Abstract:
The present invention provides a self-driven synchronous rectification boost converter having high step-up ratio. The self-driven synchronous rectification boost converter having high step-up ratio has a first switch receiving a pulse driving signal, a first winding, a second winding and a synchronous rectification circuit constructed by an auxiliary winding and a second switch. The first winding inducts a reverse voltage when the first switch is repeatedly switched on and off. The reverse voltage then is raised via the second winding, and the auxiliary winding cooperates with a switch circuit to switch on/off the second switch according to an inducted voltage, so as to achieve an object of synchronous rectification. Under a condition of outputting high current, the present invention can greatly reduce power-consumption of rectifying and enhance efficiency.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a boost converter, and more particularly to a self-driven synchronous rectification boost converter having high step-up ratio. 
       BACKGROUND OF THE INVENTION 
       [0002]    With reference to  FIG. 1 , a conventional boost circuit for driving a backlight module of a liquid crystal display device mainly has an input power Vin, a first winding L 1  connected to the input power Vin, a second winding L 2  connected to the first winding L 1 , a diode D 2  connected between the second winding L 2  and an output capacitor, and a transistor switch Q 1 . 
         [0003]    The boost circuit uses the action of repeatedly switching on-and-off of the transistor switch Q 1  to control the first winding L 1  to output an forward-biased voltage, and then to raise the voltage with the number of windings of the second winding L 2  being larger than the number of windings of the first winding L 1 , so that the output capacitor can provide an output voltage higher than the input voltage Vin to the backlight module on a load end. 
         [0004]    Foregoing boost circuit implements a boosting effect that the output voltage is higher than the input voltage. However, since the boost circuit uses the diode D 2  for rectification, as the circuit outputs a large current, power consumption of the diode will become higher and cause the efficiency of the boost circuit to decrease and a problem of heat dissipation. If the boost circuit uses a MOSFET for rectification, the circuit needs to be driven with a floating ground isolation, which causes design of the circuit to be more complicated. 
         [0005]    Hence, it is necessary to provide a self-driven synchronous rectification boost converter having high step-up ratio to overcome the problems existing in the conventional technology. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention provides a self-driven synchronous rectification boost converter having high step-up ratio to overcome the problem of high power-consumption on using diode rectifier in the conventional technology. 
         [0007]    In view of the shortcomings of the conventional technology, a primary object of the present invention is to provide a self-driven synchronous rectification boost converter having high step-up ratio that uses an auxiliary winding and peripheral circuit to implement a self-driven synchronous rectification to further replace diode rectification. 
         [0008]    To achieve the above object, the present invention provides a self-driven synchronous rectification boost converter having high step-up ratio comprising: 
         [0009]    a first switch receiving a pulse driving signal and being repeatedly switched on/off according to the pulse driving signal; 
         [0010]    a first winding connected between an input voltage source and the first switch, storing energy when the first switch is switched on and having a reverse terminal voltage when the first switch is switched off; 
         [0011]    a second winding connected to first winding; 
         [0012]    an auxiliary winding connected to the second winding; 
         [0013]    a switch circuit connected to the auxiliary winding and outputting a control signal according to the change of the terminal voltage of the auxiliary winding; and 
         [0014]    a second switch connected to the switch circuit and receiving the control signal and being switched on or off according to the control signal. 
         [0015]    In one embodiment of the present invention, the first switch and the second switch are N channel MOSFETs. 
         [0016]    In one embodiment of the present invention, the switch circuit includes a diode and a third switch, wherein the anode of the diode is connected to an terminal of the auxiliary winding; the third switch is connected between the cathode of the diode and the second switch; when the terminal voltage of the auxiliary winding is a forward voltage, the diode is in an on state, and the third switch is in an off state, the second switch is in an on state; and when the terminal voltage of the auxiliary winding is a reverse voltage, the diode is in an off state, and the third switch is in an on state, the second switch is in an off state. 
         [0017]    In one embodiment of the present invention, the third switch is a transistor, and the emitter of the third switch is connected to the cathode of the diode through a resistor and connected to the gate of the second switch through another resistor; the base of the third switch is connected between the anode of the diode and an terminal of the auxiliary winding through a resistor; the collector of the third switch is connected between the other terminal of the auxiliary winding and the source of the second switch. 
