Power adapter and power supply system using the same

The present invention is associated with a power adapter capable of simultaneously providing a low-level DC voltage and a high-level DC voltage. The power adapter includes a transformer having a primary winding for storing energy when a main switch coupled therewith is turned on and transferring the stored energy to the secondary side of the transformer when the main switch is turned off. The transformer includes a first secondary winding and a second secondary winding connected in series with each other. A first rectifier/filter circuit is connected across the first secondary winding for generating a low-level DC voltage by rectifying and filtering the energy received by the first secondary winding, and a second rectifier/filter circuit is connected across the first secondary winding and the second secondary winding for generating a high-level DC voltage by rectifying and filtering the energy received by the first secondary winding and the second secondary winding.

FIELD OF THE INVENTION

The present invention is related to a power adapter, and more particularly to a power adapter capable of simultaneously providing a low-level DC voltage and a high-level DC voltage for power converters with different specifications to proceed with power conversion operations.

BACKGROUND OF THE INVENTION

FIG. 1shows a systematic block diagram of a power supply system for a flat panel display according to the prior art. As shown inFIG. 1, a power adapter100is configured to receive an input AC voltage Vin and convert the input AC voltage into an output DC voltage Vo. The output DC voltage Vo is provided to a DC-AC converter101(or inverter) and a DC-DC converter102, respectively. The DC-DC converter102is configured to convert the output DC voltage Vo into a DC voltage with a lower voltage level for powering the control circuitry (not shown) located within the flat panel display. The DC-AC converter101is configured to convert the output DC voltage Vo into a high-frequency high-level AC voltage for illuminating the discharge lamps which functions as the backlight module for the flat panel display.

A typical power adapter for a flat panel display is configured to receive 110-V or 220-V input AC voltage and provide 12-V output DC voltage. Hence, the output DC voltage Vo provided by the power adapter100shown inFIG. 1is generally a low-level DC voltage with the voltage level being 12V. The voltage level of the output DC voltage of the DC-DC converter102can be 1.5-V, 2.5-V, 3-V, 3.3-V, 4.5-V, 5-V, 6-V, 7.5-V, 9-V, or 12-V. However, the DC-AC converter101generally produces a high-frequency AC voltage as the desired power source for illuminating the discharge lamps located within the flat panel display. Therefore, the DC-AC converter101is responsible to convert the output DC voltage Vo having a voltage of 12V into a high-frequency AC voltage.

The DC-AC converter101is configured to convert a low-level DC voltage into a high-level DC voltage through the switching operations of the internal switches (not shown) and the voltage boosting operation of the internal high-voltage transformers (not shown). In this case, the voltage transformation ratio of the DC-AC converter101will become relatively large. Therefore, the DC-AC converter101would cause considerable power loss, which would deteriorate the conversion efficiency of the DC-AC converter101. If the power adapter100can provide an output DC voltage with a higher voltage level for the DC-AC converter101to perform voltage transformation, the power loss caused by the DC-AC converter101can be reduced and the conversion efficiency of the DC-AC converter101can be enhanced.

FIG. 2is a circuit diagram showing the power adapter100ofFIG. 1. As shown inFIG. 2, the power adapter100includes a bridge rectifier201which is configured to rectify an input AC voltage into a full-wave rectified DC voltage and a transformer T21having a primary winding Np21and a secondary winding Ns21. The primary winding Np21is configured to store energy from the input AC voltage Vin when a main switch S21which is connected in series with the primary winding Np21is ON and release the stored energy to the secondary winding Ns21when the main switch S21is OFF. The switching operations of the switch S21are manipulated by a pulse-width modulator (PWM)202. The power adapter100further includes a rectifier/filter circuit which is consisted of a rectifying diode D21and a filtering capacitor C21and connected to the secondary winding Ns21. The rectifier/filter circuit (D21, C21) is configured to perform rectification and filtration to the energy received by the secondary winding Ns21so as to generate a desired output DC voltage Vo. The power adapter100further includes a feedback control circuit203which is configured to detect variations on the output DC voltage Vo and in response thereto issue a feedback signal to the pulse-width modulator202to enable the pulse-width modulator202to stabilize the output DC voltage Vo at a predetermined level.

