what is wrong with this circuit?

Thread Starter

rahulb

Joined Jun 5, 2019
39
hi Everyone,

I am just trying to make the led blink.

Please check the image below:

test.png

The led is continuously glowing. Is it due to frequency of timer 555 or because I am using 12v for both n-channel mosfet and timer 555?

thanks
 

dl324

Joined Mar 30, 2015
12,681
Is it due to frequency of timer 555 or because I am using 12v for both n-channel mosfet and timer 555?
Can't be the latter, so it must be because the frequency is too high. Do you have an oscilloscope or a high end logic probe (e.g. HP545A)?

BTW, that's a mighty ugly schematic.
 

ericgibbs

Joined Jan 29, 2010
12,258
hi rahub,
The frequency is 6Hz and the LED is On for only approx 7 millisec.
The R1 and R5 values are much too low.
E

Update:
For a quick test change R1 the 1k to say 100k

Added image.
Both R1 and R5 are 100k.
 

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Thread Starter

rahulb

Joined Jun 5, 2019
39
How are we supposed to help you if you don't give us the required information? We were all making assumptions about the setting on the "22k" pot, but you were using 50k.
no, sorry. I mean, I used 22k first, result was the same. then I used 50k pot for testing but the result turn out to be same.

Ok. I think it is related to frequency only because when I removed connection from pin 3 of timer 555, the led turned off
 

dl324

Joined Mar 30, 2015
12,681
I think it is related to frequency only because when I removed connection from pin 3 of timer 555, the led turned off
It should be pretty obvious why essentially removing the timer from the circuit would turn the LED off.

Incidentally, why are you using a MOSFET? You could drive the LED high side from the timer.
 

bertus

Joined Apr 5, 2008
21,253
Hello,

As @dl324 said, you can drive a led directly from the 555.
The cmos version can deliver 100 mA at its output.
The bipolair version can even deliver 200 mA at its output.

Bertus
 
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