Help me with a circuit:transistor can't switch off the diode

help 8051 led port 0

whit this circuit the led blink normal for about 5-10 min a after that dont turning off just the light is slower the port cant full turn off the transistor

please give a solution
thanks

help 8051 led port 0

I don't understand your problem. Is the problem that after 5-10 minutes of blinking the transistor can't switch off the diode??

Re: help 8051 led port 0

yes that is the problem

Re: help 8051 led port 0

remove the +12v and connect it to the +5v, you will get the solution .

replace the following

10k >> 4.7 k

4.7k>>1.5k

you just being to damage the port p0.

if possible check it with new chip .

thank you !

check it and reply ! we are waiting to know about it !

better use pnp switch

help 8051 led port 0

syrax,

I know you are not an electronic engineer by profession, but you should try to draw a proper schematics. There are inexpensive to free programs for drawing schematics - you can for example try http://tinycad.sourceforge.net . The schematics as is now, does not show us the type nor polarity of the transistor, you even don't have a current limiting resistor in series with the LED shown on the diagram (actually, is there any?)

We also don't know what particular 8051 derivative you used and other whereabouts of the application.

Although it's hard to tell "remotely", there are also chances that after the 5-10 minutes your application "runs away" for one cause or other, and what you see as "dimmed" LED light is simply a fast flickering LED, for example due to (nonexistent) external memory accesses.

JW

Re: help 8051 led port 0

@manish12:
I don't understand any of your suggestion, expect possibly replacing a defective processor.

Assumed, the transistor was meant to be NPN, the LED current limiting resistor missng in drawing is existing nevertheless (I guess, the 4k7 was only misplaced), and the 8051 is a standard type with open drain P0, then the circuit should operate exactly as it is.

Regards,
Frank

Re: help 8051 led port 0

wek you rigth, I'm not el. enginer the circuit that is on post are made simple on Corel Draw ) i use professional software and the led is with resistor I just put it to know there is consumer )

about power supply it is on 5V the wrong is mine , we change 2-3 transistors and start to work normal today i will chek there is not problem.

THANKS TO ALL
i will post what is result