The OP has convinced me to give him another shot. We are going to need to know the final application of this circuit please.

 

This what i asked the O/P in my first post, and he said new project.

 

automobile application
this is for my thesis the application is not specified
the voltage range is 0-20
current rage 0-5
since a breadboard can only take 5A

 

Even worse than aircraft. Automobile IS mentioned in the TOS.

 

Really now. Are you trying to undermine your own threads? Have you even read the Terms of Service of the site?

 

omg!! i haven't read the terms of service sorry
no application then
i really am just supposed to build a circuit breaker no application required at all

 

Did you even look at the circuit I showed in post #18 ?

 

Did you even look at the circuit I showed in post #18 ?

yes i did look at the circuit and it was helpful

My main issue now is how to choose my resistor values for my schmit trigger
i am required to use one, as opposed to using a logic gate or some other device.

 

You must in the future give your design constraints in the first couple of posts !. This is the first time saying "I am REQUIRED to use a Schmitt trigger"! If you had said that in the beginning you would have saved a lot of time, yours and mine!

Here's around 23,700 answers to the question - https://www.google.com/search?q=sch...87,d.aWc&fp=49428f98d57244d1&biw=1010&bih=624

 

You must in the future give your design constraints in the first couple of posts !. This is the first time saying "I am REQUIRED to use a Schmitt trigger"! If you had said that in the beginning you would have saved a lot of time, yours and mine!

Here's around 23,700 answers to the question - https://www.google.com/search?q=sch...87,d.aWc&fp=49428f98d57244d1&biw=1010&bih=624

Your circuit has zero threshold (it will switch when current≈0), and, if it DID have a threshold, would need hysteresis to prevent oscillations when current is at threshold.
Hysteresis => Schmitt trigger.

 

I found the comparator part of the circuit in a few books on power electronics. The same circuit was shown in all of them as a basic building block. And I do agree with the hysteresis, but since this is a home work/school project, shouldn't some of it be left up to the OP?

 

can't see any examples for dual supply
only single supply please help
yes it is my work but i am on the forum to get help

for single i can get trigger points of 0.43 for lower and 1.79 for upper.
using
25k/R= 0.43/15-1.79

then R1/R= 0.43/1.79-0.43

i get R as 770 and R1 as 800.

however due to the dual nature of my supply, my trigger lower trigger point falls to - which it shouldn't.

So it isn't like i am sitting on my hands @shortbus, i just would appreciate some help

 

can't see any examples for dual supply
only single please help
yes it is my work but i am on the forum to get help

If I had a clear idea of what you are trying to do, I would help design a circuit for you. You have a communication problem. I know you are trying to make a circuit breaker, but I don't know what the circuit looks like that needs to be protected. If you would post the unprotected circuit, and some idea of what might cause a fault, instead of always including your attempt at a solution, it might help.

 

If I had a clear idea of what you are trying to do, I would help design a circuit for you. You have a communication problem. I know you are trying to make a circuit breaker, but I don't know what the circuit looks like that needs to be protected. If you would post the unprotected circuit, and some idea of what might cause a fault, instead of always including your attempt at a solution, it might help.

i include my attempt at a solution to show that i am not just sitting on my hands.

i am not attempting to protect a circuit. I am simply trying to protect the load.

The load is a 200 ohm resistor in parallel with a 5 ohm resistor.

what causes the fault is when the the mechanical switch in series with this 5 ohm resistor closes.

the total load resistance becomes 4.87...

my supply is 20V, therefore total current when switch closes is 4.1A VS when the switch is open 0.1A

4.1 is the fault current.

I really hope this is clear. Please remember, the breaker is to simply protect my resistors. Thats is all.

thank you.

 

i include my attempt at a solution to show that i am not just sitting on my hands.

i am not attempting to protect a circuit. I am simply trying to protect the load.

The load is a 200 ohm resistor in parallel with a 5 ohm resistor.

what causes the fault is when the the mechanical switch in series with this 5 ohm resistor closes.

the total load resistance becomes 4.87...

my supply is 20V, therefore total current when switch closes is 4.1A VS when the switch is open 0.1A

4.1 is the fault current.

I really hope this is clear. Please remember, the breaker is to simply protect my resistors. Thats is all.

thank you.

That's pretty clear. What causes the switch to close?

 

That's pretty clear. What causes the switch to close?

i make the switch close.
sorry its pretty lame. but nothing other than me flicking the switch will close it.

 

And should the circuit breaker leave the current flowing through the 200Ω resistor, should it interrupt ALL the current?

 

And should the circuit breaker leave the current flowing through the 200Ω resistor, should it interrupt ALL the current?

yes it should interrupt all of the current.
and yes it should leave the current flowing through the 200Ω

i actually got it to work on simulation exactly how i wanted it to, by replacing my N channel mosfet with a p channel mosfet. I have no idea why it works with a P channel mosfet and not an N channel mosfet.

 

yes it should interrupt all of the current.
and yes it should leave the current flowing through the 200Ω
.

You are saying:
- there is always current through the 200R
- when closing the switch that would put the 5R resistor in parallel with the 200R resistor you want to interrupt the current through the 5R resistor

This doesn't make sense. Cut the wire to the 5R resistor and there will never be current through it. That can't be what you want.

What other requirements are there?

Every project begins with a complete definition of what happens when, in all details.

 

yes it should interrupt all of the current.
and yes it should leave the current flowing through the 200Ω

Those two statements are not consistent. Leaving current flowing through the 200Ω resistor is NOT interrupting all the current. Can you see why your posts are so confusing?

i actually got it to work on simulation exactly how i wanted it to, by replacing my N channel mosfet with a p channel mosfet. I have no idea why it works with a P channel mosfet and not an N channel mosfet.

So our work is done?