Foldback current limiter circuit

[basitccp]

hi,

i want to design a foldback current limiter circuit whose max current limit is 3 Ampere and short circuit current limit is 1 Ampere. Also output voltage is 28 volts which is same as input voltage ... can anyone help me in this regard...

Thanks in advance...

 

[berkeman]

hi,

i want to design a foldback current limiter circuit whose max current limit is 3 Ampere and short circuit current limit is 1 Ampere. Also output voltage is 28 volts which is same as input voltage ... can anyone help me in this regard...

Thanks in advance...

Welcome to the PF.

It will be hard to design a current limiting circuit that has Vin and Vout the same. You would usually need to tolerate a few tenths of a volt across a current sensing resistor, and you will need a series pass transistor to serve as the cutoff element to lower the output current. How much voltage drop Vin-Vout can you tolerate?

Also, can the short circuit current limit be less than 1A? Otherwise your pass transistor must dissipate 28W in current limit...

 

[basitccp]

Welcome to the PF.

It will be hard to design a current limiting circuit that has Vin and Vout the same. You would usually need to tolerate a few tenths of a volt across a current sensing resistor, and you will need a series pass transistor to serve as the cutoff element to lower the output current. How much voltage drop Vin-Vout can you tolerate?

Also, can the short circuit current limit be less than 1A? Otherwise your pass transistor must dissipate 28W in current limit...

Thanks..

Vout should not be less than 27.5 volts.. This is the maximum that i can tolerate when the circuit is behaving well. when it is in fold back condition obviously voltage drops. yup short circuit current can also be less than 1 Ampere there is no such limit but not more than 1 ampere..

i have design my circuit according to the attachment. but when the fold back of current starts mosfets gets very hot and then current again starts increasing because of overheating.. i have used heat sinks but still can't solve the issue. i have used 3 mosfets in parallel to reduce current i can reach a limit of 1.5 ampere max..

 

[basitccp]

also see the attachment

Thanks..

 

[NascentOxygen]

Have you labelled the type numbers on those two transistors correctly, basitccp?

 

[basitccp]

Have you labelled the type numbers on those two transistors correctly, basitccp?

sorry .. the part numbers are just replaced.

 

[basitccp]

sorry .. the part numbers are just replaced.

mosfet part number is interchanged with the transistor part number...