How Do You Calculate Duty Cycle For A 555 Timer?
The 555 timer, developed in the early 1970s, is one of the most successful integrated circuits (ICs) of all time. Chip-makers continue to churn out this 8-pin device at the rate of a billion a year. Among its many virtues is the ease of calculating its duty cycle, or the ratio of the chip’s on-time to its off-time, a number electronics designers need to know. For the 555, duty cycle depends on the values of two resistors. The chip’s datasheet lists the duty-cycle formula. Examine the 555’s datasheet. Look for application circuits for astable operation. You’ll see a timing network made of three parts, namely: two resistors, Ra and Rb, and a capacitor, C1. The timing network determines the 555 pulse’s period and duty cycle. Duty cycle involves only the two resistors and is given by the following formula: D = Rb / (Ra + 2Rb) Where D is the duty cycle, and Ra and Rb are resistances of the two resistors in ohms. Determine the values for your resistors. For example, the values for both might
