555 question

[J4e8a16n]

Hi everyone,


I don't understand the use of the third 555  on the right.

I joined a LTSpice simulation.  You will have to press escape after 3 seconds to see the raw result.  (don't know why)

[ironmonkey]

The first 555 oscilate to a low frecuency, shoots the timer that limitate the time the fence is electrified (thats the pin 4 all about) and finally the last 555 oscilates to a higher frecuency to control the flyback

[J4e8a16n]

finally the last 555 oscilates to a higher frecuency to control the flyback

   The flyback?  The newbe  don't understand.

[ironmonkey]

Flyback is the name of the circuit at the right (transistor and transformer) which elevates the voltage.

The first 555 marks the intervals between high voltage pulses, the second marks how long that bursts last and the third one drives the high voltage circuit.

If you had only the third 555 (with pin 4 connected to v+ of course) you'll get a continous high voltage output at the secondary of the transformer.

[J4e8a16n]

" the second marks how long "  it's square wave putting the reset to ground?

[ironmonkey]

More like how much time can put the reset at high (the time we can set at the second 555), thus, running the high voltage pulse train

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