Asymmetric power converter and operational method thereof

Asymmetric power converter includes an upper bridge switch, a lower bridge switch, a primary winding, a first secondary winding, a second secondary winding, a control circuit. The first secondary winding and the second secondary winding output a first output voltage and a second output voltage of a secondary side of the asymmetric power converter respectively, and voltage polarity of the first secondary winding is different from voltage polarity of the second secondary winding. The control circuit controls the lower bridge switch and the upper bridge switch according to the first output voltage and the second output voltage, respectively.

BACKGROUND OF THE INVENTION

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.

SUMMARY OF THE INVENTION

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.

DETAILED DESCRIPTION

Please refer toFIG. 1.FIG. 1is a diagram illustrating an asymmetric power converter100according to a first embodiment of the present invention, wherein the asymmetric power converter100includes an upper bridge switch102, a lower bridge switch104, an inductor-capacitor resonant tank (LC resonant tank)106, a primary winding108, a first secondary winding110, a second secondary winding112, a control circuit114, a first isolation component115, a second isolation component116, and a constant current control circuit118, and the asymmetric power converter100is an inductor-inductor-capacitor power converter (LLC power converter). As shown inFIG. 1, the upper bridge switch102and the lower bridge switch104are coupled to the primary winding108through the inductor-capacitor resonant tank106, and the upper bridge switch102, the lower bridge switch104, the inductor-capacitor resonant tank106, and the primary winding108are installed in a primary side PRI of the asymmetric power converter100, and the first secondary winding110and the second secondary winding112are installed in a secondary side SEC of the asymmetric power converter100. In addition, as shown inFIG. 1, the first secondary winding110is used for outputting a first output voltage VO1of the secondary side SEC of the asymmetric power converter100, the second secondary winding112is used for outputting a second output voltage VO2of the secondary side SEC of the asymmetric power converter100, and the control circuit114controls a turning-on time TON2of the lower bridge switch104according to the first output voltage VO1and controls a turning-on time TON1of the upper bridge switch102according to the second output voltage VO2, wherein the second output voltage VO2is greater than the first output voltage VO1, and when the second output voltage VO2is applied to a backlight drive application of light-emitting diodes of a television, the control circuit114further combines the constant current control circuit118to control the turning-on time TON1of the upper bridge switch102. In addition, the control circuit114is installed in the primary side PRI of the asymmetric power converter100, both the first isolation component115and the second isolation component116are used for isolating the primary side PRI of the asymmetric power converter100from the secondary side SEC of the asymmetric power converter100, and the first isolation component115and the second isolation component116are photo couplers. However, the present invention is not limited to the first isolation component115and the second isolation component116being photo couplers, that is, the first isolation component115and the second isolation116can be other component for isolating the primary side PRI of the asymmetric power converter100from the secondary side SEC of the asymmetric power converter100. In addition, a ground of the primary side PRI of the asymmetric power converter100and a ground of the secondary side SEC of the asymmetric power converter100can be the same or different. In addition, the asymmetric power converter100further comprises a power factor corrector circuit119coupled between the control circuit114and a bridge rectifier120, wherein the power factor corrector circuit119is used for improving a power factor of the asymmetric power converter100to make the power factor of the asymmetric power converter100close to one and suppressing a harmonic wave of a first output current IO1and a second output current IO2of the asymmetric power converter100.

