Soft-start circuit of linear voltage regulator and method thereof

Abstract

A voltage regulator circuit for providing a substantially constant output voltage is disclosed. The voltage regulator circuit has a voltage regulator, a current sensing and comparing circuit, a capacitive load circuit, and a control circuit. The voltage regulator generates an output current in response to a control signal to provide the output voltage. The current sensing and comparing circuit senses the output current and outputs a result signal according to a sensed output current and a predetermined current value. The control circuit generates the control signal according to the comparison result to limit the output current. The capacitive load circuit provides the control circuit with a first capacitance when the voltage regulator circuit changes from a first mode to a second mode and provides the control circuit with a second capacitance when the voltage regulator circuit changes from the second mode to the first mode.

Description

technical field [0001] The invention relates to a voltage converter, in particular to a soft start circuit and method for operating the voltage converter. Background technique [0002] Please refer to FIG. 1 , which is a circuit block diagram of a conventional linear voltage regulation circuit 100 . As shown in FIG. 1 , the linear voltage regulator circuit 100 includes a linear voltage regulator 102 and a current sensing and limiting circuit 104. The linear voltage regulator circuit 100 is used to control the input voltage V in to provide a fixed output voltage V out , fixed output voltage V out used as capacitor C ext and the resistor R load A reference voltage of the formed external circuit, the linear voltage regulator 102 includes a control module 108, a transfer transistor M x and two resistors R 11 and R 12 , a linear voltage regulator 102 is used to adjust the output voltage V out , and the function of the control module 108 can be implemented by a low dropout...

AI Technical Summary

Problems solved by technology

[0005] Once the enable signal EN transitions from a low logic level to a high logic level, the linear voltage regulator 102 and the current sensing and limiting circuit 104 will be disabled (disabled), that is, because the linear voltage regulator circuit 100 is disabled, So the output voltage V out Then, when the linear voltage regulating circuit 100 starts (that is, the enable signal EN becomes a low logic level), the voltage value of the node A passes through the transistor M of the current sensing and limiting circuit 104 12 And being pulled low, initially, the current sensing and limiting circuit 104 will not operate immediately to respond to the output current I out , in addition, the pass transistor M x operating in a linear region, so that a large charging current will pass through the pass transistor M x flow through capacitor C ext , if there is a current feedback path, the charging current may cause unpredictable damage to the linear voltage regulator circuit 100 or other circuits coupled to the linear voltage regulator circuit 100

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