As stated above, the output DC voltage Vo of the conventional power adapter100is a low-level DC voltage. If this low-level DC voltage Vo is provided to the DC-AC converter101shown inFIG. 1for voltage transformation, the DC-AC converter101would cause a considerable power loss and deteriorate the conversion efficiency. Here, it would be an ideal solution to the above drawbacks if a power adapter capable of simultaneously providing a low-level output DC voltage and a high-level output DC voltage is devised. The present invention can satisfy these needs.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a power adapter for simultaneously providing a low-level output DC voltage for voltage transformation and a high-level output DC voltage for voltage transformation.

According to a preferred embodiment of the present invention, a power adapter includes a rectifier for rectifying an input AC voltage into a full-wave rectified DC voltage and a transformer having a primary winding being connected in series with a main switch for storing energy when the main switch is ON and releasing the stored energy to the secondary side of the transformer when the main switch if OFF. The transformer further includes a first secondary winding and a second secondary winding, in which the first secondary winding and the second secondary winding are connected in series with each other. The power adapter further includes a first rectifier/filter circuit connected across the first secondary winding for performing rectification and filtration to the energy received by the first secondary winding and thereby generating a low-level DC voltage, and a second rectifier/filter circuit connected across the first secondary winding and the second secondary winding for performing rectification and filtration to the energy received by the first secondary winding and the second secondary winding and thereby generating a high-level DC voltage.

According to a deeper aspect of the present invention, a power supply system is provided, including a power adapter for simultaneously converting an input AC voltage into a low-level output DC voltage and a high-level output DC voltage, a DC-DC converter connected to the power adapter for receiving the low-level output DC voltage from the power adapter and converting the low-level output DC voltage into a DC voltage, and a DC-AC converter for receiving the high-level output DC voltage from the power adapter and converting the high-level output DC voltage into an output AC voltage. The power adapter includes a switch and a transformer having a primary winding, a first secondary winding and a second secondary winding. The primary winding is connected in series with the switch, and the first secondary winding and the second secondary winding are connected in series with each other. The primary winding is configured to store energy when the switch is ON and release the stored energy to the first secondary winding and the second secondary winding when the switch is OFF. The power adapter further includes a first rectifier/filter circuit connected across the first secondary winding for performing rectification and filtration to the energy received by the first secondary winding and thereby generating a low-level output DC voltage, and a second rectifier/filter circuit connected across the first secondary winding and the second secondary winding for performing rectification and filtration to the energy received by the first secondary winding and the second secondary winding and thereby generating a high-level output DC voltage.

Now the foregoing and other features and advantages of the present invention will be best understood through the following descriptions with reference to the accompanying drawings, wherein:

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment embodying the features and advantages of the present invention will be expounded in following paragraphs of descriptions. It is to be realized that the present invention is allowed to have various modification in different respects, all of which are without departing from the scope of the present invention, and the description herein and the drawings are to be taken as illustrative in nature, but not to be taken as limitative.

FIG. 3shows a power supply system having a power adapter for use with a flat panel display according to the present invention. As shown inFIG. 3, the power adapter300is configured to provide a low-level output DC voltage Vo1for a DC-DC converter302to perform voltage transformation. In the meantime, the power adapter can provide a high-level output DC voltage Vo2for a DC-AC converter301to perform voltage transformation. Because the input voltage of the DC-AC converter301is a high-level DC voltage, the voltage transformation ratio of the DC-AC converter301can be lowered, so that the power loss caused by the DC-AC converter301can be reduced and the conversion efficiency of the DC-AC converter301can be enhanced.

