Abstract:
The ESD (Equivalent Shottky Diode, or Emanuil Shvarts Diode) includes a transistor and a sensing circuit, which senses a voltage difference across the ESD. A driving circuit controls the operation of the transistor based on the sensed difference.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field the Invention  
           [0002]    The present invention is related to power electronic devices. In particular, the present invention relates to a power diode equivalent having a low voltage drop and a method thereof.  
           [0003]    2. Description of Related Art  
           [0004]    Power diodes find a variety of uses in modern electronic hardware, including wireless communications equipment. Widely known traditional power diodes such as, for example, a Shottky Diode and the like may be used, for example, for power conversion and rectifying from AC to DC, power control and distribution, and the like.  
           [0005]    Problems arise however in conventional systems which employ power diodes in that such diodes have significant voltage drop. It is typical for a power diode to drop up to one volt for a regular diode and up to half a volt for a Shottky diode. Such power drops are problematic particularly for mobile handsets where power conservation is an extremely important consideration for preserving battery life. Voltage drop is even more important for contemporary low-voltage applications (3.3 v or 2.5 v). For example, a 0.5 v voltage drop in a 2.5 v supply line means a 20% power loss.  
           [0006]    Accordingly, a continuing demand exists in the art for a power diode circuit capable of dissipating less power.  
         SUMMARY OF THE INVENTION  
         [0007]    A method and apparatus are described for providing a power diode equivalent having a very low voltage drop. The method and apparatus of the present invention result in 10-100 times decrease in the voltage drop and resulting power dissipation by using a device named “ESD” (which stands for Equivalent Shottky Diode, or Emanuil Shvarts Diode).  
           [0008]    Thus in accordance with various exemplary embodiments, a difference between an input voltage and an output voltage across a power diode equivalent (e.g., a transistor) is sensed, for example by a comparator. Using the output of this comparator, the transistor is biased in a conductive area (which corresponds to ON state of a diode), or in non-conductive area (which corresponds to OFF state of the diode). The transistor, in accordance with various exemplary embodiments of the present invention, is preferably a n-channel MOSFET. Alternatively the power diode equivalent may be a p-channel MOSFET, or bipolar transistor.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    The present invention will become more fully understood from the detailed description given hereto below in the accompanying drawings, which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:  
         [0010]    [0010]FIG. 1 is a schematic diagram illustrating a power diode equivalent circuit in accordance with various exemplary embodiments of the present invention;  
         [0011]    [0011]FIG. 2 is a schematic diagram further illustrating a power diode equivalent circuit in accordance with various exemplary embodiments of the present invention;  
         [0012]    [0012]FIG. 3 is a schematic diagram further illustrating a power diode equivalent circuit in accordance with various exemplary embodiments of the present invention;  
         [0013]    [0013]FIG. 4 is a schematic diagram further illustrating a power diode equivalent circuit in accordance with various exemplary embodiments of the present invention;  
         [0014]    [0014]FIG. 5 is a schematic diagram further illustrating a power diode equivalent circuit in accordance with various exemplary embodiments of the present invention; and  
         [0015]    [0015]FIG. 6 is a schematic diagram still further illustrating a power diode equivalent circuit in accordance with various exemplary embodiments of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]    Thus in accordance with various exemplary embodiments of the present invention a power diode equivalent circuit will be described, which circuit possesses desirable characteristics, specifically, a low voltage drop. As can be seen in FIG. 1, the Equivalent Shottky Diode (ESD) basic circuit is illustrated where Vin  103  is the input voltage, Vout  104  is the output voltage, Vcc  102  is the supply source voltage, GND  101  is the ground, and Q  110  is an n-type MOSFET transistor.  
