I am designing 7.5V , 2Amp. power supply from 230 V,50 Hz. AC using LM338,
230V to 9V ,2.5Amp. transformer...
Now, after some working out here in forum, I found my Filter capacitor value around 16667uF....
However, one other important term I come to know is Inrush Current limiter...
For, that I found two common technics 1.Resistor and 2. NTC thermistor method..
Now, the question is how to find out which value is suitable for my application???
Did you notice that all of these inrush current limiters are used with AC Line powered SMPSes; NOT linear transformer-powered supplies like you intend to build?
The reason is that the transformer naturally provides the current-limiting due to core saturation.
Did you notice that all of these inrush current limiters are used with AC Line powered SMPSes; NOT linear transformer-powered supplies like you intend to build?
The reason is that the transformer naturally provides the current-limiting due to core saturation.
Your transformer is like 10:1, so for 2A of load current, your steady-state line current will be ~0.2A. The initial surge to charge the filter cap will only last a few cycles, like 0.1sec. The peak line current will be limited by the transformer to ??? (3X to 5X the line current?). So get a 0.25A time-delay fuse that will take a 5X surge for 0.1sec.
The 100mA slow fuse is on the 230V side of the transformer, where the current is typically 65mA plus any transformer losses.
The slow fuse should account for the inrush charging the capacitor. If your transformer isn't oversize, it'll have some internal resistance that will naturally keep the current to sensible levels.
Your transformer is like 10:1, so for 2A of load current, your steady-state line current will be ~0.2A. The initial surge to charge the filter cap will only last a few cycles, like 0.1sec. The peak line current will be limited by the transformer to ??? (3X to 5X the line current?). So get a 0.25A time-delay fuse that will take a 5X surge for 0.1sec.