Inrush Current Limiter

Inrush Current Limiter

The problem is for higher current at startup is due to charging of output cap C1 which is usually called as inrush current. This inrush current will last longer till the output cap charges to input voltage level. Once output reaches input voltage level diode blocks it.

This type of problem will exist in "Hot plugging" system like battery.

Inrush can be approximately calculate by

Ipeak = Vin * sqrt(Cout/L)

approximate pulse time can be calculated by

Tpulse = Pi * sqrt(L * Cout)

There are two ways to solve this problem practically

1) Passive inrush current limiter

2) Active inrush current limiter

Passive inrush current limiter

This system includes Resistor (approx around 10 to 20 Ohm depends on practical application)



Resistor uses is of Thermistor (Resistance will drop due to rise of temperature which is due to current) type. This has its own disadvantage, resistor will get heat up lot since whole load current will pass through R1 & R2
 
Active Current Limiter

This includes Switch S1 in addition to R1&R2. S1 may be mechanical relay or any power electronics switch like Mosfet, SSR along with its control circuit.



This will serve the purpose but will include additional cost and complexity.

If there is any control over input voltage from previous stage can be solved. For simulation purpose try programmable input voltage source.