DC coupling capacitor

[KentWaters]

Dear Forums,

Happy Holidays!

I simulated this very simple circuit as attached and NPN did not turn on as what I thought that the 5V DC power would be blocked by the coupling cap.  However, I've seen this section of circuit design had been implemented in one of our products and had been in production for years.  Can anyone provide any feedback how it worked?

Thanks,

Kent

[Steve080]

Hi Kent,

When DC is first applied current will flow through the capacitor switching on the transistor until the capacitor is fully charged. When the capacitor is charged, current will no longer flow and the transistor will switch off.

This type of cuircuit might be used to perform a once off function on power on for instance. The time the transistor is switched on can be set by chosing the values of the RC network to suit the application.

Regards

Steve

[KentWaters]

Thanks Steve.  Indeed, I looked at the design later on after posting the question and figured out what exactly you mentioned here.