Hello again,
I'm trying to design a circuit that flashes an LED once a second. It needs to have 20% duty cycle. I have attached my circuit, along with the graph.
What I don't know how to do is calculate the resistor and capacitor values to get the correct duty cycle. The negative feedback resistors as well as the capacitor values in the attached schematic give the correct graph, but I don't know why it is that they work. Basically I'm looking for some way to calculate C, Rl, and Rh for certain time constants.
I've tried using τhigh=C(Rh||150k) and τlow=C(Rl||150k). I get the correct value for τhigh (.2 sec) but not for τlow.
Any help is appreciated.
Thanks, Trent
Rh is 200k in the attachment, Rl is 800k.
I'm trying to design a circuit that flashes an LED once a second. It needs to have 20% duty cycle. I have attached my circuit, along with the graph.
What I don't know how to do is calculate the resistor and capacitor values to get the correct duty cycle. The negative feedback resistors as well as the capacitor values in the attached schematic give the correct graph, but I don't know why it is that they work. Basically I'm looking for some way to calculate C, Rl, and Rh for certain time constants.
I've tried using τhigh=C(Rh||150k) and τlow=C(Rl||150k). I get the correct value for τhigh (.2 sec) but not for τlow.
Any help is appreciated.
Thanks, Trent
Rh is 200k in the attachment, Rl is 800k.