High efficiency half-bridge dc/dc convertor

Abstract

In the DC/DC converter, a switching part has first and second switches serially connected from a power supply to a ground. The first and second switches switch on/off in response to first and second switching signals having a fixed frequency. The first switching signal has a phase level that does not overlap a corresponding phase level of the second switching signal. A transformer transforms a voltage applied to a first winding into a second winding in response to switching operation of the switching part, and resonates by an inductor and a capacitor of the first winding. Also, a rectifier includes a rectifying diode for rectifying the voltage from the transformer into a direct voltage. A feedback circuit detects the voltage outputted via the rectifier. Additionally, a controller controls pulse width of the first and second switching signals in a PWM mode according to the voltage detected by the feedback circuit.

Claims

1 . A high efficiency half-bridge DC/DC converter comprising: a switching part having first and second switches serially connected from a power supply to a ground, the first and second switches switching on/off in response to first and second switching signals having a fixed frequency, the first switching signal having a phase level that does not overlap a corresponding phase level of the second switching signal; a transformer for transforming a voltage applied to a first winding into a second winding in response to switching operation of the switching part, and resonating by an inductor and a capacitor of the first winding; a rectifier including a rectifying diode for rectifying the voltage from the transformer into a direct voltage; a feedback circuit for detecting the voltage outputted via the rectifier; and a controller for controlling pulse width of the first and second switching signals in a pulse width modulation mode according to the voltage detected by the feedback circuit. 2 . The high efficiency half-bridge DC/DC converter according to claim 1 , wherein the controller sequentially controls the pulse width of the first and second switching signals, in a first operation mode, by stabilizing switching on/off state of the first and second switches and starting current to flow forwardly to charge the capacitor, in a second operation mode, by switching on/off the first and second switches so that current begins to flow inversely and gradually decreases in the second switch to completely charge the capacitor, a third operation mode, by stabilizing the switching on/off state of the first and second switches and starting to discharge the charged capacitor so that current flows forwardly in the second switch, and in a fourth operation mode, by switching on/off the first and second switches to completely discharge the capacitor. 3 . The high efficiency half-bridge DC/DC converter according to claim 2 , wherein the first switch is in a zero voltage state while current flows inversely through a body diode at off state, and switches on from the zero voltage state. 4 . The high efficiency half-bridge DC/DC converter according to claim 2 , wherein the second switch is in a zero voltage state when current flows inversely through the body diode at off state, and switches on from the zero voltage state. 5 . The high efficiency half-bridge DC/DC converter according to claim 2 , wherein current flowing in the rectifying diode is synchronized with resonance of the transformer so that the rectifying diode in the rectifier executes zero-current switching. 6 . A method for controlling a high efficiency half-bridge DC/DC converter, which includes a switching part having first and second switches serially connected from a power supply to a ground, a transformer for transforming a voltage applied to a first winding into a second winding in response to switching operation of the switching part, and resonating by an inductor and a capacitor of the first winding, a rectifier having a rectifying diode for rectifying the voltage from the transformer into a direct voltage, and a controller for controlling pulse width of the first and second switching signals having a fixed frequency in a pulse width modulation mode, the method executing: a first operation mode of stabilizing switching on/off state of the first and second switches and starting current to flow forwardly to charge the capacitor; a second operation mode of switching on/off the first and second switches so that current begins to flow inversely and gradually decreases in the second switch to completely charge the capacitor and switching the second switch on from a zero voltage state; a third operation mode of stabilizing the switching on/off state of the first and second switches and starting to discharge the charged capacitor so that current flows forwardly in the second switch; and a fourth operation mode of switching on/off the first and second switches to completely discharge the capacitor and switching the first switch on from the zero voltage state while current flows inversely in the first switch so that current flowing inversely in the first switch decreases, wherein the first, second, third and fourth operation modes are executed consecutively and cyclically.
