The difference between using one 555 timer and a 556 timer for PWM control?

Question

I have seen different site using 556 set up as one timer in astable
controlling a second timer in monostable mode. Other sites show PWM by
using only one 555 timer set up in astable mode. I would really rather
use only one 555 timer, but what is the upside to using a setup with a
556 timer?

Answer 1

Using a 555 in astable mode, you're controlling the duty cycle (on time/off time ratio) by varying the charge/discharge time of a capacitor. This has a kinda limited range for total duty cycle plus the frequency varies as you change the duty cycle.

With a 556 you have a constant frequency (number of pulses per second, pps) and the duty cycle (the pulse width of the other half of the 556 that's connected as a monostable) can be adjusted without varying the freqyency.

The 556 will also give you quite a bit wider control of the duty cycle than will a single 555 solution.


Doug

Answer 2

556 Timer

Answer 3

I think first of all, the cost, and complexity are minuscule, so why not use the 556? Second, would you get better resolution using a 556, in other words, wouldn't your project be more accurate?

The 556 is just a cascaded version of the 555, right?

SEE:
http://www.uoguelph.ca/~antoon/gadgets/555/555.html

http://www.ecs.umass.edu/ece/ece211/lab/555.htm

Answer 4

Space and cost are two upsides. 556 cost less than two 555 timers. Plus it takes less board space for one 556 than two 555's.

Answer 5

Servos need more than just a simple pulse stream. So no.