The MB3789 is a PWM (pulse width modulation) switching regulator controller supporting an external sync signal. The MB3789 incorporates two error amplifiers which can be used respectively for voltage control and current control, allowing the IC to serve as a DC/DC converter with current regulating functions. The MB3789 is the ideal IC for supplying power to the back-lighting fluorescent tube for a liquid crystal display (LCD) device such as a camera-integrated VTR.