CLAIM OF PRIORITY [0001] This application claims the benefit of Korean Patent Application Nos. 2005-61292 filed on Jul. 7, 2005 and 2006-53634 filed on Jun. 14, 2006 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to a high-efficiency DC/DC converter for use in a power supply of displays such as PDP or LCD, and more particularly, to a high-efficiency half-bridge DC/DC converter which can operate with a fixed switching frequency, a Pulse Width Modulation (PWM) mode and current resonance in order to ensure high efficiency in the entire range from a minimum load to a maximum load when applied to a power supply such as an SMPS for PDP having big load variations, and to reduce switching stress of a rectifying diode. [0004] 2. Description of the Related Art [0005] In general, a Switching Mode Power Supply (SMPS) is a power supply device for converting a direct voltage into a square wave voltage by utilizing a semiconductor device such as a power Metal Oxide Semiconductor Field Effect Transistor (MOSFET) as a switch and then supplying a direct output voltage converted via a filter. [0006] Such an SMPS controls current flow via a switching processor of the semiconductor device. Accordingly, the SMPS, as a stabilized power supply device, is more efficient, durable than a conventional linear power supply device, advantageous for smaller size and lighter weight. [0007] An asymmetric half-bridge DC/DC converter included in the conventional power supply device will be explained with reference to FIG. 1 . [0008] FIG. 1 illustrates the conventional asymmetric half-bridge DC/DC converter. [0009] The conventional asymmetric half-bridge (AHB) DC/DC converter of FIG. 1 is an asymmetric fixed frequency pulse width modulation converter. The AHB DC/DC converter includes a switching controller 21 , a switching part 22 , a transformer 23 , a rectifier 24 and a feedback circuit 25 . The switching controller 21 provides asymmetric first and second switching signals SSW 1 and SSW 2 having a fixed frequency. Here, a high level of the first switching signal SSW 1 does not overlap that of the second switching signal SSW 2 . Likewise, a low level of the first switching signal SSW 1 does not overlap that of the second switching signal SSW 2 . The switching part 22 has first and second switches Q 1 and Q 2 serially connected from a power supply Vin to a ground. The first switch Q 1 switches on/off in response to the first switching signal SSW 1 , and the second switch Q 2 switches on/off in response to the second switching signal SSW 2 . The transformer 23 transforms a voltage applied to a first winding into a second winding in response to switching operation of the switching part 22 . The rectifier 24 rectifies and smoothes the voltage from the transformer 23 . Also, the feedback circuit 25 detects the voltage outputted via the rectifier 24 and the output voltage to the switching controller 21 , thereby maintaining it at a predetermined level. [0010] This conventional asymmetric half-bridge DC/DC converter problematically suffers stress in a diode of the rectifier, which will be explained with reference to FIG. 2 . [0011] FIG. 2 is a waveform diagram illustrating diode current and voltage of the asymmetric half-bridge DC/DC converter of FIG. 1 . As shown in FIG. 2 , a first diode D 1 of the rectifier is turned on when current is not zero. Meanwhile, a second diode D 2 of the rectifier is turned off when current is not zero. At this time, the first diode D 1 has a high level of voltage VD 1 , generating stress in the first and second diodes D 1 and D 2 of the rectifier and thus undermining efficiency. [0012] FIG. 3 is a configuration view illustrating a conventional resonant DC/DC converter. [0013] The conventional resonant DC/DC converter as shown in FIG. 3 is a symmetric fixed duty ratio frequency modulation converter. The conventional resonant DC/DC converter includes a switching controller 31 , a switching part 32 , a transformer 33 , a rectifier 4 and a feedback circuit 35 . The switching controller 31 provides symmetrical first and second switching signals SSW 1 and SSW 2 having a fixed frequency. Here, a high level of the first switching signal SSW 1 does not overlap that of the second switching signal SSW 2 . Likewise, a low level of the first switching signal SSW 1 does not overlap that of the second switching signal SSW 2 . The switching part 32 has first and second switches Q 1 and Q 2 connected from a power supply Vin to a ground. The first switch Q 1 switches on/off in response to the first switching signal SSW 1 and the second switch Q 2 switches on/off in response to the second switching signal SSW 2 . The transformer 23 transforms a voltage applied to a first winding into a second winding in response to switching operation of the switching part 32 and resonates by inductors Lr and Lm and a capacitor Cr of the first winding. The rectifier 34 rectifies and smoothes the voltage from the transformer 33 . Also, the feedback circuit 35 detects the voltage outputted via the rectifier 34 and provides the output voltage to the switching controller 31 , thereby maintaining it at a predetermined level. [0014] In such a conductor, inductance of the inductors Lr and Lm and capacitance of the capacitor Cr of the first winding, which constitute the transformer, resonate each other. Then if a switching signal provided to the second switch Q 2 turns to a low level, the second switch Q 2 is turned off. At this time, current flows to the transformer via the first switch Q 1 until the second switch Q 2 is turned on. [0015] However, the conventional