How can I design an lm555 timer 50% duty cycle for 10 Khz?

ian field

Joined Oct 27, 2012
6,536
This is from the Signetics Analog Applications manual for NE/SE555:
View attachment 123616
The Nat Semi datasheet implies that 100kHz is typical:
View attachment 123617
Many years ago I bought a Manor Supplies TV colour bar/test pattern generator kit, Both timebase generators were bipolar 555. It was impossible to set up the 15,625kHz horizontal timebase so it didn't drift all over the place - in the end I built a TTL timebase divider with 10MHz master clock. On paper - the bipolar 555 is good for 200kHz, in practice they tend to get a bit flaky not all that far above the audio range. The output rise and fall times start to deteriorate about there too.

AFAICR: the CMOS 555 is good for 2MHz (on paper anyway).
 

crutschow

Joined Mar 14, 2008
34,280
The 15,625kHz horizontal frequency for the old analog TV's had to be very stable, so I'm not surprised the 555 was not up to the task.
But the op has made no statement about the frequency stability/accuracy he needs so we can only speculate as to whether the 555 is adequate.
I suspect that for many applications the 555 stability is sufficient in the ≤100kHz frequency range.
 

ian field

Joined Oct 27, 2012
6,536
The 15,625kHz horizontal frequency for the old analog TV's had to be very stable, so I'm not surprised the 555 was not up to the task.
But the op has made no statement about the frequency stability/accuracy he needs so we can only speculate as to whether the 555 is adequate.
I suspect that for many applications the 555 stability is sufficient in the ≤100kHz frequency range.
All the frequencies used in the PAL TV system are synchronised so they can be interleaved into a single carrier.

Some of the old all tube sets were fairly tolerant - but the frequency drift really was all over the place. Anything using a chip to recover the various synch pulses, simply would not lock.

There's loads of applications where a 555 simply won't do.
 
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