Driving device
A driving device comprises a first transistor (B 13 ), a second transistor (B 14 ), and a resistance element. The first transistor (B 13 ) has one terminal receiving a pulsed current and a control terminal connected to the one terminal. The second transistor (B 14 ) has one terminal connected to at least one load, the other terminal connected to a reference potential together with the other terminal of the first transistor (B 13 ), and a control terminal connected to the control terminal of the first transistor (B 13 ). The resistance element is connected between the control terminal of the first transistor (B 13 ) and the other terminal of the first transistor (B 13 ).
1. A driving device comprising:
an output terminal that outputs a pulse signal;
a plurality of input terminals connected with one terminal of a plurality of light emitting elements driven by a voltage generated based on the pulse signal;
a constant-current driver connected to each of the plurality of input terminals;
a control portion arranged to generate the pulse signal based on a signal which is input from the plurality of input terminals; and
an open detection portion connected with each of the plurality of input terminals and arranged to determine a connection state of the plurality of light emitting elements based on a signal which is input into the plurality of input terminals, and arranged to control the constant-current driver based on a result of the determination.
2. The driving device according to claim 1 , wherein the control portion includes:
an error amplifier into which a signal from the plurality of input terminals and a reference voltage are input and which is arranged to amplify and output an error between the signal and the reference voltage;
an oscillator; and
a comparator arranged to generate the pulse signal based on an output from the error amplifier and an output from the oscillator.
3. The driving device according to claim 1 , wherein the constant-current driver includes:
a first transistor, wherein a pulse-shape current is input into a first terminal of the first transistor, and wherein a second terminal of the first transistor is connected with a control terminal;
a second transistor including a first terminal connected with at least one load, the second transistor including a second terminal connected with a reference potential together with the second terminal of the first transistor, and the second transistor further including a control terminal connected with a control terminal of the first transistor; and
a resistor element connected between the control terminal of the first transistor and the second terminal of the first transistor.
4. The driving device according to claim 3 further comprising a first voltage supply portion and a second reference voltage supply portion that separately supply a predetermined voltage to one of terminals of the first transistor and one of the terminals of the second transistor.
5. The driving device according to claim 1 wherein the open detection portion is arranged to determine that the plurality of input terminals are opened if a voltage at the plurality of input terminals becomes a predetermined voltage or lower.
6. The driving device according to claim 5 wherein the open detection portion is arranged to turn off only a channel connected with a terminal of the plurality of input terminals that is judged to be opened.
7. The driving device according to claim 1 further comprising:
a second input terminal to receive a voltage based on a voltage supplied to the light emitting elements; and
an overvoltage protection circuit arranged to determine an overvoltage based on a voltage input into the second input terminal and based on a second reference voltage.