monostable multivibrator problem

[auboy]

Hi guys,

Let me introduce myself first. I'm auboy resides in Melbourne, Australia. There are some question that I want to ask. But since I'm newbie in electronics, so I hope you could help me.

Firstly I want to create a device which can made one shot pulse with amplitude of 100 V and time period of 10us like shown in picture below.





so the only thing I can come up with is by making a monostable multivibrator and then the output of the signal I have to increase the amplitude.

I have simulated a multivibrator monostable in picture below

**broken link removed**



but as you can see the output time period is about 32 ms. Perhaps you guys can suggest me how to improve the circuit to create 10 us time period?

In my opinion, my triggering time is not fast enough so the time period is so slow. If that is true, Is there any ways to trigger the circuit very fast?

Secondly is there any suggestion how to increase 9 v to 100v? I think I can not use transformer to increase it so perhaps you guys can help me in these task.

Thank you in advance,
auboy

 

[Narendra1190]

I can not see the pictures u have uploaded.
And to make monostable multivibrator circuit u should go for very poppular IC 555. It is called timer IC. u can get the output for whatever duration u want.I m sending u link which contain information about IC 555 and some projects.

https://www.555-timer-circuits.com/

enjoy with 555 projects.

 

[auboy]

I can not see the pictures u have uploaded.
And to make monostable multivibrator circuit u should go for very poppular IC 555. It is called timer IC. u can get the output for whatever duration u want.I m sending u link which contain information about IC 555 and some projects.

https://www.555-timer-circuits.com/

enjoy with 555 projects.

is that so....
So I will upload it again... In this picture is the output I want to achieve



and this is the circuit that I tried to simulate


as you can see it's only reach 32ms . By the way I tried to lookedat your link for calculate the Monostable 555 Timeout but I think it can not reach below ms.

 

[dick_freebird]

555 timer is a bit slow, but should be able to get down
to uS-range pulses with low enough R and C values.
You might prefer something from the 74HC series if
it's a 5V or lower application (much lower, maybe AC
or ACLV or ...). In any case app notes should have
formulas or nomographs for component values vs pulse.

 

[crutschow]

What is the load on the 100V pulse?

 

[auboy]

555 timer is a bit slow, but should be able to get down
to uS-range pulses with low enough R and C values.
You might prefer something from the 74HC series if
it's a 5V or lower application (much lower, maybe AC
or ACLV or ...). In any case app notes should have
formulas or nomographs for component values vs pulse.

I also thought that 555 should able to get down us range. From what I understand according to sources I had been reading, if the trigger time is more than the output time period, the output time period is longer. but from my circuit simulation, it shown that I use momentary switch as trigger. So I guess the triggering time is not fast enough to create the output time period that I wanted. Is there any ways we can trigger it fast?

What is the load on the 100V pulse?

So I want to connect this circuit into two plates separated 1 meter distance to measure the capacitance between two plates. That's why I need rather high voltage to reduce the voltage drop.

 

[crutschow]

To shorten the trigger pulse you can couple it through an RC differentiator. The RC time will determine the pulse width of the trigger.

Edit: In the 555 schematic you show, put the cap in series with the switch and a large resistor (say 100k ohm) in parallel with the cap.

 

[auboy]

To shorten the trigger pulse you can couple it through an RC differentiator. The RC time will determine the pulse width of the trigger.

Edit: In the 555 schematic you show, put the cap in series with the switch and a large resistor (say 100k ohm) in parallel with the cap.

is there any example of trigger circuit that I can learn?

 

[Audioguru]

Signetics invented the 555 IC. Then Philips bought Signetics and published this applications note:

 

[BradtheRad]

Borrowing Crutschow's idea (post #7) of an RC differentiator...

You can obtain a high-voltage spike by applying DC through a series RC.

A single close of the switch produces a spike.

The switch was closed soon after the blue line (reset).

The capacitor needs to be discharged afterward.

