Soft start circuit for switch power supply

Abstract

The invention discloses a soft start circuit for a switch power supply, comprising an oscillator, a fractional frequency counting module, a resistance network, a current sampling module, a current source I2, a resistance R100, a pulse duration modulation comparer, a phase inverter, an RS trigger and a power PMOS pipe P1, wherein, output clocks of a reset signal and the oscillator are input to the send of the fractional frequency counting module and the RS trigger together, an output signal of the fractional frequency counting module controls the resistance network to obtain output voltage which is connected with a negative input end of the pulse duration modulation comparer, the other negative input end is connected with the error voltage, the positive input end is connected with output current of the current sampling module and is overlaid with the current source I2 to obtain the voltage through the resistance R100, the output end of the pulse duration modulation comparer is input to the R end of the RS trigger after being inverted by the phase inverter, and the inverted output end of the RS trigger is connected with the grid electrode of the power PMOS pipe P1. In the invention, the soft start effect is good, the circuit structure is simple and the chip area is saved.

Description

technical field [0001] The invention relates to an analog integrated circuit design, in particular to a design of a start-up circuit in a switching power supply. Background technique [0002] Due to the continuous development of VLSI, the integration of power chips has been rapidly developed and widely used in various devices, especially portable electronic products, such as mobile phones, MP3, PDA, PMP, DSC, etc. [0003] Switching power supply (DC-DC) is an important branch of power supply IC. Compared with low-dropout linear regulator, it has the advantage of high efficiency and is one of the preferred power supply systems for portable products. [0004] For the power supply system, due to various improper use, the power supply system will be damaged, especially for the system on chip. The damage of the power supply will directly lead to the collapse of the entire chip. Therefore, in the protection function of the power supply, a soft-start circuit is generally required ...

AI Technical Summary

Problems solved by technology

Due to the existence of the output filter capacitor in the circuit, it is easy to generate a surge current when charging the capacitor. At this time, the current passing through the power tube can reach a large level, which is easy to damage the circuit system.

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