Please refer toFIGS. 2, 3.FIG. 2is a diagram illustrating operation of the inductor-capacitor resonant tank106, the primary winding108, the first secondary winding110, and the second secondary winding112when the upper bridge switch102is turned on, andFIG. 3is a diagram illustrating operation of the inductor-capacitor resonant tank106, the primary winding108, the first secondary winding110, and the second secondary winding112when the lower bridge switch104is turned on. As shown inFIG. 2, when the upper bridge switch102is turned on (the lower bridge switch104is turned off), a primary side current IPRI1flows through the upper bridge switch102, an inductor Lr of the inductor-capacitor resonant tank106, and the primary winding108to charge a capacitor Cr of the inductor-capacitor resonant tank106. At this time, because voltage polarity of the first secondary winding110is different from voltage polarity of the secondary winding112, only the first output current IO1flows through the first secondary winding110, wherein it can be known that the voltage polarity of the first secondary winding110is different from the voltage polarity of the secondary winding112through a position of a dot of the first secondary winding110and a position of a dot of the second secondary winding112. That is to say, the first output voltage VO1can be generated by a DC (direct current) voltage VIN, the inductor Lr, the primary winding108, and the first secondary winding110, wherein the DC voltage VIN is generated by an input voltage VAC (alternating current voltage) being rectified by the bridge rectifier120. Because the primary side current IPRI1charges the capacitor Cr, if the turning-on time TON1of the upper bridge switch102is longer, it means that when the lower bridge switch104is turned on (the upper bridge switch102is turned off), the capacitor Cr can provide more energy to the second secondary winding112. In addition, because the control circuit114controls the turning-on time TON1of the upper bridge switch102according to the second output voltage VO2, when the second output voltage VO2is lower, the control circuit114can increase the turning-on time TON1of the upper bridge switch102(that is, the control circuit114can make the turning-on time TON1of the upper bridge switch102be changed with the second output voltage VO2inversely), resulting in the capacitor Cr storing more energy. Therefore, when the lower bridge switch104is turned on, the capacitor Cr can provide more energy to the second secondary winding112, so that the second output current IO2flowing through the second secondary winding112is increased.

As shown inFIG. 3, when the lower bridge switch104is turned on (the upper bridge switch102is turned off), the capacitor Cr start to discharge, resulting in a primary side current IPRI2flowing through the primary winding108, the inductor Lr, and the lower bridge switch104. At this time, because the voltage polarity of the first secondary winding110is different from the voltage polarity of the second secondary winding112, only the second output current IO2flows through the second secondary winding112. That is to say, the second output voltage VO2can be generated by charges stored in the capacitor Cr, the inductor Lr, the primary winding108, and the second secondary winding112. As shown inFIG. 3, if the turning-on time TON2of the lower bridge switch104is longer, the capacitor Cr can discharge to a lower voltage level. It means that when the upper bridge switch102is turned on (the lower bridge switch104is turned off), the inductor-capacitor resonant tank106can provide more energy to the first secondary winding110. In addition, because the control circuit114controls the turning-on time TON2of the lower bridge switch104according to the first output voltage VO1, when the first output voltage VO1is lower, the control circuit114can increase the turning-on time TON2of the lower bridge switch104(that is, the control circuit114can make the turning-on time TON2of the lower bridge switch104be changed with the first output voltage VO1inversely), resulting in the capacitor Cr discharging to the lower voltage level. Therefore, when the lower bridge switch104is turned on, the inductor-capacitor resonant tank106can provide more energy to the first secondary winding110, resulting in the first output current IO1flowing through the first secondary winding110being increased.

Therefore, because the control circuit114controls the turning-on time TON2of the lower bridge switch104according to the first output voltage VO1and controls the turning-on time TON1of the upper bridge switch102according to the second output voltage VO2, the turning-on time TON1of the upper bridge switch102can be not equal to the turning-on time TON2of the lower bridge switch104. In addition, the upper bridge switch102and the lower bridge switch104are not simultaneously turned on, and a dead time TD exists between the turning-on time TON1of the upper bridge switch102and the turning-on time TON2of the lower bridge switch104, wherein as shown inFIG. 4, the dead time TD is adjustable and used for regulating the second output voltage VO2and the first output voltage VO1, and Vgs1represents a voltage of a gate of the upper bridge switch102and Vgs2represents a voltage of a gate of the lower bridge switch104. In addition, a ratio of the second output voltage VO2to the first output voltage VO1can be any real number greater than one through a feedback control method of the control circuit114controlling the turning-on time TON2of the lower bridge switch104according to the first output voltage VO1and controlling the turning-on time TON1of the upper bridge switch102according to the second output voltage VO2.

