Asymmetric power converter and operational method thereof

This application claims the benefit of U.S. Provisional Application No. 62/963,181, filed on Jan. 20, 2020 and entitled “Control method used in asymmetric half bridge LLC topology”, the contents of which are incorporated herein by reference.

1. Field of the Invention

The present invention relates to an asymmetric power converter and an operational method thereof, and particularly to an asymmetric power converter and an operational method thereof that use dual-feedback control to make a ratio of a second output voltage of the asymmetric power converter to a first output voltage of the asymmetric power converter be any real number greater than one.

2. Description of the Prior Art

In the prior art, asymmetric inductor-inductor-capacitor (LLC) power converter is a resonant circuit that can make dual output voltages of a secondary side of the inductor-inductor-capacitor power converter constant through controlling frequencies of two power switch of a primary side of the inductor-inductor-capacitor power converter (regulating frequency) wherein the inductor-inductor-capacitor power converter utilizes zero voltage turning-on corresponding to the two power switches and zero voltage turning-off corresponding to a rectifier diode of the secondary side to control the frequencies of the two power switches.

Because the two power switches are symmetrically conducted, a ratio of the dual output voltages cannot be changed, and each of the dual output voltages needs two secondary windings, resulting in the dual output voltages needing four secondary windings. In addition, because the ratio of the dual output voltages cannot be changed, an additional direct current/direct current control driving module needs to be added for a backlight drive application requiring a larger output voltage range. Therefore, how to improve the above-mentioned shortcomings of the inductor-inductor-capacitor power converter becomes an important issue of a designer of the inductor-inductor-capacitor power converter.

An embodiment of the present invention provides an asymmetric power converter, wherein the asymmetric power converter comprises an upper bridge switch, a lower bridge switch, a primary winding, a first secondary winding, a second secondary winding, and a control circuit. The upper bridge switch and the lower bridge switch are coupled to the primary winding, and the upper bridge switch, the lower bridge switch, and the primary winding are installed in a primary side of the asymmetric power converter. The first secondary winding and the second secondary winding are used for outputting a first output voltage and a second output voltage of a secondary side of the asymmetric power converter respectively, wherein the first secondary winding and the second secondary winding are installed in the secondary side of the asymmetric power converter, and voltage polarity of the first secondary winding is different from voltage polarity of the second secondary winding. The control circuit is used for controlling the lower bridge switch and the upper bridge switch according to the first output voltage and the second output voltage, respectively.

Another embodiment of the present invention provides an operational method of an asymmetric power converter, wherein the asymmetric power converter comprises an upper bridge switch, a lower bridge switch, a primary winding, a first secondary winding, a second secondary winding, and a control circuit. The operational method comprises the control circuit controlling a turning-on time of the lower bridge switch according to a first output voltage; during the turning-on time of the lower bridge switch, the inductor-capacitor resonant tank discharging and transferring energy to the second secondary winding through the primary winding to generate a second output voltage; the control circuit controlling a turning-on time of the upper bridge switch according to the second output voltage; and during the turning-on time of the upper bridge switch, a direct current (DC) voltage transferring energy to the first secondary winding through the primary winding to generate the first output voltage. Voltage polarity of the first secondary winding is different from voltage polarity of the second secondary winding.

The present invention provides an asymmetric power converter and an operational method thereof. The asymmetric power converter and the operational method thereof utilize a dual-feedback control of a control circuit controlling a turning-on time of a lower bridge switch according to a first output voltage and controlling a turning-on time of an upper bridge switch according to a second output voltage to make the asymmetric power converter only need three windings (a primary winding, a first secondary winding and a second secondary winding), a ratio of the second output voltage to the first output voltage be any real number greater than one, and the turning-on time of the upper bridge switch be not equal to the turning-on time of the lower bridge switch. Therefore, compared to the prior art, because the ratio of the second output voltage to the first output voltage can be any real number greater than one, the asymmetric power converter is very suitable for a backlight drive application such as a television requiring a larger output voltage range, and because the asymmetric power converter only needs the three windings, cost of the asymmetric power converter is lower.

These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

FIG. 1 is a diagram illustrating an asymmetric power converter according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating operation of an inductor-capacitor resonant tank, a primary winding, a first secondary winding, and a second secondary winding when an upper bridge switch is turned on.

FIG. 3 is a diagram illustrating operation of the inductor-capacitor resonant tank, the primary winding, the first secondary winding, and the second secondary winding when a lower bridge switch is turned on.

FIG. 4 is a diagram illustrating a dead time existing between a turning-on time of the upper bridge switch and a turning-on time of the lower bridge switch.

