Maker Pro
Maker Pro

Trigger Pulse for IC555 using Inverted Square Pulse

Varun Dua

Jun 18, 2015
24
Joined
Jun 18, 2015
Messages
24
Hey,
I have this circuit idea of which I'm somewhat confused about its logic on how I should on to implement it.
I have a voltage sensing section that gives me a square wave of 12V DC. This is applied to a buffer stage which produces 2 12V DC Square Waves on parallel lines. One line goes to a mosfet A which is connected to a coil load and the second one goes to an inverting circuit.

My doubt is how should I create a trigger pulse for IC555 from this inverted square wave such that the trigger is formed right at the rising edge of inverting square wave. And how would the buffer stage look like?

Furthermore, the output of IC555 will go to a mosfet B which will go on to the coil load mentioned above. Basically alternate switching from the 2 mosfets depending on the voltage sensing section.

Thanks :)
 

Arouse1973

Adam
Dec 18, 2013
5,177
Joined
Dec 18, 2013
Messages
5,177
Do you have a circuit diagram? What is the 555 timer doing in your circuit, mono-stable or something like that?
Thanks
Adam
 

Varun Dua

Jun 18, 2015
24
Joined
Jun 18, 2015
Messages
24
Yup this is the schematic diagram till now. IC555 works in a monostable mode with the option of having an option of varying the delay it can give.. 0ms, 1ms,2ms and 5msIMG_2031.JPG
 

Martaine2005

May 12, 2015
4,293
Joined
May 12, 2015
Messages
4,293
Adam!!!!!!
No Garlic or siver bullets on your diagram please..
The 555 is still alive and kicking. Cmos even more popular.
Hold your hands out and learn to love it!!

Martin
 

Martaine2005

May 12, 2015
4,293
Joined
May 12, 2015
Messages
4,293
I thought you was going to break out and dance.
I feel it, I feel it, I can feel the force!
 

AnalogKid

Jun 10, 2015
2,665
Joined
Jun 10, 2015
Messages
2,665
It would help to see the MOSFETs and their load to get a complete picture. But from what you describe, it sounds like you want FET-A to turn on during every 12 V pulse out of the sensor, and FET-B to turn on at the end of the FET-A on-time, for a variable length of time.

1. By 0 ms do you mean not turning on at all?
2. Does the 555 output drive FET-B directly?

If you trigger the monostable "right at the rising edge of invert(ed) square wave", then FET-B always is turning on right when FET-A is turning off.

OK, let me try again - Is the intent for the "trigger pulse gen" to create a variable delay from the trailing edge of the input waveform (the rising edge of the inverted square wave and the end of the FET-A on-time) so there is a time gap between when FET-A turns off and when FET-B turns on?

Here is a schematic that covers all of your circuit elements as I understand them. The correct timing components need to be calculated correctly; I just threw in some approximate values.

ak
 

Attachments

  • FET-Driver-1-c.pdf
    9.2 KB · Views: 122

Arouse1973

Adam
Dec 18, 2013
5,177
Joined
Dec 18, 2013
Messages
5,177
It would help to see the MOSFETs and their load to get a complete picture. But from what you describe, it sounds like you want FET-A to turn on during every 12 V pulse out of the sensor, and FET-B to turn on at the end of the FET-A on-time, for a variable length of time.

1. By 0 ms do you mean not turning on at all?
2. Does the 555 output drive FET-B directly?

If you trigger the monostable "right at the rising edge of invert(ed) square wave", then FET-B always is turning on right when FET-A is turning off.

OK, let me try again - Is the intent for the "trigger pulse gen" to create a variable delay from the trailing edge of the input waveform (the rising edge of the inverted square wave and the end of the FET-A on-time) so there is a time gap between when FET-A turns off and when FET-B turns on?

Here is a schematic that covers all of your circuit elements as I understand them. The correct timing components need to be calculated correctly; I just threw in some approximate values.

ak

Oh yeah another nice little circuit. Shame the OP went offline in mid flow.
Adam
 

Arouse1973

Adam
Dec 18, 2013
5,177
Joined
Dec 18, 2013
Messages
5,177
ak
Is your circuit suppose to replace the 555 timer? You show a delayed output from U1D.
Thanks
Adam
 

AnalogKid

Jun 10, 2015
2,665
Joined
Jun 10, 2015
Messages
2,665
Yes. The first RC is the variable delay. Think 2-row header with programming shunts to adjust the delay period. No shunts equals no delay (0 ms). The second RC is the fixed width output pulse.

