Peak voltage detector and related method of generating an envelope voltage

Abstract

A peak detector circuit receives an oscillating power supply signal. A capacitor is selectably coupled to the signal and charged to a value corresponding to a peak value of the signal. A switch is then opened to isolate the capacitor. When the signal rises to within a selected threshold, relative to the stored value, a comparator produces a command signal to close the switch, again coupling the capacitor to the signal. The peak detector can also include a tracking circuit that controls the capacitor to track the oscillating signal while the switch is closed, a timer circuit that closes the switch and activates the tracking circuit if more than a selected time passes without production of a command signal, a circuit that controls the polarity of a leakage current of the capacitor, a further auxiliary capacitor and a further auxiliary switch with a further control logic.

Description

BACKGROUND[0001]1. Technical Field[0002]This disclosure relates to detectors of voltage peaks of oscillating signals and more particularly to a novel architecture, realizable in a completely integrated form, adapted to generate an envelope voltage corresponding to the instantaneous peak value of an input oscillating voltage and to a related method.[0003]2. Description of the Related Art[0004]Forced switching power supplies and, more particularly, systems for active power factor correction (PFC), store information about peak values of an input voltage, that typically is the voltage of the mains, thus at a low frequency.[0005]In general, PFC pre-regulators are switching converters controlled such to obtain a regulated DC output voltage from an input AC voltage. Using particular switching techniques, PFC regulators are capable of absorbing a sinusoidal current in phase with the voltage of the mains, thus obtaining in this way a power factor close to 1 and a reduced total harmonic disto...

AI Technical Summary

Benefits of technology

The patent describes a device that can accurately detect the peaks of an electric voltage, even if there are long periods of time between them. This is made possible by a special design that can keep track of the previous peak value and is useful for analyzing the shape of the electric voltage.

Problems solved by technology

The amplifier is relatively slow thus, before being capable of following and compensating the variation, output undershoots / overshoots may occur.

A fast detection of peaks may be insufficient when they increase but also when their value decreases.

Indeed, if the detection of the peak reduction of the mains voltage is very slow, the setting of the correct feedforward action will be delayed, with a consequent excessive overshoot of the output voltage of the pre-regulator because of great variations of the supply voltage.

A drawback of this type of circuit, besides using two discrete external components, consists in that the system responds according to an exponential law with a time constant RFFCFF that, for the reasons stated above, will be relatively great (typically in the order of several hundreds of ms).

This implies a loss of effectiveness of the feedforward technique for a longer time the greater the variation of the input voltage and thus the greater the time constant RFFCFF.

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