         [0017]    In operation in accordance with one preferred exemplary embodiment, comparator  130  senses the voltage difference between Vin  103  and Vout  104  at first and second terminals  131  and  132 . A positive voltage between the first and second terminals  131  and  132  results in an output voltage at output  133  of comparator  130 , which is input to a driver  120 . Driver  120  produces a positive bias at output  121 , which is supplied to the gate of transistor  110 . Accordingly, transistor  110  will become conductive as a result of the positive difference between Vin  103  and Vout  104 , which corresponds to ON state of the ESD. If Vin  103  is less than Vout  104 , the transistor  110  will be driven to the off condition by driver  120  so that no output will be produced at output  121  and thus the gate of the transistor  110 , which places the ESD in the OFF state. It should be noted that the external voltage Vcc  102 , which powers comparator  130  and driver  120 , should be larger than the maximum value of Vin  103 .  
         [0018]    An alternative to providing Vcc  102  as an external supply source is illustrated in FIG. 2.  
         [0019]    As shown in FIG. 2, an internal DC/DC converter  200  receives inputs from both Vcc  102  and Vin  103 , and output voltage  201  is generated and provided to driver  120  and comparator  130 . It should be noted that DC/DC converter  200  is preferably a charge pump doubler or tripler, step up converter, or the like well-known in the art. While input to DC/DC converter  200  is shown as being Vcc  102  and Vin  103 , the input may also be derived from only one or the other of Vcc  102  and Vin  103 . Use of DC/DC converter  200  is advantageous when a reliable and stable source of a high bias voltage is not available.  
         [0020]    An alternative exemplary embodiment is illustrated in FIG. 3. As compared to the embodiment of FIG. 1, the comparator  130  has the second input  132  coupled to ground  101  rather than to Vout  104 . The effect of connecting the second input  132  of comparator  130  to ground  101  is that the transistor  110  will be biased on whenever Vin  103  is positive with respect to ground  101 . The transistor  110  will also be biased off when Vin  103  is negative with respect to ground  101 .  
         [0021]    [0021]FIG. 4 illustrates adding diode  400 , which is a regular diode, for example, a Shottky Diode or the like. By adding diode  400  in parallel with the transistor  110 , dynamic performance is improved especially with regard to high frequency signals associated with Vin  103 . Moreover, Diode  400  may partially compensate for any delay associated with comparator  130 , driver  120 , and the transistor  110  during signal transitions. In this case, during the transition time, diode  400  will provide rectification. Because the transition time is very low, around nanoseconds, the associated power losses will be minimal.  
         [0022]    If it is desired to produce negative rectification, then as illustrated in FIG. 5, the drain of the transistor  110  is connected to Vin  501 . Accordingly, Vout  500  is connected to the source of the transistor  110  resulting in a circuit which is similar in many regards to FIG. 1 through FIG. 4 in terms of biasing the transistor  110  as described.  
         [0023]    When an additional supply source with a voltage higher than Vin is not available, a p-type MOSFET  600  may preferably replace transistor  110  such as illustrated in FIG. 6. In this case, an internal step-up converter is not required, and the device gains in simplicity and efficiency. It should be noted that a p-type MOSFET may have substantially worse on-resistance, but an additional supply voltage can be less than Vin  602 . It should further be noted that the p-type MOSFET may be substituted for the n-type MOSFET  100  shown in FIGS.  1 - 5  with appropriate adjustments to biasing values and the like.  
         [0024]    In accordance with the various exemplary embodiments of the present invention, the difference between, for example, Vin  103  and Vout  104  may be very small, and for practical purposes comparator  130  will have a non-zero threshold. Accordingly, the transistor  110  will become conductive when Vin  103  minus Vout  104  is greater than or equal to the threshold voltage of comparator  130 , e.g. 50 mV. It should be noted that all existing traditional diodes also have a threshold, around 0.2-0.4v. For the suggested ESD, the threshold voltage is adjustable, which is a definite advantage.  
         [0025]    The invention being thus described, it will be obvious that one skilled in the art can contemplate several variations thereto. Such variations are not to be regarded as a departure from the invention, and all such modifications are intended to be included within the scope of the following claims.