MC1455

Combination of timer, optoisolator, and bridge-triggered triac keeps AC motor or other device energized for up to 1 h after control switch is depressed momentarily. Closing of switch drops voltage at pin 2 of timer below ¹/₃ V_CC, making timer output go high and thus tum LED on. At same time, capacitor at pin 7 begins charging. Output re-mains high until oapacitor reaches ²/₃ V_CC, when outputis reset to low state and motor thereby turned off.-T Mazur,Solid-State Relays Offer New to Soutions to Many Old Problems, EDN Magazine， Nov 20,1973,p 26－32.

The MC1455 monolithic timing circuit is a highly stable controller capable of producing accurate time delays or oscillation. Additional terminals are provided for triggering or resetting if desired. In the time delay mode, time is precisely controlled by one external resistor and capacitor. For astable operation as an oscillator, the free−running frequency and the duty cycle are both accurately controlled with two external resistors and one capacitor. The circuit may be triggered and reset on falling waveforms, and the output structure can source or sink up to 200 mA or drive MTTL circuits.
• Direct Replacement for NE555 Timers
• Timing from Microseconds through Hours
• Operates in Both Astable and Monostable Modes
• Adjustable Duty Cycle
• High Current Output Can Source or Sink 200 mA
• Output Can Drive MTTL
• Temperature Stability of 0.005% per °C
• Normally ON or Normally OFF Output