Generate pulses with a capacitor

Thread Starter

AMIRAAM

Joined Dec 31, 2019
37
hello everyone and thanks
Add a diode across the base emitter, cathode to base.
After some research i did on charging and discharging capacitors through diodes.
I see that both types can be used; sure we cannot find all the advantages in one type !!
Shockley Diode has high switching speed and it needs less current to switch, it can discharge the cap rapidly to near its break-over voltage which is less than the other diode like sghioto said :
This will discharge the cap rapidly to appx .35 volts when the button is pressed.
Even it is used as Relaxation Oscillator !!

But both types do not allow the capacitors to be discharged completely !!

hi AMI,
This sim shows the current thru IC1
E
#ericgibbs
Please two things I don't understand :
How to calculate the current pass to the base for biasing the transistor
Why this ripple is produced when the capacitor is being charged!? (red circle on your schematic)

ESP_ 2260.png


I reproduced my schematic:

circuit 05.png

I thought that keeping the resistor R2 helps to discharge completely the cap like Audioguru said !?

With the diode then the capacitor discharges through 1k resistor R2 and the diode when the button is pressed.
please I will appreciate any more help
Thanks
TS.
 
Last edited:

Audioguru again

Joined Oct 21, 2019
6,674
R2 slows down the discharge because it limits the current. Since your original circuit had R2 in it then I thought you wanted a slow discharge. The diode prevents a full discharge of the capacitor. A Schottky diode is not needed since an ordinary diode will work fine. The capacitor does not need to be completely discharged.
 
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