Output voltage ripple reduction technique for burst mode operation of power converter
A power converter is controlled by a control circuit that includes a burst mode operation during low load conditions. A compensation circuit modifies a control signal to reduce the number of switch cycles during a burst. The compensation circuit includes a time-variant offset to the control signal that is removed when the power converter input signal is connected to low voltage.
1 . A power converter comprising:
switches that alternately connect high and low voltages to an input to a reactive circuit;
a control circuit that controls cycling of the switches, the control circuit including a burst mode in which the switches are cycled in a burst and then held off during a wait period responsive to a control signal; and
a compensation circuit that modifies the control signal to reduce the number of switch cycles during a burst.
2 . A power converter as claimed in claim 1 , wherein the number of switch cycles is reduced to one cycle.
3 . A power converter as claimed in claim 1 , wherein -the compensation circuit adds a time-variant offset to the control signal.
4 . A power converter as claimed in claim 3 , wherein the time-variant offset is removed when the input is connected to the low voltage.
5 . A power converter as claimed in claim 1 , wherein the input is applied to an inductor of the reactive circuit.
6 . A power converter as claimed in claim 1 , wherein the control signal falls as the power converter output rises.
7 . A method of providing a power conversion comprising:
alternately switching switches to connect an input to a reactor circuit to high and low voltages;
controlling cycling of the switches in a burst mode in which the switches are cycled in a burst and then held off during a wait period responsive to a control signal; and
modifying the control signal to reduce the number of switch cycles during a burst.
8 . A method as claimed in claim 7 , wherein the switch cycles are reduced to one cycle during the burst.
9 . The method as claimed in claim 7 , wherein the control signal is modified by a time-variant offset.
10 . A method as claimed in claim 9 , wherein the offset is removed when the input is connected to a low voltage.
11 . A method as claimed in claim 7 , wherein the input is applied to an inductor of the reactive circuit.
12 . A method as claimed in claim 7 , wherein the control signal falls as -the output of the power converter rises.
13 . A power converter comprising:
switches that alternately connect an input to a reactive circuit to high and low voltages;
a control circuit that controls cycling of the switches, the control circuit including a burst mode in which the switches are cycled in a burst and then held off during a wait period responsive to a control signal; and
compensation circuit means for modifying the control signal to reduce the number of switch cycles during a burst.