| ??? 02/25/10 15:20 Read: times Msg Score: +1 +1 Good Question |
#173558 - Is that really true? Responding to: ???'s previous message |
Kai Klaas said:
A NTC limits the height of big current and a PTC the duration of big current. Both can be used to limit the inrush current.
Kai Klaas Is that really so? I seriously doubt it. The duration of the inrush current peak in a SMPS is typically in the order of 10 ms. The thermal time constant of either an NTC or PTC that can carry enough current to do the job will typically be in the order of several seconds. So the resistance of a PTC just wouldn't rise fast enough to do anything. In order to effectively reduce the peak current, you need a 'high enough' series resistance. But once the peak is over, you no longer want this high resistance, because it wastes energy. An NTC, of course, has exactly this behaviour. Rob. |
