Transistors

I made this simple schematic to ask you if the transistors would mutually turn off and on each other and to blink tgr LED as a result. Is this true? I know that transistors can switch on-off-on-off for a few picoseconds so its impossible to see any blinking.

Your schematic is totally opaque as you draw it upside down, back to front and inside out!

Before doing anything else, learn the rules - ground at the bottom, supply at the top, current
flow vertically, signal flow horizontally (left to right if at all possible). Otherwise its impossible
to read at a glance (which is the whole point of a circuit diagram, to be readable).

Having redrawn it so its intelligible, it appears to be a darlington pair driving a 220 ohm resistor
in emitter-follower mode with the first transistor's emitter voltage clamped by an LED.

Its not a useful configuration, there are easier ways to heat a resistor!

I know that transistors can switch on-off-on-off for a few picoseconds

Inside a CPU they can, real transistors you can plug into a breadboard have the issue that
signals only travel a mm or so in a few ps, so they are limited to the ns and µs ranges.

Your circuit doesn't have feedback paths and is not an oscillator, it just puts a fairly constant
current through a 220 ohm resistor as set by the forward voltage of the LED.

Thanks for your feedback on how to improve myself into circuits! Its my 1st circui by the way :slight_smile:
And no, I dont want amplification, the result I want to achieve (if I have done the circuit correctly) is to make a super fast blinking LED.
Is this possible?
Oh, and also, can you post the remade version of the circuit so I can learn it? Thank you! :slight_smile:

I think you are looking for an Astable multivibrator, aka an oscillator. the following web site should prove useful.
http://rayshobby.net/learning-electronics-1-multivibrator/

Indeed, its a good place to start - the classic astable circuit using two transistors will have many
tutorials and articles online.

For just blinking an LED with minimal fuss, the 555 oscillator is also suitable and well
documented.

Hi,
Your circuit.

I don't think it will flash, might flash once....
Q1 might get a bit hot driving the LED with no current limit resistor.

Tom... :slight_smile:

No no, Tom, the 220R is to pull-down the first transistor's base.
Actually, I should have mentioned earlier what is the circuit supposed to do:

  1. Current flows from + to Q1 base

  2. Q1 switches ON and turns the LED ON
    2.1. At the same time while Q1 is ON it turns Q2 ON too.

  3. When Q2 is ON, the 220R should make Q1's base to be pulled down and therefore switch Q1 off

  4. When Q1 is off that means that Q2 will also go off but then nothing pulls down Q1's base and it should turn ON.
    Thats all. I hope you understand me now :slight_smile:

  1. is bogus, when Q2 is on nothing else happens. Q2's base is clamped by the LED, the current through Q2
    just affects the battery life!

The circuit has voltage gains of < 1, and no feedback paths, no possibility of having oscillations or multiple
states.

Both transistors are in emitter-follower configuration, which has voltage gain of slightly less than 1.

Hi,
Circuit posted.

MarkT:
3. is bogus, when Q2 is on nothing else happens. Q2's base is clamped by the LED, the current through Q2
just affects the battery life!

Damn I have drawn it wrong... the whole mistake is at me sorry

Thats the rebuilt version

OP's updated version

The bottom transistor can not turn on at all, emitter voltage higher then base.
The LED was not on at all.

You need some petty hairy transistors to switch in pS.

But google multivibrator for many simple circuits.

Allan

billhowl:
OP's updated version

The bottom transistor can not turn on at all, emitter voltage higher then base.
The LED was not on at all.

Thats not possible, there are 2 resistors with total resisitance of 11k, at the base there is only 1k and an open transistor, the current at the base should be bigger than on the emitter unless the LED sucks so much current that you are right :smiley:

The LED has built in current limiting?

.

Can you at least try to lay out your circuits in a sensible top-to-bottom order with a minimum of overlapping wires like TomGeorge did? Both of the ones you've posted make me queasy with all the flips and spins (literal mental gymnastics) I have to do in order to get things in a more sensible arrangement. Your schematic would take many minutes to unravel and decipher, whereas with Tom's it takes about 3 seconds to see what's going on.

When you lay out your schematic properly, you'll be able to avoid embarrassing mistakes like not knowing which components are connected to which ("No no, Tom, the 220R is to pull-down the first transistor's base." when that resistor isn't even connected to Q1's base) and see that there's no actual feedback (the characteristic "criss-cross" that I'm sure you've seen) between Q1 and Q2 like in a real astable oscillator.

billhowl:
The bottom transistor can not turn on at all, emitter voltage higher then base.
The LED was not on at all.

The bottom transistor will turn on. BJTs work when emitter and collector are switched but with worse parameters. Current from base to collector will open the transistor so current may flow from emitter to collector.
If I understand the schematics right it may oscillate relying on parasitic capacitances etc. But I believe much more probable result would be both transistors half open and no oscillation.

Hi,
Updated version, my interpretation.

Tom... :slight_smile:

That almost looks like something familiar, but I just can't put my finger on it.

Still don't think it's an oscillator.