Converter In-Rush Thermistors etc, UPDATE -4
UPDATE on 17 Nov, Update 2 on 22 Nov, Update 3 on 16 Jan 14, Update 4 on 19 Oct 14. --------------- In a recent thread there was mention of how you can wreck your gizmo (in my case a converter) ...
Forum Discussion
Soft start is a standard function. It is virtually in every dc/dc converter. I've used them over 25 years ago.
LT3580
Soft start does not limit current to the input capacitors. You got an ac source (120Vac) connected to a bridge rectifier which in turn is connected to a 4,200uF capacitor. That's where the problem is. Once you turn on the ac power there's a huge inrush of current into the capacitor as it charges up to about 170Vdc. That current needs to be tamed. That's the function of the NTC thermistor. The thermistor resistance is *supposed to* be sized according to the size of the capacitor. For the OP's converter, a 1 ohm thermistor will do just fine. There's absolutely no reason to go to 5 ohms. I think that could be part of the problem.
Sal
LT3580
Soft start does not limit current to the input capacitors. You got an ac source (120Vac) connected to a bridge rectifier which in turn is connected to a 4,200uF capacitor. That's where the problem is. Once you turn on the ac power there's a huge inrush of current into the capacitor as it charges up to about 170Vdc. That current needs to be tamed. That's the function of the NTC thermistor. The thermistor resistance is *supposed to* be sized according to the size of the capacitor. For the OP's converter, a 1 ohm thermistor will do just fine. There's absolutely no reason to go to 5 ohms. I think that could be part of the problem.
Sal
ken white wrote:Salvo wrote:
The transformer turn-on/power-up current is controlled through a soft-start function. There's no problem here.
Sal
Interesting, do you have a schematic?
I would think the soft start would limit in-rush everywhere...
