# Variable duty cycle and frequency with a 555

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Hello,

I'm on a quest here.
I am trying to find a circuit with a 555 timer that can both independently
control the frequency and duty cycle(1% to 99%).
Most circuit I find is either or,  A few was actually what I thought i needed
but when completing the circuit, I found that when varying the frequency.. the
duty cycle was also changing !! or vice versa.
I know with a LM393, (and I have that circuit) it is possible. but it is not
fast enough. I can see on the scope that the 555 pulse starts to deteriorates
2.5us  while the lm393 starts about at 100us
thanks for the help

ken

Re: Variable duty cycle and frequency with a 555

control the frequency and duty cycle(1% to 99%).

but when completing the circuit, I found that when varying the frequency.. the
duty cycle was also changing !! or vice versa.

fast enough. I can see on the scope that the 555 pulse starts to deteriorates
2.5us  while the lm393 starts about at 100us

Use the 555 (ugh!) to make a triangle wave of constant amplitude and variable
frequency. Then use a comparator to turn that into a variable duty cycle.

--

John Larkin                  Highland Technology Inc
www.highlandtechnology.com   jlarkin at highlandtechnology dot com

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Re: Variable duty cycle and frequency with a 555
On Thu, 25 Apr 2013 10:24:27 -0700 (PDT), captoro

control the frequency and duty cycle(1% to 99%).

but when completing the circuit, I found that when varying the frequency.. the
duty cycle was also changing !! or vice versa.

fast enough. I can see on the scope that the 555 pulse starts to deteriorates
2.5us  while the lm393 starts about at 100us

Since you seem to be operating at relatively high frequencies, you
could alter the duty cycle with a pot and diodes and use a variable
capacitor to change the frequency.

You could also do it with a microcontroller with appropriate
peripherals on-chip (ADC inputs and a suitable timing peripheral)

Re: Variable duty cycle and frequency with a 555
On Thursday, April 25, 2013 1:24:27 PM UTC-4, captoro wrote:

y control the frequency and duty cycle(1% to 99%).

eded but when completing the circuit, I found that when varying the frequen
cy.. the duty cycle was also changing !! or vice versa.

not fast enough. I can see on the scope that the 555 pulse starts to deteri
orates 2.5us  while the lm393 starts about at 100us

HI,

With further testing today I found that with Pic chip i was able to get bet
ter rise and fall time. I am not looking for high frequency, just fast rise
time. The Pic chip starts to deteriorate at 2.5us  and the 555 chip at 50u
s... now i'm thinking maybe there is something else faster then that !!

Ken

Re: Variable duty cycle and frequency with a 555

control the frequency and duty cycle(1% to 99%).

but when completing the circuit, I found that when varying the frequency.. the
duty cycle was also changing !! or vice versa.

fast enough. I can see on the scope that the 555 pulse starts to deteriorates
2.5us  while the lm393 starts about at 100us

rise and fall time. I am not looking for high frequency, just fast rise time.
The Pic chip starts to deteriorate at 2.5us  and the 555 chip at 50us... now i'm
thinking maybe there is something else faster then that !!

The edges out of a pic should be nanoseconds, not microseconds. Is your scope
OK?

--

John Larkin                  Highland Technology Inc
www.highlandtechnology.com   jlarkin at highlandtechnology dot com

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Re: Variable duty cycle and frequency with a 555
On Thu, 25 Apr 2013 13:17:12 -0700, the renowned John Larkin

wrote:

control the frequency and duty cycle(1% to 99%).

needed but when completing the circuit, I found that when varying the
frequency.. the duty cycle was also changing !! or vice versa.

fast enough. I can see on the scope that the 555 pulse starts to deteriorates
2.5us  while the lm393 starts about at 100us

rise and fall time. I am not looking for high frequency, just fast rise time.
The Pic chip starts to deteriorate at 2.5us  and the 555 chip at 50us... now i'm
thinking maybe there is something else faster then that !!

If one were to load it directly with a reasonably hefty MOSFET gate,
it could easily degrade to microseconds. Maybe 100-200nC would do it.

A driver circuit (a couple BJTs or a chip) would take care of it, were
that to be the case.

