Ramp rate control - simple inrush current limiter

For a very simple inrush current limiter, we can use a P-MOSFET and external RC to slow-start the power on sequence.

E.g. input voltage connected to Source, capacitor in between Source and Gate, and resistor in between Gate and GND. Output Drain to the load, with huge filtering capacitor.

As we know I = C (dv/dt), how to justify the dv/dt based on RC we have?

Thanks.

Such a circuit actually doesn't constitute an inrush current limiter, it's just a delay element: after reaching |Vgs| > |Vth|, the drain current will increase rapidly.

Thanks erikl.

I am thinking the RC delay will slow-start the power so as the potential inrush current.

Hi,
Inrush current control and delayed start of the circuit are two different factors. Even inrush current be controlled on slow start or slow started circuits. For example:
You drop ONE KILO weight from a height of 2 feet, it will have some some impact at the final surface. Now you drop the same load but hanged with a spring, it will have same impact but will take longer time than earlier, is the delayed circuit start.
Now you want to drop 1 kg weight to the same height but want 1 kg at final destination, so what you do is divide that 1kg into 10 times and the distance into 10 times also. Start dropping that weight and add up that unit weight on every one unit traveled distance, finally when it reaches the destination will not have that impact which will have 1kg in lump sum.
That is INRUSH current control.
Hope I could make understanding.

Hi Raza,
could you please explain in detail how to limit Inrush current.... I need a complete design...you can chose one example and explain. like 100A/200uS

shelsd96,
Can you please explain where this 200 A current will be used, means what equipment will be fed from this current, like feeding some AC motors or feeding some transformer and the load is inductive or capacitive ?. As the this is very high current and will need some sophisticated circuit.

Raza its a Ballast controller. its seems like inductive load and its inrush current rating is 100A/200uSec.... I am not much aware about it.