Feed-forward control method and circuit for converter

Abstract

The invention provides a feed-forward control method and circuit for a converter. According to the feed-forward control method and circuit for the converter, when the conduction voltage of the drain of a power tube is greater than the saturation voltage drop of the drain, the power tube is located at a saturation region; the startup limiting current of the power tube is directly controlled throughsaturation mirroring according to internal bias current which is inversely proportional to an input voltage; and after the conduction voltage of the drain of the power tube is smaller than the saturation voltage drop, the power tube enters a linear region, and compensation current which rises along with the drop of the voltage of the drain end of the power tube is superposed on the internal biascurrent, so that the current loss of the power tube in the linear region can be compensated. With the feed-forward control method and circuit for the converter of the invention adopted, the problems of chip heat emission and capacitive load which occur when constant-voltage converters with the same power level and different input voltages set startup limiting current are solved; and chip pins do not need to be arranged, so that PCB layout resources are saved; and in a range of + / -10% of the same input voltage, the control of the startup limiting current can still be realized, so that startup heat emission and capacitive load capacity control is more flexible.

Description

technical field [0001] The invention is suitable for switch-type converters, especially for the feed-forward control method and circuit of converters in full-bridge and push-pull converters. Background technique [0002] Constant-voltage power modules often use full-bridge converters and push-pull converter topologies. Such as figure 1 , taking the full-bridge converter as an example, for a constant voltage system, the output voltage is close to zero during start-up or output short-circuit stage, the voltage drop on the primary winding is clamped to a very low level, and most of the voltage drop falls at At the drain end of the switch tube, when the power tube is turned on, a very large saturation current will flow through it, which is easy to burn out. In the steady-state stage after the output is established, the load current on the secondary side directly determines the current flowing through the power tube on the primary side, and the danger of burning is eliminated. ...

AI Technical Summary

Problems solved by technology

However, these methods require external chip pins and devices, and for a system with a fixed primary and secondary turn ratio, within the range of ±10% of the nominal input voltage, the fixed start-up limited current start-up limited current Ist and timing The time Td can no longer be adjusted. At this time, it is easy to cause the temperature of the system to rise or the capacitive load capacity to weaken under extreme conditions.

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