I thought he did this and it still didn't turn off completely?

I may have it wrong but my read was he started with and continued with the PNP transistor. Beats me?

Ron

 

Oh. Sorry. I thought he tried it. Yes the 555 should work both by itself.

 

Yup. The only remaining problem seems to be that the 555 only goes up to Vcc minus 1.7v when it turns on (as a couple of people pointed out yesterday) so you still need two diodes in series with the LED. No transistor tho.

 

HI

Try this:

 

Your simulator is completely wrong. The output high of an NE555 does not go anywhere near +12V when it has a +12V supply. It goes only to about +10.7. Then the 2N2222 base will go to 10.7V and its emitter will go to only +10V leaving the green LED glowing with 12V - 10V= 2V across it and its resistor. A modern green LED will not glow unless it has at least about 2.8V across it.

Why add old little transistors to the output of a powerful 555? Its output can produce 200mA up and down.

 

Try this:

You used the idealizedl 555 model from LTspice (below) for your simulation, which does not represent the exact operation of a real 555.
You need to use a transistor level model, such as the NE555-1, which much more accurately simulates the real device.

 

Your simulator is completely wrong. The output high of an NE555 does not go anywhere near +12V when it has a +12V supply. It goes only to about +10.7. Then the 2N2222 base will go to 10.7V and its emitter will go to only +10V leaving the green LED glowing with 12V - 10V= 2V across it and its resistor. A modern green LED will not glow unless it has at least about 2.8V across it.

I fixed the sim.

Why add old little transistors to the output of a powerful 555? Its output can produce 200mA up and down.

Because you can supply more LED current with the external transistors.
And you can use the CMOS version (TLC555) of the timer if you want.

eT

 

You used the idealizedl 555 model from LTspice (below) for your simulation, which does not represent the exact operation of a real 555.
You need to use a transistor level model, such as the NE555-1, which much more accurately simulates the real device.

View attachment 193759

Hi C

Thanks....I'm using the right model now.
I corrected post #24

eT

 

Here's the simulation with the NE555-1 for two red LEDs with no transistors:

 

I'm using the right model now.

Note that the green LED current does not go completely to zero due to the offset in the high output voltage from the 555, plus the base-emitter drop from Q2, which further reduces the output voltage.

If you used the CMOS 555, it likely would go to zero.

 

You used the idealizedl 555 model from LTspice (below) for your simulation, which does not represent the exact operation of a real 555.
You need to use a transistor level model, such as the NE555-1, which much more accurately simulates the real device.

View attachment 193759

Even in that simulation the current through the green LED does not fall to zero. There is still about 1mA even when it should be off.

 

Yup. The only remaining problem seems to be that the 555 only goes up to Vcc minus 1.7v when it turns on (as a couple of people pointed out yesterday) so you still need two diodes in series with the LED. No transistor tho.View attachment 193748

Thanks, I should had done this preferably

 

Add a diode (1N4148 or similar) in series with the LED.

Thanks, that could also had worked, or two diodes like someone else mentioned. I retreat, I am going to read more textbooks and I'll be back...