Hello,
I have been on this forum a lot and love this place. I'm pretty experienced with lots of circuits but one thing I have never used is a 555 timer.
I know where to come for advice, because I know that some great people here are experts on the 555.
I just put one on a board as a power-on indicator, and I meant it to blink about every 2s, for a brief blip. But it is not working. Attached is the circuit I used.
I am using an ICM7555 from NXP for low current draw as compared to other 555s. My supply is over 9V (six AA cells in series).
What is happening: the LED is always on but very very dim. I am using an LED with 1.8V for Vf and 2mA rating. I used the 5K resistor so it should get about 1.6 mA when OUTPUT is low. However, OUTPUT is not going low. It is always staying high but about 0.1V lower than V+. This is enough for the LED to glow just very dim.
Any ideas what is wrong? Does the circuit look right? As far as I can see, it is the same one in the data sheet for astable operation. I checked the pinout many times, and it seems right to me.
Any clues? If you 555 experts say it looks good then I will try another chip, perhaps this one is fried somehow.
Thanks in advance.
Sage
I have been on this forum a lot and love this place. I'm pretty experienced with lots of circuits but one thing I have never used is a 555 timer.
I know where to come for advice, because I know that some great people here are experts on the 555.
I just put one on a board as a power-on indicator, and I meant it to blink about every 2s, for a brief blip. But it is not working. Attached is the circuit I used.
I am using an ICM7555 from NXP for low current draw as compared to other 555s. My supply is over 9V (six AA cells in series).
What is happening: the LED is always on but very very dim. I am using an LED with 1.8V for Vf and 2mA rating. I used the 5K resistor so it should get about 1.6 mA when OUTPUT is low. However, OUTPUT is not going low. It is always staying high but about 0.1V lower than V+. This is enough for the LED to glow just very dim.
Any ideas what is wrong? Does the circuit look right? As far as I can see, it is the same one in the data sheet for astable operation. I checked the pinout many times, and it seems right to me.
Any clues? If you 555 experts say it looks good then I will try another chip, perhaps this one is fried somehow.
Thanks in advance.
Sage
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