555 Model / Emulation Using Comparators

Smode: \ = NS LM555 - = NE555 et al. The DISCHARGE circuit (consisting of BJT, base resistor, and collector/output pull-up resistor) is excluded due to # of components limitation. The circuit Single-Supply (+5 V) Model Of 555 Timer includes a simplified model of the DISCHARGE circuit. For simplicity a comparator is also used to model the RESET input. The RESET circuit of a real 555 Timer will have a large deviation from this almost ideal comparator. The circuit is saved with dual power supply but it can operate with single power supply. For 5 kΩ reference divider resistors these values can be used: 4.99 kΩ ±1%, 5.11 kΩ ±1% 5.11 kΩ ±2% 5.1 kΩ ±5% Generally, highly accurate value of these resistors will not be needed.