Soft Start Circuit for POE

[goofson]

Hello,

I want to put a soft start circuit for powering amplifiers. The 24V input is from POE and the POE dc-dc converter needs to see 24V before a certain timer or else it will shut off. Problem is the amplifier has large electrolytic caps which pull the voltage down due to inrush current. That's why I wanted to put this soft-start circuit in, but I am not sure how it works. Please help me understand what the soft-start circuit does to limit inrush current.

Another problem being that the inductor L1 when put in the circuit between the voltage source and POE causes the softstart to not work under cold temperatures (-3 deg C : 37.4 F). I would like to know why and would welcome any guesses.


In the image I used R2 as a theoretical load to act on behalf of the electrolytic caps mentioned previously.

[moffy]

When the voltage V1 is applied and the PMOSFET starts to turn on (> Vd2) the output voltage across R2 starts to rise. As this voltage starts to rise C1 provides negative feedback trying to turn the gate off. It is the negative feedback provided by C2 across R3 that limits the rise time of the output voltage and acts as a soft start. Not sure about the temp sensitivity of L1 but it might be introducing some sort of oscillation?