In addition, please refer toFIGS. 1-3, 5.FIG. 5is a flowchart illustrating an operational method of an asymmetric power converter according to a second embodiment of the present invention. The operational method ofFIG. 5is illustrated using the asymmetric power converter100inFIG. 1. Detailed steps are as follows:

Step502: The control circuit114controls the turning-on time TON2of the lower bridge switch104according to the first output voltage VO1.

Step504: During the turning-on time TON2of the lower bridge switch104, the inductor-capacitor resonant tank106discharges and transfers energy to the second secondary winding112through the primary winding108to generate the second output voltage VO2.

Step506: The control circuit114controls the turning-on time TON1of the upper bridge switch102according to the second output voltage VO2.

Step508: During the turning-on time TON1of the upper bridge switch102, the DC voltage VIN transfers energy to the first secondary winding through the primary winding108to generate the first output voltage VO1, go to Step502.

In Step502and Step504, as shown inFIG. 3, when the lower bridge switch104is turned on (the upper bridge switch102is turned off), the capacitor Cr start to discharge, resulting in the primary side current IPRI2flowing through the primary winding108, the inductor Lr, and the lower bridge switch104. At this time, because the voltage polarity of the first secondary winding110is different from the voltage polarity of the second secondary winding112, only the second output current IO2flows through the second secondary winding112. That is to say, the second output voltage VO2can be generated by charges stored in the capacitor Cr, the inductor Lr, the primary winding108, and the second secondary winding112. As shown inFIG. 3, if the turning-on time TON2of the lower bridge switch104is longer, the capacitor Cr can discharge to the lower voltage level. It means that when the upper bridge switch102is turned on (the lower bridge switch104is turned off), the inductor-capacitor resonant tank106can provide more energy to the first secondary winding110. In addition, because the control circuit114controls the turning-on time TON2of the lower bridge switch104according to the first output voltage VO1, when the first output voltage VO1is lower, the control circuit114can increase the turning-on time TON2of the lower bridge switch104(that is, the control circuit114can make the turning-on time TON2of the lower bridge switch104be changed with the first output voltage VO1inversely), resulting in the capacitor Cr discharging to the lower voltage level. Therefore, when the lower bridge switch104is turned on, the inductor-capacitor resonant tank106can provide more energy to the first secondary winding110, resulting in the first output current IO1flowing through the first secondary winding110being increased.

In Step506and Step508, as shown inFIG. 2, when the upper bridge switch102is turned on (the lower bridge switch104is turned off), the primary side current IPRI1flows through the upper bridge switch102, the inductor Lr of the inductor-capacitor resonant tank106, and the primary winding108to charge the capacitor Cr of the inductor-capacitor resonant tank106. At this time, because the voltage polarity of the first secondary winding110is different from the voltage polarity of the secondary winding112, only the first output current IO1flows through the first secondary winding110. That is to say, the first output voltage VO1can be generated by the DC voltage VIN, the inductor Lr, the primary winding108, and the first secondary winding110. Because the primary side current IPRI1charges the capacitor Cr, if the turning-on time TON1of the upper bridge switch102is longer, it means that when the lower bridge switch104is turned on (the upper bridge switch102is turned off), the capacitor Cr can provide more energy to the second secondary winding112. In addition, because the control circuit114controls the turning-on time TON1of the upper bridge switch102according to the second output voltage VO2, when the second output voltage VO2is lower, the control circuit114can increase the turning-on time TON1of the upper bridge switch102(that is, the control circuit114can make the turning-on time TON1of the upper bridge switch102be changed with the second output voltage VO2inversely), resulting in the capacitor Cr storing more energy. Therefore, when the lower bridge switch104is turned on, the capacitor Cr can provide more energy to the second secondary winding112, so that a second output current IO2flowing through the second secondary winding112is 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.