SYSTEM AND METHOD FOR IMPROVED LINE TRANSIENT RESPONSE IN CURRENT MODE BOOST CONVERTERS
An improved DC-DC power converter employs a feed-forward circuit to improve the response of the output voltage to transient signals on the input voltage. A portion of the input voltage generated by the feed-forward circuit is combined with either the sense voltage or the set point reference to offset one of the voltages applied to the PWM circuit comparator. The feed-forward circuit essentially bypasses the PWM feedback loop to quickly pre-compensate for the input transient and allow the output voltage to settle rapidly at a new operating point. The feed-forward circuit can be implemented with a resistive voltage divider network connected to the input voltage.
1 . A boost-mode power converter exhibiting improved input transient response comprising:
an input voltage source;
a boost switch coupled to the input voltage source;
a Pulse Width Modulation (PWM) circuit coupled to the boost switch and configured to selectively open and close the boost switch;
a current sense circuit configured to provide a sense voltage indicative of a current flowing through the boost switch;
a ramp generator configured to generate a periodic voltage ramp;
a feed-forward circuit configured to generate a feed-forward voltage comprising a portion of the input voltage;
a summing junction configured to combine the sense voltage, the periodic voltage ramp, and the feed-forward voltage to create a feedback ramp voltage;
a comparison circuit configured to compare a voltage set point and the feedback ramp voltage and to trigger the PWM circuit when the feedback ramp voltage exceeds the voltage set point;
2 . The boost-mode power converter of claim 1 , wherein the feed-forward circuit comprises a resistive divider network.
3 . The boost-mode power converter of claim 1 , wherein the comparison circuit comprises a voltage comparator.
4 . The boost-mode power converter of claim 1 , further comprising a current limit circuit configured to measure a current flowing through the boost switch and to prevent the PWM circuit from switching the boost switch when the current flowing through the boost switch exceeds a preset threshold level.
5 . The boost-mode power converter of claim 1 , further comprising a slope compensation circuit configured to apply a voltage ramp to the voltage set point.
6 . A boost-mode power converter exhibiting improved input transient response comprising:
an input voltage source;
a boost switch coupled to the input voltage source;
a Pulse Width Modulation (PWM) circuit coupled to the boost switch and configured to selectively open and close the boost switch;
a current sense circuit configured to provide a sense voltage indicative of a current flowing through the boost switch;
a ramp generator configured to generate a periodic voltage ramp;
a feed-forward circuit configured to generate a feed-forward voltage comprising a portion of the input voltage;
a summing junction configured to combine the sense voltage and the periodic voltage ramp to create a feedback ramp voltage;
a voltage set point combined with the feed-forward voltage to form a comparison voltage;
a comparison circuit configured to compare the comparison voltage and the feedback ramp voltage and to trigger the PWM circuit when the feedback ramp voltage exceeds the comparison voltage;
7 . The boost-mode power converter of claim 6 , wherein the feed-forward circuit comprises a resistive divider network.
8 . The boost-mode power converter of claim 6 , wherein the comparison circuit comprises a voltage comparator.
9 . The boost-mode power converter of claim 6 , further comprising a current limit circuit configured to measure a current flowing through the boost switch and to prevent the PWM circuit from switching the boost switch when the current flowing through the boost switch exceeds a preset threshold level.
10 . The boost-mode power converter of claim 6 , further comprising a slope compensation circuit configured to combine a voltage ramp with the voltage set point and the feed-forward voltage.
11 . A boost-mode power converter exhibiting improved input transient response comprising:
an input voltage source;
a boost switch coupled to the input voltage source;
a Pulse Width Modulation (PWM) circuit coupled to the boost switch and configured to selectively open and close the boost switch;
a current sense circuit configured to provide a sense voltage indicative of a current flowing through the boost switch;
a ramp generator configured to generate a periodic voltage ramp;
a feed-forward circuit comprising a resistive divider network operatively coupled to the input voltage source and configured to produce an output reflective of the input voltage;
a summing junction configured to combine the sense voltage, the periodic voltage ramp, and the output of the feed-forward circuit to create a composite ramp voltage;
a comparison circuit configured to compare a voltage set point and the composite ramp voltage and to trigger the PWM circuit when the composite ramp voltage exceeds the voltage set point.
12 . The boost-mode power converter of claim 11 , wherein the comparison circuit comprises a voltage comparator.
13 . The boost-mode power converter of claim 11 , further comprising a current limit circuit configured to measure a current flowing through the boost switch and to prevent the PWM circuit from switching the boost switch when the current flowing through the boost switch exceeds a preset threshold level.
14 . The boost-mode power converter of claim 11 , further comprising a slope compensation circuit configured to apply a voltage ramp to the voltage set point.
15 . In a boost-mode power convert comprising an input voltage source, a boost switch coupled to the input voltage source, a Pulse Width Modulation (PWM) circuit coupled to the boost switch and configured to selectively open and close the boost switch, a ramp generator configured to generate a periodic voltage ramp, a comparison circuit, and a feed-forward circuit; a method for improved transient response comprises the steps of:
generating a sense voltage indicative of a current flowing through the boost switch;
generating a periodic ramp voltage;
generating a feed-forward voltage indicative of the input voltage;
combining the ramp voltage, the sense voltage, and the feed-forward voltage to create a feedback ramp voltage;
generating a voltage set point;
comparing the voltage set point and the feedback ramp voltage;
generating a comparison trigger at a time when the feedback ramp voltage exceeds the voltage set point; and
triggering the PWM circuit with the comparison trigger.
16 . The method of claim 15 further comprising the step of preventing the PWM circuit from switching the boost switch when a measured current flowing through the boost switch exceeds a preset threshold level.
17 . The method of claim 15 further comprising the step of applying a voltage ramp to the voltage set point.
18 . In a boost-mode power convert comprising an input voltage source, a boost switch coupled to the input voltage source, a Pulse Width Modulation (PWM) circuit coupled to the boost switch and configured to selectively open and close the boost switch, a ramp generator configured to generate a periodic voltage ramp, a comparison circuit, and a feed-forward circuit; a method for improved transient response comprises the steps of:
generating a sense voltage indicative of a current flowing through the boost switch;
generating a periodic ramp voltage;
generating a feed-forward voltage indicative of the input voltage;
combining the ramp voltage and the sense voltage to create a feedback ramp voltage;
generating a voltage set point;
combining the voltage set point with the feed-forward voltage to form a comparison voltage;
comparing the comparison voltage and the feedback ramp voltage;
generating a comparison trigger at a time when the feedback ramp voltage exceeds the comparison voltage; and
triggering the PWM circuit with the comparison trigger.
19 . The method of claim 18 further comprising the step of preventing the PWM circuit from switching the boost switch when a measured current flowing through the boost switch exceeds a preset threshold level.
20 . The method of claim 18 further comprising the step of applying a voltage ramp to the voltage set point.