variable frequency symmetric resonant converter, when applied to a power supply such as the SMPS for PDP having big load variations, experiences increase in frequency at a minimum load, which however excessively shortens switching-on time thereof. Therefore, the conventional variable frequency symmetric resonant converter switches off before current flows enough to excite circulating current of a resonance tank. Accordingly, energy from a primary coil of the transformer is hardly transferred to a secondary coil thereof, thereby degrading efficiency. SUMMARY OF THE INVENTION [0016] The present invention has been made to solve the foregoing problems of the prior art and therefore an object according to certain embodiments of the present invention is to provide a high-efficiency half-bridge DC/DC converter which can operate with a fixed switching frequency, a PWM mode and current resonance in order to ensure high efficiency in the entire range from a minimum load to a maximum load when applied to a power supply such as an SMPS for PDP having big load variations and to reduce switching stress of a rectifying diode. [0017] According to an aspect of the invention for realizing the object, there is provided a high efficiency half-bridge DC/DC converter comprising: a switching part having first and second switches serially connected from a power supply to a ground, the first and second switches switching on/off in response to first and second switching signals having a fixed frequency, the first switching signal having a phase level that does not overlap a corresponding phase level of the second switching signal; a transformer for transforming a voltage applied to a first winding into a second winding in response to switching operation of the switching part, and resonating by an inductor and a capacitor of the first winding; a rectifier including a rectifying diode for rectifying the voltage from the transformer into a direct voltage; a feedback circuit for detecting the voltage outputted via the rectifier; and a controller for controlling pulse width of the first and second switching signals in a pulse width modulation mode according to the voltage detected by the feedback circuit. [0018] The controller sequentially controls the pulse width of the first and second switching signals, in a first operation mode, by stabilizing switching on/off state of the first and second switches and starting current to flow forwardly to charge the capacitor, in a second operation mode, by switching on/off the first and second switches so that current begins to flow inversely and gradually decreases in the second switch to completely charge the capacitor, a third operation mode, by stabilizing the switching on/off state of the first and second switches and starting to discharge the charged capacitor so that current flows forwardly in the second switch, and in a fourth operation mode, by switching on/off the first and second switches to completely discharge the capacitor. [0019] The first switch is in a zero voltage state while current flows inversely through a body diode at off state, and switches on from the zero voltage state. [0020] The second switch is in a zero voltage state when current flows inversely through the body diode at off state, and switches on from the zero voltage state. [0021] Current flowing in the rectifying diode is synchronized with resonance of the transformer so that the rectifying diode in the rectifier executes zero-current switching. [0022] According to another aspect of the invention for realizing the object, there is provided a method for controlling a high efficiency half-bridge DC/DC converter, which includes a switching part having first and second switches serially connected from a power supply to a ground, a transformer for transforming a voltage applied to a first winding into a second winding in response to switching operation of the switching part, and resonating by an inductor and a capacitor of the first winding, a rectifier having a rectifying diode for rectifying the voltage from the transformer into a direct voltage, a controller for controlling pulse width of the first and second switching signals having a fixed frequency in a pulse width modulation mode, the method executing: a first operation mode of stabilizing switching on/off state of the first and second switches and starting current to flow forwardly to charge the capacitor; a second operation mode of switching on/off the first and second switches so that current begins to flow inversely and gradually decreases in the second switch to completely charge the capacitor and switching the second switch on from a zero voltage state; a third operation mode of stabilizing the switching on/off state of the first and second switches and starting to discharge the charged capacitor so that current flows forwardly in the second switch; and a fourth operation mode of switching on/off the first and second switches to completely discharge the capacitor and switching the first switch on from the zero voltage state while current flows inversely in the first switch so that current flowing inversely in the first switch decreases, wherein the first, second, third and fourth operation modes are executed consecutively and cyclically. BRIEF DESCRIPTION OF THE DRAWINGS [0023] The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: [0024] FIG. 1 is a configuration view illustrating a conventional asymmetric half-bridge DC/DC converter; [0025] FIG. 2 is a waveform diagram illustrating current and voltage of the asymmetric half-bridge DC/DC converter of FIG. 2 ; [0026] FIG. 3 