Switching regulator
View Patent ↗Provided is a switching regulator which is capable of reducing soft start time when being activated, and prolonging battery life. The switching regulator has a configuration in which a clamp circuit for clamping a reference voltage is provided in a soft start circuit, and a predetermined period of time since the switching regulator has been activated is divided into a plurality of segments to increase the reference voltage with different slopes for each of the plurality of segments. At an early stage of the activation, the reference voltage is set to be low for preventing an inrush current from a power source, and thereafter, a rate of increase in reference voltage is gradually increased, to thereby reduce the soft start time.
1. A switching regulator for converting an input voltage, which is input to an input terminal thereof, into a predetermined constant voltage and outputting the predetermined constant voltage as an output voltage from an output terminal thereof, comprising:
a switching element;
a coil which is charged with the input voltage through switching of the switching element;
a switch circuit for switching the switching element;
the coil which is charged with the input voltage through the switching of the switching circuit;
an error amplifier for amplifying a voltage difference between the output voltage and a reference voltage and outputting an error signal;
a soft start circuit for, when the switching regulator is activated, clamping the error signal by a ramp voltage to be output and causing the ramp voltage to have a voltage value of the error signal in a predetermined period of time;
a triangular wave generator for generating a triangular wave; and
a control circuit unit for comparing the ramp voltage with a voltage of the triangular wave, and outputting a pulse signal indicating a result of the comparing to the switch circuit to perform switching control on the switching circuit,
wherein, when the switching regulator is activated, the soft start circuit increases the reference voltage at a predetermined angle and to a predetermined voltage value for the predetermined period of time, and the predetermined period of time comprises a plurality of segments to increase the ramp voltage at slopes which are different for each of the plurality of segments;
the soft start circuit includes, as constant current power sources for which different thresholds are set, a plurality of constant current power sources for feeding a constant current when a voltage input thereto exceeds a threshold; and
when the reference voltage increases to exceed thresholds of a larger number of the plurality of constant current power sources, and thus the larger number of the plurality of constant current power sources operate, the soft start circuit adds current values of the operating constant current power sources and converts the added current values into a voltage value to generate the slopes which are different for each of the plurality of segments within the predetermined period of time.
2. A switching regulator according to claim 1 , wherein, when the switching regulator is activated, the soft start circuit starts charging a first capacitor with a current of a constant current power source for reference voltage to gradually increase the reference voltage.
3. A switching regulator according to claim 2 , wherein:
the plurality of constant current power sources each include:
a switching element connected in series therewith; and
a comparator corresponding thereto;
the comparator comprises one input terminal input with a voltage having a threshold which is different among the comparators of the plurality of constant current power sources, and another input terminal input with the reference voltage; and
when the reference voltage exceeds the threshold, the comparator outputs an on-signal to the switching element corresponding to the comparator, and the corresponding constant current power source outputs a current.
4. A switching regulator according to claim 1 , wherein, when output currents of the plurality of constant current power sources are added and are charged into a second capacitor, the ramp voltage is generated.