Best regards,
Spehro Pefhany
--
"it's the network..."                          "The Journey is the reward"
snipped-for-privacy@interlog.com             Info for manufacturers: http://www.trexon.com
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Re: Variable duty cycle and frequency with a 555

etter rise and fall time. I am not looking for high frequency, just fast ri
se time. The Pic chip starts to deteriorate at 2.5us  and the 555 chip at 5
0us... now i'm thinking maybe there is something else faster then that !!

Which PIC?  PIC32MX can toggle I/O at 80MHz (12ns cycle) with rise and fall
time of 5ns.

Re: Variable duty cycle and frequency with a 555
On Thu, 25 Apr 2013 10:24:27 -0700 (PDT), captoro

control the frequency and duty cycle(1% to 99%).

but when completing the circuit, I found that when varying the frequency.. the
duty cycle was also changing !! or vice versa.

fast enough. I can see on the scope that the 555 pulse starts to deteriorates
2.5us  while the lm393 starts about at 100us

Are you looking for voltage control, or via a potentiometer, or what?

Maximum frequency of operation?  Slicing via a comparator can easily
give you the independent duty cycle but may not be adequate at very
narrow slivers if your frequency is high.

...Jim Thompson
--
| James E.Thompson                                 |    mens     |
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Re: Variable duty cycle and frequency with a 555
On Thu, 25 Apr 2013 10:24:27 -0700 (PDT), captoro

control the frequency and duty cycle(1% to 99%).

but when completing the circuit, I found that when varying the frequency.. the
duty cycle was also changing !! or vice versa.

fast enough. I can see on the scope that the 555 pulse starts to deteriorates
2.5us  while the lm393 starts about at 100us

---
I have exactly the circuit you want, but I'm not willing to divulge it

Email me if you're interested.

--
JF

Re: Variable duty cycle and frequency with a 555
wrote:

control the frequency and duty cycle(1% to 99%).

but when completing the circuit, I found that when varying the frequency.. the
duty cycle was also changing !! or vice versa.

fast enough. I can see on the scope that the 555 pulse starts to deteriorates
2.5us  while the lm393 starts about at 100us

--

John Larkin                  Highland Technology Inc
www.highlandtechnology.com   jlarkin at highlandtechnology dot com

We've slightly trimmed the long signature. Click to see the full one.
Re: Variable duty cycle and frequency with a 555
On Thu, 25 Apr 2013 18:03:30 -0700, John Larkin

control the frequency and duty cycle(1% to 99%).

but when completing the circuit, I found that when varying the frequency.. the
duty cycle was also changing !! or vice versa.

fast enough. I can see on the scope that the 555 pulse starts to deteriorates
2.5us  while the lm393 starts about at 100us

---

I have a nice digital circuit which can keep the duty cycle of a
variable-frequency signal constant.

How much of your intellectual property have you ever given away?

--
JF

Re: Variable duty cycle and frequency with a 555
On Fri, 26 Apr 2013 16:24:26 -0500, John Fields

control the frequency and duty cycle(1% to 99%).

needed but when completing the circuit, I found that when varying the
frequency.. the duty cycle was also changing !! or vice versa.

fast enough. I can see on the scope that the 555 pulse starts to deteriorates
2.5us  while the lm393 starts about at 100us

I can guess why you don't want to show it in public.

Tons, here and elsewhere. Being generous is a better long-term
strategy than being stingy and paranoid. I can't give away some of the
crown jewels, because I do have responsibilities to the company and
the employees.

--

John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot com
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Re: Variable duty cycle and frequency with a 555
On Fri, 26 Apr 2013 15:02:14 -0700, John Larkin

control the frequency and duty cycle(1% to 99%).

needed but when completing the circuit, I found that when varying the
frequency.. the duty cycle was also changing !! or vice versa.

not fast enough. I can see on the scope that the 555 pulse starts to
deteriorates 2.5us  while the lm393 starts about at 100us

---
And what would that guess be?
---

---
Examples?
---

---
You profess that, yet the "solutions" you offer are almost always
stingy since you don't assign values to the circuit components.
---

---
Neither can I.

Check?

