PROXIMITY SWITCH

PURPOSE:To increase the response speed by providing a resonance circuit, a current mirror circuit outputting a feedback current to the resonance circuit and a switching element increasing/decreasing the feedback current intermittently to a current feedback oscillation circuit. CONSTITUTION:A transistor (TR) 5 is turned off for this period only in providing a negative pulse (p) with a small duty ratio to a base of the TR 5 via terminal 5. Thus, the feedback current being a current I1 at the on-state goes into I1+I2, then the oscillating state of a resonance circuit 5 is increased. When an object to be detected, however, is being parted and the resonance circuit 3 is going to start the oscillation. a slope (s) in the increased oscillation amplitude, shown C in figure is made steep while the TR 5 is turned off. Thus, the time from the oscillation start till the saturated oscillation is much shortened.