1. Field of the Invention
The instant disclosure relates to a charge pump circuit; in particular, to a charge pump circuit having a high efficiency and a motor using the same.
2. Description of Related Art
As technology develops, the motor becomes more and more an essential electric device. The common motors, such as the DC motor, the AC motor, the step motor and the like, have been widely used for driving fans.
There is usually a power supply circuit needed in the motor to provide voltages to each element of the motor. The motor changes the polarities of the motor rotator or the motor stator via the high-side bridge switch and the low-side bridge switch, which makes the motor keep operating. The bootstrap circuit and the charge pump circuit are most commonly used.
There are at least one bootstrap diode and at least one bootstrap capacitor in the bootstrap circuit, to correspondingly control the high-side bridge switch and the low-side bridge switch. If the phase number of the motor becomes more (such as a three-phase motor), there are more bootstrap diodes and bootstrap capacitors needed in the bootstrap circuit, such that the chip area and the production cost of the bootstrap circuit increase. Moreover, the working mechanism of the bootstrap circuit is related to orderly turning on the high-side bridge switch and the low-side bridge switch. In other words, the high-side bridge switch and the low-side bridge switch cannot be continually turned on via the motor using the bootstrap circuit. Therefore, the charge pump circuit is often used in the motors currently.
Please refer to FIG. 1. FIG. 1 shows a circuit diagram of a traditional charge pump circuit. The traditional charge pump circuit comprises a first transistor M1_1, a second transistor M1_2, a third transistor M1_3, a fourth transistor M1_4, a first capacitor C1_1 and a second capacitor C1_2. The first transistor M1_1 is electrically connected to the second transistor M1_2, and the first transistor M1_1 receives a first supply voltage VCC1. The third transistor M1_3 is electrically connected to the fourth transistor M1_4, and the third transistor M1_3 receives a second supply voltage VCC2. One end of the first capacitor C1_1 is electrically connected between the first transistor M1_1 and the second transistor M1_2, and another end of the first capacitor C1_1 is electrically connected between the third transistor M1_3 and the fourth transistor M1_4. The second capacitor C1_2 is electrically connected to the fourth transistor M1_4 and the output end Vo.
As the charge pump circuit operates, the first transistor M1_1 and the fourth transistor M1_4 are turned off, and the second transistor M1_2 and the third transistor M1_3 are turned on. At this moment, the current flows to the second transistor M1_2 via the third transistor M1_3 and the first capacitor C1_1. The voltage of the first end point N1_1 is zero, and the voltage of the second end point N1_2 is VCC2. In other words, the first capacitor C1_1 is charging till the voltage across the first capacitor C1_1 reaches to VCC2. After the first capacitor C1_1 has finished charging, the first transistor M1_1 and the fourth transistor M1_4 are turned on and the second transistor M1_2 and the third transistor M1_3 are turned off. At this moment, the current flows to the fourth transistor M1_4 via the first transistor M1_1 and the first capacitor C1_1. The voltage of the first end point N1_1 is VCC1, and the voltage of the second end point N1_2 is VCC1 +VCC2. That is, the first capacitor C1_1 is charging the second capacitor C1_2 until the voltage across the second capacitor C1_2 is VCC1 +VCC2.
However, the traditional charge pump circuit has several disadvantages. As the charge pump circuit operates in a high-voltage environment, the first transistor M1_1, the second transistor M1_2, the third transistor M1_3 and the fourth transistor M1_4 need to be the high-voltage elements that can withstand high voltages. For example, VCC1 is 24V and VCC2 is 5V. As the first capacitor C1_1 is charging, the voltage across the first transistor M1_1 and the fourth transistor M1_4 is 24V according to the current direction. On the other hand, as the second capacitor C1_2 is charging, the voltage across the second transistor M1_2 and the third transistor M1_3 is also 24V. Thus, the first transistor M1_1, the second transistor M1_2, the third transistor M1_3 and the fourth transistor M1_4 need to be the high-voltage elements to withstand the 24V voltage.
Moreover, the first transistor M1_1, the second transistor M1_2, the third transistor M1_3 and the fourth transistor M1_4 need to be the high-voltage elements having their conducting resistances. The smaller the conducting resistances are, the smaller the voltages across the first transistor M1_1, the second transistor M1_2, the third transistor M1_3 and the fourth transistor M1_4 would be. Also, the current actually provided to the first capacitor C1_1 and the second capacitor C1_2 would be larger. In order to decrease the conducting resistances, the areas of the first transistor M1_1, the second transistor M1_2, the third transistor M1_3 and the fourth transistor M1_4 need to increase. However, increasing the areas of the first transistor M1_1, the second transistor M1_2, the third transistor M1_3 and the fourth transistor M1_4 would not only increase the entire circuit area but also take more time to pre-drive the first transistor M1_1, the second transistor M1_2, the third transistor M1_3 and the fourth transistor M1_4, such that it becomes harder to drive the first transistor M1_1, the second transistor M1_2, the third transistor M1_3 and the fourth transistor M1_4.