is a configuration view illustrating a conventional resonant DC/DC converter; [0027] FIG. 4 is a configuration view illustrating a high-efficiency DC/DC converter according to the invention; [0028] FIG. 5 is a waveform diagram illustrating major signals in operating a fixed frequency of the high efficiency DC/DC converter according to the invention; [0029] FIG. 6 is a waveform diagram illustrating diode current of the resonant DC/DC converter of FIGS. 4 and 5 ; [0030] FIG. 7 a is a waveform diagram illustrating major signals of the conventional resonant DC/DC converter at a minimum load, and FIG. 7 b is a waveform diagram illustrating major signals of the converter of the invention at a minimum load; [0031] FIGS. 8 ( a ) to ( d ) are circuit diagrams corresponding to the switching operation of FIG. 4 ; [0032] FIGS. 9 ( a ) to ( b ) are graphs illustrating efficiency of the conventional resonant DC/DC converter of FIG. 3 and a DC/DC converter of the invention, respectively; and [0033] FIG. 10 is a flow chart illustrating a method for controlling a high efficiency half-bridge DC/DC converter of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT [0034] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, in which the same reference numerals are used throughout the different drawings to designate the same or similar components. [0035] FIG. 4 is a configuration view illustrating a half-bridge DC/DC converter according to the invention. [0036] Referring to FIG. 4 , the high-efficiency half-bridge DC/DC converter of the invention includes a controller 100 , a switching part 200 , a transformer 300 , a rectifier 400 and a feedback circuit 500 . [0037] The controller 100 provides asymmetric first and second switching signals SSW 1 , SSW 2 having variable pulse width. Here, a high level of the first switching signal SSW 1 does not overlap that of the second switching signal SSW 2 . Likewise, a low level of the first switching signal SSW 1 does not overlap that of the second switching signal SSW 2 . The controller 100 varies pulse width of the first and second switching signals SSW 1 , SSW 2 in the PWM mode depending on size of an output voltage. [0038] The switching part 200 includes first and second switches Q 1 and Q 2 serially connected from a power supply Vin to a ground. The first switch SSW 1 switches on/off in response to a first switching signal SSW 1 and the second switch SSW 2 switches on/off in response to a second switching signal SSW 2 . [0039] The transformer 300 transforms a voltage applied to a first winding into a second winding in response to switching operation of the switching part 200 . In addition, current resonates by inductance from inductors Lr and Lm and capacitance from a capacitor Cr of the first winding. [0040] The rectifier 400 rectifies the voltage from the transformer 300 into a direct voltage. [0041] In order to maintain the output voltage at a predetermined level, the feedback circuit 500 detects the voltage outputted via the rectifier 400 and provides it to the controller 100 . [0042] Furthermore, the controller 100 executes first to fourth operation modes OM 1 to OM 4 consecutively and cyclically according to levels of the first and second switching signals SSW 1 , SSW 2 . In the first operation mode OM 1 , switching on/off state of the first and second switches Q 1 , Q 2 are stabilized and current starts to flow forwardly to charge the capacitor Cr. In the second operation mode OM 2 , the first and second switches Q 1 , Q 2 are switched on/off so that current begins to flow inversely and gradually decreases in the second switch Q 2 to completely charge the capacitor Cr. In the third operation mode OM 3 , the switching on/off state of the first and second switches are stabilized and the charged capacitor Cr starts to discharge so that current flows forwardly in the second switch Q 2 . Also, in the fourth operation mode, the first and second switches Q 1 and Q 2 are switched on/off to completely discharge the capacitor Cr. [0043] The first switch Q 1 is in a zero voltage state while current flows inversely through a body diode at off state and switches on from the zero voltage state. The second switch Q 2 is in a zero voltage state while current flows inversely through the body diode at off state and switches on from the zero voltage state. [0044] In this fashion, the first and second switches Q 1 , Q 2 execute zero voltage switching (ZVS). [0045] In addition, current flowing in the rectifying diode of the rectifier 400 is synchronized with resonance of the transformer so that the rectifying diode in the rectifier 400 executes zero-current switching. Such zero current switching alleviates switching stress of the diode of the rectifier 400 . [0046] FIG. 5 is a waveform diagram illustrating major signals in operating a fixed frequency of a high efficiency half-bridge DC/DC converter of the invention. FIG. 5 plots waveforms of major signals at a maximum load. [0047] In FIG. 5 , P 1 denotes a range where the first and second switches Q 1 and Q 2 are turned on from off or turned off from on. [0048] FIG. 6 is a waveform diagram illustrating current of the resonant DC/DC converter of FIGS. 4 and 5 . In FIG. 6 , VD 1 is a voltage charged on a first diode D 1 of the rectifier, ID 1 is current flowing in the first diode D 1 of the rectifier and ID 2 is current flowing in a second diode D 2 of the rectifier. [0049] FIGS. 7 a and 7 b are waveform diagrams illustrating major signals of the conventional DC/DC converter of FIG. 3 and the DC/DC converter of the invention, respectively, at a minimum load. FIG. 