Discontinuous conduction mode (DCM) using sensed current for a switch-mode converter

A method for controlling a switch-mode converter which has a switch and an inductor coupled to the switch wherein the switch-mode converter receives an input voltage and provides an output voltage and wherein a sensed current is observed from the switch-mode converter, comprising:

• in configuring to operate the switch-mode converter in a discontinuous conduction mode (DCM) and responsive to comparisons made by the comparing:
• comparing a sensed current value representative of the sensed current and a peak current value representative of a peak current, wherein the peak current is determined by a product of a multiplying factor and a target current wherein further the multiplying factor is greater than or equal to two;
• turning on the switch and observing an on-time duration of the switch until the sensed current reaches the peak current;
• calculating a switching period of a switch control signal for controlling the switch wherein the switching period is responsive to the peak current and the observed on-time duration;
• and
• varying the switching period responsive to the on-time duration and the multiplying factor such that an average of the sensed current equals the target current.

A power factor corrector (PFC), comprising:

• a switch-mode boost stage having a switch and an inductor coupled to the switch wherein the switch-mode boost stage receives a rectified line input voltage and provides a link output voltage and wherein a sensed current is observed from the switch-mode boost stage;
• a target current generator for receiving the link output voltage and for generating a target current proportionate to the rectified line input voltage;
• a comparator for receiving and comparing a sensed current value representative of the sensed current and a peak current value representative of a peak current, wherein the peak current is determined by a product of a multiplying factor and a target current, wherein further the multiplying factor is greater than or equal to two;
• and
• a finite state machine, configured to operate the switch-mode converter in a discontinuous conduction mode (DCM), responsive to comparisons made by the comparator, for:
• turning on the switch and observing an on-time duration of the switch until the sensed current reaches the peak current;
• calculating a switching period of a switch control signal for controlling the switch wherein the switching period is responsive to the peak current and the observed on-time duration;
• and
• varying the switching period responsive to the on-time duration and the multiplying factor such that an average of the sensed current equals the target current.

A method for power factor correction (PFC), comprising:

• coupling a switch and an inductor together to form a switch-mode boost stage that receives a rectified line input voltage and provides a link output voltage;
• observing a sensed current from the switch-mode boost stage;
• receiving the link output voltage;
• generating a target current proportionate to the rectified line input voltage;
• and
• in configuring to operate the switch-mode converter in a discontinuous conduction mode (DCM) and responsive to comparisons made by the comparing:
• comparing a sensed current value representative of the sensed current and a peak current value representative of a peak current, wherein the peak current is determined by a product of a multiplying factor and a target current wherein further the multiplying factor is greater than or equal to two;
• turning on the switch and observing an on-time duration of the switch until the sensed current reaches the peak current;
• calculating a switching period of a switch control signal for controlling the switch wherein the switching period is responsive to the peak current and the observed on-time duration;
• and
• varying the switching period responsive to the on-time duration and the multiplying factor such that an average of the sensed current equals the target current.

An integrated circuit which incorporates a switch-mode converter controller for controlling a switch-mode converter which has a switch and an inductor coupled to the switch wherein the switch-mode converter receives an input voltage and provides an output voltage and wherein a sensed current is observed from the switch-mode converter, and wherein the switch-mode converter controller includes a comparator and a finite state machine, the integrated circuit configured to:

• in configuring to operate the switch-mode converter in a discontinuous conduction mode (DCM) and responsive to comparisons made by the comparing:
• compare a sensed current value representative of the sensed current and a peak current value representative of a peak current, wherein the peak current is determined by a product of a multiplying factor and a target current wherein further the multiplying factor is greater than or equal to two;
• turn on the switch and observing an on-time duration of the switch until the sensed current reaches the peak current;
• calculate a switching period of a switch control signal for controlling the switch wherein the switching period is responsive to the peak current and the observed on-time duration;
• and
• vary the switching period responsive to the on-time duration and the multiplying factor such that an average of the sensed current equals the target current.