An operational circuit, comprising:
- a first stage, having a first input terminal for receiving an input signal and a second input terminal for receiving an output signal of the operational circuit, for outputting a first control signal at a first output terminal and a second control signal at a second output terminal according to the input signal and the output signal;
- a second stage, coupled to the first stage, for generating the output signal according to a first driving current controlled by the first control signal and a second driving current controlled by the second control signal;
- and
- a protection circuit, coupled between the first stage and the second stage, for adjusting the first driving current from a first predetermined threshold current towards a second predetermined threshold current when the first driving current reaches the first predetermined threshold current;
- wherein the protection circuit comprises:
- a first detecting element, for detecting the first driving current to selectively generate a first detecting signal;
- a first adjusting element, having a first terminal coupled to a first supply voltage;
- and
- a first control element, having a first terminal coupled to a second terminal of the first adjusting element, and a second terminal coupled to the first output terminal of the first stage, wherein the first detecting element generates the first detecting signal to adjust a conductivity between the first terminal of the first control element and the second terminal of the first control element when the first driving current reaches the first predetermined threshold current;
- and
- the second stage comprises:
- a first driving element, coupled to the first output terminal of the first stage, for receiving the first control signal to generate the first driving current;
- and
- a second driving element, coupled to the second output terminal of the first stage, for receiving the second control signal to generate the second driving current;
- and
- the first detecting element comprises:
- a sensing element, coupled to the first output terminal, for sensing the first driving current to generate a first sensing current;
- an adjustable current generator, for selectively generating a first reference current with respect to the first predetermined threshold current or a second reference current with respect to the second predetermined threshold current;
- and
- a current comparator, coupled to the sensing element and the adjustable current generator, for comparing the first sensing current and the first reference current before the first driving current reaches the first predetermined threshold current, and comparing the first sensing current and the second reference current to generate the first detecting signal when the first driving current reaches the first predetermined threshold current;
- and
- the operational circuit further comprises:
- a specific detecting circuit, coupled to the second stage, arranged to disconnect the first terminal of the first control element from the second terminal of the first control element, and to control the adjustable current generator to switch the second reference current into the first reference current according to the output signal.