Patent ID: 7679296

Claim:
A drive circuit, comprising: a constant voltage circuit configured to supply a constant voltage to one terminal of a load; a constant current circuit configured to supply a predetermined constant current to another terminal of the load in accordance with a pulse signal input externally; and a first reference voltage generator configured to generate and output a first reference voltage in accordance with an output voltage at an output terminal of the constant current circuit, wherein the constant voltage circuit makes the first reference voltage proportional to the output voltage output to the load, and wherein the first reference voltage generator increases the first reference voltage when the output voltage at an output terminal of the constant current circuit is equal to or below a second reference voltage, decreases the first reference voltage when the output voltage at the output terminal of the constant current circuit is equal to or larger than a third reference voltage larger than the second reference voltage, and keeps the first reference voltage constant when the output voltage at the output terminal of the constant current circuit is between the second reference voltage and the third reference voltage.