What is a fold back current limit?

[basitccp]

That is impossible unless you increase the load resistance. You can't reduce the current without reducing the current with a fixed load. With a constant load the voltage has to drop if the current drops. Otherwise you would be breaking Ohm's law (and the Ohm's law police would be at your door :wink.

Thanks for the help.. will ask you some more things when needed.. one more thing can u please give me the working link of spice software ... cracked version... i want it for my simulations..

Thanks again ..
:smile:

 

[crutschow]

I, and many on these forums, use LTspice, which is free from Linear Technology.

 

[basitccp]

I, and many on these forums, use LTspice, which is free from Linear Technology.

thanks......

 

[basitccp]

thanks......

i have implemented this circuit using IRF9540 Mosfet that is P-channel. when i connect a load of 6.8 ohm it gives current almost 3 A. but current value is constantly decreasing with time .. i think its becoz of MOSFET heating..can u suggest me any other P-channel MOSFET,,

Thanks

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i have implemented this circuit using IRF9540 Mosfet that is P-channel. when i connect a load of 6.8 ohm it gives current almost 3 A. but current value is constantly decreasing with time .. i think its becoz of MOSFET heating..can u suggest me any other P-channel MOSFET,,

Thanks

can u tell me how i use this circuit using N-channel MOSFET...?? becoz if have a N-channel MOSFET tested at 4 to 5 Ampere ..

Thanks..

 

[ahi91]

If Vin-Vout is essentially zero in your circuit then that part of the equation goes to zero and can be ignored.

Below is my LTspice simulation of the circuit with the load going from 0.1 ohm to 10 ohms. The foldback limit starts at about 1A for a short (not shown) and reaches a peak of 5A at a 5.3 ohm load.

The MOSFET is one that happened to be available in the model library. You can use any P-MOSFET that meets your current and voltage requirements. For 28V and 5A I would use one rated for at least 50V and 10A. A higher current transistor will have a lower ON resistance and thus lower voltage drop at the output.


View attachment 82506

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You should be aware that foldback limiting is to protect the power supply from excessive power dissipation due to a short, not to protect the other circuits. A high current won't damage the other systems, just perhaps the one drawing the excessive current.

Hi everyone, sorry for reviving an old thread. Does anyone know how to add a manual reset for this circuit?