Switch circuit

This application claims the benefit of Taiwan application Serial No. 101143087, filed Nov. 19, 2012, the disclosure of which is incorporated by reference herein in its entirety.

1. Technical Field

The disclosed embodiments relate in general to a switch circuit, and more particularly to a switch circuit having capacitors and switch elements.

2. Description of the Related Art

Current electronic products, having entered a portable era, are developed towards targets of being compact and low in market prices. However, due to a large number of external components, a volume of a printed circuit board (PCB) is increased to limit a size and an appearance of a product. For example, in most market-available power conversion circuits such as DC/DC converters, charge pump circuits and switched capacitor circuits, elements from power switches, passive elements to control circuits, are all formed by discrete components. Since not only component prices are reducing at a slow and have small margins left for further reduction, but also raw materials are also becoming more costly, assembly costs are increased as the number of employed discrete components grows. Consequently, a PCB becomes larger and heavier.

Further, compared to resistors or ceramic capacitors, magnetic elements have a greater volume and higher costs. Electrolytic capacitors in light-emitting diodes (LED) are prone to interference from the LEDs, and hence have a shortened lifecycle. With a temperature rise of every 10 degree Celsius, the lifecycle of electrolytic capacitors is reduced by 50%. Therefore, there is a need for a driver circuit free of magnetic elements and free of electrolytic capacitors. To effectively reduce the product weight and volume, the integrated circuit technology is a crucial development. Integrated circuits are capable of integrating most external discrete components, e.g., transistors, capacitors and diodes. By replacing a conventional PCB with an integrated circuit having an extremely small volume, the volume and weight can be decreased while also increasing the transmission speed and reliability. However, in addition to high manufacturing costs, an integrated circuit also has a chip area that is directly proportional to costs.

Further, assuming that power switch elements in power conversion circuits are to be integrated to an integrated circuit, a chip area occupied by the power switch elements is quite considerable. In general, a high-power switch element occupies an area of above 5 to 10 times of that of overall control circuits. That is to say, a significant amount of manufacturing costs is consumed if numerous power switch elements are employed in the circuit. Under a condition of generating three to four step-down modes using three capacitors in a conventional switched capacitors, at least eight to nine power switch elements are required and thus render a much too large chip size.

According to one embodiment, a switch circuit is provided. The switch circuit includes multiple energy storage elements, and multiple switch elements coupled to the energy storage elements to generate a step-down mode.

According to another embodiment, a switch circuit is provided. The switch circuit includes multiple energy storage elements, and multiple switch elements coupled to the energy storage elements to generate either a step-down mode or a step-up mode.

FIG. 1 shows a switch circuit according to one embodiment.

FIG. 2 shows an application example of the capacitors and switches in FIG. 1 .

FIG. 3 shows a first step-down mode of FIG. 2 .

FIG. 4(A) and FIG. 4(B) show a second step-down mode of FIG. 2 .

FIG. 5(A) and FIG. 5(B) show a third step-down mode of FIG. 2 .

FIG. 6(A) and FIG. 6(B) show a fourth step-down mode of FIG. 2 .

FIG. 7 shows a switch circuit according to another embodiment.

FIG. 8 shows an application example of the capacitors and switches in FIG. 7 .

FIG. 9 shows a first step-down mode of FIG. 8 .

FIG. 10(A) and FIG. 10(B) show a second step-down mode of FIG. 8 .

FIG. 11(A) and FIG. 11(B) show a third step-down mode of FIG. 8 .

FIG. 12(A) and FIG. 12(B) show a fourth step-down mode of FIG. 8 .

FIG. 13(A) and FIG. 13(B) show a first step-up mode of FIG. 8 .

FIG. 14(A) and FIG. 14(B) show a second step-up mode of FIG. 8 .

FIG. 15 shows a circuit block diagram of an application according to one embodiment.

In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing.

