A soft start circuit for buck converter

Abstract

The invention belongs to the technical field of electronic circuits, and in particular relates to a soft start circuit for a DC-DC converter. The circuit of the present invention is mainly to charge the external capacitor through a constant current source to generate a stable and slowly rising slope voltage, which replaces the reference voltage in the soft start stage to participate in the comparison with the feedback voltage VFB. After the soft start is completed, the slope voltage exits ; When the slope voltage is greater than the reference voltage, the control signal will control to turn on the current source, and quickly pull the slope voltage to close to the power supply potential. The beneficial effect of the present invention is that the slow rise of the output is ensured in the soft start stage, and the surge current is prevented; when the slope voltage is greater than the reference voltage, the fast charging branch is opened; The current and constant current sources will eventually pull the slope voltage to zero potential to prevent the instantaneous large current from damaging the circuit.

Description

technical field [0001] The invention belongs to the technical field of electronic circuits, and in particular relates to a soft start circuit for a BUCK converter. Background technique [0002] With the widespread application of handheld devices and portable electronic products, the demand for power management ICs continues to rise. Switching power supplies are widely used due to their high conversion efficiency, large output current, small quiescent current, and wide output load range. The switching power supply works by converting the error signal into a duty cycle control signal to drive the switch. In the start-up phase, the error amplifier is in an unbalanced state, making the loop work at a 100% duty cycle, so after the power transistor is turned on, a large surge current will be generated to charge the capacitor. It is possible to damage the switch tube and other components, resulting in abnormalities in the system circuit system. In addition, in practical applicat...

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Problems solved by technology

However, due to the need for additional microcontroller control and the need to start working before the power supply circuit is powered on, for general-purpose switching power supplies, this type of soft-start circuit is too complicated and the cost is too high; Capacitor charging to clamp the input or output of the error amplifier, thereby limiting the duty cycle of the PWM

This kind of soft start circuit method is relatively simple, but it needs to add a constant current source and an external capacitor for charging; and the small charging current has poor anti-interference ability, and the instantaneous large current may damage the circuit during the discharge stage of the large soft start capacitor.

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