Confirming/correcting circuit a design

[malc9141]

Hello:

I have been given a diagram but wonder if there is a mistake. It is meant to deliver a short but variable pulse to a FET, and I want confirmation that the RC timer is correct.
In fact there are two of these, one for a very short pulse (Fire), the other, longer, up to about 5 ms. (Hold)

In particular, is R1 correct or should it be a capacitor? Also is the timer around C5 correct?

Thank you for any help.

 

[eTech]

Hello:

I have been given a diagram but wonder if there is a mistake. It is meant to deliver a short but variable pulse to a FET, and I want confirmation that the RC timer is correct.
In fact there are two of these, one for a very short pulse (Fire), the other, longer, up to about 5 ms. (Hold)

In particular, is R1 correct or should it be a capacitor? Also is the timer around C5 correct?

Thank you for any help.

If you have the .asc file, can you post it please?

 

[tepalia02]

You can post your design here:https://www.pcbway.com/project/question/
You may get more expert opinions here.

 

[rjenkinsgb]

In fact there are two of these, one for a very short pulse (Fire), the other, longer, up to about 5 ms. (Hold)

In particular, is R1 correct or should it be a capacitor? Also is the timer around C5 correct?

It looks reasonable to me.

R1 sets the minimum resistance so the 555 discharge transistor is not shorted to power and damaged, when the timing control is at minimum value.

The C5 + Trim2 network sets the duration the second MOSFET is on, as well as the first.

 

[malc9141]

To E and T, there is nothing to add to the diagram. I haven't a clue how to send an asc file.

 

[malc9141]

To JRW, thanks. Someone said the R1 should be a cap. You are correct that the Fire & Hold overlap (intentional). I have no electronic background, built this after advice (long story), and it stopped varying Hold, but I could not see a fault.

Will keep in touch, if I may.

 

[Nigel Goodwin]

To JRW, thanks. Someone said the R1 should be a cap.

That someone was an idiot

If R1 was a capacitor then the 555 wouldn't work at all.

 

[BillKrajcik]

If you want to be certain that your Circuit Design is working perfectly, you can try these software as well.

 

[malc9141]

To Nigel:
He was on this board!!

Malc

 

[Nigel Goodwin]

To Nigel:
He was on this board!!

Malc

Being on this board doesn't mean they aren't an idiot

But here or not, it could have been an honest mistake/typo with the component reference.

 

[eTech]

To E and T, there is nothing to add to the diagram. I haven't a clue how to send an asc file.

The schematic looks to created by LTspice. I thought you might have the file to make it easy to analyze.

 

[eTech]

Hello:

I have been given a diagram but wonder if there is a mistake. It is meant to deliver a short but variable pulse to a FET, and I want confirmation that the RC timer is correct.
In fact there are two of these, one for a very short pulse (Fire), the other, longer, up to about 5 ms. (Hold)

In particular, is R1 correct or should it be a capacitor? Also is the timer around C5 correct?

Thank you for any help.

Since the "Hold" and "Fire" outputs trigger on the same signal, the "Hold" output time is always greater than or equal to the Fire output, so the "Hold" output always overrides the "Fire" output. So, basically, the Fire output doesn't do anything. Lcoil is always energized by "Hold".

 

[rjenkinsgb]

Since the "Hold" and "Fire" outputs trigger on the same signal, the "Hold" output time is always greater than or equal to the Fire output, so the "Hold" output always overrides the "Fire" output. So, basically, the Fire output doesn't do anything. Lcoil is always energized by "Hold".

It's a power reduction or energy saving system,

The solenoid gets double current for a short time to pull in, then the fire FET turns off and the Hold one keeps it engaged, at half current, for the rest of the time.

It's quite common, in some form or other, with DC operated solenoids and contactors etc., to give positive operation without excess long term current or coil heating.

The simplest form is just an under-voltage rated coil plus a series ballast resistor to set the correct current, and an appropriate size capacitor across the resistor to give the appropriate high current pull-in pulse.

 

[eTech]

It's a power reduction or energy saving system,

The solenoid gets double current for a short time to pull in, then the fire FET turns off and the Hold one keeps it engaged, at half current, for the rest of the time.

It's quite common, in some form or other, with DC operated solenoids and contactors etc., to give positive operation without excess long term current or coil heating.

The simplest form is just an under-voltage rated coil plus a series ballast resistor to set the correct current, and an appropriate size capacitor across the resistor to give the appropriate high current pull-in pulse.

Oh..OK.

R6/R8 are subject to getting very hot depending on the rate of trigger.

 

[augustinetez]

Look up LM1949 - an ic specifically for the job (well, fuel injectors, but it can be repurposed).

 

[danadak]

Ref handbooks for 555 timer : https://archive.org/search.php?query=555+timer&sin=


Regards, Dana.