Patent Application
20080068203
Although the phase shift technique has been employed in several power inverter designs, there are still rooms for improvement. The present invention provides a digital and an analog method to implement the phase shift mechanism which can produce a system that is cost effective and has fewer components. The digital method utilizes a digital circuit to construct a module whose function is to provide a plurality of phased periodic PWM signals. The digital circuit is further controlled by precise timing and by several additional parameters to modify the phase delay between different driving signals. The digital means can provide users with friendly operational interface which is very important in the field of consumer electronic products. The digital means has the advantage of a module-based design method which can accelerate chips development process and shorten the time to market. Beside the digital method, an analog method can also be applied in order to drive a lighting system used in a large panel or in a harsh environment. Using the analog method, a driving system that supports high voltage and high current in order to obtain good quality illumination can be achieved.
This embodiment uses a digital scheme to add a phase shift to an original input signal 31, wherein the digital scheme comprises a period counter 33, a divider 34, an adder 35, a pulse width counter 36, a pulse width recording buffer 37, and a comparator 38. The original input signal 31 can be a signal with various waveforms. For example, a periodic square waveform 32 is depicted in
The operation of the digital scheme is described herein. First, the original input signal 31 is sent to the period counter 33 where the period of the input signal 31 can be determined. In the interim, the input signal 31 is also sent to the pulse width counter 36 where the pulse width of the input signal 31 can be counted based on a specific frequency or a specific clock. Second, the divider 34 divides the period of the input signal 31 according to a predetermined parameter. The divider 34 can calculate the necessary phase shift between the output signal 39 and the input signal 31. In other embodiments, the predetermined parameter can be changed. Therefore, users can modify the digital scheme to obtain an appropriate phase shift. Moreover, users can change the parameter to adapt the digital scheme to various environmental factors. Third, the adder 35 adds the necessary phase shift to the pulse width of the input signal 31 to generate an end indicator.
Finally, a phase delay signal can be obtained by using the above digital blocks. A comparator 38 receives (1) the period information from the period counter 33, (2) a start indicator from the divider 34, and (3) the end indicator from the adder 35. After the comparison performed by the comparator 38, the comparator 38 can generate a phase delay output signal 39. For example, the comparator 38 may output high when the start indicator is less than the period and the end indicator is greater than the period. Otherwise, the output 39 keeps low active.
It is possible to expand the digital scheme to generate a series of phase delayed signals. It is also possible to adjust the phase shift according to different conditions to those skilled in the art. Thus, various modifications apply to the digital scheme should still fall within the scope of the present invention.
In this embodiment, an analog scheme comprises a first ramp wave generator 41, a first comparator 43, a one shot generator 44, a second ramp wave generator 45, a second comparator 46, and two resistors 47, 48. The ramp wave generator 41 generates a ramp wave 42 having a period T. In the figure, the dotted line indicates the ramp wave 42 starts at time t=0. This starting time is the same for the output 410 such that a generated phase shift can be clearly illustrated.
Before the comparator 43 compares the ramp wave 42, a predetermined voltage is created by the resistors 47, 48. For example, a specific voltage VH is coupled to the resistor 47, and a ground is coupled to the resistor 48. A reference voltage in the range between the voltage VH and the ground can be determined. The reference voltage can also be adjusted by changing the resistance of the resistors 47, 48. The reference voltage is used to determine how much phase shift will be generated, which is similar to the start indicator in the digital scheme.
The first comparator 43 first compares the voltage of the ramp wave 42 to the reference voltage, and then it generates the comparison result to the one shot generator 44. The comparison operation may be configured in such manner that it generates either a high voltage level when the ramp wave 42 is greater than the reference voltage; or a low voltage level when the ramp wave 42 is lower than the reference voltage. Therefore, the phase delay information can be determined when the output of the first comparator 43 creates voltage jumps, e.g., positive edges.
The one shot generator 44 can generate pulses when detecting signal edges from the first comparator 43. These pulses act as reset signals to the second ramp wave generator 45. The second ramp wave generator 45 use these reset signals to decide the starting point of the ramp wave. Accordingly, a phase delayed ramp wave is generated wherein the phase delayed is determined by changing the reference voltage.
Finally, a second comparator 46 compares the phase delayed ramp wave to a second reference voltage Vref. A periodic square wave 49 with a desirable pulse width can be generated from the output 410 of the second comparator 46. For example, the second comparator 46 may output high when the voltage of the phase delayed ramp wave is lower than that of the second reference voltage Vref. Otherwise, when the voltage of the phase delayed ramp wave is higher than that of Vref, it will output low. If the pulse width is not wide enough, the voltage level of the second reference voltage Vref may be changed to a higher level.
The analog scheme in
It will be apparent to those skilled in the art that various modifications can be made to the present invention without departing from the scope of the invention. For example, the reference voltages may be generated by regulators instead of a chain of resistors. Moreover, the one shot generator may comprise a delay circuit and a logic circuit.
