EMI REDUCTION OF POWER CONVERTERS BY WAY OF CONTROLLED RANDOMIZED MODULATION OF OSCILLATING SIGNALS

摘要

A switching control circuit for a switching power converter utilizes an oscillating signal that causes reduced electromagnetic interference by the power converter by way of modulating the frequency of the oscillating signal within a specified frequency range. An output voltage monitor circuit monitors the output voltage of the power converter, thus producing an output voltage monitor signal. Also, a randomized signal generator creates a randomized signal, which is then used to drive a frequency range converter that is employed to produce a frequency modulation signal. The current state of the frequency modulation signal is based on the current state of the randomized signal, with the frequency range converter limiting the current state of the frequency modulation signal so that the oscillating signal will only operate within the specified frequency range. A variable frequency oscillator then generates the oscillating signal whose frequency is based on the current state of the frequency modulation signal. A comparator then compares the oscillating signal with the output voltage monitor signal to produce a switch control signal, which is then employed to control a switching element of the power converter.