If you absolutely want 100V, a zener diode installed somewhere will do the job. However it may affect the RC time constant, depending on where you install the zener.

 

[auboy]

Signetics invented the 555 IC. Then Philips bought Signetics and published this applications note:

wow that's very nice. I will definitely try to implemented it

Borrowing Crutschow's idea (post #7) of an RC differentiator...

You can obtain a high-voltage spike by applying DC through a series RC.

A single close of the switch produces a spike.

The switch was closed soon after the blue line (reset).

The capacitor needs to be discharged afterward.

If you absolutely want 100V, a zener diode installed somewhere will do the job. However it may affect the RC time constant, depending on where you install the zener.

that is nice as well but shape of the wave is not that I needed. What I need is pulse like this



by the way I tried to implement Crutschow's idea into the circuit. And the result is quiet nice although there are some difficulties

so this is the circuit



and this is the result


as you can see there are some excess of signal I think it's because in multisim there is no momentary switch so I have to press the switch twice to open the circuit. but the first signal is 10us which I wanted.

The next question is how to make the amplitude higher. Some people say dc-dc converter but is that true?

thank you

 

[auboy]

is there anyone could help me??

 

[crutschow]

The way you connected the capacitor won't help. The resistor and parallel capacitor should be in series with the switch before the connection to the 555 input. This resistor is in addition to R2, which should stay at 1kΩ.

You didn't answer my question about the 100V load. I can't answer your questions if you don't answer mine. ;-)

 

[Audioguru]

The small value capacitor in series with the trigger input is a differentiator that shortens the trigger pulse so that it has ended before the timeout.
I saw nothing in your schematic to make a very short trigger pulse so the differentiator will do it.

 

[auboy]

The way you connected the capacitor won't help. The resistor and parallel capacitor should be in series with the switch before the connection to the 555 input. This resistor is in addition to R2, which should stay at 1kΩ.

You didn't answer my question about the 100V load. I can't answer your questions if you don't answer mine. ;-)

I did answer your question in post 6

So I want to connect this circuit into two plates separated 1 meter distance to measure the capacitance between two plates. That's why I need rather high voltage to reduce the voltage drop.

 

[crutschow]

I did answer your question in post 6

So I want to connect this circuit into two plates separated 1 meter distance to measure the capacitance between two plates. That's why I need rather high voltage to reduce the voltage drop.

Sorry I missed that.

So if you don't have a supply that can provide 100Vdc, can you buy a commercial one or do you have to make it?

 

[auboy]

Sorry I missed that.

So if you don't have a supply that can provide 100Vdc, can you buy a commercial one or do you have to make it?

If you mean 100vdc supply only not 100Vdc pulse, I think if there is commercial one in Australia that's good, or built is also okay. But if you mean 100Vdc one pulse, there is one but it's not for commercial. It's only for research purposes and it's extremely expensive, (around $13000) so I have to made one

 

[BradtheRad]

Here is a way to use the spike-generating RC series network. Run it through a fast op amp (or comparator).

Feed the pulse to a transistor. It can have a supply of 100V, or 330V, etc.

 

[auboy]

Here is a way to use the spike-generating RC series network. Run it through a fast op amp (or comparator).

Feed the pulse to a transistor. It can have a supply of 100V, or 330V, etc.

thank you so much for helping me but I tried to implement your circuit in circuit wizard and I try to simulate turn out it flat zero even I tried to switch it like picture below. Perhaps I'm doing it wrong though. Perhaps you can tell me in which component did I do wrongly

 

[BradtheRad]

thank you so much for helping me but I tried to implement your circuit in circuit wizard and I try to simulate turn out it flat zero even I tried to switch it like picture below. Perhaps I'm doing it wrong though. Perhaps you can tell me in which component did I do wrongly

Your time scale appears to be in seconds. I think you want to magnify it so that it is in micro-seconds, give or take. Then it will resemble my timescale which covers 16.91 uSec (per label at bottom right).