interfacing source power and driven power from controller

In this circuit this is an LED connected with controller and push button also....
The LED will blink in different time interval...Ex.10sec to 200 secs.
And the LED should on when the push button is pressed means also...

My doubt is while running the LED from controller during this time if the switch is pressed means what will happen in TIP125..?

When push button is pressed more than 2seconds means the output from controller will turned off(I didn't mention in schematic)....
I this while is their any damage will occur in TIP125 or controller..?

Hi,

My doubt is while running the LED from controller during this time if the switch is pressed means what will happen in TIP125..?

Click to expand...

I assume the bjt´s collector current is going to zero. No damage.

***
* to give more detailed informations we need the vlaues of the devices. (R, LED, ...)
* There are free and easy to use simulation tools available

****
What´s the idea behind driving a LED with 12V?

***

Klaus

KlausST said:

Hi,



I assume the bjt´s collector current is going to zero. No damage.

***
* to give more detailed informations we need the vlaues of the devices. (R, LED, ...)
* There are free and easy to use simulation tools available

****
What´s the idea behind driving a LED with 12V?

***

Klaus

Click to expand...

Nothing behind 12V....The source power is +12V.So i'm using directly to powerup LED.
Simulation softwares are their but I need to get advice from experts..Because simulation tools shows some result..But I dono what's the practical result will be while executing the ciruit.

As KlausST said, to be able to judge whether your circuit will work properly, we need the values used for each component.

That said, pressing the switch while the TIP125 is also turned on from the controller will not damage the transistor. If the switch is in good condition, its resistance will be almost zero when it's pressed. Most of the LED current will flow through the switch and very little through the transistor.

If the switch is not of good quality (or an old one in poor condition) and has considerable resistance, then some of the LED current will flow through the switch and the rest through the transistor. Even then, the transistor will not be damaged just because the switch is pressed while the transistor is also turned on by the controller.

It will not happen anything. Both transistors will get saturated and that is it.
TIP125 will get very saturated when the switch is pressed and BC547 is on. When this happens, the current through the collector of BC547 will be around 34 mA and in the emitter of the TIP will be around 34 mA and in the collecter of the TIP will be very little.

The circuit will work but it could be simplified. It's not necessary to have a two-stage interface to drive the LED. The BC547 alone is quite sufficient.

Also, the value of R1 is unnecessarily low and draws much more current from the processor than is needed. 10k or at most 4.7k will provide enough base current to saturate the BC547.