7 a plots waveforms of major signals of the conventional converter at a minimum load (Min load) in operating a variable frequency. FIG. 7 b plots waveforms of major signals of the DC/DC converter of the invention at a minimum load (Min load) in operating the fixed frequency. [0050] In FIG. 7 b , P 2 and P 3 exhibit energy transferred to a secondary coil of the transformer, which is identical to that transferred to a primary coil thereof, at a minimum load. In FIG. 7 a , PO 1 and PO 2 indicate little energy transferred to the secondary coil of the transformer at a minimum load. [0051] In FIG. 5 and FIG. 7 b , the first switching signal SSW 1 and the second switching signal SSW 2 each have a fixed frequency. The first and second switching signals SSW 1 and SSW 2 are inversely phased, thereby exhibiting different pulse width. Here, a high level of the first switching signal SSW 1 does not overlap that of the second switching signal SSW 2 . Likewise, a low level of the first switching signal SSW 1 does not overlap that of the second switching signal SSW 2 . VDS 1 is an interstage voltage between a source and a drain of the first switch Q 1 for switching on/off in response to the first switching signal SSW 1 . The VDS 2 is an interstage voltage between a source and a drain of the second switch Q 2 for switching on/off in response to the second switching signal SSW 2 . IQ 1 is current flowing through the first switch Q 1 and IQ 2 is current flowing through the second switch Q 2 . Also, ID 1 to ID 4 are current flowing through respective bridge diodes D 1 to D 4 of the rectifier 400 . [0052] FIGS. 8 ( a ) to ( d ) are circuit diagrams corresponding to switching operation of FIG. 4 . [0053] FIG. 8 ( a ) is a current flow when a converter of the invention is in a first operation mode. FIG. 8 ( b ) is a current flow when the converter of the invention is in a second operation mode. FIG. 8 ( c ) is a current flow when the converter of the invention is in a third operation mode. Also, FIG. 8 ( d ) is a current flow when the converter of the invention is in a fourth operation mode. [0054] FIGS. 9 ( a ) and ( b ) are graphs illustrating efficiency properties of a conventional resonant DC/DC converter and a DC/DC converter of the invention, respectively. [0055] FIG. 9 ( a ) is a graph illustrating efficiency properties of the conventional converter and FIG. 9 ( b ) is a graph illustrating efficiency properties of the converter of the invention. [0056] FIG. 10 is a flowchart illustrating a method for controlling a high-efficiency half-bridge DC/DC converter of the invention. [0057] In FIG. 10 , the first mode is executed in S 910 , in which switching on/off state of the first and second switches are stabilized and current starts to flow forwardly to charge the capacitor. [0058] The second mode is executed in S 920 , in which the first and second switches are switched on/off so that current begins to flow inversely and gradually decreases in the second switch to completely charge the capacitor and the second switch is switched on from a zero voltage state. [0059] The third mode is executed in S 930 , in which the switching on/off state of the first and second switches are stabilized and the charged capacitor starts to discharge so that current flows forwardly in the second switch. [0060] Then, the fourth mode is executed in S 940 , in which the first and second switches are switched on/off to completely discharge the capacitor and the first switch is switched on from the zero voltage state while current flows inversely in the first switch so that current flowing inversely in the first switch decreases. [0061] A detailed explanation will be given hereunder about operations and effects of the invention with reference to the accompanying drawings. [0062] The invention will be explained with reference to FIGS. 4 to 10 . [0063] In FIG. 4 , a controller 100 of the invention provides asymmetric first and second switching signals SSW 1 and SSW 2 having a fixed frequency. Here, a high level of the first switching signal SSW 1 does not overlap that of the second switching signal SSW 2 . Likewise, a low level of the first switching signal SSW 1 does not overlap that of the second switching signal SSW 2 . Pulse width of the first and second switching signals SSW 1 and SSW 2 is controlled in a PWM mode and can be varied in the PWM mode depending on size of an output voltage. A first switch Q 1 of a switching part 200 switches on/off in response to the first switching signal SSW 1 and a second switch Q 2 of the switching part 200 switches on/off in response to the second switching signal SSW 2 . [0064] Then, a transformer 300 is synchronized with switching operation of the switching part 200 to resonate. Also the transformer 300 transforms a voltage applied to a first winding into a second winding at a winding ratio. A rectifier 400 of the invention rectifies the voltage from the transformer 300 into a direct voltage. In addition, a feedback circuit 500 of the invention detects the voltage outputted via the rectifier and provides the detected voltage to the controller 100 , thereby maintaining it at a predetermined level. [0065] At this time, the controller 100 varies pulse width of the first and second switching signals SSW 1 and SSW 2 in the PWM mode based on the voltage detected by the feedback circuit 500 and controls the voltage outputted from the rectifier 400 to stay at a predetermined level. [0066] In this high-efficiency half-bridge DC/DC converter of the invention, the switching controller 100 , as just described, provides first and second