POWER SUPPLY DEVICE FOR POSITIVE/NEGATIVE OUTPUT VOLTAGES SUPPLYING CURRENT OUTPUT FROM SERIES CONTACT BETWEEN LIGHT EMITTING DIODE AND RECTIFYING CIRCUIT TO THE LIGHT EMITTING DIODE

摘要

PURPOSE: A power supply device for positive/negative output voltages is provided to supply a current output from a series contact between a light emitting diode and a rectifying circuit to the light emitting diode. CONSTITUTION: A power supply device for positive/negative output voltages includes a coil, a switch, a rectifying and smoothing circuit, a positive output voltage detecting circuit(11), a switching power circuit(10), a negative output voltage setting circuit(20), and a negative output voltage generating circuit(30). The switch switches the coil based on a voltage supplied to the coil. The rectifying and smoothing circuit processes a voltage on a series contact between the coil and the switch and outputs the result as the positive output voltage. The positive output voltage detecting circuit generates a positive output voltage detection voltage from the positive output voltage. The switching power circuit adjusts the positive output voltage detection voltage to be equal to a reference voltage. The negative output voltage setting circuit generates the negative output voltage setting voltage lower than the positive output voltage by a predetermined amount. The negative output voltage generating circuit generates the negative output voltage according to the voltage at the series contact and the negative output voltage setting voltage.