monostable multivibrator problem

[auboy]

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).

this the smallest that I can get it's gone to negative and no spike what so ever. Sorry:sad:

 

[crutschow]

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

I mean 100V steady DC. If you have that it's relatively easy to generate a pulse. The supply can have a current rating of 0.1A or less since you will be using very little current to generate the pulse.

 

[auboy]

I mean 100V steady DC. If you have that it's relatively easy to generate a pulse. The supply can have a current rating of 0.1A or less since you will be using very little current to generate the pulse.

Currently I do not have the steady 100Vdc. Sorry. I think I have variac autotransformer if I'm not mistaken but it's in ac though.

 

[crutschow]

If you have a mains isolation transformer then you could connect the variac to that and then use a diode rectifier and capacitor filter to get 100Vdc. You don't want to connect a variac directly to mains for this purpose since it provides no isolation and thus creates a serious electrocution hazard.

 

[auboy]

If you have a mains isolation transformer then you could connect the variac to that and then use a diode rectifier and capacitor filter to get 100Vdc. You don't want to connect a variac directly to mains for this purpose since it provides no isolation and thus creates a serious electrocution hazard.

Is the mains isolation transformer like this one?

**broken link removed**

If it's like that one I do not think I habe one since we will be working on 100V and most isolation transformer is in 240V in here

 

[crutschow]

An isolation transformer can be any transformer (except an autotransformer) that is rated for the mains input voltage and has an output voltage of at least a 100V. It could be a 240V to 120V transformer for example. I assume your variac is rated for 240V (?).

 

[auboy]

An isolation transformer can be any transformer (except an autotransformer) that is rated for the mains input voltage and has an output voltage of at least a 100V. It could be a 240V to 120V transformer for example. I assume your variac is rated for 240V (?).

According to the variac. It shows 0-415 V, it can be 1 phase and 3 phase, and there is an earth plug in to it just like a variac that they use in the lab.

So just a regular step down like this one?

**broken link removed**

 

[phongphanp]

You can reduce voltage output of trigger by Use the two: Plus-opamp for + side signal and Negative-opamp for - side signal etc.

Opamps for large signal is needed , also.

 

[crutschow]

According to the variac. It shows 0-415 V, it can be 1 phase and 3 phase, and there is an earth plug in to it just like a variac that they use in the lab.

So just a regular step down like this one?

**broken link removed**

Yes, that should work, or any regular mains transformer with the desired voltage output. It doesn't necessarily have to say "isolation" in the description as long as it's not an autotransformer.

 

[auboy]

Yes, that should work, or any regular mains transformer with the desired voltage output. It doesn't necessarily have to say "isolation" in the description as long as it's not an autotransformer.

That means a multi tap toroidal transformer is also okay? Then what should I do after that?

 

[crutschow]

That means a multi tap toroidal transformer is also okay? Then what should I do after that?

As long as the output is not common with the primary and the output voltage is sufficient (at least 100V). A resistance check between the primary and secondary can confirm isolation. Then just connect the variac to the output of the transformer.

 

[auboy]

As long as the output is not common with the primary and the output voltage is sufficient (at least 100V). A resistance check between the primary and secondary can confirm isolation. Then just connect the variac to the output of the transformer.

So connect the output of transformer to the input of the variac?

I don't think that's good idea because according to nameplate the input should be 240V or 415V .

And what is the relationship of connecting those with the 555 monostable circuit?

 

[crutschow]

So connect the output of transformer to the input of the variac?

I don't think that's good idea because according to nameplate the input should be 240V or 415V .

And what is the relationship of connecting those with the 555 monostable circuit?

Yes, connect the transformer output to the variac input.

The variac will operate on any input voltage equal to or below its rated voltage. There is no minimum voltage rating for a variac only a maximum (rated) voltage.

This combination is just to get an adjustable AC voltage that you can rectify with a diode and capacitor filter to get a DC voltage you can adjust to your desired 100Vdc. You then use a high voltage transistor connected to the 555 pulse output to switch the 100V to your load.

 

[phongphanp]

What's the number and type of ICs in your circuit ?

 

[auboy]

You can reduce voltage output of trigger by Use the two: Plus-opamp for + side signal and Negative-opamp for - side signal etc.

Opamps for large signal is needed , also.

Sorry for late reply I did not know that you posted. What is the difference between using differentiator and using opamp as triggering?

That means a multi tap toroidal transformer is also okay? Then what should I do after that?

Yes, connect the transformer output to the variac input.

The variac will operate on any input voltage equal to or below its rated voltage. There is no minimum voltage rating for a variac only a maximum (rated) voltage.

This combination is just to get an adjustable AC voltage that you can rectify with a diode and capacitor filter to get a DC voltage you can adjust to your desired 100Vdc. You then use a high voltage transistor connected to the 555 pulse output to switch the 100V to your load.

what is the specification of the transistor for making it happen?? and which type of transistor?

What's the number and type of ICs in your circuit ?

Currently I'm using IC 555 for making the monostable multivibrator but I'm thinking to make it faster but I think 555 is useless in high frequency. So is there any suggestion for high frequency? say 10MHz for example

 

[phongphanp]

10 MHz , I think should try Microcontroller , MC8052 or PIC , and use crystal at 15-20 MHz for the base . Because Digital world has immune the white noise, etc.

 

[D.A.(Tony)Stewart]

The capacitance of large plates separated by a meter will be a very small capacitance on the order of a picofarad. How you intend to use this information or rather what frequency of interest or what you are trying to accomplish will determine a better solution.

For example if you are trying to detect any variations or an object between them, you may have to change your tactic to use a higher frequency.

One could also use a bridge method and a self resonant frequency oscillator method or an optical method or.... so it depends more on functional spec which comes first before design implementation.

 

[auboy]

What's the number and type of ICs in your circuit ?

what is the specification of the transistor for making it happen?? and which type of transistor?

- - - Updated - - -

10 MHz , I think should try Microcontroller , MC8052 or PIC , and use crystal at 15-20 MHz for the base . Because Digital world has immune the white noise, etc.

But I still need a quiet high voltage such as 100 V or more. Does the digital device able to withstand it?

- - - Updated - - -

The capacitance of large plates separated by a meter will be a very small capacitance on the order of a picofarad. How you intend to use this information or rather what frequency of interest or what you are trying to accomplish will determine a better solution.

For example if you are trying to detect any variations or an object between them, you may have to change your tactic to use a higher frequency.

One could also use a bridge method and a self resonant frequency oscillator method or an optical method or.... so it depends more on functional spec which comes first before design implementation.

Perhaps the object will remain the same but i want to made a variation with the frequency and the voltages so I can study the voltage drop and the signal change after it travels.

I do not know what do you mean about bridge method and a self resonant frequency oscillator method, could you explain what method do they use??

 

[crutschow]

......................
what is the specification of the transistor for making it happen?? and which type of transistor?

A BJT with a voltage rating of at least 150V, for example a 2N5550. The design of the circuit depends upon the capacitance of the load.

 

[auboy]

A BJT with a voltage rating of at least 150V, for example a 2N5550. The design of the circuit depends upon the capacitance of the load.

Is there any math formula or which specification that important for choosing the transistor? Because I'm thinking to raise the voltages up to 500 V.