NE555 Precision Timers
These devices are precision timing circuits capable of producingaccurate time delays or oscillation. In the time-delay or monostablemode of operation, the timed interval is controlled by a singleexternal resistor and capacitor network. In the astable mode ofoperation, the frequency and duty cycle can be controlled independentlywith two external resistors and a single external capacitor.
The threshold and trigger levels normally are two-thirds and one-third,respectively, of VCC. These levels can be altered by use of thecontrol-voltage terminal. When the trigger input falls below thetrigger level, the flip-flop is set, and the output goes high. If thetrigger input is above the trigger level and the threshold input isabove the threshold level, the flip-flop is reset and the output islow. The reset (RESET) input can override all other inputs and can beused to initiate a new timing cycle. When RESET goes low, the flip-flopis reset, and the output goes low. When the output is low, alow-impedance path is provided between discharge (DISCH) and ground.
The output circuit is capable of sinking or sourcing current up to 200mA. Operation is specified for supplies of 5 V to 15 V. With a 5-Vsupply, output levels are compatible with TTL inputs.
- Timing From Microseconds to Hours
- Astable or Monostable Operation
- Adjustable Duty Cycle
- TTL-Compatible Output Can Sink or Source up to 200 mA