FIG. 1 shows a switch circuit according to one embodiment. The switch circuit includes multiple energy storage elements and multiple switch elements. The switch elements are coupled to the energy storage elements to generate step-down modes. The energy storage elements include a first energy storage element C 1 , a second energy storage element C 2 and a third energy storage element C out . The switch elements include a first switch element S 1 , a second switch element S 2 , a third switch element S 3 , a fourth switch element S 4 , a fifth switch element S 5 , a sixth switch element S 6 and a seventh switch element S 7 . As shown in FIG. 1 , the first energy storage element C 1 has one terminal coupled to the first, fourth and sixth switch elements S 1 , S 4 and S 6 , and the other terminal coupled to the third and fifth switch elements S 3 and S 5 . The second energy storage element C 2 has one terminal coupled to the second, third and seventh switch elements S 2 , S 3 and S 7 , and the other terminal coupled to the fourth and fifth switch elements S 4 and S 5 . The third energy storage element C out has one terminal coupled to the sixth and seventh switch elements S 6 and S 7 . In the embodiment, the energy storage elements may be capacitors, and the switch elements may be metal oxide semiconductor (MOS) or bipolar junction transistor (BJT) elements. In the embodiment, the step-down modes are generated according to charging/discharging operations of the energy storage elements and switching operations of the switch elements, and are thus in plural. In the embodiment, the polarity of the capacitor C 2 is inverted, and the capacitors C 1 and C 2 are jointly grounded via the switch elements S 2 and S 3 , so that the embodiment saves one power switch element compared to a conventional switch circuit. Further, via the switch element S 4 , the two capacitors C 1 and C 2 may also directly connect to an input power V in to similarly save one power switch element. Therefore, in the embodiment, four step-down modes are provided by using merely seven power transistors, thereby enhancing circuit adaptivity as well as reducing circuit development costs.

FIG. 2 shows an application example of the capacitors and switches in FIG. 1 . FIGS. 3 to 6 show four step-down modes of FIG. 2 . Table-1 shows a voltage ratio (V out /V in ) of the step-down modes and the switch elements to be turned on between charging (phase 1 ) and discharging (phase 2 ) of the energy storage elements.

FIG. 3 shows a first step-down mode of FIG. 2 . Referring to FIG. 3 , when the voltage ratio (V out /V in ) of a desired output voltage to the input voltage is 1, the switch elements S 1 , S 2 , S 3 , S 4 and S 6 need to be turned on regardless of when the energy storage elements are charged (phase 1 ) or discharged (phase 2 ).

FIG. 4 shows a second step-down mode of FIG. 2 . When the voltage ratio (V out /V in ) of a desired output voltage to the input voltage is ½, the switch elements S 1 , S 3 , S 4 and S 7 need to be turned on when the energy storage elements are charged (phase 1 ), as shown in FIG. 4(A) ; and the switch elements S 2 , S 3 , S 4 and S 6 need to be turned on when the energy storage elements are discharged (phase 2 ), as shown in FIG. 4(B) .

FIG. 5 shows a third step-down mode of FIG. 2 . When the voltage ratio (V out /V in ) of a desired output voltage to the input voltage is ⅓, the switch elements S 1 , S 5 and S 7 need to be turned on when the energy storage elements are charged (phase 1 ), as shown in FIG. 5(A) ; and the switch elements S 2 , S 3 , S 4 and S 6 need to be turned on when the energy storage elements are discharged (phase 2 ), as shown in FIG. 5(B) .

FIG. 6 shows a fourth step-down mode of FIG. 2 . When the voltage ratio (V out /V in ) of a desired output voltage to the input voltage is ⅔, the switch elements S 1 , S 3 , S 4 and S 7 need to be turned on when the energy storage elements are charged (phase 1 ), as shown in FIG. 6(A) ; and the switch elements S 2 , S 5 and S 6 need to be turned on when the energy storage elements are discharged (phase 2 ), as shown in FIG. 6(B) .

FIG. 7 shows a switch circuit according to another embodiment. The switch circuit includes multiple energy storage elements and multiple switch elements. The switch elements are coupled to the energy storage elements to generate either a step-down mode or a step-up mode. The energy storage elements include a first energy storage element C 1 , a second energy storage element C 2 and a third energy storage element C out . The switch elements include a first switch element S 1 , a second switch element S 2 , a third switch element S 3 , a fourth switch element S 4 , a fifth switch element S 5 , a sixth switch element S 6 , a seventh switch element S 7 , and an eighth switch element S 8 . As shown in FIG. 7 , the first energy storage element C 1 has one terminal coupled to the first, second and seventh switch elements S 1 , S 2 and S 7 , and the other terminal coupled to the fourth and fifth switch elements S 4 and S 5 . The second energy storage element C 2 has one terminal coupled to the second and fourth switch elements S 2 and S 4 , and the other terminal coupled to the third, fifth, sixth and eighth switch elements S 3 , S 5 , S 6 and S 8 . The third energy storage element C out has one terminal coupled to the seventh and eighth switch elements S 7 and S 8 . In the embodiment, an integrated switch circuit for simultaneously achieving step-down and step-up characteristics is disclosed. In the embodiment, with eight power switch elements, six switching modes (four step-down modes and two step-up modes) are provided to implement a switch circuit adopting least switch elements and rendering most modes, thereby enhancing adaptivity for circuit post-end applications and reducing hardware costs.

