Control circuit of the switching power supply for the light emitting element driving, driving circuit of the light-emitting element, and a light-emitting device and an electronic device using the same

摘要

PROBLEM TO BE SOLVED: To solve the problem that, if the duty factor of a lighting control pulse signal is small, startup time is extended.;SOLUTION: A gm amplifier 21 generates a current corresponding to an error between a detection voltage V_LED generated in a current drive circuit 8 (CS_i) and a reference voltage V_REF. A feedback switch SW1, which is provided between a feedback terminal FB having a feedback capacitor C_FB connected thereto and an output terminal of the gm amplifier 21, turns a lighting control pulse signal PWM on. A soft start circuit 32 generates a soft start voltage V_SS which changes with time. A clamp circuit 40 is activated for some period of time after a switching power supply 4 has started operating, thereby controlling a feedback voltage V_FB generated on the feedback terminal FB so that it will equal the soft start voltage V_SS regardless of the level of the detection voltage V_LED.;COPYRIGHT: (C)2013,JPO&INPIT