Abstract:
The Lus Semiconductor in this invention is characterized by replacing the static shielding diode (SSD) of traditional Power Metal Oxide Semiconductor Field Effect Transistors (Power MOSFETs) with polarity reversed (comparing with traditional SSD) SSD, Schottky Diode, or Zener Diode, or face-to-face or back-to-back coupled Schottky Diodes, Zener Diodes, Fast Diodes, or Four Layer Devices such as DIAC and Triac. With the proposed Power MOSFETs of which the drain to source resistors (Rds) are quite low, two major functions of high efficiency AC/DC conversion and DC voltage regulation may be achieved.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention is related to Power Metal Oxide Semiconductor Field Effect Transistors, Power MOSFETs, especially Power MOSFETs with novel structures replacing conventional Static Shielding Diodes, SSDs. According to this invention, traditional SSDs in Power MOSFETs may be replaced with polarity reversed (comparing with traditional SSD) SSDs, Schottky Diodes, or Zener Diodes, or face-to-face/back-to-back coupled Schottky Diodes, Zener Diodes, Fast Diodes, or Four Layer Devices such as DIAC and Triac such that conventional functions are preserved and need only to consider the amplitude of the reverse biased voltage for proper semiconductor operating voltage. As shown in  FIG. 2  (E) or (F), the amplitude of the reverse biased operating voltage, i.e. Zener Voltage, may be configured according to the needs in this invention and would be higher than the DC output voltage in actual applications. That is, the voltage of conventional SSD in Power MOSFETs is higher than the AC voltage at input side, and the Zener voltage of the polarity reversed coupled Zener Diode is higher than the DC output voltage. According to such design philosophy of this invention, functions of half-wave rectification and voltage regulation may be achieved with a single Power MOSFET in coordination with auxiliary circuits, and functions of full-wave rectification and voltage regulation may be achieved with two pieces of Power MOSFETs in coordination with auxiliary circuits. Hence, functions of high efficiency rectification and voltage regulation may be achieved.  
         [0003]     2. Description of the Related Art  
         [0004]     In order to get stable output voltage in conventional switching power supplies, it is necessary to implement circuits with rectifier diodes and feedback circuits of PWM systems.  FIG. 3  (A) shows the structure of a conventional N-channel power MOSFET and  FIG. 3  (B) shows the structure of a conventional P-channel power MOSFET, both with static shielding diodes, SSD.  FIG. 4  shows a power regulation circuit utilizing UC3842, in which VD 6  and VD 7  are responsible for rectification and IC2 TL431, photo coupler 4N35 and PWM IC MC3842 are responsible for voltage regulation. Such scheme comes with the following drawbacks:  
         [0005]     1. While the current through diode VD 6  is set to be IF=1.5 A and the voltage drop of the forward biased voltage of a diode VD 2  is approximately VF≈0.7V, then the power consumption is about 0.7V*1.5 A=1.05 W. If the output is 20 A, the power consumption becomes 0.7V*20 A=14 W, which is too much power consumption to utilize in actual practice.  
         [0006]     2. While supplying multiple DC output of different amplitude of voltage in a PWM system, some DC output may not be regulated by such system. For example, the primary output 12V, 1.5 A in  FIG. 4  is regulated while the secondary output 5V, 0.2 A is not regulated.  
         [0007]     3. Noise is an inevitable problem in PWM power regulation systems.  
       SUMMARY OF THE INVENTION  
       [0008]     In order to provide semiconductor devices which may elevate the efficiency of rectification and provide function of voltage regulation, this invention is proposed according to the following objects.  
         [0009]     The first object of this invention is to provide semiconductor devices that eliminate the drawback of high power consumption of conventional power rectifiers utilizing diodes, such as Schottky diodes.  
         [0010]     The second object of this invention is to provide semiconductor devices that require no feedback circuits applying to the front end circuit for stable output.  
         [0011]     The third object of this invention is to eliminate the drawback that only certain groups of output voltage are able to be regulated while other plurality of output may not be able to be regulated in the conventional PWM switching power circuits.  
         [0012]     In order to solve the problem of high power consumption in conventional rectification and voltage regulation systems, the present invention possess the following characteristics:  
         [0013]     1. Unlike the manufacture process of conventional power MOSFETs, the polarity of single parasitic diode, SSD, is reversed or replaced the SSD with two pieces of face-to-face/back-to-back coupled diodes, i.e., in the manufacture process of power MOSFETs, coupling characteristic structures of Lus Semiconductor between drain node and source node as shown in  FIG. 2 .  
