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frequency adjustable PWM IC's

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Armagdn03

New Member
Nother newb question:


Preface:

Thank you all for the help you have given me over the years! wish I could contribute more, but im no expert. thought I would just say thanks before I ask more of you guys, lol.

problem / question:

I have been playing around with some irf510's and some 555 chips for pulse width modulation, but the problem is that they seem to be very finicky without fine control. I have seen some PWM ic's such as the TL494, but from what I can gather the pulse width only is adjustable!!! I was wondering if there are any pwm chips out there that are frequency adjustable as well as I am using these to drive MOSFET's into resonant tank circuits and precise frequency is important.

Any help would be greatly appreciated, thanks!
 
Armagdn03 said:
Nother newb question:


Preface:

Thank you all for the help you have given me over the years! wish I could contribute more, but im no expert. thought I would just say thanks before I ask more of you guys, lol.

problem / question:

I have been playing around with some irf510's and some 555 chips for pulse width modulation, but the problem is that they seem to be very finicky without fine control. I have seen some PWM ic's such as the TL494, but from what I can gather the pulse width only is adjustable!!! I was wondering if there are any pwm chips out there that are frequency adjustable as well as I am using these to drive MOSFET's into resonant tank circuits and precise frequency is important.

Any help would be greatly appreciated, thanks!

After having seen this post, I wonder how a new topic could start with thanking for help over the years.... hope the date of joining membership is just June2007.

However, the frequency is variable in TL494 and other chips like 352x or the current mode chips like 384x. these are all R C driven.
one of the parameter (R or C )could be brought into the control loop deliberately with little experimentation.

these devices could be externally fed even. once started with some oscillator, perhaps it should be possible to shift it to the resonant clock as you wish from the said resonant tank a part could be fed back as external clock and the original RC disabled.

I do agree it involves some hard work and experimentation. All said, the thought appears new and rather unconventional.
 
I've seen 555 circuits that allow both frequency and duty cycle variability.
 
thanks for the replies!

I will look at what you have suggested. I am actually trying to get away from using 555's since they are not smooth in their adjustment, and are a little flaky.
 
Armagdn03 said:
thanks for the replies!

I will look at what you have suggested. I am actually trying to get away from using 555's since they are not smooth in their adjustment, and are a little flaky.
to be frank please check the frequency dependent graphs, 555 is very linear.
one problem- rather difficult to get 1:1 ratio.
 
mvs sarma said:
to be frank please check the frequency dependent graphs, 555 is very linear.
one problem- rather difficult to get 1:1 ratio.

No, it's dead simple to get 1:1, and make it variable either side as well, you just need a couple of diodes to create separate charge and discharge paths.
 
The problem is, as you use PWM to alter the frequency the duty cycle changes. You can get round this by adding a divide by two counter on the output, a CD4013 will do.

A better way of doing this would be to just use an NE566 and a comparator, this will enable you to alter the duty cycle and frequency independantly.
 
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