Hybrid soft-start for isolated converter
AssigneeAnalog Devices, Inc.
InventorSubodh Prakash Madiwale
Life of this patent
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Abstract
Apparatus and methods are provided for starting up an isolated power converter. In an example, an integrated circuit for controlling an isolated power converter can include a control circuit configured to control a duty cycle of a primary switch according to an startup schedule during an initial interval of a start-up period of the isolated power supply, and to switch to a closed-loop control mode of the primary switch during a second interval of the start-up period after a voltage level of the DC output power signal is above a start-up threshold.
Claims25
A power converter comprising:
- an electrical isolator having a primary side and a secondary side that is electrically isolated from current from the primary side, the isolator configured to receive an input voltage on the primary side and to provide an oscillating power signal on the secondary side;
- a primary switch, configured to complete a primary side circuit in a first state and to interrupt the primary side circuit in a second state, the primary side circuit including the primary side of the isolator;
- a secondary circuit configured to receive the oscillating power signal and to provide a direct current (DC) output power signal;
- a control circuit configured to control a duty cycle of the primary switch according to an open-loop duty cycle during a first interval of a start-up period of the isolated power converter, and to switch to a closed-loop control mode of the primary switch during a second interval of the start-up period after a voltage level of the DC output power signal is determined to be above a start-up threshold value;
- and
- wherein the control circuit includes a peak current detector circuit configured to receive a representation of current in the primary side of the isolator during the first interval of the start-up period and to store in memo a last duty cycle indicative of a peak current of the primary side of the isolator during the on-time of the primary switch.
An integrated circuit for controlling an isolated power converter, the isolated power converter having a primary side configured to receive an input voltage and a secondary side configured to provide a direct-current (DC) supply voltage, the primary side and the secondary side electrically isolated from each other, the integrated circuit comprising:
- a control circuit configured to control a duty cycle of the primary switch according to an open-loop duty cycle schedule during an initial interval of a start-up period of the isolated power supply, and to switch to a closed-loop control mode of the primary switch during a second interval of the start-up period after a voltage level of the DC supply voltage is above a start-up threshold, wherein the control circuit includes:
- an error amplifier configured to provide a comparison of a representation of a voltage level of the DC supply voltage and a second threshold and an error signal based on the comparison;
- a current detector configured to store a peak current value of the primary switch during the initial interval of a start-up period in a memory circuit;
- a current limit comparator, the current limit comparator including;
- a first input to receive a representation of current passing through the primary switch;
- a second input to receive an isolated version of the error signal;
- and
- wherein the current limit comparator is configured to, during at least a first switching cycle of the closed loop control mode provide a current limit signal based on a comparison of the representation of current passing through the primary switch and the peak current value.
A method of soft-starting an isolated power converter, the method comprising:
- receiving an input voltage on a primary side of an isolation element of the isolated power converter;
- providing an oscillating power signal on the secondary side of the isolation element;
- receiving the oscillating power signal at a secondary side circuit of the isolated power converter;
- providing a direct current (DC) output power signal at an output of the secondary side circuit;
- controlling a primary side switch of the isolated power converter in an open-loop mode during an initial interval of a start-up period of the isolated power converter, the primary side switch electrically coupled with the primary side of the isolation element of the isolated power converter;
- storing a last duty cycle of the primary switch during the initial interval of a start-up period in memory to provide a stored last duty cycle;
- and
- controlling the primary side switch in a closed-loop mode during a second interval of the start-up period, the second interval immediately subsequent to the initial interval, wherein the controlling the primary side switch in a closed-loop mode includes using the stored last duty cycle as an initial duty cycle of the closed loop mode.
Dependencies are inferred from the claim text.