The present application is based on, and claims priority from JP Application Serial Number 2019-033689, filed Feb. 27, 2019, the disclosure of which is hereby incorporated by reference herein in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to a light emission control device, a light source device, a projection-type video display apparatus, and the like.

2. Related Art

For example, a light emission control device that controls alight source used in a projector or the like is known. The light emission control device dims a light emission amount of a light emission element based on a PWM signal and a dimming control voltage supplied from an external processing device. A dimming mode includes an analog dimming mode in which the light emission amount is dimmed by a voltage value of a dimming control voltage, and a PWM dimming mode in which the light emission amount is dimmed by a pulse width of a PWM signal. Dimming is performed in the analog dimming mode from a maximum luminance to a predetermined luminance, and dimming is performed in the PWM dimming mode below the predetermined luminance. The related art of such a light emission control device is disclosed, for example, in JP-A-2012-043657.

The light emission control device in JP-A-2012-043657 includes a plurality of light emission control circuits, and each light emission control circuit outputs a control signal to a switching element for switching and regulating a current flowing through an inductor. The light emission element emits light when the current of the inductor flows through the light emission element. In JP-A-2012-043657, the plurality of light emission control circuits are shifted in switching phase from each other. In JP-A-2012-043657, in the PWM dimming mode, the current flowing through the light emission element is PWM-controlled by stopping the switching of the switching element when the PWM signal is inactive.

In the PWM dimming mode in JP-A-2012-043657, switching of the switching element is restarted when the PWM signal changes from inactive to active. In this case, since a phase relationship between the PWM signal and the switching is arbitrary, there is a possibility that a first on period after the switching is restarted is shortened. When the on period of the switching element is shortened, sufficient energy is not accumulated in the inductor in the on period, so that there is a problem that a sufficient current may not flow through the light emission element.

SUMMARY

An aspect of the present disclosure relates to a light emission control device for controlling a first switching element provided in series with a first light emission element between a first power source node and one end of a first inductor, a second switching element provided between the other end of the first inductor and a second power source node, a third switching element provided in series with a second light emission element between the first power source node and one end of a second inductor, and a fourth switching element provided between the other end of the second inductor and the second power source node, the device including: a first light emission control circuit outputting a first control signal for controlling turning on/off of the first switching element based on a first PWM signal and a second control signal for controlling turning on/off of the second switching element in a period in which the first PWM signal is active; and a second light emission control circuit outputting a third control signal for controlling turning on/off of the third switching element based on a second PWM signal and a fourth control signal for controlling turning on/off of the fourth switching element in a period in which the second PWM signal is active. In a first PWM dimming mode in which a light emission amount of the first light emission element is set by an on-duty of the first PWM signal, the first light emission control circuit controls a phase of the second control signal based on the first PWM signal. In a second PWM dimming mode in which a light emission amount of the second light emission element is set by an on-duty of the second PWM signal, the second light emission control circuit controls a phase of the fourth control signal based on the second PWM signal. In a first analog dimming mode in which the first PWM signal is fixed to be active, and a second analog dimming mode in which the second PWM signal is fixed to be active, the second light emission control circuit outputs the fourth control signal having a phase different from that of the second control signal.

