Pulse LED with 555timer

Status
Not open for further replies.
E

emer

Newbie level 1
Joined
Apr 26, 2016
Messages
1
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
10
I have used a 555timer to output a pulsed signal. The amplitude is 4.6V. I am then inputting this signal into a transistor to pulse the LED. However when I do this the amplitude drops to 0.8V. How do stop the amplitude from falling when I put it through the transistor? :?:
 

Hi,

Please post your complete schematic, with additional information like currents, voltages, frequency...description.

Klaus
 

Did you consider whether to drive the led directly from the 555 IC?

If you wish to use the transistor, then put the led in the collector leg, not the emitter leg.

Whatever method you use, add a safety resistor of course.
 

I'm guessing that you have the transistor emitter connected to ground and the base connected directly to the 555 (not through a resistor). In that case, as the base voltage is increased it will start to pass current into the base and through to the emitter. This will limit the voltage at the base to 0.6-0.8 volts which is the voltage drop across the base-emitter "equivalent" diode.
Always drive the base through a series resistor.
Susan
 
Status
Not open for further replies.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…