         [0018]    In one embodiment of the present invention, when the pulse driving signal received by the first switch is in a high electric potential, the first switch is in an on state, the first winding is in an energy-storing state, the voltage applied to the terminals of the auxiliary winding is forward voltage; when the pulse driving signal received by the first switch is in a low electric potential, the first switch is in an off state, a terminal voltage of the first winding is a reverse voltage, and the terminal voltage of the auxiliary winding is a reverse voltage. 
         [0019]    In one embodiment of the present invention, the dotted terminal of the first winding is connected to the input voltage source and the non-dotted terminal thereof is connected to the source of the first switch; the dotted terminal of the second winding is connected to the source of the first switch; the dotted terminal of the auxiliary winding is connected to the non-dotted terminal of the second winding and the collector of the third switch, and the non-dotted terminal of the auxiliary winding is connected to the base of the third switch. 
         [0020]    The present invention is to use the coupling of the auxiliary winding and the second winding to control the action of rectifying switch with a switch circuit. The present invention implements a self-driven synchronous rectification that replaces conventional diode rectification technology, enhances operation efficiency and lowers power-consumption. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a circuit diagram of a boost circuit for driving a backlight module of a liquid crystal display device in accordance with the prior art; 
           [0022]      FIG. 2  is a circuit diagram of a preferred embodiment of a self-driven synchronous rectification boost converter having high step-up ratio in accordance with the present invention; and 
           [0023]      FIG. 3  is a wave diagram relative to voltage and current according to a preferred embodiment of a self-driven synchronous rectification boost converter having high step-up ratio of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]    The foregoing objects, features and advantages adopted by the present invention can be best understood by referring to the following detailed description of the preferred embodiments and the accompanying drawings. Furthermore, the directional terms described in the present invention, such as upper, lower, front, rear, left, right, inner, outer, side and etc., are only directions referring to the accompanying drawings, so that the used directional terms are used to describe and understand the present invention, but the present invention is not limited thereto. 
         [0025]    With reference to  FIG. 2 ,  FIG. 2  is a circuit diagram of a preferred embodiment of a self-driven synchronous rectification boost converter having high step-up ratio in accordance with the present invention. The self-driven synchronous rectification boost converter having high step-up ratio mainly comprises a first switch  100 , a first winding  110 , a second winding  111 , an auxiliary winding  112 , a switch circuit  120  and a second switch  102 . 
         [0026]    The first switch  100  is used to receive a pulse driving signal Vg 1  having high and low electric potentials, and is thereby driven by the pulse driving signal to be repeatedly switched on and off. The pulse driving signal Vg 1  is shown in  FIG. 3 , the first switch  100  is switched on in high electric potential and switched off in low electric potential, therefore the first switch has a switching period T, a conducting time Ton, and a duty ratio D=Ton/T. In this embodiment, the first switch is an N-channel MOSFET. 
         [0027]    The first winding  110  is connected between an input voltage source V 1  and the first switch  100 , wherein the dotted terminal thereof is connected to the input voltage source V 1 , and the non-dotted terminal thereof is connected to the drain of the first switch  100 . The first winding  110  stores energy when the first switch  100  is switched on, and the electric potential on the dotted terminal is higher than the electric potential on the non-dotted terminal in the meantime. Besides, when the first switch  100  is switched off, the terminals of the first winding  110  inducts a reverse voltage, and in the meantime the electric potential on the non-dotted terminal is higher than the dotted terminal. In this embodiment, when the first switch  100  is switched off, a terminal voltage on the drain thereof  100  is V 1 /(1−D), and the reverse voltage on the terminals of the first winding  110  is V 1  (1−D)−V 1 =V 1 D/(1−D). 
         [0028]    The second winding  111  is connected to the first winding  110 , wherein the dotted terminal of the second winding  111  is connected to the source of the first switch  100 . In this embodiment, the winding ratio of the second winding  111  to the first winding  110  is N:1. When the first winding  110  is in energy-storing state, the electric potential on the dotted terminal of the second winding  111  is higher than the electric potential on the non-dotted terminal thereof; when the first winding  110  is inducting a reverse voltage of V 1 D/(1−D), the electric potential on the non-dotted terminal of the second winding  111  is higher than the electric potential on the dotted terminal thereof, and a terminal voltage thereof is N*V 1 D/(1−D). 
         [0029]    The auxiliary winding  112  is connected to the second winding  111 , wherein the dotted terminal of the auxiliary winding  112  is connected to the non-dotted terminal of the second winding  111 . In this embodiment, the winding ratio of the auxiliary winding  112  to the second winding  111  is M:N. When the first winding  110  is in energy-storing state, the electric potential of the auxiliary winding  112  is higher than the electric potential of the non-dotted terminal thereof; when the first winding  110  is inducting a reverse voltage of V 1 D/(1−D), the electric potential on the non-dotted terminal of the auxiliary winding  112  is higher than the electric potential on the dotted terminal thereof, and a terminal voltage thereof is M*V 1 D/(1−D). 
         [0030]    The switch circuit  120  is connected to the auxiliary winding  112  and outputs a control signal according to the change of the terminal voltage of the auxiliary winding  112 . In this embodiment, the switch circuit  120  includes a diode  104  and a third switch  103 . In this embodiment, the anode of the diode  104  is connected to the non-dotted terminal of the auxiliary winding  112 . The third switch  103  is connected to the cathode of the diode  104 . In this embodiment, when the terminal voltage of the auxiliary winding  112  is a forward voltage, the diode  104  is in an on state and the third switch  103  is in an off state; when the terminal voltage of the auxiliary winding  112  is a reverse voltage, the diode  104  is in an off state and the third switch  103  is in an on state. The third switch  103  is preferably a transistor, wherein the emitter thereof is connected to the cathode of the diode  104  via a resistor, the base thereof is connected between the anode of the diode  104  and the non-dotted terminal of the auxiliary winding  112  via another resistor; and the collector thereof is connected to the dotted terminal of the auxiliary winding  112 . 
         [0031]    The second switch  102  is connected to the switch circuit  120  and receives the control signal and is switched on or off according to the control signal. When the third switch  103  is in an off state, the second switch  102  is in an on state; when the third switch  103  is in an on state, the second switch  102  is in an off state. In more details, the second switch  102  is an N-channel MOSFET, the gate thereof is connected to the emitter of the third switch  103  via a resistor; the source thereof is connected to the collector of the third switch  103 ; and the drain thereof is connected to an output capacitor  105 . 
         [0032]    When the pulse driving signal Vg 1  is in high electric potential, the first switch  100  is in an on state, the first winding  110  is in an energy-storing state. With reference to  FIG. 3 , the current IL through the first winding  110  is linearly increasing by a slope of V 1 /L (L is the inductor value of the first winding  110 ), the terminal voltage of the auxiliary winding  112  is then a forward voltage, and the diode  104  is in an off state, and the third switch  103  is in an on state. Since the gate of the second switch  102  is connected to the source of the third switch  103 , the second switch  102  is thereby in an off state. 
         [0033]    When the pulse driving signal Vg 1  is in low electric potential, the first switch  100  is in an off state, the terminal voltage of the first winding  110  is a reverse voltage, the terminal voltage of the auxiliary winding  112  is a reverse voltage, and the diode  104  is in an on state, and the third switch is in an off state, the second switch  102  is switched on since the voltage applied to the gate of the second switch  102  is higher than the voltage applied to the source thereof, so as to achieve synchronous rectification. With reference to  FIG. 3 , a wave form of a signal Vg 2  that drives the second switch  102  is opposite to the wave form of the pulse driving signal in phase. 
         [0034]    With the foregoing description, the present invention utilizes the auxiliary winding  112  to synchronously induct the voltage variation of the second winding  111  in the front stage that changes between forward and reverse voltages and then to cooperate with the diode  104  and the third switch  103  to control the second switch  102  to be switched on and off, so as to achieve self-driven synchronous rectification. When applying to a large-sized backlight driving circuit, since the load has a large amount of parallel-connections and has a large output current, the present invention uses a MOSFET, the second switch, to replace conventional diode on rectification, is able to enhance working efficiency and lowers power-consumption. Besides, self-driven synchronous rectification does not require a floating ground isolation, and thereby has lower cost. 
         [0035]    The present invention has been described with a preferred embodiment thereof and it is understood that many changes and modifications to the described embodiment can be carried out without departing from the scope and the spirit of the invention that is intended to be limited only by the appended claims.