Patent ID: 8680831
Filing Date: 2014-03-25
Classification: H02M

Abstract:
1. A constant frequency ON-time control system applied to a voltage regulator, the voltage regulator determining a time length of an input voltage inputted into the voltage regulator according to an ON-time and thereby regulating an output voltage, the constant frequency ON-time control system comprising: a constant frequency ON-time control circuit, for setting the ON-time according to a system duty cycle of the voltage regulator and a frequency setting parameter; and a frequency setting parameter adjusting circuit, for generating a frequency setting parameter adjust value according to an OFF-time, which is corresponding to the ON-time of the voltage regulator, and generating the frequency setting parameter through performing an operation on the frequency setting parameter adjust value and a preset frequency setting parameter, wherein, the frequency setting parameter adjusting circuit modulates the frequency setting parameter through changing a result of the operation based on the frequency setting parameter adjust value when the OFF-time is shorter than an OFF-time reference value, thereby increases the ON-time, wherein the frequency setting parameter adjusting circuit comprises: an error amplifier, for outputting an error amplified signal according to a difference between a control voltage representing the OFF-time and a reference voltage representing the OFF-time reference value, wherein the error amplified signal has a specific polarity when the OFF-time is shorter than the OFF-time reference value; a low-pass filter, for outputting a low-pass filtered error amplified signal through performing a low-pass filtering operation on the error amplified signal; a polarity selection circuit, for outputting the frequency setting parameter adjust value according to the low-pass filtered error amplified signal, and adjusting the frequency setting parameter adjust value to an non-zero value when the low-pass filtered error amplified signal is with the specific polarity; and a computing circuit, for generating the frequency setting parameter through computing the preset frequency setting parameter and the frequency setting parameter adjust value, and providing the frequency setting parameter to the constant frequency ON-time control circuit.