Switching regulator having soft start circuit
View Patent ↗A switching regulator has a soft start circuit having a current source, a capacitor, and a MOS transistor connected between the current source and the capacitor for undergoing controlled operations between ON/OFF states to control a time period required for soft start of the switching regulator.
1. A switching regulator comprising:
an output terminal;
a power supply;
a coil connected to a terminal of the power supply;
a diode connected between the coil and the output terminal;
a voltage dividing circuit connected to the output terminal;
a reference voltage circuit;
a current source;
a first MOS transistor having a gate connected to the current source and a source connected to the reference voltage dividing circuit;
a second MOS transistor for controlling a soft start time period in accordance with a level of an output voltage to a soft start control terminal, the second MOS transistor having a source connected to the current source and a gate connected to the soft start control terminal;
a capacitor connected to a drain of the second MOS transistor;
an error amplifying circuit connected to an output of the voltage dividing circuit and a drain of the first MOS transistor;
a duty control circuit connected to the error amplifying circuit; and
a switching transistor having a gate connected to the duty control circuit and a source connected to the coil.
2. A switching regulator comprising:
an output terminal;
a power supply;
a coil connected to a terminal of the power supply;
a diode connected between the coil and the output terminal;
a voltage dividing circuit connected to the output terminal;
a error amplifying circuit connected to an output of the voltage dividing circuit;
a duty control circuit connected to the error amplifying circuit;
a switching transistor having a gate connected to the duty control circuit and a source connected to the coil;
a reference voltage circuit; and
a soft start circuit comprised of a capacitor, a current source, a first MOS transistor, and a second MOS transistor for undergoing controlled operations between ON/OFF states to control a time period required for soft start of the switching regulator, the first MOS transistor having a drain connected to the error amplifying circuit, a gate connected to the current source and a source connected to the reference voltage circuit, and the second MOS transistor having a source connected to the current source and a drain connected to the capacitor.
3. A switching regulator according to claim 2 ; wherein the second MOS transistor undergoes controlled operations between ON/OFF states to arbitrarily control a time period required for soft start of the switching regulator by control of a time period required to charge the capacitor with electricity using the second MOS transistor.