FIG. 5 is a flowchart illustrating an operational method of an asymmetric power converter according to a second embodiment of the present invention.

Please refer to FIG. 1 . FIG. 1 is a diagram illustrating an asymmetric power converter 100 according to a first embodiment of the present invention, wherein the asymmetric power converter 100 includes an upper bridge switch 102 , a lower bridge switch 104 , an inductor-capacitor resonant tank (LC resonant tank) 106 , a primary winding 108 , a first secondary winding 110 , a second secondary winding 112 , a control circuit 114 , a first isolation component 115 , a second isolation component 116 , and a constant current control circuit 118 , and the asymmetric power converter 100 is an inductor-inductor-capacitor power converter (LLC power converter). As shown in FIG. 1 , the upper bridge switch 102 and the lower bridge switch 104 are coupled to the primary winding 108 through the inductor-capacitor resonant tank 106 , and the upper bridge switch 102 , the lower bridge switch 104 , the inductor-capacitor resonant tank 106 , and the primary winding 108 are installed in a primary side PRI of the asymmetric power converter 100 , and the first secondary winding 110 and the second secondary winding 112 are installed in a secondary side SEC of the asymmetric power converter 100 . In addition, as shown in FIG. 1 , the first secondary winding 110 is used for outputting a first output voltage VO 1 of the secondary side SEC of the asymmetric power converter 100 , the second secondary winding 112 is used for outputting a second output voltage VO 2 of the secondary side SEC of the asymmetric power converter 100 , and the control circuit 114 controls a turning-on time TON 2 of the lower bridge switch 104 according to the first output voltage VO 1 and controls a turning-on time TON 1 of the upper bridge switch 102 according to the second output voltage VO 2 , wherein the second output voltage VO 2 is greater than the first output voltage VO 1 , and when the second output voltage VO 2 is applied to a backlight drive application of light-emitting diodes of a television, the control circuit 114 further combines the constant current control circuit 118 to control the turning-on time TON 1 of the upper bridge switch 102 . In addition, the control circuit 114 is installed in the primary side PRI of the asymmetric power converter 100 , both the first isolation component 115 and the second isolation component 116 are used for isolating the primary side PRI of the asymmetric power converter 100 from the secondary side SEC of the asymmetric power converter 100 , and the first isolation component 115 and the second isolation component 116 are photo couplers. However, the present invention is not limited to the first isolation component 115 and the second isolation component 116 being photo couplers, that is, the first isolation component 115 and the second isolation 116 can be other component for isolating the primary side PRI of the asymmetric power converter 100 from the secondary side SEC of the asymmetric power converter 100 . In addition, a ground of the primary side PRI of the asymmetric power converter 100 and a ground of the secondary side SEC of the asymmetric power converter 100 can be the same or different. In addition, the asymmetric power converter 100 further comprises a power factor corrector circuit 119 coupled between the control circuit 114 and a bridge rectifier 120 , wherein the power factor corrector circuit 119 is used for improving a power factor of the asymmetric power converter 100 to make the power factor of the asymmetric power converter 100 close to one and suppressing a harmonic wave of a first output current IO 1 and a second output current IO 2 of the asymmetric power converter 100 .

Please refer to FIGS. 2, 3 . FIG. 2 is a diagram illustrating operation of the inductor-capacitor resonant tank 106 , the primary winding 108 , the first secondary winding 110 , and the second secondary winding 112 when the upper bridge switch 102 is turned on, and FIG. 3 is a diagram illustrating operation of the inductor-capacitor resonant tank 106 , the primary winding 108 , the first secondary winding 110 , and the second secondary winding 112 when the lower bridge switch 104 is turned on. As shown in FIG. 2 , when the upper bridge switch 102 is turned on (the lower bridge switch 104 is turned off), a primary side current IPRI 1 flows through the upper bridge switch 102 , an inductor Lr of the inductor-capacitor resonant tank 106 , and the primary winding 108 to charge a capacitor Cr of the inductor-capacitor resonant tank 106 . At this time, because voltage polarity of the first secondary winding 110 is different from voltage polarity of the secondary winding 112 , only the first output current IO 1 flows through the first secondary winding 110 , wherein it can be known that the voltage polarity of the first secondary winding 110 is different from the voltage polarity of the secondary winding 112 through a position of a dot of the first secondary winding 110 and a position of a dot of the second secondary winding 112 . That is to say, the first output voltage VO 1 can be generated by a DC (direct current) voltage VIN, the inductor Lr, the primary winding 108 , and the first secondary winding 110 , wherein the DC voltage VIN is generated by an input voltage VAC (alternating current voltage) being rectified by the bridge rectifier 120 . Because the primary side current IPRI 1 charges the capacitor Cr, if the turning-on time TON 1 of the upper bridge switch 102 is longer, it means that when the lower bridge switch 104 is turned on (the upper bridge switch 102 is turned off), the capacitor Cr can provide more energy to the second secondary winding 112 . In addition, because the control circuit 114 controls the turning-on time TON 1 of the upper bridge switch 102 according to the second output voltage VO 2 , when the second output voltage VO 2 is lower, the control circuit 114 can increase the turning-on time TON 1 of the upper bridge switch 102 (that is, the control circuit 114 can make the turning-on time TON 1 of the upper bridge switch 102 be changed with the second output voltage VO 2 inversely), resulting in the capacitor Cr storing more energy. Therefore, when the lower bridge switch 104 is turned on, the capacitor Cr can provide more energy to the second secondary winding 112 , so that the second output current IO 2 flowing through the second secondary winding 112 is increased.

