Electronic fuse

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
I need electronic scheme of the current limitation circuit on the scope of 20 mA to 2A, working voltage up to 30V DC

circuit should have little resistance, because after him I'd put LM317 to adjust voltage from 0-30V

little about the circuit:

need to have 2 states:

1st state - conducting - green LED glows
2nd state - not conducting - red LED glows

when the current reaches max value it should remove current completely and not to hold a limited supply, like real fuse

of course, point to expulsion can be adjusted by potentiometer

does someone has such a scheme?
 
i guess i need voltage comparator and flip flop or at least IC that has those

here (LM723) i see just one potentiometer,i need one for voltage and second for current and reset switch


An externally hosted image should be here but it was not working when we last tested it.





this looks too basic...

An externally hosted image should be here but it was not working when we last tested it.
 
Last edited:
Something like this?

current_clamp.jpg

w
 
I wrote this a bunch of years ago:

An externally hosted image should be here but it was not working when we last tested it.


Downside is the shunt resistor voltage drop. To minimize that, and eliminate the Vbe tempco, you'll need a voltage reference (e.g. TL431, or whatever your reg has), voltage divider and comparator. You can use the flip-flop as shown, or something else. An LM393 could be used, using the other half as a flip-flop (lots of hysteresis).

The circuit looks worse if you need high-side switching instead.

Tim
 
Sch3mat1c very nice circuit

what i dont like is that is shutting down the negative side and has resistance in "-" wire

i like the reset switch but potentiometer for current regulating is missing



Ive found this on google http://www.edn.com/file/14043-Figure_1.pdf?force=true

I like it but it needs improvement like flip flop on mosfets gate and better comparator than 2n3906 b-e but it is good for start

at least now its very clear what i am after for
 
and you are measuring voltage drop on mosfet itself as i see...thats not going to work,im afraid...what is going to be measured when mosfet isnt conducting?

When MOSFET goes off, R7 pulls output down to ground, feedback to non-inverting input of U2:A turns U1:A off, turns U2:B on, turns MOSFET off until switch is pushed when R9 pulls inputs to AND gate on, turns U2:B off, turns MOSFET on, turns U2:A on, holds AND gate on, holds U2B off, holds MOSFET on until voltage at output droops below pot set voltage.

w
 
Last edited:
ok,so it will work,i guess

but it is measuring drop on mosfet,right? it is nice idea not to have 0.1 ohm or similar resistor,but im not sure how it will work with measuring on such nonlinear resistor like transistor

can you make version with measuring on 0.1 ohm resistor just in case?

i wonder how would it looks with D or T flip flop instead of AND circuits?
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.