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How do i make a 556 based frequency/pwm generator?

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jpoopdog

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Basically i need to control frequency and duty cycle independantly, and no, i am aware that a microcontroller could handle this easily, but this circuit does not merit the use of a uC. Plus i already have the 556.

I was told once that using a 556 somehow i could make a circuit that could independantly determine the frequency and duty cycle. this circuit is for a controller that needs to be tuned to a high voltage generator.
I also wanted to make one for like, general use too and anticipate ill probably fry the timer chip often also why i dont want to use a uC, harder to interchange and certainly not as cheap, and even if not, theres other hassles.

Anyway, how would i go about doing this? I would really appreciate the help and this specific type of circuit doesnt seem easy to search up.
Thanks
 

Nigel Goodwin

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Basically i need to control frequency and duty cycle independantly, and no, i am aware that a microcontroller could handle this easily, but this circuit does not merit the use of a uC. Plus i already have the 556.
Even replacing a single 555 timer DOES warrant a micro-controller, as it's far superior to any 555 timer, or combination of them - and costs very little.

I'm sure googling will find plenty of examples with 555's and 556's, but they will all be fairly poor and limited.

However, I would suggest you simply order one (or more) of these:

https://www.banggood.com/1Hz-150Khz...-p-1270834.html?rmmds=search&cur_warehouse=CN

I've recently bought some, they work really well and make any 555 based design look crap.
 

alec_t

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Does this help?
 

Tony Stewart

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When I started in R&D > 40 yrs ago, I could breadboard this and get it working in 15 minutes. Now it takes me an hour to remember then simulate to verify it , so you can use it in 10 seconds. (small learning curve on Falstad's user interface.) Nigel could whip up the code for a uC version in his sleep. and it only uses 1 Schmitt Trigger Inverter and 1 normal inverter 5V.

PFM 30:1 frequency range 750Hz to 120kHz
PWM 1~99%
 
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AnalogKid

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A possible issue with using two timers, one as the oscillator to set the frequency and one as a monostable to set the output pulse width (duty cycle), is that it is possible for the pulse width to be wider than one cycle of the oscillator frequency. In this regard, it is better to use a single 555 as as an oscillator with independently adjustable frequency and duty cycle. This is a common circuit that is recognized by having two diodes.

OTOH, that Banggood module sure is cute.

ak
 

AnalogKid

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Analogkid, my design does not have this issue as the PWM is complete independent of PFM
Agree. So would something based on an LM358. My comments were directed at posta #1 and #3. The only reason I stuck with the 555 family in my response is ...
i already have the 556.
ak

Note - I'm not a huge 555 fan, but it does have exceptionally stable transition level ratios, especially compared to logic devices
 

Tony Stewart

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Since the LM358 is not rail to rail, which affects the PWM accuracy, unless tweaked with a bandgap ref. set the amplitude and DC offset for the PWM. I used 3:1 R ratio to correlate with the 1/3 Hysteresis range so ideally it operates 1~99% but designs with bandgap refs and rail to rail output may offer improvements.
 

dr pepper

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You can do what you ask fairly easily with a couple of pots.
If however you need voltage control of pwm and freq, then you'll need some extra circuitry to support that, like maybe a 555 / comparator.
You can use pin 5 to roughly control freq using a voltage on the 555, and you can crudely control pwm using reset.
 
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