Flyback converter control with feed forward
AssigneeInternational Business Machines Corporation
InventorGirish C. Johari
Life of this patent
Estimating the term…
Abstract
A constant loop gain is achieved in a flyback type DC to DC converter by use of feedback to correct for load variations and feed forward to correct for line voltage variations. The feedback signal and a reference voltage are compared by an error amplifier. An output of the error amplifier is multiplied by a constant and is added to a signal proportional to line voltage. The resulting sum causes modification of the slope of a ramp voltage which is compared to the voltage at the output of the error amplifier to control the "on" times of the converter switching devices.
Claims15
In a DC to DC converter having a flyback connected power transformer secondary winding, rectification, and filter circuit, and switching circuitry for selectively energizing the primary winding of said transformer, regulation circuitry comprising:
- means for amplifying the difference between a portion of an output voltage of said power supply and a reference voltage to generate an error voltage;
- means for generating a ramp voltage waveform having a ramp angle proportional to the sum voltage of a portion of said error voltage and a portion of a DC voltage applied to said converter;
- means for inhibiting said means for generating said ramp voltage waveform regardless of ramp voltage magnitude and for maintaining said ramp voltage generating means in an inhibited state for a predetermined time duration;
- means for comparing said error voltage with said ramp voltage waveform;
- and
- means, during the rising period of said ramp voltage, for applying a signal to said switching circuitry to energize said primary winding while said error voltage exceeds said ramp voltage.
In a DC to DC converter in which a feedback signal derived from the converter output is compared to a reference voltage for generation of an error voltage which error voltage is compared to the instantaneous amplitude of a ramp voltage for control of the "on" times of converter switching devices, wherein a feed forward signal proportional to line voltage is applied to a ramp generator to control the slope of said ramp voltage, the improvement comprising:
- means for multiplying said error voltage by a constant to generate a first signal;
- summing means receiving said feed forward signal as an input and having an output applied to said ramp generation circuit to affect the slope of said ramp;
- said summing means receiving said first signal as a second input thereto for addition of said first signal to said feed forward signal;
- and
- said ramp generation circuit including means for inhibiting the generation of said ramp voltage regardless of ramp voltage magnitude and for maintaining said ramp voltage generation circuit in an inhibited state for a predetermined time duration.
Dependencies are inferred from the claim text.