Switching control circuit, switching circuit and constant switching-on time control method

Abstract

The invention provides a switching control circuit, a switching circuit and a constant switching-on time control method. When switching-on time of a main pipe reaches constant switching-on time, whether inductive current reaches instruction current or not is detected; if the inductive current does not reach the instruction current, the switching-on time of the main pipe is prolonged; the main pipe is switched off and an auxiliary pipe is switched on after the inductive current reaches the instruction current or exceeds the instruction current by a certain threshold value; when the main pipe is switched off and the auxiliary pipe is switched on, whether the instruction current is lower than the instruction current or not is detected in real time; and if the auxiliary pipe is switched off, the main pipe is switched on again. The switching control circuit, the switching circuit and the constant switching-on time control method, provided by the invention, aim at realizing stable-voltage control of output voltage, so that the voltage conversion with a relatively large duty cycle is realized.

Description

technical field [0001] The invention relates to the technical field, in particular to a switch control circuit, a switch circuit and a constant on-time control method. Background technique [0002] Such as figure 1 As shown, the traditional constant on-time (COT, Constant on time) control method realizes converting the input voltage into an output voltage to drive the load by controlling the main switch to be turned on for a constant time. In the step-down circuit (BUCK circuit) figure 1 In (a), the upper tube M00 is the main switching tube, and the lower tube M01 is the freewheeling diode or auxiliary switching tube; in the boost circuit (BOOST circuit) figure 1 In (b), the lower tube M01 is the main switching tube, and the upper tube M00 is the freewheeling diode or the auxiliary switching tube. [0003] In constant on-time control, after the main switch is turned on, the main switch is turned off after a constant time, at this time the freewheeling diode or auxiliary s...

AI Technical Summary

Problems solved by technology

[0004] The traditional solution has the advantages of relatively simple circuit, easy implementation, and relatively low cost, but mainly has the following disadvantages: 1. When the duty cycle is relatively large in constant on-time control, the current dynamic response is relatively slow (the inductor current cannot follow the command current), such as image 3 shown

2. In constant on-time control, due to the fixed on-time of the main switch and the minimum off-time, the maximum duty cycle of the switching circuit is limited

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