Electronics > Beginners
Can someone please help me with this circuit
(1/2) > >>
uk.casmith:
Can someone please help me with this circuit.

The base of the transistor is connected to a 555 timer.

Please could someone talk me through what happens when the 555 timer fires and when it doesn't fire.

Why do we need a voltage divider when we are using a digital circuit? I thought we only used voltage dividers with transistors to stop the signal from clipping below 0volts.

I've been stuck on this for awhile; please could someone walk me through what is happening here in as easy to follow language.

Thanks in advance for your time,

Cameron.
ArthurDent:
The resistors set the base voltage on the transistor at about 1/11 of the Vcc so if you have a supply of 5 VDC then the base is at about 0.45 volts and the transistor will not conduct. When the 555 fires, there is a pulse sent to the base through the cap that raises the base voltage and the transistor conducts until the charges equalize on the cap.
uk.casmith:
Why do we need to set the base voltage? Surly when the 555 timer fires this will be enougth to open the transitor and close it again? Why add that extra complication?
uk.casmith:
Just re-read what I put and thought I sounded a bit mean. Sorry about that please read it in a cheerful way :(
ArthurDent:
Sounded like a question to me.  :) Besides being good practice to set the voltage on the base rather than let it float, the coupling cap is quite large so the 100? Mfd electrolytic and the 1K resistor form a R-C network that give a time delay so the base voltage stays high when the 555 triggers and the transistor will conduct until the voltage on the base decays below the point where the transistor conducts, maybe around .6 volts.
Navigation
Message Index
Next page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod