Electronic fuse

[vasko]

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?

 

[wakibaki]

Resettable polyfuse:

http://www.littelfuse.com/data/en/Data_Sheets/Littelfuse_PTC_2016L.pdf

You can't adjust the value, but you can get different values, so you could switch different ones into the circuit.

google 'resettable polyfuse'

w

 

[vasko]

thank you wakibaki but i'd like to build one my own with power tranasistor (bipolar or mosfet),two LEDs and potentiometer and reset switch

does some one has such schematic?

 

[tomchr]

Sounds like you're building a lab supply. How about using an LM723 instead? It has provisions for both current limit and voltage regulation built in. Add a power device like the ancient 2N3055 (or something newer) and you're in business.

~Tom

 

[richie00boy]

Google foldback current limiting.

 

[vasko]

yes,you can call it lab supply

i looked at LM723 data sheet,if I got correctly current is just limited at some value

what I need is current turned down completely and red LED turned on in case of reaching max value

richie im googling this right now

 

[vasko]

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.

 

[wakibaki]

Something like this?



w

 

[vasko]

I definitely want to use transistor(mosfet(for less resistance),but bipolar is ok too), no relay.

 

[Sch3mat1c]

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

 

[vasko]

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

 

[vasko]

and this is useful too

 

[vasko]

anyone?

 

[TechGuy]

This is what you want:

LM2673
3A Step-Down Voltage Regulator with Adjustable Current Limit
LM2673 - 3A Step-Down Voltage Regulator with Adjustable Current Limit

Efficiency up to 94%
Resistor programmable peak current limit over a range of 2A to 5A.
adjustable (1.2V to 37V )
Wide input voltage range: 8V to 40V
Softstart capability
Small number of external components

 

[vasko]

Resistor programmable peak current limit over a range of 2A to 5A.

i need range 20mA to 2A

I need this for circuits testing purpose

 

[wakibaki]

MOSFET huh? No guarantees, I just DREW this:



Must be rail-rail output opamp. Output 0~2.7 amps with 0.4 ohm RDSon. You can change R12 to 50k, you will get ~5.5A max.

w

 

[vasko]

you made schematic based on my specifications...impressive

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?

this is circuit to start with...just comparator and flip flop to be added,i guess

http://www.edn.com/file/14043-Figure_1.pdf?force=true

 

[vasko]

double post

 

[wakibaki]

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

 

[vasko]

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?