Light emitting apparatus

A control circuit configured to control a switching power supply for supplying a driving voltage to a first terminal of a light-emitting element, and to generate a driving current that flows through the light-emitting element, the control circuit comprising:

• a connection terminal to be connected to a second terminal of the light-emitting element;
• a current driving circuit connected to the connection terminal, and configured to generate an intermittent driving current that corresponds to a dimming pulse signal;
• an error amplifier configured to generate a feedback voltage that corresponds to a difference between a detection voltage that occurs at the connection terminal and a predetermined reference voltage;
• a pulse modulator configured to generate a pulse signal having a duty ratio that corresponds to the feedback voltage;
• a driver configured to drive a switching element of the switching power supply according to the pulse signal;
• a fault detection comparator configured to generate a fault detection signal which is asserted when the detection voltage is lower than a predetermined threshold voltage;
• a pull-up circuit configured to be switchable between an active state and an inactive state, and to supply a current to the connection terminal when it is set to the active state;
• and
• a fault detection circuit configured to set the pull-up circuit to the active state when the fault detection signal is asserted, and to detect whether or not the fault detection signal is asserted after the pull-up circuit is set to the active state.

A control circuit configured to control a switching power supply for supplying a driving voltage to a first terminal of a light-emitting element, and to generate a driving current that flows through the light-emitting element, the control circuit comprising:

• a current driving circuit connected to a second terminal of the light-emitting element, and configured to supply the light-emitting element with an intermittent driving current that corresponds to a dimming pulse signal;
• a transconductance amplifier configured to generate a current that corresponds to a difference between a predetermined reference voltage and a detection voltage that occurs between the terminals of the current driving circuit;
• a feedback terminal to be connected to a feedback capacitor;
• a feedback switch arranged between the feedback terminal and an output terminal of the transconductance amplifier, and configured to turn on according to the dimming pulse signal;
• a soft start circuit configured to generate a soft start voltage which changes with time;
• a clamp circuit configured to be set to an active state so as to control a feedback voltage that develops at the feedback terminal such that it becomes equal to the soft start voltage regardless of the detection voltage level during a predetermined period after the switching power supply starts to operate;
• a pulse modulator configured to generate a pulse signal having a duty ratio that corresponds to the feedback voltage;
• and
• a driver configured to drive a switching element of the switching power supply according to the pulse signal during a period in which the dimming pulse signal indicates a turn-on instruction, and to turn off the switching element during a period in which the dimming pulse signal indicates a turn-off instruction.

A driving circuit for a light-emitting element, comprising:

• a current driving circuit connected to one end of a light-emitting element, and configured to supply the light-emitting element with an intermittent driving current that corresponds to a dimming pulse signal;
• and
• an on-state detection circuit configured to detect whether or not the light-emitting element has become able to emit light,
• and wherein the current driving circuit comprises:
• a driving transistor and a current detection resistor arranged between the one end of the light-emitting element and a fixed voltage terminal;
• and
• an operational amplifier having an inverting input terminal connected to a connection node that connects the driving transistor and the current detection resistor, and having a non- inverting input terminal to which a control voltage indicating the driving current is applied,
• and wherein the on-state detection circuit is configured to compare a voltage at a control electrode of the driving transistor with a predetermined voltage level in a period in which the dimming pulse signal indicates a turn-on instruction, so as to detect whether or not the driving current that flows through the light-emitting element reaches a predetermined level,
• and wherein the on-state detection circuit comprises:
• a P-channel MOSFET having a source connected to a high voltage side power supply terminal of the operational amplifier, and having a gate connected to the control electrode of the driving transistor;
• a current source arranged between a drain of the P-channel MOSFET and a low voltage side power supply terminal of the operational amplifier;
• an N-channel MOSFET having a gate connected to the drain of the P-channel MOSFET, and having a source connected to the low voltage side power supply terminal;
• and
• a load arranged between a drain of the N-channel MOSFET and the high voltage side power supply terminal,
• wherein the on-state detection circuit is configured to output, as a signal which indicates a detection result, a signal that corresponds to a drain voltage of the N-channel MOSFET that develops in a period in which the dimming pulse signal indicates a turn-on instruction.