         [0014]     2. The characteristic structures of Lus Semiconductor may be externally coupled between drain node and source node as shown in  FIG. 2  if no parasitic diodes exist in conventional power MOSFETs.  
         [0015]     3. Lus Semiconductors in the present invention may also be applied in conventional PWM power supply systems. For example, in  FIG. 4 , VD 6  may be replaced with Lus Semiconductors for rectification purpose only, and VD 7  may also be replaced with Lus Semiconductors such that the efficiency of rectification may be improved.  
         [0016]     According to the defects of the conventional technology discussed above, a novel solution, the Lus Semiconductor, is proposed in the present invention, which provides power MOSFETs with the two functions of rectification and voltage regulation. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  shows the structures of an N-Channel Power MOSFET and a P-Channel Power MOSFET of the Lus Semiconductor according to the present invention.  
         [0018]      FIG. 2  shows characteristic circuit structures of the Lus Semiconductor coupled between the drain and source of the power MOSFETs shown in  FIG. 1 .  
         [0019]      FIG. 3  shows the structures of a conventional N-Channel MOSFET and a conventional P-Channel MOSFET.  
         [0020]      FIG. 4  shows a power regulation circuit utilizing UC3842.  
         [0021]      FIG. 5  shows an application circuit utilizing one embodiment of the Lus Semiconductor according to the present invention.  
         [0022]      FIG. 6  shows another application circuit utilizing one embodiment of the Lus Semiconductor according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]      FIG. 1  shows the structures of an N-Channel power MOSFET ( 100 ) and a P-Channel power MOSFET ( 200 ) of Lus Semiconductor according to the present invention.  FIG. 2  shows several characteristic circuit structures ( 101 ) of Lus Semiconductor that may be coupled between the drain node and the source node of power MOSFETs shown in  FIG. 1 . A pair of face-to-face coupled Schottky diodes and a pair of back-to-back coupled Schottky diodes are shown in  FIG. 2  (A) and  FIG. 2  (B) respectively, and each of the two may be then coupled to the drain node and the source node of the power MOSFETs. A pair of face-to-face coupled SSDs and a pair of back-to-back coupled SSDs are shown in  FIG. 2  (C) and  FIG. 2  (D) respectively, and each of the two may be then coupled to the drain node and source node of the power MOSFETs. A pair of face-to-face coupled Zener diodes and a pair of back-to-back coupled Zener diodes are shown in  FIG. 2  (E) and  FIG. 2  (F) respectively, and each of the two may be then coupled to the drain node and source node of the power MOSFETs.  FIG. 2  (G) shows a pair of face-to-face coupled Schottky diode and Zener diode, which may then be coupled to the drain node and the source node of the power MOSFETs.  FIG. 2  (H) shows a pair of face-to-face coupled Schottky diode and SSD which may then be coupled to the drain node and the source node of the power MOSFETs.  FIG. 2  (I) shows a pair of face-to-face coupled Zener diode and fast diode which may then be coupled to the drain node and the source node of the power MOSFETs.  FIG. 2  (J) shows a DIAC four layer semiconductor and  FIG. 2 K  shows a Triac four layer semiconductor, each of the two may then be coupled to the drain node and the source node of the power MOSFETs. The characteristic circuit structures ( 101 ) shown in  FIG. 2  (A)˜(K) may all be coupled to the drain node and the source node of the power MOSFETs and Lus Semiconductors ( 100 )( 200 ) are thus constructed. With the characteristic circuit structures ( 101 ) shown in FIGS.  2  (A)˜(K), high efficiency rectification and voltage regulation may be achieved, with a single power MOSFET. Comparing with the structures of a conventional N-Channel MOSFET or a conventional P-Channel MOSFET shown in  FIG. 3 , one can tell that thy are the totally different from the characteristic circuit structures of Lus Semiconductors.  
         [0024]     In order to meet the needs of conventional PWM power supplies, as shown in  FIG. 2 (L),  FIG. 2 (M) and  FIG. 2 (N), the polarities of the parasitic diodes of conventional N-Channel or P-Channel MOSFETs may be reversed, thus become the characteristic circuit structures ( 101 ) of Lus Semiconductors which may replace rectifiers in conventional circuits, for example, VD 6  and VD 7  in  FIG. 4 , and still preserve the characteristic functions of those of conventional SSDs.  
