A detect/modulate circuit comprises a plurality of modulate resistors connected to a main resistor of a bandgap in series, and each module resistor is connected to a transistor switch in parallel, and each transistor switch is connected to a logic controller, and the logic controller is connected in sequence to a plurality of detect circuits and fuses corresponding to the quantity of the transistor switches. When the detect circuit receives a low-to-high power-on reset signal to detect whether or not the fuse is fused, the detect circuit will issue a voltage level signal "0" for the fuse being not fused or a voltage level signal "1" for the fuse being fused to the logic controller. The logic controller converts the received voltage level signal according to a logic conversion table to control the electric connection of the corresponding transistor switch, so as to fine turn the main resistance of the bandgap.