Author Topic: Knowing when a capacitor finshed discharging  (Read 1180 times)

0 Members and 1 Guest are viewing this topic.

Offline jorx

  • Newbie
  • Posts: 2
  • Country: no
Knowing when a capacitor finshed discharging
« on: February 19, 2017, 09:32:20 am »
Hi!

I'm working on a digital project that have a sinking frequenzy using a voltage controlled oscillator (made of a 555). But I need a signal from the VCO when its done oscillating. So how can I get a signal from the capacitor that is producing the sinking voltage when it's done discharging?

I suppose 99% of the users can answer this :)
 

Online Zero999

  • Super Contributor
  • ***
  • Posts: 13881
  • Country: gb
  • 0999
Re: Knowing when a capacitor finshed discharging
« Reply #1 on: February 19, 2017, 10:02:33 am »
If the capacitor is connected to a resistor (not a constant current sink) then it never finishes discharging. The voltage dies away exponentially, never falling to zero.

In reality, we consider the capacitor to be discharged, when the voltage falls below a certain level or after a number of RC time constants.
 

Offline jorx

  • Newbie
  • Posts: 2
  • Country: no
Re: Knowing when a capacitor finshed discharging
« Reply #2 on: February 19, 2017, 10:54:48 am »
Thanks for the reply.

Let me put it like this. How can I make a circuit that gives a high bit when the voltage falls under a certain level (almost zero) without having an impact on the discharge?
 

Online Zero999

  • Super Contributor
  • ***
  • Posts: 13881
  • Country: gb
  • 0999
Re: Knowing when a capacitor finshed discharging
« Reply #3 on: February 19, 2017, 11:00:00 am »
Thanks for the reply.

Let me put it like this. How can I make a circuit that gives a high bit when the voltage falls under a certain level (almost zero) without having an impact on the discharge?
Yes. You need a comparator such as the LM393 or LM311.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf