Digital soft start circuit in switching power source

Abstract

The invention discloses a digital soft start circuit in a switching power source. The digital soft start circuit comprises a frequency divider composed of six D triggers. The of each D trigger is connected with the clock signal input end of the next D trigger, the of the sixth D trigger serves as the output end and generates a clock signal VA and the clock signal input end of the first D trigger is connected with a clock signal of a whole loop; the clock signal VA serves as an input signal, a rising delayed clock signal VC is generated through two phase inverters and an RC series loop, the clock signal VC is then shaped and filtered through a Schmitt trigger, and therefore a clock signal VB is obtained; a control clock signal VD is obtained by the clock signal VA and the clock signal VB through a NAND gate, the clock signal VD is connected with a grid electrode of an MOS tube M2 after clock absorption and controls the MOS tube M2 to be connected and disconnected, a source electrode and a drain electrode of the MOS tube M2 are connected with a constant current source I1 and a capacitor C2 respectively, the capacitor C2 is intermittently charged by the constant current source I1, and therefore a soft start voltage is obtained. The complexity of the circuit is reduced and the circuit is conveniently integrated in a chip.

Description

technical field

[0001] The invention relates to a power management module in the field of analog integrated circuit design, in particular to a digital soft start circuit in a switching power supply. Background technique

[0002] With the continuous growth of portable electronic products in the fields of communications, computers and consumer electronics, the demand for power management ICs is also on the rise. The DC-DC switching power supply is capable of stepping up or stepping down DC voltages and has high efficiency, and has been widely used. The switching power supply works by converting the error signal into a duty cycle control signal to control the power switch tube. At the beginning of the power-on start-up phase, the error amplifier is in an unbalanced state, making the loop work at a 100% duty cycle, so it will There is a large surge current flowing into the load, which causes a large overshoot of the output voltage, and the excessive surge current may damage the...

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