Constant voltage generator circuit operating at low voltage potential difference between input voltage and output voltage

A constant voltage generator circuit comprising:

• an output transistor that is connected between a power source and a load, and controls an output current;
• a first amplifier circuit that drives the output transistor based on a reference voltage generated based on a voltage of the power source;
• a second amplifier circuit that is connected in parallel to the first amplifier circuit, operates at a speed higher than that of the first amplifier circuit, and drives the output transistor based on the reference voltage corresponding to the power source;
• a protection circuit configured to limit the output current flowing through the load from the output transistor during a predetermined operation;
• and
• a control circuit configured to control an operation of the second amplifier circuit,
• wherein the second amplifier circuit includes a first differential amplifier circuit including a first transistor pair, which includes a first differential pair including a first internal node to which a first bias voltage is applied to determine an operating point of the second amplifier circuit,
• wherein the first transistor pair includes
• a first input transistor circuit that inputs a first input voltage applied to a non-inverting input terminal of the first differential amplifier circuit of the second amplifier circuit, and
• a second input transistor circuit that inputs a second input voltage applied to an inverting input terminal of the first differential amplifier circuit of the second amplifier circuit,
• wherein the first input transistor circuit includes a first transistor, the first input voltage is input to a gate of the first transistor, a drain of the first transistor is connected to the power source via a second transistor, and a source of the first transistor is grounded via a first current source,
• wherein the second input transistor circuit includes a third transistor, the second input voltage is input to a gate of the third transistor, a drain of the third transistor is connected to the first internal node and is connected to the power source via a fourth transistor, and a source of the third transistor is grounded via the first current source,
• wherein the control circuit controls the second amplifier circuit not to operate until the output current increases from a current during a light load and reaches a predetermined second threshold current, and to operate when the output current is equal to or greater than the second threshold current, and the control circuit controls the second amplifier circuit to operate until the output current decreases from a current during a heavy load and reaches a predetermined first threshold current smaller than the second threshold current, and not to operate when the output current is equal to or less than the first threshold current,
• wherein the second amplifier circuit further includes a first operation voltage potential fixing circuit that fixes an operation voltage potential of the first internal node during non-operation of the second amplifier circuit, and
• wherein the first operation voltage potential fixing circuit includes one of the following:
• (A) a first bias voltage generator circuit configured to fix the operation voltage potential by applying the first bias voltage to the first internal node during the non-operation of the second amplifier circuit;
• or
• (B) a first current generator circuit that fixes the operation voltage potential by applying a predetermined first current to the first internal node during the non-operation of the second amplifier circuit.