Voltage control means

A voltage control device includes a first light emitting unit, a first transistor electrically connected to the first light emitting unit and operated in a saturation region in accordance with a first control signal, and a control unit; the control unit includes a selection comparison module electrically connected to the first light emitting unit, a charge switch module electrically connected to the selection comparison module, a discharge switch module electrically connected to the selection comparison module, and a capacitor electrically connected with charge/discharge switch module and the first transistor. The cross voltage of the capacitor as the first control signal; when a first comparison signal is at a high level, a charging current of the charge switch module flows into the capacitor so that the capacitor is charged with the charging current; and when the first comparison signal is at a low level, the capacitor is discharged via the discharge switch module.