switching signals SSW 1 and SSW 2 having the fixed frequency. Here, a high level of the first switching signal SSW 1 does not overlap that of the second switching signal SSW 2 . Likewise, a low level of the first switching signal SSW 1 does not overlap that of the second switch signal SSW 2 . Also the switching controller 100 provides power Vin to the switching part 200 . The switching controller 100 executes the first to fourth operation modes OM 1 to OM 4 according to levels of the first and second switching signals SW 1 and SW 2 . The first to fourth operation modes will explained hereunder with reference to FIGS. 4 to 10 . [0067] Referring to FIGS. 4 to 10 , in the first operation mode OM 1 , the first and second switching signals SSW 1 and SSW 2 each are stabilized into a high level and a low level, and accordingly, the first and second switches Q 1 and Q 2 are stabilized into an on and off state. [0068] That is, as shown in FIGS. 4 and 5 , if the first and second switching signals SSW 1 and SSW 2 each are stabilized into a high level and a low level, the first switch Q 1 is stabilized into an on state and the second switch Q 2 is stabilized into an off state. Thus current begins to flow forwardly through the first switch Q 1 to charge the capacitor Cr and no current IQ 2 flows through the second switch Q 2 . [0069] As a result, the first switch Q 1 exhibits a low level of a drain-source voltage VDS 1 and the second switch Q 2 exhibits a high level of a drain-source voltage VDS 2 . [0070] An explanation will be given about a first current loop of the transformer in the first operation mode with reference to FIG. 4 and FIG. 8 ( a ). [0071] Referring to FIG. 4 , if the first switch Q 1 is stabilized into an on-state and the second switch Q 2 is stabilized into an off-state, current from a primary coil of the transformer 300 , as shown in FIG. 8 ( a ), flows through the first switch Q 1 , a capacitor Cr and coils Lr, Lm. [0072] Therefore, current from a secondary coil of the transformer 300 flows through the first and fourth diodes D 1 and D 4 of the rectifier 400 as in S 910 of FIG. 10 . [0073] Next, in the second operation mode OM 2 , the first and second switching signals SSW 1 and SSW 2 each transit to a low level and a high level, and the first and second switches Q 1 and Q 2 switch on/off. [0074] That is, as shown in FIGS. 4 and 5 , the first and second switching signals SSW 1 and SSW 2 each transit to a low level and a high level. Then, current flows inversely through a body diode of the second switch Q 2 and the second switch Q 2 is turned on from a zero voltage state to thereby execute zero voltage switching (ZVS). Thus the capacitor Cr is completely charged and the first switch is turned off. [0075] Accordingly, no current IQ 1 flows through the switch Q 1 , and current IQ 2 flowing through the body diode of the second switch Q 2 gradually decreases. Here, the first switch Q 1 has a high level of a drain-source voltage VDS 1 and the second switch Q 2 has a low level of a drain-source voltage VDS 2 . [0076] Furthermore, an explanation will be given about the first current loop of the transformer in the second operation mode with reference to FIGS. 4 and 8 ( b ). [0077] Referring to FIG. 4 , if the first and second switching signals SSW 1 and SSW 2 each transit to a low level and a high level, the first and second switches Q 1 and Q 2 are turned on/off. This eliminates an existing current loop. Also, with the second switch Q 2 turned on, current flowing through the second switch Q 2 , as shown in FIG. 8 ( b ), flows through the second switch Q 2 , the primary coil Lr and Lm of the transformer 300 and the capacitor Cr. [0078] Accordingly, current in the primary coil of the transformer 300 flows through the first and fourth diodes D 1 and D 4 of the rectifier 400 as shown in S 920 of FIG. 10 . [0079] Meanwhile, if the first switch Q 1 is turned off and the second switch Q 2 is stabilized into an on-state, the second operation mode OM 2 proceeds to the third operation mode OM 3 , and rectifying diodes D 1 to D 4 of the rectifier execute zero current switching ZCS by current resonance of the transformer. [0080] Thereafter, in the third operation mode OM 3 , the first and second switching signals SSW 1 and SSW 2 each are stabilized into a low level and a high level, and the first and second switches Q 1 and Q 2 are stabilized into an on/off state. [0081] That is, as shown in FIGS. 4 and 5 , if the first and second switching signals SSW 1 and SSW 2 each are stabilized into a low level and a high level, the first switch Q 1 is stabilized into an off state and the second switch Q 2 is stabilized into an on state. Then, the capacitor Cr starts to discharge. Also, no current IQ 1 flows through the switch Q 1 and current IQ 2 flowing through the second switch Q 2 increases and then decreases. [0082] As a result, the first switch Q 1 exhibits a high level of a drain-source voltage VDS 1 and the second switch Q 2 exhibits a low level of a drain-source voltage VDS 2 . [0083] An explanation will be given hereunder about the first current loop of the transformer in the third operation mode with reference to FIGS. 4 and 8 . [0084] Referring to FIG. 4 , as described above, if the first and second switching signals SSW 1 and SSW 2 each are stabilized into a low level and a high level, the first and second switches Q 1 and Q 2 are stabilized into an off/on state. At this time, current in the primary coil L 1 of the transformer 300 , as described in FIG. 8 ( c ), flows through the second switch Q 2 , the primary coil of the transformer 