LIGHT EMITTING DEVICE DRIVING CIRCUIT

摘要

A constant current source (2) is connected in series to an LED array (7) to be driven. A booster circuit (3) boosts an input voltage (Vin) and supplies the obtained boost-up voltage (Vb) to the LED array (7) and the constant current source (2). A differential amplifier (4) detects the voltages at both ends of the constant current source (2), and a differential amplifier (5) compares the detected voltage with a reference voltage (E1). The booster circuit (3) changes the level of the boost-up voltage (Vb) according to the analog boost-up control signal (10) output from the differential amplifier (5). In a chopper-type booster circuit (3a), the switch that switches the flow of the current having passed through a coil is controlled by a control signal, the duty ratio of which varies according to the boost-up control signal (10). In a charge-pump-type booster circuit (3b), the switch that switches the connection states of a capacitor is also controlled by the control signal. This enables a light emitting device to be stably driven by a constant current at a low power consumption.