THE PROBLEM
LM555N is causing me some major problems in my project (PIR sensor project, The Projects Forum). It is re-triggering itself. I've been reading some datasheets and posts on forums and I've learned that it (and 555's in general) creates some huge current spikes during transitions. That spikes are totally ruining my circuit operation. I connected some bypass capacitors (22 μF electrolytic in parallel with 0.1 μF) across it's Vcc pin and GND pin but it didn't help me at all. I've reached the deadline with my project and the whole circuit is soldered (IC's have sockets).
A SOLUTION?
Would it help to replace the LM555N with CMOS 555, for example with ICM7555. Here is a datasheet.
View attachment ICM7555.pdf
On page 5 you can see a comparison of supply current transients between ICM7555 and other 555's. Huge difference! Is it really that good or is it exaggerated?
A GENERAL QUESTION
Are the CMOS 555's more effective than the standard (BJT) 555's when it comes to supply current spikes and to what extent? What are the other key advantages? Any disadvantages?
Just for the information the project is not a complete failure. Circuit sometimes works correctly but to often it gets re-triggered because of the 555 supply current spike.
LM555N is causing me some major problems in my project (PIR sensor project, The Projects Forum). It is re-triggering itself. I've been reading some datasheets and posts on forums and I've learned that it (and 555's in general) creates some huge current spikes during transitions. That spikes are totally ruining my circuit operation. I connected some bypass capacitors (22 μF electrolytic in parallel with 0.1 μF) across it's Vcc pin and GND pin but it didn't help me at all. I've reached the deadline with my project and the whole circuit is soldered (IC's have sockets).
A SOLUTION?
Would it help to replace the LM555N with CMOS 555, for example with ICM7555. Here is a datasheet.
View attachment ICM7555.pdf
On page 5 you can see a comparison of supply current transients between ICM7555 and other 555's. Huge difference! Is it really that good or is it exaggerated?
A GENERAL QUESTION
Are the CMOS 555's more effective than the standard (BJT) 555's when it comes to supply current spikes and to what extent? What are the other key advantages? Any disadvantages?
Just for the information the project is not a complete failure. Circuit sometimes works correctly but to often it gets re-triggered because of the 555 supply current spike.
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