300 , and the coils Lr and Lm. Also, current in the primary coil of the transformer 300 flows through second and third diodes D 2 and D 3 of the rectifier 400 as in S 930 of FIG. 10 . [0085] In the third operation mode as just described, as shown in FIG. 6 , at a zero current state, the first and fourth diodes D 1 and D 2 of the rectifier 400 are turned off and the second and third diodes D 2 and D 3 of the rectifier 400 are turned on, thereby achieving zero current switching (ZCS). The zero current switching reduces switching stress of the diode of the rectifier 400 . [0086] Also, in the fourth operation mode OM 4 , the first and second switching signals SSW 1 and SSW 2 each transit to a high level and a low level so that the first and second switches Q 1 and Q 2 are turned on/off. [0087] That is, as shown in FIGS. 4 and 5 , if the first and second switching signals SSW 1 and SSW 2 each transit to a high level and a low level, current begins to flow inversely through the body diode of the first switch Q 1 so that the first switch Q 1 is turned on from a zero voltage state, achieving the zero current switching. Thereby, the capacitor Cr completely discharges and then the second switch Q 2 switches off. [0088] Accordingly, current IQ 1 flowing through the body diode of the first switch decreases gradually and no current IQ 2 flows through the second switch Q 2 . Furthermore, the first switch Q 1 has a low level of a drain-source voltage VDS 1 and the second switch Q 2 has a high level of a drain-source voltage VDS 2 . [0089] An explanation will be given hereunder about the first current loop of the transformer in the fourth operation mode with reference to FIGS. 4 and 8 ( d ). [0090] Referring to FIG. 4 , if the first and second switching signals SSW 1 and SSW 2 each transit to a high level and a low level, the first and second switches Q 1 and Q 2 switch on/off. This eliminates an existing current loop. With the first switch Q 1 turned on, current flowing through the first switch Q 1 , as shown in FIG. 8 ( d ), flows through the first switch Q 1 , the capacitor Cr and the coils Lr and Lm. [0091] Therefore, current in the primary coil of the transformer 300 flows through the second and third diodes D 2 , D 3 of the rectifier 400 as in S 940 of FIG. 10 . [0092] Meanwhile, if the second switch Q 2 is stabilized into an off state and the first switch Q 1 is stabilized into an on state, the fourth operation mode OM 4 is again followed by the first operation mode. Then, the rectifying diode of the rectifier achieves the zero current switching (ZCS) by current resonance in the transformer. [0093] As described above, in comparison of FIGS. 7 a and 7 b , the high-bridge DC/DC converter of the invention exhibits higher efficiency that the conventional converter, as noted in Table 1. TABLE 1 Conventional (variable Inventive (fixed frequency resonance) frequency resonance) Efficiency Low (at a minimum load High (at a minimum load ( FIG. 7b )) ( FIG. 7a )) Properties Low efficiency at a low High efficiency at all load loads Application Unsuitable in case of big Suitable for SMPS for PDP load variations with big load variations [0094] Referring to PO 1 and PO 2 of FIG. 7 a , the conventional variable frequency type converter experiences increase in switching frequency at a minimum load, thus excessively shortening switching time. This prevents circulating current from a primary coil of the variable frequency type transformer from being sufficiently transferred to a secondary coil of the transformer, thereby increasing reactive power. When compared with FIG. 7 b , the conventional variable frequency type converter exhibits relatively lower efficiency at a minimum load than the converter of the invention. [0095] In contrast, referring to P 2 and P 3 of FIG. 7 b , the fixed frequency type converter of the invention demonstrates uniform switching time regardless of load. Therefore sufficient switching time is assured even at a minimum load and accordingly, circulating current from the primary coil of the transformer is sufficiently transferred to the secondary coil of the transformer, thereby increasing active power. Given such operation, the converter of the invention shows high efficiency at a minimum load. [0096] The converter of the invention described above operates with high efficiency, especially even at a minimum load. This will be explained hereunder with reference to FIG. 9 . [0097] Referring to FIG. 9 ( a ), the conventional converter operates with less than 90% efficiency at a load of 80 W or less but with 96% or more only at a load of 380 W to 500 W. In contrast, referring to FIG. 9 ( b ), the converter of the invention operates with 96% or more efficiency at a load of 50 W to 500 W. This confirms that the converter of the invention can be suitably used for a sustain voltage part for PDP having big load variations. [0098] According to this disclosure of the invention as described above, a high-efficiency half-bridge DC/DC converter of the invention is applied to a power supply of displays such as PDP or LCD. The converter of the invention employs a fixed switching frequency, a PWM mode, and current resonance. Therefore, when adopted in the power supply such as an SMPS for PDP having big load variations, the converter of the invention ensures high efficiency in the entire range from a minimum load to a maximum load, thereby relieving switching stress of a rectifying diode. [0099] While the present invention has been shown and described in connection with the preferred embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.

