# monostable multivibrator

Discussion in 'The Projects Forum' started by Amryan, Mar 30, 2014.

1. ### Amryan Thread Starter New Member

Aug 14, 2013
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0
I need help for my project, I hope you guys can help me. So basically I want to create a circuit that can generate a 100 V pulse with time period of 10 us like picture 1st picture shown below (ansys simplorer.jpg).

so I came up with simple 555 to generate 10 us signal but with amplitude of 12 V like shown in picture 2 (schem.jpg) then I will try to increase the amplitude to Voltage that I desired. But as you can see in the last picture(oscilloscope.jpg) it's not perfectly 10 us time period, I need your opinion about it and explain how to made the time period perfectly 10 us also I do not know how increase the amplitude, I hope you can suggest me the way to increase the amplitude.

Or, is there any other ways to create signal like in the first picture.

Thank you for your attention,
Amri

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2. ### #12 Expert

Nov 30, 2010
17,815
9,119
Add a potentiometer on the timing circuit and add a transistor to switch the 100 volt source.

3. ### Amryan Thread Starter New Member

Aug 14, 2013
16
0
the potentiometer put in series R1??

Could you be more specific about adding a transistor to switch the 100 volt source?

thank you

4. ### #12 Expert

Nov 30, 2010
17,815
9,119
Yes. It is rare to find a capacitor that is accurate to 1% of its label. I see on the graph that your oscillator is running too fast. If you want accuracy, you must install a potentiometer to raise the value of the 9.09k resistor leg in order to compensate for the capacitor.

To switch a high voltage on and off, a resistor is connected to the output pin so it can bring current to a transistor. That transistor switches the 100 volts in time with the chip.

I can not read the schematic well enough to tell if you have it wired correctly to run continuously and you have not said whether you want the 100 volts to be the same polarity as the output pin of the chip, opposite, or it doesn't matter.

5. ### Amryan Thread Starter New Member

Aug 14, 2013
16
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with this post I attached the circuit in much bigger and detail view so you can read properly.

Which transistor should I choose and how big is the resistor?

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6. ### ScottWang Moderator

Aug 23, 2012
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854
Last edited: Mar 30, 2014
7. ### Amryan Thread Starter New Member

Aug 14, 2013
16
0
I've looked into the variable high voltage power supply 0-300V. That's nice but how do we incorporated the output from the high voltage power supply with the 555 output?

Is there any example or circuit diagram as a sample so I can lean from it? Does it able to create one shot only? Because I need only one pulse after that turns to zero.

Last edited: Mar 30, 2014
8. ### ScottWang Moderator

Aug 23, 2012
5,424
854
NE555 12V to 180V.

NE555 12V to 120V - Needs transformer.

You may using NE555 to generate from 12V to 180V, and using the 300V mosfet circuit to adjust the output voltage.

Aug 23, 2012
5,424
854
10. ### Amryan Thread Starter New Member

Aug 14, 2013
16
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I think this circuit is too complicated as I am a beginner in electronics. Perhaps I will try this circuit as I think I can manage:

but I tried to simulate the circuit in multisim, ltspice, and circuit wizard turn out the specific transistor is not available in those software. Is there any alternative for the transistor?

as for this circuit I think I can not do that because the it needs transformer and I think that there is no transformer that suit the output that I wanted.

11. ### ScottWang Moderator

Aug 23, 2012
5,424
854
4Mhz Xtal Oscillator using CD4069 ← you only need to pick up the CD4069 area.
You can using 74LS90(or 74HC390) to divide by 5 and divide by 2.

If you want to simulate and can't find the high voltage transistor, then you can choosing the Vceo >=40V to try.

For the transformer that it just using it to reverse as output become the input and the input become the output.

12. ### AnalogKid AAC Fanatic!

Aug 1, 2013
5,562
1,574
It appears from your descriptionthat you do not have a 100V power source that you can use, and just gate its output on and off, but that you need to generate both the timing pulse and the 100 volts. If that is true, there are two basic apporaches.

First, questions. What is the 100V pulse used for? How much current must it deliver when it is on? How fast must the rise and fall times be? The answers control the design.

One way is to generate a steady 100V supply wih one circuit, and gate it's output into whatever your are doing with another circuit. Another way is to generate a 100V pulse directly from the 12V supply. This can be done with a switching transistor, an inductor, and a zener diode - if you don't need much current or a very fast fall time. Basically, it's a 100V version of an automotive ignition system.

ak

No TTL was expressed or implied in the making of this response.

13. ### wayneh Expert

Sep 9, 2010
13,406
4,232
100V pulses combined with the word "beginner" is an eyebrow raiser. We place a high value on safety around here. You may get more feedback if you can share what you are doing with the pulses and how you are ensuring the safety of those around you, and of course your own.

14. ### Amryan Thread Starter New Member

Aug 14, 2013
16
0
sorry for late reply... I mean I'm a beginner in electronic building.... Usually I only simulate on software not build it

So my project is to inject a pulse to a cable wirelessly with 1 m distance between the cable and the sensor

so this is my capacitive coupler

http://www.imagebam.com/image/72ee6e319633186

after I simulate it and got the capacitance... I replace the capacitive coupler with real capacitor like shown below

http://www.imagebam.com/image/ac6385319634204

And if you ask why I need 100V pulse, it's because I will inject the pulse while the cable is energised with 22 kV. That's why I choose 100 V so the pulse can be seen if we looked at the ocsilloscope... I think 100 V is not big enough but since you said even 100 V is not safe, so I stick to 100V then

so to generate that I use the normal monostable multivibrator like shown below

http://www.imagebam.com/image/6dbaf6319635031

the output that I wanted is 9V with time period of 10 us but as you can see it's not 10 us

There are few questions that I want to ask.
1. is there any ways we can generate single trigger pulse faster than 10 us? If there is way, how?

2. I've asking few friends about increasing the the amplitude from 9 V to 100V, and according to them, I can use BJT transistor. Is that true? If it's true which specification should I looked into befor choosing the Transistor according to the output that I wanted?

I think it's the same like wayneh....

Last edited: Apr 8, 2014
15. ### #12 Expert

Nov 30, 2010
17,815
9,119
You have a lot bigger problems than 100 volts if you think you are going to use an oscilloscope to measure 22 thousand volts.

16. ### Amryan Thread Starter New Member

Aug 14, 2013
16
0
I do not know what kind of oscilloscope that we use in here but it used to measure impulse voltage which is usually high in transmission line.

17. ### THE_RB AAC Fanatic!

Feb 11, 2008
5,435
1,309
I have a commercially made 50kV handheld probe (about a foot long) that has outputs to connect to a 'scope or multimeter.