555 Timer

d3x0r

555 Timer
« on November 13th, 2012, 08:39 PM »
I have an application for a timer signal that generates very short pulses, was wondering if you knew how short you could get a stable signal from the 555, given highest frequency and shortest duty cycle; and what the frequency range of a 555 is.... and if you had already posted a schematic, can you give me a link?  I tried search for 555, but couldn't even get to a page that mentioned 555.

Gunther Rattay

RE: 555 Timer
« Reply #1, on November 14th, 2012, 03:03 AM »
Quote from d3x0r on November 13th, 2012, 08:39 PM
I have an application for a timer signal that generates very short pulses, was wondering if you knew how short you could get a stable signal from the 555, given highest frequency and shortest duty cycle; and what the frequency range of a 555 is.... and if you had already posted a schematic, can you give me a link?  I tried search for 555, but couldn't even get to a page that mentioned 555.
up to 3 MHz for the cmos version as shown in the datasheet http://www.ti.com/lit/ds/symlink/lmc555.pdf

the cmos version is much faster than the bipolar version.



Gunther Rattay

RE: 555 Timer
« Reply #3, on November 14th, 2012, 08:33 AM »
Quote from d3x0r on November 14th, 2012, 08:17 AM
Quote from bussi04 on November 14th, 2012, 03:03 AM
up to 3 MHz for the cmos version as shown in the datasheet http://www.ti.com/lit/ds/symlink/lmc555.pdf

the cmos version is much faster than the bipolar version.
and what's the shortest duty cycle? 3Mhz is 333ns for a full cycle....
look at the working dynamics of 555: pulse on/off = duty depends on charging and discharging a single capacitor controlled by 2 resistors. voltage levels for on/off are between 1/3 and 2/3 of supply voltage. there are calculation programs in the internet showing values for C and R at specific frequencies.
nevertheless you are not totally free because frequency and duty controlled by a single C and R influence each other.

for exact values you have to try. If your duty gets too high or low the pulse will stop immediately because charge/discharge dynamics come to an end.




element 119

RE: 555 Timer
« Reply #4, on November 14th, 2012, 07:29 PM »
Quote from d3x0r on November 13th, 2012, 08:39 PM
I have an application for a timer signal that generates very short pulses, was wondering if you knew how short you could get a stable signal from the 555, given highest frequency and shortest duty cycle; and what the frequency range of a 555 is.... and if you had already posted a schematic, can you give me a link?  I tried search for 555, but couldn't even get to a page that mentioned 555.
This is page from Forrest M. Mims III  Engineer’s Mini-Notebook.

Not sure if this is what you are looking for.

See attachment.

element 119

d3x0r

RE: 555 Timer
« Reply #5, on November 14th, 2012, 08:36 PM »
Quote from element 119 on November 14th, 2012, 07:29 PM
Quote from d3x0r on November 13th, 2012, 08:39 PM
I have an application for a timer signal that generates very short pulses, was wondering if you knew how short you could get a stable signal from the 555, given highest frequency and shortest duty cycle; and what the frequency range of a 555 is.... and if you had already posted a schematic, can you give me a link?  I tried search for 555, but couldn't even get to a page that mentioned 555.
This is page from Forrest M. Mims III  Engineer’s Mini-Notebook.

Not sure if this is what you are looking for.

See attachment.

element 119
I really just need to know in practice, and since Russ has such a thing already configured, if not destroyed already :-/  ... Just need to tune it down with a scope attached.  I have a TL-494 that operates similarly, but minimum pulse is 200ns (and only a few hundred Khz, so the 555's better there...) but below that, and I don't get a real output, it's sometimes not there, and soemtimes is there.

I'm working on a replication of Dally's Replication of TK's generators.... it is for a worthy cause :)

Gunther Rattay

RE: 555 Timer
« Reply #6, on November 15th, 2012, 01:21 AM »
Quote from d3x0r on November 14th, 2012, 08:36 PM
Quote from element 119 on November 14th, 2012, 07:29 PM
Quote from d3x0r on November 13th, 2012, 08:39 PM
I have an application for a timer signal that generates very short pulses, was wondering if you knew how short you could get a stable signal from the 555, given highest frequency and shortest duty cycle; and what the frequency range of a 555 is.... and if you had already posted a schematic, can you give me a link?  I tried search for 555, but couldn't even get to a page that mentioned 555.
This is page from Forrest M. Mims III  Engineer’s Mini-Notebook.

Not sure if this is what you are looking for.

See attachment.

element 119
I really just need to know in practice, and since Russ has such a thing already configured, if not destroyed already :-/  ... Just need to tune it down with a scope attached.  I have a TL-494 that operates similarly, but minimum pulse is 200ns (and only a few hundred Khz, so the 555's better there...) but below that, and I don't get a real output, it's sometimes not there, and soemtimes is there.

I'm working on a replication of Dally's Replication of TK's generators.... it is for a worthy cause :)
for bipolar version http://home.cogeco.ca/~rpaisley4/LM555.html#3