Controller for isolated boost converter with improved detection of RMS input voltage for distortion reduction and having load-dependent overlap conduction delay of shunt MOSFET

A method for detecting and conditioning RMS information for a power factor correction controller, said method comprising the steps of:

• storing a voltage signal proportional to the average value of a rectified AC input line voltage signal over at least one cycle;
• converting said stored voltage signal into a digital signal corresponding to said stored voltage signal;
• and
• converting said digital signal into an analog signal for further processing by an analog computational circuit consistent with power factor correction between said rectified AC input line voltage signal and a current signal associated with said rectified AC input line voltage signal.

A delay circuit for controlling the time at which a low power transition switch switches in an isolated boost converter circuit having at least one high power boost switch, said delay circuit comprising:

• signal processing means responsive to a feedback signal in the isolated boost converter circuit for providing a load signal indicative of an output load of said isolated boost converter circuit;
• reference means responsive to a transition signal indicating an off transition of the high power boost switch in said isolated boost converter circuit for providing a first reference signal;
• comparing means for comparing said load signal and said first reference signal;
• and
• switching the low power transition switch at a time determined by the comparison between the load signal and the first reference signal.

A method for controlling the time at which a low power transition switch switches in an isolated boost converter circuit having at least one high power boost switch, said method comprising the steps of:

• processing a feedback signal in the isolated boost converter circuit;
• providing a load signal indicative of an output load of said isolated boost converter circuit based upon said processed feedback signal;
• providing a reference signal following an off transition of the high power boost switch in said isolated boost converter circuit;
• comparing said load signal and said reference signal;
• and
• switching the low power transition switch at a time determined by the comparison between the load signal and the reference signal.

A controller for use as part of a switching preregulator providing substantially DC output power from rectified AC line power, comprising:

• a pulse-width modulator operative to generate high-frequency switch-control signals to be supplied to switching elements in the preregulator, the respective duty cycles of the switch-control signals varying in response to the magnitude of a current control signal;
• a multiply-divide circuit operative to generate the current control signal such that the value of the current control signal is proportional to the product of an error signal and a feedforward signal divided by a distortion-reducing signal, the error signal representing the deviation of the actual preregulator output voltage from a desired DC preregulator output voltage, the feedforward signal being proportional to the rectified AC line voltage;
• an integrate-and-hold circuit operative during each cycle of the AC line power to integrate the feedforward signal over one half of the cycle and to hold the integrated value over the other half of the cycle;
• an A/D converter operative to convert the value held by the integrate-and-hold circuit to a digital value;
• a register operative during each cycle of the AC line power to store the digital value from the A/D converter;
• and
• a multiplying D/A converter continually operative to generate the distortion-reducing signal such that the value of the distortion-reducing signal is proportional to the square of the value stored in the register.