As shown in FIG. 3 , when the lower bridge switch 104 is turned on (the upper bridge switch 102 is turned off), the capacitor Cr start to discharge, resulting in a primary side current IPRI 2 flowing through the primary winding 108 , the inductor Lr, and the lower bridge switch 104 . At this time, because the voltage polarity of the first secondary winding 110 is different from the voltage polarity of the second secondary winding 112 , only the second output current IO 2 flows through the second secondary winding 112 . That is to say, the second output voltage VO 2 can be generated by charges stored in the capacitor Cr, the inductor Lr, the primary winding 108 , and the second secondary winding 112 . As shown in FIG. 3 , if the turning-on time TON 2 of the lower bridge switch 104 is longer, the capacitor Cr can discharge to a lower voltage level. It means that when the upper bridge switch 102 is turned on (the lower bridge switch 104 is turned off), the inductor-capacitor resonant tank 106 can provide more energy to the first secondary winding 110 . In addition, because the control circuit 114 controls the turning-on time TON 2 of the lower bridge switch 104 according to the first output voltage VO 1 , when the first output voltage VO 1 is lower, the control circuit 114 can increase the turning-on time TON 2 of the lower bridge switch 104 (that is, the control circuit 114 can make the turning-on time TON 2 of the lower bridge switch 104 be changed with the first output voltage VO 1 inversely), resulting in the capacitor Cr discharging to the lower voltage level. Therefore, when the lower bridge switch 104 is turned on, the inductor-capacitor resonant tank 106 can provide more energy to the first secondary winding 110 , resulting in the first output current IO 1 flowing through the first secondary winding 110 being increased.

Therefore, because the control circuit 114 controls the turning-on time TON 2 of the lower bridge switch 104 according to the first output voltage VO 1 and controls the turning-on time TON 1 of the upper bridge switch 102 according to the second output voltage VO 2 , the turning-on time TON 1 of the upper bridge switch 102 can be not equal to the turning-on time TON 2 of the lower bridge switch 104 . In addition, the upper bridge switch 102 and the lower bridge switch 104 are not simultaneously turned on, and a dead time TD exists between the turning-on time TON 1 of the upper bridge switch 102 and the turning-on time TON 2 of the lower bridge switch 104 , wherein as shown in FIG. 4 , the dead time TD is adjustable and used for regulating the second output voltage VO 2 and the first output voltage VO 1 , and Vgs 1 represents a voltage of a gate of the upper bridge switch 102 and Vgs 2 represents a voltage of a gate of the lower bridge switch 104 . In addition, a ratio of the second output voltage VO 2 to the first output voltage VO 1 can be any real number greater than one through a feedback control method of the control circuit 114 controlling the turning-on time TON 2 of the lower bridge switch 104 according to the first output voltage VO 1 and controlling the turning-on time TON 1 of the upper bridge switch 102 according to the second output voltage VO 2 .

In addition, please refer to FIGS. 1-3, 5 . FIG. 5 is a flowchart illustrating an operational method of an asymmetric power converter according to a second embodiment of the present invention. The operational method of FIG. 5 is illustrated using the asymmetric power converter 100 in FIG. 1 . Detailed steps are as follows:

Step 502 : The control circuit 114 controls the turning-on time TON 2 of the lower bridge switch 104 according to the first output voltage VO 1 .

Step 504 : During the turning-on time TON 2 of the lower bridge switch 104 , the inductor-capacitor resonant tank 106 discharges and transfers energy to the second secondary winding 112 through the primary winding 108 to generate the second output voltage VO 2 .

