A soft start circuit

Abstract

The present invention discloses a soft starting circuit. The soft starting circuit comprises an output voltage detection circuit, an error amplifier, a clock control circuit and a reference voltage selection circuit. The reference voltage output terminal VREF of the reference voltage selection circuit and the feedback voltage terminal VFB of the output voltage detection circuit are accessed together to the error amplifier, and the error amplifier outputs error signals VC. A shifting register is employed to generate control signals, a digital control mode is employed to achieve soft starting with no need for capacitors and microcontrollers, and therefore, the soft starting circuit is simple in external interface, low in power consumption, fast in start and extensible, and can solve the problem that a DC-DC switching power source circuit is large in surge current in the starting phase.

Description

technical field [0001] The invention belongs to the field of electronic technology, and in particular relates to a soft start circuit. Background technique [0002] DC-DC switching power supply has the characteristics of high conversion efficiency, wide input voltage range, large output current, small quiescent current, strong driving ability, etc., and is widely used in power management chips. The DC-DC switching power supply drives the switching tube to work by converting the error signal into a pulse width modulation (PWM) signal. [0003] In the start-up phase of the DC-DC switching power supply, since the output voltage slowly rises from zero to the set output voltage value, the feedback voltage is much higher than the set reference voltage during the start-up phase, so that the error amplifier works in the nonlinear region. The output of the error amplifier is the highest voltage value, during which the output of the PWM comparator does not flip, and the system works ...

AI Technical Summary

Problems solved by technology

At present, there are several types of commonly used soft-start circuits: the first type is to charge the capacitor with a resistance or a constant current source. When the required delay is long, this method requires a large capacitor and is not easy to integrate; the second type It adopts segmental control to divide the rising process of output voltage into several sections. This method is complicated to control and costs a lot. The third type is the method of digitally controlling the digital-to-analog converter to realize the slow rise of the reference voltage. This method requires Another microcontroller with more external interfaces

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