ERASING DEVICE OF P-ROM

摘要

PURPOSE:To erase the content of memory of a P-ROM sufficiently in a short time, even if the intensity of ultraviolet rays is decreased, by controlling the lighting time automatically so as to make the amount of ultraviolet rays required for erasure constant at all times. CONSTITUTION:In depressing a start switch 11, an ultraviolet ray generator 2 is turn on. A visual light is irradiated from a fluorescent lamp 8 for ultraviolet ray detection, a photo transistor (TR) 9 receives the light and a current proportional to the intensity of the visual light flows. A voltage is produced across a resistor 12, the voltage is converted into a frequency at a voltage-frequency converter 14 and a pulse width corresponding to the lighting time is formed at a timer. A pulse signal obtained from the timer 15 is applied to a base of a TR18 via a resistor 17, then the TR18 is conductive, a contact of a relay 19 is closed, the power supply is applied, and the ultraviolet ray generator 2 is turn on. When a time required for the erasure of a P-ROM is elapsed, a pulse signal from the timer 15 is lost, the TR18 is nonconductive and the contact of the relay 19 is opened. Even if the ultraviolet ray generator is deteriorated because of the operation for a long time and the intensity is decreased, since an output frequency of the converter 14 is proportional to an input voltage, the less the input voltage becomes, the less the output frequency becomes. Since the output signal of the timer has a pulse width inversely proportional to the frequency, the width is wider by the decrement in the frequency, and the lighting time is longer inversely proportional to the intensity of ultraviolet rays.