLOGY AND IC ASSEMBLY TECHNIQUES, Murari, ESSDERC &#39;96, pp. 4044, 1996; and U.S. Pat. No. 5,739,582. Additionally, a switching power converter employing a partially-integrated self-oscillating converter using a relatively expensive flyback transformer is used in the Philips “Greeny” chip (part number TEA 1501 ). All of the foregoing prior-art configurations suffer to some degree from the disadvantages of complexity, inefficiency, high cost, large size and/or the inability to achieve maximum possible integration.  
       [0006] Accordingly, it would be desirable to have an integrated switching power converter which is relatively simple, efficient, economical, compact, and easily integrated.  
       SUMMARY OF THE INVENTION  
       [0007] It is therefore an object of the invention to provide an integrated circuit switching power converter which is simple and compact in construction, efficient to operate, economical to produce, and easily integrated into a single IC package, with a minimum of external components. In accordance with the invention, these objects are achieved by a new IC switching power converter of the type having a main power supply and an auxiliary power supply, in which all of the integrated components of the main power supply and the auxiliary power supply are formed in a single IC die which is mounted in a single IC package.  
       [0008] In a preferred embodiment of the invention, the main power supply and the auxiliary power supply share at least one external electrical connection pin of the single IC package.  
       [0009] In a further preferred embodiment of the invention at least one circuit is shared in common by the main power supply and the auxiliary power supply, thus making the power converter circuit simpler, more compact and more economical to manufacture.  
       [0010] These and other objects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
     [0011] The invention may be more completely understood with reference to the following description, to be read in conjunction with the accompanying drawing, in which:  
     [0012]FIG. 1 shows a simplified block diagram of an integrated circuit switching power converter in accordance with a first embodiment of the invention;  
     [0013]FIG. 2 shows a simplified block diagram of an integrated circuit switching power converter in accordance with a second preferred embodiment of the invention; and  
     [0014]FIG. 3 shows a simplified block diagram of an integrated circuit switching power converter in accordance with a third preferred embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0015] A simplified diagram of an integrated circuit switching power converter is shown in FIG. 1. In the block diagram of FIG. 1, an integrated circuit switching power converter  10  includes a single IC package  12  containing a single IC die  14  which has both a main power supply section  16  and an auxiliary power supply section  18  which are separated for purposes of illustration by a dashed line.  
     [0016] Although various different configurations for the main power supply and auxiliary power supply are contemplated within the scope of the invention, for purposes of illustration the main power supply  16  as shown in FIG. 1 is composed of a control circuit  20  coupled to a level shift circuit  22  which in turn feeds an output circuit  24  which drives an external load  26 . While various different types of output circuits can be employed, a half-bridge output circuit  24  is shown for illustration.  
     [0017] The auxiliary power supply  18 , also on IC die  14 , illustratively includes an oscillator and control circuit  28  feeding a level shift circuit  30 , which in turn drives output circuit  32 . Again, it should be emphasized that many different configurations are possible for the individual circuits of the auxiliary power supply as well as the main power supply, and accordingly such circuits are not shown in further detail herein.  
     [0018] In the block diagram of FIG. 1, package or die pins are shown by small solid squares. In accordance with the invention, at least one external electrical connection pin of the single IC package  12  is shared by the main power supply  16  and the auxiliary power supply  18 , both of which are formed on the single IC die  14 . In FIG. 1, the shared connection pins are the high (main) voltage input pin  34 , AUX (auxiliary) SUPPLY pin  36 , and ground (GND) pin  38 . Additionally, it is noted that the output circuit  32  of the auxiliary power supply  18  is connected in a down (or “buck”) converter configuration with diode  50 , capacitor  60  and inductor  40 . The output of this down converter, designated AUX SUPPLY, can be used as the low-voltage supply for control circuit  20  of the main power supply and the oscillator and control circuits  28  of the auxiliary power supply (pin  36 ), and other circuits requiring a low voltage supply.  
     [0019] By incorporating all of the integrated components of the main power supply and the auxiliary power supply into a single IC die which is mounted in a single IC package, and then providing one or more common external electrical connection pins for both internal power supply circuits, a simple, compact and economical construction is achieved.  
     [0020] Further preferred embodiments of the invention are shown in FIGS. 2 and 3, in which components already described in connection with FIG. 1 are provided with like reference numerals and are not further described in the interest of brevity.  
     [0021] The main feature shown in the simplified block diagram of FIG. 2 is the sharing of circuitry between the main power supply  16  and the auxiliary power supply  18 , both of which are formed on the same IC die  14 . Since both power supplies are mounted on the same IC die, certain circuits, such as voltage reference circuit  42 , under voltage lockout circuit  44  and oscillator circuit  46 , can be provided once on the IC die  14  and used to provide signals to both the main and auxiliary power supplies, thus further reducing cost, size and complexity. For example, whereas block  28  of the auxiliary power supply in FIG. 1 requires its own oscillator, in FIG. 2 block  28  need only be a control circuit, with the oscillator ( 46 ) being shared in common with the block  20  of the main power supply. It will be recognized that the particular circuits being shown as shared in FIG. 2 are illustrative in nature, and that various other circuits may be shared by the two power supplies as appropriate for the particular power supply configuration being employed in a given application. It should also be noted that such circuit sharing can not only decrease size, cost and power consumption, but can also improve performance. For example, the use of a common oscillator  46  for the two power supplies, rather than two separate oscillators can improve the electrical noise performance of the entire system.  
     [0022] A further reduction in cost may be achieved by using the configuration shown in the simplified block diagram of FIG. 3. In the embodiment shown in FIGS. 1 and 2, the auxiliary power supply  18  is provided with a “freewheeling” diode  50  to provide a current path when the output circuit  32  is switched off. In FIGS. 1 and 2, as in the prior art, this diode is provided as a discrete component, external to the IC die. However, a further saving in cost can be achieved by integrating this diode (or an active equivalent) into the IC die  14 , as shown in FIG. 3. Furthermore, as also shown in FIG. 3, the diode  50  function may be performed by a synchronous rectifier, shown schematically as a diode  52  connected in parallel with a transistor switch  54  that is turned on during the diode conduction time. Such a configuration will improve the efficiency of the auxiliary power supply while providing a compact and cost-effective configuration. It should be noted that in the actual physical implementation of the synchronous rectifier, the diode  52  would be a part of the structure of MOS transistor  54  and not a separate element. Finally, it should be noted that integrated circuit switching power converters in accordance with the invention may be fabricated by any one of a number of semiconductor fabrication technologies well known to those of ordinary skill in the art. A particularly advantageous process technology for fabrication of the present invention employs the use of a high-voltage silicon-on-insulator semiconductor fabrication process, such as the Philips Semiconductors&#39;EZ-HVTM process, which supports high-voltage transistors that can float to high voltages above ground potential. In such a technology, the various control circuits for the main and auxiliary power supplies can be referenced to ground potential, while other circuits, such as the output circuit of the auxiliary converter, can be at a high potential.  
     [0023] In this manner, the present invention provides an integrated circuit switching power converter which is simply and compact in construction, efficient to operate, economical to produce, and easily integrated into a single IC package, with a minimum of external components.  
     [0024] While the invention has been particularly shown and described with reference to several preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the spirit or scope of the invention. In this application it should be understood that the word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements, and that the word “comprising” does not exclude the presence of other elements or steps than those described or claimed.