Analog variable-frequency controller and switching converter therewith

#1. Field of the Invention

#The present invention relates to a controller and a switching converter, and more particularly to an analog variable-frequency controller and the switching converter therewith.

#2. Description of the Related Art

#The objectives, technical contents and characteristics of the present invention can be more fully understood by reading the following detailed description of the preferred embodiments, with reference made to the accompanying drawings, wherein:

#FIG. 1a and FIG. 1b schematically illustrate a relationship between a load current and a switching frequency, and a relationship between a load current and an optimized power efficiency, respectively;

#FIG. 2 is a block diagram schematically illustrating an analog variable-frequency controller according to one embodiment of the present invention;

#Referring to FIG. 2, the analog variable-frequency controller 10 according to one embodiment, includes a first current generator 11, a second current generator 12, a clock generator 14 and a light/heavy load selector 13. The first current generator 11 receives a load current signal VLoad and outputs a corresponding first voltage signal; and the second current generator 12 also receives the load current signal VLoad and outputs a corresponding second voltage signal. The light/heavy load selector 13 is electrically connected to the first current generator 11, the second current generator 12 and the clock generator 14. The light/heavy load selector 13 receives a control signal ZC to control the clock generator 14 to select receiving the first voltage signal output by the first current generator or the second voltage signal output by the second current generator. The clock generator 14, based on the first voltage signal or the second voltage signal, generates a corresponding switching frequency signal fSW.

#In one embodiment, the switching frequency signal fSW output by the clock generator 14 receiving the first voltage signal output by the first current generator 11 is positively correlated with the first voltage signal, i.e. the larger the first voltage signal, the faster the switching frequency fSW. On the other hand, the switching frequency signal fSW output by the clock generator 14 receiving the second voltage signal output by the second current generator 12 is negatively correlated with the second voltage signal, i.e. the larger the second voltage signal, the slower the switching frequency signal fSW. According to the aforementioned description, the analog variable-frequency controller 10, according to an embodiment, can generate optimized switching frequency signals fSW for both light-load and heavy-load operations.

#The following embodiment is intended to illustrate the analog variable-frequency controller 10, however, it is not intended to limit the scope of the present invention. Referring to FIG. 3, the clock generator 14 includes a first P-type channel metal oxide semiconductor field effect (PMOS) transistor M1, a second PMOS transistor M2, a first comparator CPH, a second comparator CPL, a capacitor C, an SR latch 141 and a discharge switch M4. The source of the first PMOS transistor M1 is electrically connected to a voltage source VDD, its drain is electrically connected to the light/heavy load selector 13, and its gate is electrically connected to its drain. The source of the second PMOS transistor M2 is electrically connected to the voltage source VDD, and its gate is electrically connected to the gate of the first PMOS transistor M1 to form a current mirror circuit.