Constant current circuit of DC converter

Abstract

The invention relates to a constant current circuit of a DC converter. The constant current circuit comprises an operational amplifier, a lower pull tube and a bias voltage generating circuit. An output end of an error amplifier in the DC converter is a first node and connected with a drain electrode of the lower pull tube and a non-inverting input end of the operational amplifier, a grid electrode of the lower pull tube is connected with an output end of the operational amplifier, and a source electrode of the lower pull tube is grounded; and an output end of the bias voltage generating circuit is connected to an inverting input end of the operational amplifier, and an input end of the bias voltage generating circuit is connected to an input end of a driving circuit in the DC converter. The constant current circuit provided by the invention is more accurate in limiting the current and faster in response speed. When voltage of the first node is smaller than the bias voltage, the lower pull tube is closed; and when the voltage of the first node rises to a bias voltage value, the operational amplifier suppresses the voltage of the first node to the bias voltage. The bias voltage generating circuit is additionally arranged, and the bias voltage outputted by the bias voltage generating circuit equals to the sum of a fixed voltage and a voltage related to output clock of the driving circuit, thereby enabling a switch to limit the current to maintain constant.

Description

technical field [0001] This invention relates to integrated circuit design, in particular to a constant current limiting circuit for use in DC converters (BUCK). Background technique [0002] The working loop of the DC converter in the prior art includes a sawtooth wave generating circuit, a voltage conversion circuit with a BLCK structure, an output voltage feedback circuit and a switch current limiting circuit. The slope of the sawtooth wave is added by two parts: the first part is a fixed slope, which is provided by an integrated component other than the converter; the slope of the second part is proportional to the switch current, and is obtained by the switch current detection circuit from the NMOS connected to the input voltage. Obtained on the drain of the switching tube. The output voltage of the conversion circuit generates a feedback voltage through the feedback network, which is connected to the negative input terminal of the error amplifier, and the output termi...

AI Technical Summary

Problems solved by technology

[0004] 1. There is a certain process and temperature deviation in the threshold of the pull-down tube itself, and the voltage of the first node also has a certain value, which affects the accuracy of the current limit.

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