555 Help

shortbus

Joined Sep 30, 2009
10,045
@Timescope, I'm a complete dummie at this stuff.

Since Waveguy needs this to be AC, can your circuit be made to do the negative side too?
 

Thread Starter

waveguy

Joined Apr 17, 2013
46
Hi waveguy,



I will assume that the waveform you posted is 1.286 kHz and work out the component values.

@shortbus, thanks. I also wish that I had your knowledge. That's why we are here in this great forum.

Timescope
Actually Timescope i cant remember the frequency... i think it was between 1k and 5k but I really cant remember...Im limited with the LM358 dual Op Amp if that will help with those values, its all I have on hand.
 

Thread Starter

waveguy

Joined Apr 17, 2013
46
@Timescope, I'm a complete dummie at this stuff.

Since Waveguy needs this to be AC, can your circuit be made to do the negative side too?
We can forget about actually needing it into an AC form... but it will need a variable high current stage... if using a transformer it will need to be rectified :/
 

Thread Starter

waveguy

Joined Apr 17, 2013
46
Hi waveguy, I'm back after a hectic day.

I want to use a 9v to 12v supply for the circuit if that will be ok.

Timescope
Yes Sir buddy, I aint in no hurry... hectic days seem to fly by like a monday ;) a power on and signal out indicator led's should be all we need.. I wish i knew if we'll need to regulate any voltage for those or an opto, ( h11d1 )for higher output stage... Im just very greatfull to have you on board mr. !!! Ive discovered guessing resistor values is not a very good idea lol .
 
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timescope

Joined Dec 14, 2011
298
@Timescope, I'm a complete dummie at this stuff.

Since Waveguy needs this to be AC, can your circuit be made to do the negative side too?
You are not alone. None of us knows how the OP intends to use the waveform he requested. I have a feeling that it's something like the horizontal output stage of a CRT tv. Just a guess.

Timescope.
 

timescope

Joined Dec 14, 2011
298
Hi waveguy,

First, let's start with the original circuit that you posted. I have corrected the pin number errors and added the transformer data. I calculated the turns ratio of the transformer (11.2) and assumed that you connected it to step up the voltage. The output voltage of the transformer is 37.2v with a 3.2v input and has damaged the mosfet. Remove the mosfet from the circuit and test the terminals with an ohm meter : you will find continuity between the gate and source showing that it is damaged that is why

I have a big problem now... my 555 gets burning hot soon as i take source of any transistor or FET to ground
.

This short circuit appears at the output of the 555 circuit

For some reason my circuit isnt working now,the 555 is getting hot when connecting any transistor or FET source to ground.



The next post will look at the waveform.

Timescope
 

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timescope

Joined Dec 14, 2011
298
Hi waveguy,

It is possible to derive any waveform if we know what you want.

1. Post a drawing of the waveform that you want showing the amplitude and frequency.
The waveform I need is on page 1
The scope waveform lacks the required information as you have not stated the volts/division and time/division settings. I have assumed that the frequency is 1.286 kHz and the vertical scale is 2v/division and calculated the voltages and slopes of the waveform :

0v to 3.31v : slope = 34.9 mv/us

3.31v to 1.86v : slope = -110.4 mv/us

1.86v to 0v : slope = -9.7 mv/us

The LM358 has a slew rate of 500mv/us so should be ok to use.

You will need a peak voltage of about 10v to drive the mosfet properly.

If this is what you want, let me know and I will insert these values into the calculations for the TSG.




Timescope
 

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Thread Starter

waveguy

Joined Apr 17, 2013
46
You are correct with the volt div. on the scope, they were set at 2v per div at 50micro seconds on the scope shot.I am not sure the exact frequency the scope shot was running at, but the scale of the waveform is correct, we just need the amplitude at 10v able to drive a FET.Im assuming we will be able to vary each slope independantly wich would be awsome.Shzo what we need is that waveform pictured with an amplitude of 10v and a frquency range from at least 1khz to 5 k.. a broader range in frequency would be most desirable but not an absolute must.The 555 section wont be a problem for anyone to get the frequency range with in range of thier project/s but the rest of the circuits values are being a bear to figure out without smoking capacitors and op amps .
 
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Thread Starter

waveguy

Joined Apr 17, 2013
46
That means that the the above needs correcting to 50us/division. I will do it and post later.

Timescope
Hey Timescope, if the results you were getting with the above calulations gave the waveform we're after, those values will be fine.If I can get the op amps to output the deisired waveform with a 10v peak amplitude to drive the gate of a FET is all I need.Tweaking of the frequency values and space ratio may be required later anyways.Im thinking the Space ratio of the waveform may need to be at a fixed possition but wont know that untill much later. all I need is that waveform able to drive a FET from a 12v power supply for now.
 

Thread Starter

waveguy

Joined Apr 17, 2013
46
Hey Timescope, im getting a nice sharp negative ramp from output 1 of the first op amp.im having problems from r 2 - 3
 
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Thread Starter

waveguy

Joined Apr 17, 2013
46
What values did you use ? I have been working on a fully adjustable version of the circuit that is not finished yet.

Timescope
Ive lost it Timescope, I changed something i cant find again or burnt up sometrhing i havent found yet :/ Is there kind of program to help figure them out or anything ?
 

timescope

Joined Dec 14, 2011
298
I designed the TSG circuit for a fixed frequency of 1.286 kHz

Im wanting a variable frequency and duty cycle with the circuit as well but even a fixed frequency of around 1286k will work.
Then I found out that the scope was set to 50us/division so the frequency is
5.827 kHz which I calculated from the waveform with the scope set at 50us/ division.

Actually Timescope i cant remember the frequency... i think it was between 1k and 5k
what we need is that waveform pictured with an amplitude of 10v and a frquency range from at least 1khz to 5 k.. a broader range in frequency would be most desirable but not an absolute must.
So I am designing a variable version which is more complex and consists of two circuits : one to set the pulse repetition rate and the other to control the shape of the waveform.

Timescope
 
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