Description

Topics

Download Full PDF Version (Non-Commercial Use)

Patent Citations (7)

    Publication numberPublication dateAssigneeTitle
    US-2004090801-A1May 13, 2004Qing Chen, Lee Victor Ke-JiHighly efficient, tightly regulated dc-to-dc converter
    US-5189601-AFebruary 23, 1993Eni Div. Of Astec America, Inc.Half bridge converter with current mode controller
    US-5282123-AJanuary 25, 1994At&T Bell LaboratoriesClamped mode DC-DC converter
    US-5986895-ANovember 16, 1999Astec International LimitedAdaptive pulse width modulated resonant Class-D converter
    US-6320764-B1November 20, 2001Yimin Jiang, Hengchun MaoRegulation circuit for a power converter and method of operation thereof
    US-6392902-B1May 21, 2002Delta Electronics, Inc.Soft-switched full-bridge converter
    US-6442047-B1August 27, 2002Lambda Electronics, Inc.Power conversion apparatus and methods with reduced current and voltage switching

NO-Patent Citations (0)

    Title

Cited By (31)

    Publication numberPublication dateAssigneeTitle
    CN-102783004-ANovember 14, 2012德州仪器公司通过操作模式切换进行的llc软启动
    CN-103168414-AJune 19, 2013松下电器产业株式会社Electric power supply apparatus
    CN-104135154-ANovember 05, 2014浙江大学, 英飞特电子(杭州)股份有限公司Isolated four-element resonance circuit and control method
    US-2007281755-A1December 06, 2007Linear Technology CorporationControlling switching circuits to balance power or current drawn from multiple power supply inputs
    US-2011090197-A1April 21, 2011Yoo-Jin SongPlasma display and driving apparatus thereof
    US-2011139605-A1June 16, 2011Spp Process Technology Systems Uk LimitedIon beam source
    US-2011169426-A1July 14, 2011Sadwick Laurence P, Sackett William BFluorescent Lamp Power Supply
    US-2011299301-A1December 08, 2011Texas Instruments IncorporatedFixed-frequency llc resonant power regulator
    US-2012104984-A1May 03, 2012Krishnan RamuPower factor correction circuits for switched reluctance machines
    US-2013069439-A1March 21, 2013Axel Mertens, Lennart BaruschkaTransformerless cycloconverter
    US-2014334191-A1November 13, 2014Fuji Electric Co., Ltd.Dc-dc conversion device
    US-2014362606-A1December 11, 2014Fuji Electric Co., Ltd.Dc-dc conversion device
    US-2015333801-A1November 19, 2015Murata Manufacturing Co., Ltd.Wireless power supply apparatus
    US-2016175024-A1June 23, 2016Ethicon Endo-Surgery, Inc.High power battery powered rf amplifier topology
    US-8536803-B2September 17, 2013Innosys, IncFluorescent lamp power supply
    US-8704599-B2April 22, 2014Canon Kabushiki KaishaSwitching power supply circuit
    US-8754605-B2June 17, 2014Regal Beloit America, Inc.Power factor correction circuits for switched reluctance machines
    US-8952591-B2February 10, 2015Regal Beloit America, Inc.Rotor lamination shaping for minimum core loss in SRMs
    US-8968535-B2March 03, 2015Spp Process Technology Systems Uk LimitedIon beam source
    US-9048741-B2June 02, 2015Murata Manufacturing Co., Ltd.Switching power supply device
    US-9054567-B2June 09, 2015Regal Beloit America, Inc.High power density SRMs
    US-9106141-B2August 11, 2015Murata Manufacturing Co., Ltd.Switching power supply device
    US-9130467-B2September 08, 2015Murata Manufacturing Co., Ltd.Switching power supply device
    US-9190921-B2November 17, 2015Siemens AktiengesellschaftTransformerless cycloconverter
    US-9312733-B2April 12, 2016Regal Beloit America, Inc.High power density SRM
    US-9350255-B2May 24, 2016Fuji Electric Co., Ltd.DC-DC conversion device including pulse width modulation control
    US-9378888-B2June 28, 2016Murata Manufacturing Co., Ltd.Power transfer system
    US-9660536-B2May 23, 2017Murata Manufacturing Coo., Ltd.Switching power supply device performs power transmission by using resonance phenomenon
    US-9705325-B2July 11, 2017Linear Technology CorporationControlling switching circuits to balance power or current drawn from multiple power supply inputs
    WO-2011084379-A2July 14, 2011Texas Instruments Incorporated, Texas Instruments Japan LimitedDémarrage doux dans un llc par commutation de mode opératoire
    WO-2011084379-A3October 06, 2011Texas Instruments Incorporated, Texas Instruments Japan LimitedDémarrage doux dans un llc par commutation de mode opératoire