Switching regulator
View Patent ↗Provided is a switching regulator for preventing generation of an inrush current flowing through a switching element of an output stage, which is provided in the switching regulator. A soft start control circuit ( 116 ) detects a current flowing through a PMOS transistor ( 104 ) serving as a switching element of an output stage. When the detected current is equal to or larger than a current limiting value for limiting the current flowing through the PMOS transistor ( 104 ), the soft start control circuit ( 116 ) controls the PMOS transistor ( 104 ) to be turned off. Accordingly, it is possible to prevent generation of the inrush current flowing through the PMOS transistor ( 104 ).
1. A switching regulator having a soft start function, comprising:
a switching element of an output stage;
a detection circuit for detecting a current flowing through the switching element;
a control circuit for controlling the switching element to be turned off to limit the current flowing through the switching element when the current flowing through the switching element is equal to or larger than a current limiting value; and
a current limiting value control circuit that outputs a soft start signal, wherein the soft start signal is a signal that causes the current limiting value to gradually increase upon turning on of a power supply.
2. The switching regulator according to claim 1 , wherein the current limiting value control circuit comprises:
a reference voltage source;
a soft start signal output terminal for outputting the soft start signal;
a transistor connected between the reference voltage source and the soft start signal output terminal; and
a lowpass filter connected between the transistor and the soft start signal output terminal.
3. The switching regulator according to claim 1 , wherein the switching element comprises a PMOS transistor and the detection circuit comprises a first transistor connected with the PMOS transistor to form a first current mirror circuit.
4. The switching regulator according to claim 3 , the control circuit comprising a comparator configured to compare a first predetermined voltage with a second predetermined voltage, wherein the output of the comparator is input to a gate electrode of the PMOS transistor for controlling the PMOS transistor.
5. The switching regulator according to claim 4 , the detection circuit further comprising a second current mirror circuit connected to the first current mirror circuit such that the current limiting value corresponding to the switching element is a function of a reference current flowing through transistors of the second current mirror circuit, wherein a mirror ratio between the transistors of the second current mirror circuit is approximately 1:1:1.
6. The switching regulator according to claim 5 , wherein the first and second predetermined voltages are a function of the reference current.
7. The switching regulator according to claim 5 , wherein the soft start signal causes the reference current to gradually increase upon turning on of the power supply.