Converter In-Rush Thermistors etc, UPDATE -4

How can you keep getting it so wrong? The 2 ohm device does not dissipate way more energy. During turn-on, the 2 ohm and 5 ohm device dissipate EQUAL amount of energy. Further, the energy dissipated is 1/2 * C * V^2. The energy consumed by any thermistor in the OP's converter is equal to 31 J. The part fails at 300 J. Turn-on is not the problem. I've covered that a long time ago.

Arguing high inrush current can compromise the power switch is a bunch of baloney. This surge is for such a short time duration, it has no energy behind it. If you're concerned about surge currents then take a look at the surge when turning on the A/C. That is orders of magnitude worse.

Regarding Ken. I don't see his posts any more. I'm done with his childish nonsense.

Sal

ktmrfs wrote:

Salvo wrote:
Size doesn't matter that much. The 2 ohm device can take almost twice as much energy (to destruction) as the 5 ohm device. Go for the 2 ohm. It's a slam dunk.

Sal

Hardly a slam dunk. First the two ohm device also has to absorb way more energy, and second allows way more inrush current across the power switch contacts.

It seems like folks are ignoring the effects on other parts of the circuit. Do NOT ignore the effects of high inrush current on the power switch. It occurs as the switch contacts are bouncing on contact and can result is premature failure of the power switch as well.

And then there is diode current etc.

The idea it to provide a safe controlled startup current not to slap in a thermistor and think it is doing what is expected when it may not be.

BTW just prior to Ken Whites post on energy absorption, (see previous page) I did an analysis and my caculations resulted in essentially the same conclusion.

But Ken did a much better job of explaining than I would have, so there was nothing I could add to the concise explaination and result summary.