Hybrid circuit breaker

[knowledgeseeki]

I am trying to design a  series HCB
to protect my circuit which is the 200ohm resistor supplied by 20V. 

The HCB is designed to interrupt the circuit to stop the flow of fault current simulated by the 5ohm resistor in series with the switch from damaging the load. 

i am working with the assumption that if the 4.1 A that will flow through the 200ohm resistor when the switch closes will damage the 200ohm resistor if the Mosfet and voltage controlled switch don't break the circuit quickly enough to stop the flow of current. 

I am finding it difficult to set threshold values for my voltage controlled switch which will be acting as a mechanical switch when i attempt to build the circuit

Also can anyone please explain based on the schematic what they think should happen 

Also if anything i said is unclear please let me know 

Attachments:

[justinec]

Hey knowledgeseeki! One of the members from the Engineering Discussion Board asked what the R26 value is? You can get back to me with the value either here or search for the post on the discussion board.

[Hung Kieu]

www.facebook.com/groups/594511053910398/permalink/616650038363166/ here are people answering your question. Reply back to them if you want!

[matheuslps]

I posted this aswer on the facebook page too:

This circuit do not make sense. Look: The way it is designed, you do not need a protection on the 200 ohms resistor. If the switch U8 is open or closed, the current through the 200 ohms will not increase. This will be always 0.1A. If you close the switch U8, the extra current will go through the 5ohm resistor and not through the 200 ohms one.

To ilustrate, I will assume R1 = 200 ohms, and R2 = 5 ohms. The current through R1 is i1 and through R2 is i2.

First, we calculte the equivalent resistor:

R_eq = (R1 * R2)/(R1 + R2)
R_eq = 4.88 ohms.

So, we know that the total current will be:

i_total = V/R_eq
i_total = 20/4.88
i_total = 4.1 A

Using current divider rule:

I1 = R2 * i_total/(R1 +R2)

I1 = 5 * 4.1/(200 + 5)
I1 = 0.1A or 100mA

I2 = R1 * i_total/(R1 +R2)

I2 = 200 * 4.1/(200 + 5)
I2 = 4A

So, the 5 ohms resisto will not damage your load.

bye

[knowledgeseeki]

Thanks i understand now that the current in the 200ohm wont increase.
My 5ohm in series with a switch simply simulated a fault condition that the rest of my circuit has to reduce this simulated fault that increases the current coming into the mosfet from 0.1 to 3.5 back to zero. Does this explanation make more sense??

[knowledgeseeki]

Hey how do i set my hysteresis trigger points to -1V and 3V
fully struggling to do that

[knowledgeseeki]

EVERYONE PLEASE NOTE IT IS SUPPOSED TO BE A BIPOLAR SCHMITT TRIGGER NOT A UNIPOLAR
THE -V IS SUPPOSED TO BE SUPPLIED WITH -15V.

sorry for the caps!!....just making sure everyone can see it