Switching controller capable of reducing acoustic noise for power converters
View Patent ↗The present invention provides a switching controller capable of reducing acoustic noise of a transformer for a power converter. The switching controller includes a switching circuit, a comparison circuit, an activation circuit, and an acoustic-noise eliminating circuit. The acoustic-noise eliminating circuit comprises a first-check circuit, a second-check circuit, a pulse-shrinking circuit, and a limit circuit. The first-check circuit receives a switching-current signal which is correlated to a switching current of the power converter and a PWM signal to generate a trigger signal. The second-check circuit receives the trigger signal to generate a control signal. When the frequency of the trigger signal falls into audio band, the control signal will be enabled to limit the switching current. Therefore, the acoustic noise of the transformer can be eliminated.
1. A switching controller capable of reducing acoustic noise of a power converter, comprising:
a switching circuit, generating a PWM (pulse-width-modulation) signal;
a comparison circuit, resetting said switching circuit cycle by cycle;
an activation circuit, generating a reset signal; and
an acoustic-noise eliminating circuit, receiving said PWM signal, a switching-current signal, and said reset signal and generating a switching signal and a limit signal, wherein said switching-current signal is correlated to a switching current of said power converter.
2. The switching controller as claimed in claim 1 , wherein said comparison circuit comprises:
a first comparator, comparing said switching-current signal and a first threshold, wherein said first comparator disables said PWM signal whenever said switching-current signal exceeds said first threshold;
a second comparator, comparing a feedback signal and said switching-current signal, wherein said second comparator disables said PWM signal whenever said switching-current signal exceeds said feedback signal; and
a third comparator, comparing said limit signal and said switching-current signal, wherein said third comparator disables said PWM signal whenever said switching-current signal exceeds said limit signal.
3. The switching controller as claimed in claim 2 , wherein said activation circuit comprising:
a fourth comparator, comparing said feedback signal and a second threshold; and
an AND gate, having an input coupled to an output of said fourth comparator and another input receiving a system reset signal, wherein said acoustic-noise eliminating circuit receives said reset signal from an output of said AND gate.
4. The switching controller as claimed in claim 3 , wherein said acoustic-noise eliminating circuit comprises:
a one-shot circuit, receiving said PWM signal to generate a width signal;
a first-check circuit, receiving said PWM signal and said switching-current signal and generating a trigger signal, wherein said first-check circuit enables said trigger signal whenever said switching-current signal exceeds a current threshold or whenever a pulse width of said PWM signal is greater than a value which is determined by a pulse-width threshold;
a second-check circuit, receiving said trigger signal and said reset signal and generating a control signal, wherein said second-check circuit enables said control signal whenever the frequency of said trigger signal falls into the audio band;
a limit circuit, providing said third comparator with said limit signal for comparison; and
a pulse-shrinking circuit, receiving said PWM signal, said width signal, and said control signal for generating said switching signal, wherein a pulse width of said switching signal decreases to limit said switching current of said power converter when said control signal is enabled.
5. The switching controller as claimed in claim 4 , wherein said pulse width of said switching signal is equal to that of said width signal whenever said control signal is enabled.
6. The switching controller as claimed in claim 4 , wherein said limit signal drops to a fifth threshold to limit said switching current of said power converter when said control signal is enabled.
7. The switching controller as claimed in claim 4 , wherein said limit signal beginning to gradually increase at the transient that said control signal is disabled from enabled state.
8. The switching controller as claimed in claim 3 , wherein said fourth comparator detects a light-load condition to activate said acoustic-noise eliminating circuit.