This paper proposes an electronic ballast circuit for fluorescent lamps with low lighting flicker. The electronic ballast with constant-frequency control, in which the DC-bus voltage is fed by a power-factor corrector, has a low-frequency ripple, which can cause lighting flickers in fluorescent lamps. Precise image-detecting systems require lighting sources (such as fluorescent lamps) with low levels of lighting flicker. The presented ballast operates by detecting the DC-bus voltage ripple as a feed-forward signal in order to modulate the switching frequency of the inverter. Thus, the voltage gain of the resonant tank is adjustable. As a result, the lighting flicker caused by the DC-bus voltage ripple can be decreased. Finally, the experimental and simulation results are in agreement, so the functionality of the proposed circuit is verified.