1 kHz with 60% high, E12 series
- Input
- f=1 kHz, D=60%, E12
- Expected output
- RA 1,8 kΩ, RB 3,9 kΩ, C 150 nF = 1,0019 kHz
High duty cycle of 59.4%, frequency error of 0.19%.
Carregando ferramenta… / Loading tool…
555 resistor values for a target frequency
Switch the direction to Timing to parts, type the frequency, the high-level duty cycle and the resistor series. The table lists the best combinations, ordered by smallest error, and Use sends the chosen one back to the direct calculation.
High duty cycle of 59.4%, frequency error of 0.19%.
High duty cycle of 68.8%.
High duty cycle of 10.8%.
Exactly 50% duty, but 5.3% below the requested frequency in the E12 series.
In the standard circuit the high duty cycle always stays above 50%.
Per the TI datasheet, f = 1 / T and T = 0.693 x (RA + 2RB) x C, giving f ≈ 1.44 / ((RA + 2RB) x C). With RA = 1 kΩ, RB = 10 kΩ and C = 1 µF, T is 14.56 ms and f is 68.7 Hz.
The TI datasheet recommends 100 kHz at most for the bipolar 555. The search still computes above that, but the screen warns, and for higher frequencies the datasheet suggests a CMOS 555.
Among combinations with equal error, the one closest to 100 nF comes first, because ceramic and film capacitors in that range have little leakage. You can pick any other row of the table.
Because commercial resistors and capacitors only exist in discrete values. A finer series such as E96 reduces the error, and a trimmer in series with a fixed resistor lets you tune the frequency on the bench.
With 5% on the resistors and 10% on the capacitor: frequency from 911.7 mHz to 1.232 Hz and high duty cycle from 50.3% to 50.4%.
Everything is calculated in your browser. No values are sent to servers.