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Boulder, CO (August 2024) - This test explored the difference between two 555 timers: the NE555P and the TLC555IP. The NE555P is a general-purpose timing device that operates at up to 100 kHz with an output current of up to 225 mA. The TLC555IP is a precision general-purpose timing device that operates at up to 2.1 MHz with an output current of up to 15 mA. Overall the TLC555IP is a higher-speed device with a lower current output and higher cost when compared to the NE555P.
Figure 1: Wiring diagram for the 555 timers. RA and RB used 1KΩ resistors, C used a 1µF capacitor, and RL was not used. The image was taken from the NE555 data sheet.
Both 555 timers were wired according to the diagram in Figure 1 using a 1KΩ resistor for RA and RB in conjunction with a 1µF capacitor for C. Equations (1) and (2) provided from the datasheet show that this combination results in a frequency of 480 Hz and a duty cycle of 66.67%.
The output and rise time for the NE555P and TLC555IP are shown in Figures 2 and 3, respectively. The two devices performed similarly to the theoretical values: the frequency error was approximately 3% and the duty cycle error was approximately 1%. The TLC555IP has a shorter rise time and avoids the overshoot and jitter exhibited by the NE555P. However, the NE555P results in brighter LEDs due to the higher current output.
Figure 2: Scope trace for the NE555P showing a frequency of approximately 469 Hz and a duty cycle of 66%
Figure 3:Scope trace for the NE555P showing a rise time of 100.0 ns.
Figure 4: Scope trace for the TLC555IP showing a frequency of approximately 466 Hz and a duty cycle of 66%.
Figure 5: Scope trace for the TLC555IP showing a rise time of 13.8 ns.
The NE555P will be used for the business card circuit board. The added performance and cost of the TLC555IP are not warranted for a simple LED driver. The board will be plugged into external power instead of battery-powered which means the power-saving benefits from the TLC555IP will be negligible. Additionally, having brighter LEDs will make for a more visually appealing display on the business card circuit board.
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