Very low duty cycle oscillator circuit based on 7414 IC

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cd_sharp posted this 1 weeks ago

Friends, I'm going to try to make an oscillator with these requirements:

  • very low, adjustable duty cycle in range 0.01% - 0.1%
  • adjustable frequency above 50 Hz
  • use IC 7414

I will use as a starting point this circuit from Chris:

which translates to:

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Chris posted this 1 weeks ago

Hey CD,

For Input Pins not used, good idea to Ground them. See Video:

 

I believe this is correct unless I have missed something simple:

 

 

Note, this is not enough to achieve your Goal, extra stages are needed.

See: 74HC14 Datasheet

I redrew the Circuit from Akula's Circuit:

 

 

When you replicate the Circuit, you will see some parts are redundant, not necessary. This is a handy circuit to have on hand for simple tests!

   Chris

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cd_sharp posted this 1 weeks ago

Thanks, Chris, but the circuit is a little bit different. I've put it directly in Circuit Wizard, exactly how I see it in the video, except the Pin13 connection to the ground, which the author neglected. It's more stable with it.

I prototyped it on a bread board:

It looks good, it's stable, goes from 200 Hz to about 90 KHz, and despite what's being said in the video, the variable resistor adjusts the frequency and the duty cycle at the same time.

Still, this is a step forward.

 

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Chris posted this 1 weeks ago

Hey CD,

Yes, you're right, the grounding is for stability.

Excellent work! I should say, the Diodes, they are acting as Directional Devices, the Resistance on one path is different from the other path, thus the Duty Cycle can be adjusted ever so slightly, but the video is not the best way to do it, as you noted!

The stages help, start with a Frequency Stage, push this on to another stage and start looking to adjust the Duty Cycle on another Stage, this way the Duty can be adjusted without affecting the Frequency. Because they are on different stages:

 

 

I hope this makes sense.

One of my Breadboard Prototypes: Notice no Grounded Inputs in my layout...

 

 

I started the same as you!

   Chris

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Chris posted this 6 days ago

@CD

Re-reading my last post, this may have been a little confusing.

The simplest 74HC14 Circuit is as follows:

 

 

This uses One Hex Inverter, what I meant by a Stage..

 

 

The Diode is better if its a Signal Diode, they are faster than the 1N4001's faster the better. Replace the Diode with a Resistor of the same Value as R1 and this should change the Circuit dramatically.

I am sorry if I was confusing. Also the above Circuit, the Capacitor should be Ground one leg, Pin One the other leg. I will fix this and replace the image.

   Chris

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cd_sharp posted this 6 days ago

Thanks buddy, it's a real pleasure to think how this stuff works.

This

is this:

Also, I found out and checked practically that this controls the duty cycle only:

These are the stages, but I didn't understand yet how they can work together. I'll do some more studying.

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Chris posted this 5 days ago

Hey CD,

The goal, Short Sharp Duty Cycle, I have tried for sometime and its not an easy goal.

I have used Microcontrollers to get some pretty good results. Thus the Microcontroller Category on the right hand side at the top under Hardware.

I have done some Arduino and also .NET Microfamework. 

About as low as I can get is 0.1 Duty Cycle, but its nice and sharp.

I can share some more data if you wish?

   Chris

cd_sharp posted this 5 days ago

Hi, Chris! Thanks for letting me know. 0.1 duty cycle is also the limit of my function generator. I'll stick to Akula's circuit, I'll try to reverse engineer it, although that is very tough considering the low quality video of lantern no 4. I can definitely see he has 2 transistors near the integrated circuit. A mistery to solve..

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Chris posted this 5 days ago

Hey CD,

The two Transistors are a Push Pull driver for the Coil Pulsing Transistor. You can see the Push Pull on some of Ruslan's replications:

 

 

The average Mosfet Driver is based on the same ideas:

 

Ewf: https://www.quora.com/What-is-the-purpose-of-a-MOSFET-gate-driver

 

 

Not all Mosfet Driver IC's are based on the same layout, but generally the Mosfet Gate is bought up High and bought don low as fast as the signal input requires.

 

Note: Akula used a KT805 Transistor to drive the Coils.

 

 

Its worth noting: Class A and B Amplifiers use a similar NPN PNP Transistor pair called a Push Pull Transistor Array.

 

 

I am no EE Guru, I know enough to be dangerous, but this is what I have learnt.

I would not use a Push Pull Transistor pair as in the Akula Circuit, I would replace this with a proper Ultra High Speed Driver. Way easier to get a good result!

   Chris

 

High Def is available, but only one person has it, how did they get the High De Version?

 

 

Chris posted this 5 days ago

Hey CD,

A little research on the fastest Hex Inverter, fastest I can find is: 2.5 ns

This is the: 74LVC04

Most are around 6 to 12 ns. 2.5 ns is a big difference!

   Chris

 

Attached Files

Vidura posted this 5 days ago

Hi Chris,

This super-fast IC are very good indeed, but we have to consider if it is really necessary , for building a nanopulser it might be a good choice, but i don't think that it's really necessary for this circuits, and if it makes much sense. A fast mosfet driver have also a rise-fall-time of 5 to 10 ns, then the mosfet and all other components AND wires -traces have an inductance,which has a notable effect when we are dealing with nanoseconds. I would guess that better improvements can be made relatively easy and cheap making a good ,clean layout and wiring, the important components close together, use the capacitors nearby the mosfet, eventually use hi frequency electrolytic caps, so you can achieve a quite fast response. I hope that this helps a little.

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