A couple of components walk into a bar....

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2DrTahoe

Joined Dec 14, 2016
40
Unfortunately it was a ground bar and they all shorted out. Budum-bum! I'm here all week folks.

Actually I've been looking for a solution for a few days and working on what most of you would consider fundamental. However, I am just a hobbyist and I need your opinion/help.

My issue is that I need to keep an SSR active after power is removed. I searched for 555 timer circuits but NPN transistor circuits keep popping up and after a closer look seem to make more sense. Below is a circuit drawing.

Power goes in and out of the SSR to an NPN. Then to a capacitor then on to the N-Channel mosfet. The source side is to ground. The mosfet gate is controlled on/off elsewhere. When it is off, I would like the SSR to be kept alive for about 5 seconds. IDK if the values of the resistor and capacitor are correct, they are just random values for now. I added the separate ground to the capacitor. My thinking is that if the only ground is through the mosfet and it gets shut off, then there is no other ground for the NPN circuit to work and the whole thing would just shut off.

What do you guys think? Will this work? For the life of me I cant get this to sim in LTSpice.

Thanks
Carlo

1608666990342.jpeg
 

Thread Starter

2DrTahoe

Joined Dec 14, 2016
40
How is that going to work? :confused:
Max.
My initial design just included the N-Channel mosfet. My understanding is that the Gate needs to be more positive than the source, thus the source is ground. The load is on the drain side. This is a circuit I found to be a basic one and there is a ton of info on it being designed like that. I added the NPN transistor circuit in between to as a way to keep the SSR alive. Again, a ton of info and videos on that working. I was just trying to combine the 2. I thought that the NPN/cap could power the SSR just as it does for the LED in the example.
 

jpanhalt

Joined Jan 18, 2008
10,963
This was circuit I found. I figure it gets powered after the cap is charged up?
What current/voltage source charges the capacitor?

Perhaps more important, if power to the SSR is cut (i.e., you mean the power to keep it closed), then what good does grounding its input do?
 

MaxHeadRoom

Joined Jul 18, 2013
22,036
Yes, what is the nature of your signal?
How is the bi-polar going to turned on, never mind remain on?
Show a circuit you have obtained off the web etc?
Max.
 

Thread Starter

2DrTahoe

Joined Dec 14, 2016
40
What current/voltage source charges the capacitor?

Perhaps more important, if power to the SSR is cut (i.e., you mean the power to keep it closed), then what good does grounding its input do?
1.2v is needed to power the SSR. That would also be what would charge the cap. Like I said, when the mosfet is shut off, then there is no other ground for the circuit to work. If the Cap charges the base of the NPN, then the circuit can flow....I think.

1.2v is needed to power the SSR. That would also be what would charge the cap. Like I said, when the mosfet is shut off, then there is no other ground for the circuit to work. If the Cap charges the base of the NPN, then the circuit can flow....I think.
Your circuit doesn't show how that 100 uF cap gets charged.

That doesn't look what you have achieved in you drawing at all?
Max.
I put the SSR in place of the buzzer. The NPN circuit sits between the mosfet,. Consider the mosfet just an on/off switch. Consider the attached file as another example at the 1:17 min mark .https://www.youtube.com/watch?v=7GOM_cNTt0Q

Your circuit doesn't show how that 100 uF cap gets charged.
Consider this example without the added ground on the cap.IMG_20201222_151734.jpg
 

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Thread Starter

2DrTahoe

Joined Dec 14, 2016
40
So you are saying, your posted circuit is working for you? :(
Your circuit is nothing like the examples!
Max.
I dont know if it works, thats why Im here. My drawing is a combined version of the 2 the best I can come up with. If you have no advic,e then I thank you for your time.
 

MaxHeadRoom

Joined Jul 18, 2013
22,036
But you have not explained exactly what you want to do?
And what you are interfacing with?
A circuit depends on required details!
Max.
 

Thread Starter

2DrTahoe

Joined Dec 14, 2016
40
But you have not explained exactly what you want to do?
And what you are interfacing with?
A circuit depends on required details!
Max.
That's all well and good. But you havn't asked what I want to do. You asked me how it works. If i knew that I wouldn't be here making stupid jokes and asking stupid questions! In fact if you read my first post, and subsequent ones, I state my intentions. BTW, I have been in your position in other forums on other subjects from automotive to cooking. I have always answered to the best of my knowledge and ability without making the asker look small. In electronic forums, I find the opposite to be true. This is the only place where your meant to look stupid while the "expert" has to show off for some reason and then squeeze the [Offensive language removed]

Moderator's note:
Sorry you are dissatisfied with the service. Please maintain decorum and understand that these people are really trying to help you but they need to understand how to help you.


P.S. If a moderator finds this, please delete this thread. Its a complete waste of [offensive language removed] time.
 
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