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RC circuit

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Wimberleytech:

--- Quote from: Nikos A. on May 15, 2020, 09:03:56 am ---Hi everyone,

I try to design an RC delay circuit but it doesn't work as it is expected.

First of all, I want to choose the largest possible resistor value in order to minimize the capacitor's size. I noticed that when I am using big resistors e.g 1Mohm then capacitor's output voltage never reaches Vdd (in my case Vss is 3.3V). For example, using a 1.2Mohm resistor and 6.8uF cap the output voltage after around 10s is only 1.5V and stops increasing. If a use a small resistor e.g 6.8k then capacitor's voltage reaches 3.3V in around 225ms

I cannot understand this behavior...

Also, I want to achieve fast discharging. So, I placed a diode in parallel with the resistor but it didn't work.. The discharging response remains the same with and without the diode..

This is the circuit



Any advice?

Thanks in advance

--- End quote ---
In addition to the other comments...avoid drawing four-way connections.  In your drawing, you should have, at least, drawn a dot at the four-way.  This circuit is so simple, there is no confusion, but a very bad habit may develop.  Just don't do it.  Break the common connection and offset the wires.

Nikos A.:

--- Quote from: Wimberleytech on May 16, 2020, 02:30:25 am ---In addition to the other comments...avoid drawing four-way connections.  In your drawing, you should have, at least, drawn a dot at the four-way.  This circuit is so simple, there is no confusion, but a very bad habit may develop.  Just don't do it.  Break the common connection and offset the wires.

--- End quote ---

Hi, Wimberleytech yes you're right. Actually, I always place dots at junctions but in that case, I just draw the circuit in a simple editor (that do no add junction automatically) and I was a bit lazy :)

Wimberleytech:

--- Quote from: Nikos A. on May 16, 2020, 06:35:57 am ---
--- Quote from: Wimberleytech on May 16, 2020, 02:30:25 am ---In addition to the other comments...avoid drawing four-way connections.  In your drawing, you should have, at least, drawn a dot at the four-way.  This circuit is so simple, there is no confusion, but a very bad habit may develop.  Just don't do it.  Break the common connection and offset the wires.

--- End quote ---

Hi, Wimberleytech yes you're right. Actually, I always place dots at junctions but in that case, I just draw the circuit in a simple editor (that do no add junction automatically) and I was a bit lazy :)

--- End quote ---

Looks like you are drawing in visio...my favorite vector graphic tool!

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