Step 506 : The control circuit 114 controls the turning-on time TON 1 of the upper bridge switch 102 according to the second output voltage VO 2 .

Step 508 : During the turning-on time TON 1 of the upper bridge switch 102 , the DC voltage VIN transfers energy to the first secondary winding through the primary winding 108 to generate the first output voltage VO 1 , go to Step 502 .

In Step 502 and Step 504 , as shown in FIG. 3 , when the lower bridge switch 104 is turned on (the upper bridge switch 102 is turned off), the capacitor Cr start to discharge, resulting in the primary side current IPRI 2 flowing through the primary winding 108 , the inductor Lr, and the lower bridge switch 104 . At this time, because the voltage polarity of the first secondary winding 110 is different from the voltage polarity of the second secondary winding 112 , only the second output current IO 2 flows through the second secondary winding 112 . That is to say, the second output voltage VO 2 can be generated by charges stored in the capacitor Cr, the inductor Lr, the primary winding 108 , and the second secondary winding 112 . As shown in FIG. 3 , if the turning-on time TON 2 of the lower bridge switch 104 is longer, the capacitor Cr can discharge to the lower voltage level. It means that when the upper bridge switch 102 is turned on (the lower bridge switch 104 is turned off), the inductor-capacitor resonant tank 106 can provide more energy to the first secondary winding 110 . In addition, because the control circuit 114 controls the turning-on time TON 2 of the lower bridge switch 104 according to the first output voltage VO 1 , when the first output voltage VO 1 is lower, the control circuit 114 can increase the turning-on time TON 2 of the lower bridge switch 104 (that is, the control circuit 114 can make the turning-on time TON 2 of the lower bridge switch 104 be changed with the first output voltage VO 1 inversely), resulting in the capacitor Cr discharging to the lower voltage level. Therefore, when the lower bridge switch 104 is turned on, the inductor-capacitor resonant tank 106 can provide more energy to the first secondary winding 110 , resulting in the first output current IO 1 flowing through the first secondary winding 110 being increased.

In Step 506 and Step 508 , as shown in FIG. 2 , when the upper bridge switch 102 is turned on (the lower bridge switch 104 is turned off), the primary side current IPRI 1 flows through the upper bridge switch 102 , the inductor Lr of the inductor-capacitor resonant tank 106 , and the primary winding 108 to charge the capacitor Cr of the inductor-capacitor resonant tank 106 . At this time, because the voltage polarity of the first secondary winding 110 is different from the voltage polarity of the secondary winding 112 , only the first output current IO 1 flows through the first secondary winding 110 . That is to say, the first output voltage VO 1 can be generated by the DC voltage VIN, the inductor Lr, the primary winding 108 , and the first secondary winding 110 . Because the primary side current IPRI 1 charges the capacitor Cr, if the turning-on time TON 1 of the upper bridge switch 102 is longer, it means that when the lower bridge switch 104 is turned on (the upper bridge switch 102 is turned off), the capacitor Cr can provide more energy to the second secondary winding 112 . In addition, because the control circuit 114 controls the turning-on time TON 1 of the upper bridge switch 102 according to the second output voltage VO 2 , when the second output voltage VO 2 is lower, the control circuit 114 can increase the turning-on time TON 1 of the upper bridge switch 102 (that is, the control circuit 114 can make the turning-on time TON 1 of the upper bridge switch 102 be changed with the second output voltage VO 2 inversely), resulting in the capacitor Cr storing more energy. Therefore, when the lower bridge switch 104 is turned on, the capacitor Cr can provide more energy to the second secondary winding 112 , so that a second output current IO 2 flowing through the second secondary winding 112 is increased.

To sum up, the asymmetric power converter and the operational method thereof utilize a dual-feedback control of the control circuit controlling the turning-on time of the lower bridge switch according to the first output voltage and controlling the turning-on time of the upper bridge switch according to the second output voltage to make the asymmetric power converter only need three windings (the primary winding, the first secondary winding and the second secondary winding), the ratio of the second output voltage to the first output voltage be any real number greater than one, and the turning-on time of the upper bridge switch be not equal to the turning-on time of the lower bridge switch. Therefore, compared to the prior art, because the ratio of the second output voltage to the first output voltage can be any real number greater than one, the asymmetric power converter is very suitable for a backlight drive application such as a television requiring a larger output voltage range, and because the asymmetric power converter only needs the three windings, cost of the asymmetric power converter is lower.

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.