Better 555 Duty Cycle Control (PWM).

[@JaenEngineering]

2:50 if you place a resistor between the junction of R1,R2 and pin 7 you can normalise the mark/space ratio. Also, as the 555 has a push pull output, you can drive the charge/discharge cycle of the cap from the output via a single resistor

[@therealjammit]

I've got a story. I needed a signal source, duty cycle and exact frequency not needed. Just something that makes noise. The only 555 timer I found in my junk box just happened to have a blown discharge transistor in it, otherwise it worked. I did what you suggested just to make some noise come out from it.

[@paulpkae]

Thanks for the comment.
Yes the output can indeed sink or source current. But, bear in mind that in the arrangement you suggest, your intended output load will affect the frequency.

[@JaenEngineering]

@@paulpkae true, although you could also use the discharge pin as an open collector output.

[@Pyroteknikid]

I like to use the 555 "output" to drive the timing part of the PWM, since it is inherently sink/source.
Can very easily implement frequency and duty control.
Most gate drivers have very high input resistance so they dont affect the timing, or the "discharge" can become the output.

[@Mark1024MAK]

That arrangement is also handy if you want or need an open collector output.

[@foogod4237]

11:14 You really don't need all of those components in the "adjustable duty cycle" configuration. First, you never really needed the diode on Rb to begin with. You can just connect Rb directly to the "discharge" pin (across the other diode). In the charging situation, it means a bit of current will take a path through Rb instead of the diode, but since the diode will still be clamping it to basically the same forward voltage the whole time, the end result will be the same. And now that we've gotten rid of that diode, notice that "discharge", Ra, and Rb are both connected to the same point. You can actually replace *both* of Ra and Rb with a single potentiometer, resulting in a single capacitor, diode, and a pot which can adjust from 0% to 100% duty cycle. (Though, as you said, actually turning it all the way down to 0% (or 100%) is probably not a great idea..)

[@paulpkae]

Thanks for the comment. I think I would prefer the additional current protection and avoid over powering the internal NPN discharge transistor.

[@JusticeAlways]

I'd like to make a adjustable time delay control for the windshield wipers on my car (has just a plain on/off/fast/slow speed control).
The "on" time pulse be long enough to get wipers started from "park position"....the "off" time value be roughly 5 ~ 30 seconds set by potentiometer.
Because wiper motor draws high current maybe use a relay to handle load. Energizing / de-energizing relay coil would send voltage spikes to timer's output...possible damage? How to address that issue.
Being a novice at electronics...I thought this might a great project...and I'd get time delay control on my car's wipers.

[@Mark1024MAK]

If driving a relay coil, you need a suitable diode wired in parallel with the coil. The diode anode connects to the coil connection that is wired to the positive part of the circuit and the diode cathode connects to the coil connection that is wired to the negative part of the circuit.

[@varkenvarken]

would there be a way to prevent current running from the supply rail during the discharge phase altogether, without raising Ra to ridiculously high values? (useful in long running battery operated scenarios for example)

[@MrRohailbootwala]

Smaller capacitor and higher resistor value. That's what I do to solve that without lowering frequency

[@Mark1024MAK]

@@MrRohailbootwalaAlso use the CMOS version, called the ICM7555 which has a lower power consumption compared to the NE555.