Square wave or "pulse" phase shift

[Armagdn03]

Hello, hoped you all could help

I am trying to create a circuit that will take an input from a PWM circuit (only needs to be 50% duty cycle) such as 555 or any other integrated PWM, and be able to create 2 or more signals phase shifted from one another. so for example, say I want a 50 hz signal in, and two 50hz signals out with an adjustable phase shift. Then maybe I can go on to a fet driver to up the signal. Any ideas? lemme know if you want me to be more specific. thanks!

 

[Armagdn03]

oh I forgot, I would like the two signals to come out of two different pins, so that I can control separate fets

 

[MrAl]

Hi,

Can you live with 100Hz input and two 50Hz outputs?

 

[Armagdn03]

sure, input can go anywhere up to 1.4mhz, I just want to be able to control the output freq and phase in order to drive 2 or more mosfets,

 

[Roff]

Do you want 50% on the phase shifted outputs, or variable duty cycle, or...? What frequency and phase shift ranges do you want?

 

[Mikebits]

Why do you think you need phase shift?

 

[MrAl]

Hi again,

If you can stand 100Hz on input and 50Hz for both outputs and you want to
vary the phase of one output you can run the 100Hz into a flip flop, the output
Q will give you the first 50Hz output at 0 degrees, and run the 100Hz into a one
shot for a delay, then run the one shot output into another flip flop, the output
Q would be phase variable from 0 to almost 180 degrees, and the output Q'
would be phase variable from 180 to almost 360 degrees. Both outputs would
have a 50 percent duty cycle.
You may have to set up the one shot to have different cap values
however for higher and lower bands of frequencies.

 

[Mikebits]

One shots have one big inherent problem. That is the analog portion and stability. It would be futile to expect predictable results from a one shot. Stabilty and reproducibility would never make a one shot a viable idea.
Again I question the need for phase shift.

 

[MrAl]

One shots have one big inherent problem. That is the analog portion and stability. It would be futile to expect predictable results from a one shot. Stabilty and reproducibility would never make a one shot a viable idea.
Again I question the need for phase shift.

Hi Mike,

I guess that's why they dont make one shots anymore? he he.

I used a one shot for many circuits, including one that is very very
similar to this one that had to control the phase angle of another
circuit trigger, and it had to be adjustable.
I also know people use 555's for controlling servos, but i've never
done this myself. In fact, i think 555's are used for one shots
quite a bit.
What i dont know is if the OP uses uC's or not yet. That would
be my first choice.

 

[Armagdn03]

Thanks for the repplies

As to why I need the phase shift, it is because I am experimenting with rotating magnetic fields and would like manual control of the phase angle. The one shot is a brilliant idea, but I had not heard of its inherent instability, which would be a big problem as the circuitry would be driving resonant loads.

I know there is such a thing as a shift register IC but have not used them. Perhaps someone with a bit of experience in this field would be able to point to a good IC and perhaps a schematic.

 

[MrAl]

Hi,

The so called "instability" is relative to the application.
In other words, any jitter would be a small percentage of the
total period and this would only affect the application slightly.
Whether or not that jitter would ruin the application is something
that would have to be assessed of course, but one example
where the jitter is small relative to the time period is with the
control of a triac trigger, where the one shot produces a
delay after the zero crossing so the gate can be fired at
some time later, which regulates the output power.
This works out extremely well for regulating the power to
an ac operated device like a motor or lamp. The motor runs
very smooth and the speed goes from full down to almost
zero. The frequency is rather low however, around 60Hz,
so the jitter affects it probably less than 0.1 percent. At
higher frequencies it might affect the phase shift more so
you'd have to try it.

Other ways of adjusting phase are possible, for example
using a phase shift network and then detect the zero
crossing, but this isnt as easy to get the full 0 to 360
degree (or nearly that) phase shift, and after all nothing
is going to be perfect.

A PLL is another idea.

Generating a ramp and detecting a particular voltage level
is another way to do this.

Depending on the frequency and what kind of phase step
increment you need, you might also use divider chips or
of course a microcontroller.

It might be a good idea if you tell us the min and max
frequency you will be working with. The lower the
better actually. Also, what the min step in phase you
need, such as 1 degree. The bigger steps are easier
to generate.

 

[Roff]

He never answered my questions. It's hard to help someone who won't answer questions.