---

--
JF

Re: Variable duty cycle and frequency with a 555
On Fri, 26 Apr 2013 17:35:21 -0500, John Fields

control the frequency and duty cycle(1% to 99%).

needed but when completing the circuit, I found that when varying the
frequency.. the duty cycle was also changing !! or vice versa.

not fast enough. I can see on the scope that the 555 pulse starts to
deteriorates 2.5us  while the lm393 starts about at 100us

Larkin's narcissism is without bounds.

...Jim Thompson
--
| James E.Thompson                                 |    mens     |
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Re: Variable duty cycle and frequency with a 555
On Fri, 26 Apr 2013 17:35:21 -0500, John Fields

control the frequency and duty cycle(1% to 99%).

needed but when completing the circuit, I found that when varying the
frequency.. the duty cycle was also changing !! or vice versa.

not fast enough. I can see on the scope that the 555 pulse starts to
deteriorates 2.5us  while the lm393 starts about at 100us

That they would be embarassing.

I've posted Spice files, entire PDF sheets of schematics from real
products, photos and layouts of real boards, some sketches with
values, and some sketches without.

Why does a no-values topology bother you so much? Can't visualize how
a circuit might work? Can't figure out values for yourself?

Every no-values thing that I've posted would work, except for a few
that were fun and silly, and declared to be such. Pick one of my
recent 5v/12v LED circuits and demonstrate why it won't work. I *can*
demonstrate that one of Jim's doesn't work; in fact, he did it for me

When we brainstorm around here, we might scribble dozens of circuits
in one session, until we get one or two that we like. We certainly
don't want to stop and do the math on every one while we're playing.
Some things, like filters and some amplifiers, might take hours to
finish up.

Is your PWM thing a crown jewel? Several PWMs come free in a typical
PIC or an ARM. One of the TI chips has a PWM that interpolates between
clock edges, to picosecond resolution.

--

John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot com
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Re: Variable duty cycle and frequency with a 555
On Fri, 26 Apr 2013 16:24:26 -0500, John Fields

control the frequency and duty cycle(1% to 99%).

needed but when completing the circuit, I found that when varying the
frequency.. the duty cycle was also changing !! or vice versa.

fast enough. I can see on the scope that the 555 pulse starts to deteriorates
2.5us  while the lm393 starts about at 100us

Larkin has never had any... let alone any to give away >:-}

...Jim Thompson
--
| James E.Thompson                                 |    mens     |
We've slightly trimmed the long signature. Click to see the full one.
Re: Variable duty cycle and frequency with a 555
captoro wrote:

control the frequency and duty cycle(1% to 99%).

but when completing the circuit, I found that when varying the frequency.. the
duty cycle was also changing !! or vice versa.

fast enough. I can see on the scope that the 555 pulse starts to deteriorates
2.5us  while the lm393 starts about at 100us

Single digit ns comparator example
http://www.ti.com/lit/ds/sbos321d/sbos321d.pdf

You can do both the triangle oscillator and comparator with
the dual version of that..

THat is just an example, there are many that can do the low ns
time.

Jamie

Re: Variable duty cycle and frequency with a 555
On 4/25/2013 4:10 PM, Jamie wrote:

When you personally applied this part to the task, how did you manage
the reliable 1% and 99% duty factors with low jitter?
And how did you compensate for the delay through the part?

I used to design pulse/function generators for a living, so be
as technical as necessary.

Re: Variable duty cycle and frequency with a 555

Damn!  I almost suffocated on the Chardonnay that went up my nose when
I started laughing >:-}

...Jim Thompson
--
| James E.Thompson                                 |    mens     |
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Re: Variable duty cycle and frequency with a 555

[snip]

Speaking of mentoring, this was posted recently to my LinkedIn profile
by a person I can't even remember working with....

[snip]
"I have had the pleasure of working on and off with Jim since 1989 at
Honeywell and also as a contractor. Jim is one of the most creative
inventors and truly one of the early pioneers of many famous circuits.
I learned a great deal from Jim yet only scratched the surface of his
knowledge. Jim is also a real kick to talk to and work with great
people skills. Jim has probably the most experience, noted by his many
accomplishments, of any designer I know. I've known a lot. Jim is a
great asset to have as he will always come up with something elegant,
making you think, “Now why didn't I think of that, it was right under
my nose?” I highly recommend Jim and would gladly work with him in the
future."

...Jim Thompson
--
| James E.Thompson                                 |    mens     |