2pole RC time delay?

[AndrewT]

Hi all.

the voltage on a Capacitor fed from DC through resistor builds up asymtotally towards the DC input level.

By the time one RC time constant has expired the Cap voltage will be about 70% of the DC feed voltage.

If one builds a 2pole or multi pole low pass filter to monitor the DC offset from a power amp rather than a single pole filter, it becomes difficult (for me) to calculate the time delay for the final cap voltage being fed to the trigger circuit.

Q. is there a simple way to simulate the voltages vs time on the capacitors as the DC voltage feeds through a multi-pole RC low pass filter?

 

[sreten]

Hi,

why don't you use a circuit simulator ?

/sreten.

 

[AndrewT]

Hi,
I have not learned how to yet.

Will it/they give me a voltage vs time graph?

Frequency analysis does not help here.

 

[djk]

Pretend it is an active filter and calculate the frequency, remember both caps are charging at the same time.

Look at the DH500 circuit. It will pass 40V at 8hz, and trips at about 1.5V DC in about 100mS or so. The trip level is fine for hi-fi, but I changed them to 7.5V for PA use.

 

[AndrewT]

Hi Djk,
how did you work this out

and trips at about 1.5V DC in about 100mS or so.

Does the speed of tripping depend on the DC offset voltage?
Of course it does, but how?

 

[sreten]

Hi,
I have not learned how to yet.

Will it/they give me a voltage vs time graph?

Frequency analysis does not help here.

http://focus.ti.com/docs/toolsw/folders/print/tina-ti.html

Try this, its very good and I find it very easy.

/sreten.

 

[jcx]

if you're going to use a free spice why not one without limits, used by pros who have budgets for the K$ packages:

http://www.linear.com/company/software.jsp

LtSpice / SwcadIII is pretty good in absolute terms, insanely good for free