Patent ID: 9490739
Filing Date: 2016-11-08
CPC Classification: F04D,H02P,Y02B

Claim Text:
1. A rotation speed control circuit with function of auto-calibrating rotation speed error, comprising: a first multiplexer, connected to a calibration clock signal and a rotation speed clock signal, for outputting a first switch signal according to a mode switch signal, wherein after an edge-trigger detector receives the first switch signal, the edge-trigger detector respectively outputs a second switch signal and a third switch signal with high voltage level when the first switch signal is in high voltage level; a second multiplexer, connected to a calibration voltage and a reference voltage, for outputting a target voltage according to the mode switch signal; an error amplifier, connected to an external capacitor and the second multiplexer, for outputting an error voltage according to a capacitor voltage and the target voltage; a current compensation circuit, having a preset current value, connected to the first switch signal, the current compensation circuit adjusting a first current so as to compensate the external capacitor; a sampling and hold circuit, connected to the error amplifier, for receiving the second switch signal and accordingly sampling the error voltage and maintaining for a period of time, and outputting an sampling and hold voltage signal; and a comparator, receiving a preset triangular wave signal and the sampling and hold voltage signal and accordingly performing comparison operation so as to output a PWM rotation speed signal, wherein in a calibration mode, the first and the second multiplexer choose the calibration clock signal and the calibration voltage respectively according to the mode switch signal and the rotation speed control circuit adjusts current value of the first current, wherein when the capacitor voltage of the external capacitor is larger than or equal to the target voltage, a calibration task is finished and voltage level of the error voltage is changed to high voltage level so that the current compensation circuit stops adjusting current value of the first current for compensating the external capacitor; wherein the current compensation circuit makes current value of the first current increase gradually so as to increase the capacitor voltage until the capacitor voltage is equal to the target voltage, for compensating change of the external capacitor.