         [0025]      FIG. 5  shows an application circuit utilizing one embodiment of the Lus Semiconductor according to the present invention. As shown in this figure, all N-Channel power MOSFETs are replaced with N-Channel Lus Semiconductors ( 100   a,    100   b ). In operation, while a high frequency AC voltage at the node  8  of the first secondary winding of the high frequency transformer  300  is at positive half cycle, the positive voltage passes through the current-limiting resistor R 1 , diode D 1  and the LED of the photo coupler Ph 1  and reaches the middle node  9 . Meanwhile the high frequency voltage across node  11  and node  12  of the second secondary winding of the high frequency transformer  300  is half-wave rectified by the high frequency diode D 3  such that a DC voltage V 1  is obtained across the filter capacitor C 1 . The positive voltage V 1  reaches a voltage-dividing resistor RH through the output side of the photo coupler Ph 1 , and conducts the drain and source of the Lus Semiconductors ( 100   a,    100   b ). The positive half cycle AC voltage at node  8  passes through the drain and source of the Lus Semiconductor ( 100   a ) and a π-type filter constructed with a filter capacitor C 2 , an inductor L 1  and a filter capacitor C 3 , thus becomes DC output voltage V 2 . While the AC voltage at the node  10  of the first secondary winding of the high frequency transformer  300  is at positive half cycle, the operation is identical to that while the AC voltage at the node  8  of the first secondary winding of the high frequency transformer  300  is at positive half cycle. Because those two half-cycle circuits are commonly connected at node A, full-wave rectification may be achieved.  
         [0026]     While the output voltage V 2  is higher than a pre-defined voltage, an adjustable precision shunt regulator integrated circuit IC 1  may be activated and meanwhile the collector and the emitter at the output side of a photo coupler Ph 3  may be conducted that makes the gate and the source of the Lus Semiconductors ( 100   a,    100   b ) short-circuited and stops rectifying, thus voltage V 2  may drop. While the voltage V 2  is low enough that deactivates IC 1 , the Lus Semiconductors ( 100   a,    100   b ) may then start rectifying and make voltage V 2  rise. According to the operation, the Lus Semiconductors ( 100   a ,  100   b ) are capable of rectification and voltage regulation. While the voltage at node  8  of the high frequency transformer  300  is set to be positive, the reverse biased break down voltage of the Schotty diode of the characteristic circuit structure ( 101   a ) of the Lus Semiconductor ( 100   a ) is higher than the positive voltage at node  8 , thus the voltage at node  8  may not pass through the reversed Shottky diode but through the drain and source of the Luz Semiconductor ( 100   a ). While the output voltage V 2  is present, even though the voltage at node  8  is at the negative half cycle of the AC voltage, because the reverse biased break down voltage of the reverse coupled Schotty diode in the characteristic circuit structure ( 101   a ) is higher than the output voltage V 2 , the possibility that the first secondary winding may be burned out by the reverse current of conventional power MOSFETs can be eliminated. The operation of the characteristic circuit structure ( 101   b ) in the Lus Semiconductor ( 100   b ) at node  10  is identical. According to the operation of the characteristic circuit structure ( 101 ) in the present invention, the reverse biased break down voltage may be configured according to applications and shall not be limited.  
         [0027]      FIG. 6  shows another application circuit utilizing another embodiment of the Lus Semiconductor ( 100 ) according to the present invention. Actually it is the circuit identical to that shown in  FIG. 4  except for the power MOSFET is replaced by a Lus Semiconductor ( 100   c ). In  FIG. 6 , while the voltage at node  8  of the first secondary winding of the high frequency transformer  300  is positive, it passes through the diode D 1  and the voltage-dividing resistor R 3  and supplies positive voltage to the gate of the Lus Semiconductor ( 100   c ) such that the drain node and the source node are conducted. Thus, the π-type filter thereafter gets a positive voltage. Because the resistor RDS measured between the drain and the source of the power MOSFET is small, most current may flow through the drain node and the source node instead of through the diode in the characteristic circuit structure ( 101   c ). While the AC voltage at node  8  is at negative half cycle, the DC voltage of the π-type filter may not flow back to the node  8  of the first secondary windings of the high frequency transformer  300 , therefore protects node  8  of the first secondary windings from being burned out by the reverse current source. On the contrary, in  FIG. 4 , because the polarity of the SSD of the conventional power MOSFETs is reverse coupled comparing with the SSD of the present invention, node  8  of the first secondary winding may possibly be burned out by the reverse DC current. This also shows some concrete evidence of the benefit of the present invention. The operations of PWM voltage regulation in UC3842 are known to the people skilled in the art and will not be discussed here. One thing to be emphasized is that the Lus Semiconductor ( 100 ) shown in  FIG. 6  may also be implemented with the auxiliary circuit shown in  FIG. 5 , and shall not be limited.