The more I read the TS requirements, the less clear they were, so I just threw out a guess. It might be that the pulse width or pulse frequency from the voltage sensor varies, and she wants the incoming pulse width maintained while having a variable delay. That would take more gates.

And I just had a thought. Recently on one of the forums was a thread about a variable pulse delay that maintained the pulse width, and how tricky it is to match the leading and trailing edge delays. It got into frequency doubling and flipflops, PLL's etc. There might be a more simple way, and it might be easiest to implement using the <<<gasp>>> 555. Only one R and one C set both edge delays equally. As the input pulse width varies, so does the output pulse, and the delay is independent of everything. Hmmmmm.............

ak
 

Varun Dua

Jun 18, 2015
24
Joined
Jun 18, 2015
Messages
24
I somehow didn't understand the circuit you just posted :p
Forget the delay part and mosfet's..
Now, how will you convert an inverted square wave(rising edge triggered) to a trigger pulse for IC555
 

AnalogKid

Jun 10, 2015
2,665
Joined
Jun 10, 2015
Messages
2,665
What is the reason for the inverter before the trigger pulse generator in your schematic? A 555 is triggered with a negative edge, which is the trailing edge of the signal out of the buffer stage before the inverter.

ak
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
Joined
Jan 21, 2010
Messages
25,505
That transistor you have there is an inverting stage.

remove it and your 555 will be triggered on the other edge of the waveform (kinda). However it's not quite that simple as you really should convert the edge to a pulse. Look on the web for 555 trigger circuits to see how a capacitor is used to effect edge triggering.
 

Varun Dua

Jun 18, 2015
24
Joined
Jun 18, 2015
Messages
24
Ok I'll try to explaining the whole circuit at the best I can.

The first stage is a voltage sensing stage. It's output is such that if the Input voltage is above 60% of 230V.. we get a positive 12V DC as output but if lesser than 60% then we get a 0V DC Output thus creating a Square Wave.

The buffer stage splits the output of Voltage Sensing Stage into 2 Equal lines of Square Waves of 12V DC each. The 1st once drives a MOSFET A (as a switch) such that when there's a postive peak of the Square Wave, it will switch ON the MOSFET and thus charge a coil connected to the MOSFET.

The other 12V DC Square Wave line goes to an IC555 (in monostable mode) which is connected to a MOSFET B (as a switch). The MOSFET B should switch ON when the Square Wave comes down to 0V. The IC555 gives a delay of 5 seconds which is connected to the Gate of the MOSFET B. The MOSFET B is connected to the same coil mentioned above for charging purposes.

There is a capacitor bank connected to MOSFET B which provides charging of the coil when there is a LOW on square wave which starts after MOSFET A closes. The duration of the charging by the Capacitor Bank is decided by the output of IC555 which is 5 seconds.

I hope this helps..
 

Varun Dua

Jun 18, 2015
24
Joined
Jun 18, 2015
Messages
24
So this is the logic that I want to implement. Voltage Sensing part is designed. So that's not much to worry about. My only doubt is how will the buffer stage exactly look like and how will the trigger pulse be generated in accordance to the logic I mentioned above.
 

Arouse1973

Adam
Dec 18, 2013
5,177
Joined
Dec 18, 2013
Messages
5,177
Yes. The first RC is the variable delay. Think 2-row header with programming shunts to adjust the delay period. No shunts equals no delay (0 ms). The second RC is the fixed width output pulse.

The more I read the TS requirements, the less clear they were, so I just threw out a guess. It might be that the pulse width or pulse frequency from the voltage sensor varies, and she wants the incoming pulse width maintained while having a variable delay. That would take more gates.

And I just had a thought. Recently on one of the forums was a thread about a variable pulse delay that maintained the pulse width, and how tricky it is to match the leading and trailing edge delays. It got into frequency doubling and flipflops, PLL's etc. There might be a more simple way, and it might be easiest to implement using the <<<gasp>>> 555. Only one R and one C set both edge delays equally. As the input pulse width varies, so does the output pulse, and the delay is independent of everything. Hmmmmm.............

ak

Hi ak
Dumb blonde question again, sorry :) Is the output (U1D) suppose to have a delay before it triggers high as in your diagram? I was going to build the circuit and show what the waveforms will look like for the OP. But I had another look over the circuit before I started and thought I better ask the question before I build it.
Cheers
Adam
 

AnalogKid

Jun 10, 2015
2,665
Joined
Jun 10, 2015
Messages
2,665
Who knows. With each explanation, the problem gets worse, not better. Now there is a 5-second delay somewhere. Or pulse width, or whatever. The early posts described FET-B being turned on after FET-A, and showed a pulse former and a 555 monostable, so that's what id whipped up (with inverters instead of a 555). PArt of the problem probably is ESL, and a variable meaning for the word "delay".

ak
 

AnalogKid

Jun 10, 2015
2,665
Joined
Jun 10, 2015
Messages
2,665
Let's try this again.