The circuit diagram of the power adapter according to the present invention is illustrated inFIG. 4. As shown inFIG. 4, the power adapter300includes a bridge rectifier401which is configured to rectify an input AC voltage Vin into a full-wave rectified DC voltage and a transformer T41having a primary winding Np41, a first secondary winding Ns41and a second secondary winding Ns42. The primary winding Np41is configured to store energy received from the input AC voltage Vin when a main switch S41which is connected in series with the primary winding Np41is ON and release the stored energy to the first secondary winding Ns41and the second secondary winding Ns42when the main switch S41is OFF. The switching operations of the main switch S41is manipulated by the pulse-width modulator402. The power adapter300further includes a first rectifier/filter circuit and a second rectifier/filter circuit, in which the first rectifier/filter circuit is consisted of a rectifying diode D41and a filtering capacitor C41and connected across the first secondary winding Ns41, and the second rectifier/filter circuit is consisted of a rectifying diode D42and a filtering capacitor C42and connected across the first secondary winding Ns41and the second secondary winding Ns42. The first rectifier/filter circuit (D41, C41) is configured to perform rectification and filtration to the energy received by the first secondary winding Ns41to generate a desired low-level output DC voltage Vo1, and the second rectifier/filter circuit (D42, C42) is configured to perform rectification and filtration to the energy received by the first secondary winding Ns41and the second secondary winding Ns42to generate a desired high-level output DC voltage Vo2. The power adapter300further includes a feedback control circuit403which is configured to detect variations on the output DC voltages Vo1and Vo2and in response thereto issue a feedback signal to the pulse-width modulator402to enable the pulse-width modulator402to respectively stabilize the output DC voltages Vo1and Vo2at a predetermined level.

As is well know in the art, the voltage level of the output voltage of the power adapter300depends on the turn ratio of the transformer. In order to allow the power adapter300to provide a higher-level output DC voltage to the DC-AC converter301ofFIG. 3for voltage transformation, an additional secondary winding is needed to be mounted on the secondary side of the transformer and connected in series with the inherent secondary winding of the transformer, and an additional rectifier/filter circuit is needed to be connected across the secondary side of the transformer. In this way, the transformer turn ratio selected by the additional rectifier/filter circuit can be maximized. As shown inFIG. 4, the power adapter300according to the present invention includes a second secondary winding Ns42which is connected in series with the intrinsic secondary winding Ns4l as the additional secondary winding, and includes a second rectifier/filter circuit (D42, C42) which is connected across the first secondary winding Ns41and the second secondary winding Ns42as the additional rectifier/filter circuit. The input voltage of the second rectifier/filter circuit (D42, C42) depends on the turn ratio between the first and second secondary windings (Ns41, Ns42) and the primary winding Np41. Under this condition, the output DC voltage Vo2provided by the second rectifier/filter circuit (D42, C42) will have a higher voltage level than the output DC voltage Vo1provided by the first rectifier/filter circuit (D41, C41).

It is to be noted that the circuit architecture of the first rectifier/filter circuit and the second rectifier/filter circuit is not limited to the form disclosed herein, but can be implemented by other rectifying/filtering elements. For example, the rectifying diode and the filtering capacitor employed in the first rectifier/filter circuit and the second rectifier/filter circuit can be replaced with a power factor correction (PFC) boost converter.

In conclusion, the power adapter according to the present invention is configured to simultaneously output a low-level DC voltage and a high-level DC voltage, and respectively provide the low-level DC voltage and the high-level DC voltage to a DC-DC converter and a DC-AC converter for voltage transformation. In order to allow the power adapter to simultaneously output a low-level DC voltage and a high-level DC voltage, an additional secondary winding is mounted on the secondary side of the transformer and connected in series with the intrinsic secondary winding of the transformer. Also, an additional rectifier/filter circuit is mounted and connected across the intrinsic secondary winding and the additional secondary winding, so that the turn ratio of the transformer selected by the additional rectifier/filter circuit is maximized. Thus, the additional rectifier/filter circuit can generate an output voltage having a voltage level being larger than the voltage level of the output voltage of the intrinsic rectifier/filter circuit. This high-level output DC voltage is provided to the DC-AC converter for voltage transformation. Because the voltage level of the input voltage of the DC-AC converter is increased dramatically, the voltage transformation ratio of the DC-AC converter is lowered and the power loss caused by the DC-AC converter is reduced. Therefore, the conversion efficiency of the DC-AC converter is enhanced.