Power factor improvement

Claim 2

A power supply including a boost convertor comprising an electronic switch controlling current through a boost inductance, rectifier means for charging capacitor means which accumulate the resulting boost charge from the boost inductance, means for repeatedly switching the electronic switch, pulse width modulation means for varying the relative on/off period of each cycle of switching to cause the peak switch current to follow a variable amplitude wave of shape corresponding to the input voltage applied to the boost convertor and amplitude controlled by an error amplifier and multiplier thereby regulating the output voltage, a ramp signal generator for pulse width stability, and means for correcting for the difference between average current in the boost inductor and peak switch current to modify the pulse width modulation means to reduce distortion of the line current waveform.

Claim 3

A power supply as claimed in Claim 1 in which means are provided for monitoring the slope of the ripple current in the inductor, the output from those means being used both to generate an error correction signal as a figure proportional to the sum of the positive and negative slopes of the ripple current plus a bias for stable control at low output levels, and to control the ramp signal generator for pulse width stability.

Claim 4

A power supply as claimed in Claim 2 in which the means for monitoring the slope of the ripple current in the inductor are a small value supplementary inductor operated within its linear region and not biased into saturation by the line current passing through it.

Claim 5

A power supply as claimed in Claim 2 in which the means for monitoring the slope of the ripple current in the inductor are a current sensing resistor and an electronic differentiating circuit used to generate the required error correction signal.

Claim 6

A power supply including a boost convertor comprising an electronic switch controlling current through a boost inductance, rectifier means for charging capacitor means which accumulate the resulting boost charge from the boost inductance, means for repeatedly switching the electronic switch, pulse width modulation means for varying the relative on/off period of each cycle of switching to cause the peak switch current to follow a variable amplitude wave of shape corresponding to the input voltage applied to the boost convertor and amplitude controlled by an error amplifier and multiplier thereby regulating the output voltage, the multiplier including a comparator which switches on/off at a duty cycle determined by the error amplifier, a supplementary inductor operated within its linear region and not biased into saturation by the line current passing through it in series with the boost inductance, an output from the supplementary inductor following the slope of the ripple current caused by the switching of the boost inductor, the output from those means being used both to generate an error correction signal signal as a figure proportional to the sum of the positive and negative slopes of the ripple current plus a bias for stable control at low output levels, and to control a ramp signal generator for pulse width stability, and means for adding the error correction siganl to the variable amplitude waveform to reduce line current distortion, and means for generating a ramp signal and adding it to the switch current signal for pulse width stability.

Claim 7

A power supply including a boost convertor comprising an electronic switch controlling current through a boost inductance, rectifier means for charging capacitor means which accumulate the resulting boost charge from the boost inductance, means for repeatedly switching the electronic switch, pulse width modulation means for varying the relative on/off period of each cycle of switching to cause the peak switch current to follow a variable amplitude wave of shape corresponding to the input voltage applied to the boost convertor and amplitude controlled by an error amplifier and multiplier thereby regulating the output voltage, the multiplier including a comparator which switches on/off at a duty cycle determined by the error amplifier, a supplementary inductor operated within its linear region and not biased into saturation by the line current passing through it in series with the boost inductance, an output from the supplementary inductor following the slope of the ripple current caused by the switching of the boost inductor, the output from those means being used both to generate an error correction signal signal as a figure proportional to the sum of the positive and negative slopes of the ripple current plus a bias for stable control at low output levels, and to control a ramp signal generator for pulse width stability, and means for adding the error correction siganl to the variable amplitude waveform to reduce line current distortion, and means for generating a ramp signal and adding it to the switch current signal for pulse width stability.

Claim 8

A power supply as claimed in Claim 3 or Claim 5 in which negative parts of the said waveform generated across the supplementary inductor are detected by a diode and stored on a capacitor controlling a current source comprising transistor and resistor for charging a capacitor at a linear rate, that capacitor being discharged at the end of each cycle.

Claim 9

A power supply as claimed in any preceding claim in which the multiplier is a two-stage multiplier whose dynamic range is the product of the range of each stage.

Claim 10

A power supply as claimed in any preceding claim in which one or more slave boost convertors are connected in parallel with a master boost convertor, the error corrected sine wave reference signal being fed to all pulse width modulators, causing all boost convertors to share current equally, a master oscillator providing clock signals for synchronisation with equal phase angles between clock signals.