Hi. In this image is the so-called standard 555 timer astable circuit.
**broken link removed**
THe diode is not there when the duty cycle is >50% (charges up through R1+R2 and discharges through just R2), and the diode is there when the duty cycle is less than 50% (charges up through R1 and discharges through R1+R2).
I've seen this basic circuit used a lot at least in tutorials, etc. Never ever have I seen a version where the + capacitor node is attached to both
+Vs through a charge resistor
and to DISCHARGE through a discharge resistor
Why on earth isn't this the basic astable circuit? It would allow for independent control of the on-time and off-time wouldn't it? Why is the basic astable circuit limited to >50% duty cycle unless there is a diode? Why does everyone (or all the tutorials at least) insist on using R2 for both charge and discharge, and then placing a diode across it when they need <50% duty cycle (and also introducing an error due to the diode voltage drop) when they could just change the position of on resistor? It's silly isn't it?
I also saw a circuit for 50% duty cycle where neither discharge or +Vs are connected to the capacitor. Instead, the capacitor is charged/discharged through a single resistor using OUTPUT.
**broken link removed**
THe diode is not there when the duty cycle is >50% (charges up through R1+R2 and discharges through just R2), and the diode is there when the duty cycle is less than 50% (charges up through R1 and discharges through R1+R2).
I've seen this basic circuit used a lot at least in tutorials, etc. Never ever have I seen a version where the + capacitor node is attached to both
+Vs through a charge resistor
and to DISCHARGE through a discharge resistor
Why on earth isn't this the basic astable circuit? It would allow for independent control of the on-time and off-time wouldn't it? Why is the basic astable circuit limited to >50% duty cycle unless there is a diode? Why does everyone (or all the tutorials at least) insist on using R2 for both charge and discharge, and then placing a diode across it when they need <50% duty cycle (and also introducing an error due to the diode voltage drop) when they could just change the position of on resistor? It's silly isn't it?
I also saw a circuit for 50% duty cycle where neither discharge or +Vs are connected to the capacitor. Instead, the capacitor is charged/discharged through a single resistor using OUTPUT.
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