A soft start circuit and a dc-dc circuit including the soft start circuit

Abstract

The invention provides a soft-start circuit and a DC-DC circuit which includes the soft-start circuit. In the DC-DC circuit, output of a pulse-width modulation comparator is controlled through an error amplifier so that a stable output voltage can be output at last. At the same time, in the soft-start circuit, a reference-source voltage output by the soft start is controlled through a switch capacitance-resistance circuit so that the reference-source voltage rises slowly and becomes stable as a reference voltage at last and a DC-DC output voltage is enabled to rise slowly with the reference-source voltage output by the soft start so that generation of an overshoot voltage in a start process is prevented and a soft-start function is realized and thus the circuit is protected better.

Description

technical field [0001] The invention relates to the field of integrated circuit manufacturing, specifically, to a soft start circuit and a DC-DC circuit including the soft start circuit. Background technique [0002] With the widespread use of portable devices, DC-DC (direct current / direct current conversion circuit) converters have developed rapidly due to their high efficiency, large output current, and low quiescent current. During the power-on process of a traditional DC / DC switching power supply, the output voltage rises from zero to the maximum value. Due to the effect of negative feedback, the duty cycle of the PWM (PulseWidthModulation, pulse width modulation comparator) control signal of the power tube changes from the maximum value and gradually decreases until the circuit is stable. Due to the existence of the output filter capacitor in the circuit, the Capacitor charging is easy to generate surge current. At this time, the current passing through the power tube ...

AI Technical Summary

Problems solved by technology

This method requires a large capacitor to realize. In practical applications, it is often necessary to connect resistors and capacitors outside the chip, which increases the complexity of the application.

If the delay time is too short, the effect of soft start is not obvious, and when a delay of milliseconds is required, the implementation cost of the circuit in this way is relatively high;

[0006] The second type is to use segmented control, divide the rising process of the voltage into several stages, judge through several voltage comparators, and then control the resistance value of the connected capacitor to change the charging speed of the capacitor to achieve a slow rise. purpose, but its control method is complex and the cost of implementation is relatively high;

[0010] However, this patent is to adjust the duty ratio of the DC-DC conversion part, and cannot adjust the output voltage. The output voltage may not reach a desired stable voltage value, and thus cannot be adjusted.

[0011] To sum up, in the prior art, if the zero voltage is to be slowly raised to the set value, the cost is relatively high, and the control method is relatively complicated. , to best realize the function of the soft-start circuit to protect the circuit

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