FIG. 8 shows an application example of the capacitors and switches in FIG. 7 . FIGS. 9 to 14 show four step-down modes and two step-up modes of FIG. 7 . Table-2 shows a voltage ratio (V out /V in ) of the step-down and step-up modes as well as the switch elements to be turned on between charging (phase 1 ) and discharging (phase 2 ) of the energy storage elements.

FIG. 9 shows a first step-down mode of FIG. 8 . Referring to FIG. 9 , when the voltage ratio (V out /V in ) of a desired output voltage to the input voltage is 1, the switch elements S 1 , S 2 , S 5 , S 6 and S 7 need to be turned on regardless of when the energy storage elements are charged (phase 1 ) or discharged (phase 2 ).

FIG. 10 shows a second step-down mode of FIG. 8 . When the voltage ratio (V out /V in ) of a desired output voltage to the input voltage is ½, the switch elements S 1 , S 2 , S 5 and S 8 need to be turned on when the energy storage elements are charged (phase 1 ), as shown in FIG. 10(A) ; and the switch elements S 2 , S 5 , S 6 and S 7 need to be turned on when the energy storage elements are discharged (phase 2 ), as shown in FIG. 10(B) .

FIG. 11 shows a third step-down mode of FIG. 8 . When the voltage ratio (V out /V in ) of a desired output voltage to the input voltage is ⅔, the switch elements S 1 , S 2 , S 5 and S 8 need to be turned on when the energy storage elements are charged (phase 1 ), as shown in FIG. 11(A) ; and the switch elements S 4 , S 6 and S 7 need to be turned on when the energy storage elements are discharged (phase 2 ), as shown in FIG. 11(B) .

FIG. 12 shows a fourth step-down mode of FIG. 8 . When the voltage ratio (V out /V in ) of a desired output voltage to the input voltage is ⅓, the switch elements S 1 , S 4 and S 8 need to be turned on when the energy storage elements are charged (phase 1 ), as shown in FIG. 12(A) ; and the switch elements S 2 , S 5 , S 6 and S 7 need to be turned on when the energy storage elements are discharged (phase 2 ), as shown in FIG. 12(B) .

FIG. 13 shows a first step-up mode of FIG. 8 . When the voltage ratio (V out /V in ) of a desired output voltage to the input voltage is 2, the switch elements S 1 , S 2 and S 6 need to be turned on when the energy storage elements are charged (phase 1 ), as shown in FIG. 13(A) ; and the switch elements S 2 , S 3 and S 7 need to be turned on when the energy storage elements are discharged (phase 2 ), as shown in FIG. 13(B) .

FIG. 14 shows a second step-up mode of FIG. 8 . When the voltage ratio (V out /V in ) of a desired output voltage to the input voltage is 3, the switch elements S 1 , S 2 , S 5 and S 6 need to be turned on when the energy storage elements are charged (phase 1 ), as shown in FIG. 14(A) ; and the switch elements S 3 , S 4 and S 7 need to be turned on when the energy storage elements are discharged (phase 2 ), as shown in FIG. 14(B) .

FIG. 15 shows a circuit block diagram of an application according to one embodiment. Referring to FIG. 15 , a DC voltage input V dc _ in first passes through a voltage detection circuit 11 , provides a detection signal to a mode selector 12 for mode switching, and provides a signal to the voltage input V in of the switch circuit 13 of the disclosure according to the selected mode. As such, the switch circuit 13 outputs a voltage V out , for driving a driver device 14 (e.g., an LED). Further, different modes switch different control signals for controlling the switch elements. For example, in the circuit in FIG. 2 , seven different control signals are switched for controlling the seven switch elements in FIG. 2 .

With the embodiments, a switch circuit free of electromagnetic elements and free of electrolytic capacitors is provided. Power switch elements, a controller and a part of resistors in a circuit are all integrated to an integrated circuit, leaving only several resistors and ceramic capacitors as external discrete components. Thus, the volume and weight of a driving circuit are effectively reduced to further lower system costs and prolong the lifecycle of lighting devices.

It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.