Step-down switching regulator capable of providing high-speed response with compact structure

A step-down switching regulator comprising:

• a switching element formed of a high-voltage NMOS transistor and turned on and off based on a control signal input to a gate, configured to charge an inductor with an input voltage not smaller than a withstand voltage of a low-voltage MOS transistor but smaller than a withstand voltage of a high-voltage MOS transistor input to an input terminal;
• a rectifier configured to discharge the inductor when the switching element is turned off to stop charging the inductor;
• a voltage generator configured to generate a predetermined first power supply voltage not greater than a withstand voltage of the low-voltage MOS transistor;
• a first drive circuit formed of a low-voltage MOS transistor and configured to turn on and off the switching element based on the input control signal;
• a capacitor connected in parallel with the first drive circuit and configured to store charge from the voltage generator to supply power to the first drive circuit, one end of which is connected to a junction node between the switching element and the inductor and the other end of which is supplied with the first power supply voltage generated by the voltage generator;
• a controller configured to generate the control signal for turning on and off the switching element and output the control signal to the first drive circuit, such that the input voltage is converted into a predetermined constant voltage to be output from an output terminal;
• a constant voltage circuit configured to generate a predetermined constant voltage and output the predetermined constant voltage;
• and
• a first source follower circuit formed of an NMOS transistor of the high-voltage MOS transistor and configured to receive the output voltage generated by the constant voltage circuit at a gate and receive the input voltage at a drain while outputting the first power supply voltage from a source.