Varun: The first stage is a voltage sensing stage. It's output is such that if the Input voltage is above 60% of 230V.. we get a positive 12V DC as output but if lesser than 60% then we get a 0V DC Output thus creating a Square Wave.

ak: Does this mean that the sensor output is a square wave at 50 Hz or 60 Hz? If so, what is the width of the positive 12 V pulse?

Varun: The buffer stage splits the output of Voltage Sensing Stage into 2 Equal lines of Square Waves of 12V DC each. The 1st once drives a MOSFET A (as a switch) such that when there's a postive peak of the Square Wave, it will switch ON the MOSFET and thus charge a coil connected to the MOSFET.

ak: What is the power source for charging the coil? Is FET-A N-channel or P-channel? Are you switching the coil to ground or to a positive voltage? What is the coil, and how many terminals or wires does it have?

Varun: The other 12V DC Square Wave line goes to an IC555 (in monostable mode) which is connected to a MOSFET B (as a switch).

ak: Is FET-B the same type as FET-A? Is its source connected to the same potential (ground, +12V, etc.)?

Varun: The MOSFET B should switch ON when the Square Wave comes down to 0V. The IC555 gives a delay of 5 seconds which is connected to the Gate of the MOSFET B.

ak: What to you mean by "delay"? Do you mean that the 555 is a monostable with a 5-second output pulse width, of that the 555 waits for 5 seconds before it makes a pulse?
ak: Also, earlier you wanted a 5 millisecond delay. Is the 5-second delay a new requirement, or a change in the old one?

Varun: The MOSFET B is connected to the same coil mentioned above for charging purposes.

ak: Is it connected to the same end as FET-A? In other words, are the two FEETs connected in parallel, or to opposite ends of the same coil, or what?

Varun: There is a capacitor bank connected to MOSFET B which provides charging of the coil when there is a LOW on square wave which starts after MOSFET A closes.

ak: You really need to provide a sketch or schematic of the connections among the FETs, the coil, and the capacitors. If the capacitors are used to charge the coil, what charges the capacitors?

The duration of the charging by the Capacitor Bank is decided by the output of IC555 which is 5 seconds.

ak: Is the 5 seconds adjustable or fixed?

Also, can you draw a timing diagram that shows the sensor input and the gate signals for FET-A and FET-B?

ak
 

Varun Dua

Jun 18, 2015
24
Joined
Jun 18, 2015
Messages
24
ak: Does this mean that the sensor output is a square wave at 50 Hz or 60 Hz? If so, what is the width of the positive 12 V pulse?
No not 50Hz, It is dependent on the Voltage Sensing section.. as in it variable on the input that is provided to the sensing section. If it is greater than 60% of 230V AC then we get a positive in the square wave otherwise if lesser than 60% of 230V AC then 0V.

What is the power source for charging the coil? Is FET-A N-channel or P-channel? Are you switching the coil to ground or to a positive voltage? What is the coil, and how many terminals or wires does it have?
These are N channel E-MOSFET's

ak: Is FET-B the same type as FET-A? Is its source connected to the same potential (ground, +12V, etc.)?
Yes the same type. Yup connected to the same potential - ground

ak: What to you mean by "delay"? Do you mean that the 555 is a monostable with a 5-second output pulse width, of that the 555 waits for 5 seconds before it makes a pulse?
ak: Also, earlier you wanted a 5 millisecond delay. Is the 5-second delay a new requirement, or a change in the old one?
It's like the 555 is powered ON when the square wave goes to 0V. And it produces a pulse width of 5 seconds. 5 second is a change to the previous one.. :p

Is it connected to the same end as FET-A? In other words, are the two FEETs connected in parallel, or to opposite ends of the same coil, or what?
Yup the same end as FET-A

ak: You really need to provide a sketch or schematic of the connections among the FETs, the coil, and the capacitors. If the capacitors are used to charge the coil, what charges the capacitors?
The Capacitor bank charges with the system is powered ON and provides its charge to the Coil when MOSFET B is switched ON.

ak: Is the 5 seconds adjustable or fixed?
I'm actually asked to provide the user a rotary switch with which we can change this time pulse width. It is 1 second, 3 seconds and 5 seconds. Depending on what the user selects, he gets the pulse width.View attachment 20827

IMAG0271_1.jpg
 
Last edited:
Top