Lamp illumination adjusting apparatus

Claim 1

A lamp illumination adjusting apparatus comprising: a reference triangular wave generating circuit including a first operation amplifier for outputting a reference triangular wave signal having a predetermined triangular voltage level and frequency cycle; an adjusting voltage setting circuit, including a variable resistor having one terminal connected to a power source and its other end connected through another resistor to ground, for outputting a selected constant, adjusting voltage signal indicating a power level to be applied for lamp illumination, wherein said other end of said variable resistor is also connected to supply an operation voltage as an input to one terminal of said first operation amplifier of said reference triangular wave generating circuit; a comparator circuit, including a second operation amplifier receiving at one input terminal said constant, adjusting voltage signal and at its other input terminal said triangular wave signal, for comparing the reference triangular wave signal of the reference triangular wave generating circuit to the adjusting voltage signal set by the adjusting voltage setting circuit, and outputting a comparison signal composed of ON components for a time period of each cycle when the voltage of the triangular wave signal is exceeded by the voltage of the adjusting voltage signal; and a driver circuit including a MOS field effect transistor having a gate to which only the output comparison signal from the comparator circuit is applied, said driver circuit being connected in series with a lamp via power source so that the MOS field effect transistor is directly ON/OFF controlled by the comparison signal to apply power to the lamp corresponding to the time period of the ON components thereof.