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Originally posted by bigben2k
Thanks for the vote of confidence
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And what confidence do you expect? You started this thread nearly six months ago and still don't have solutions to fundamental issues.
Quote:
Originally posted by bigben2k
So by switching the drain and source, all I'm doing is switching the problem around: the PSU can now feed the power bus, with minimal voltage drop (up to 1.3) through the same diode, the same way.
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I'm not sure what the problem is. I thought the goal was for the PSU to feed the power bus when it is on and working correctly.
Quote:
Originally posted by bigben2k
Otherwise, I'm only aware that I may not get enough voltage to drive the MOSFET for the +12 line, on each PSU, but I've already mentionned that. Since Vgs needs to be 2.0 to 4.0, given a 12v supply, the gate voltage needs to be at 14 to 16 volts, and preferably higher, where the driver output appears to be clamped at 14. Yo_Duh and I discussed that, and he assures me that the output will be sufficient, based on the maximum rated voltage increase of the output over the supply, of 13v which, above a supply of 5, would output 18v: plenty to drive the MOSFET of the +12 line.
I already knew that.
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Ben, you still don't know how to interpret the Vgs(th) spec. That spec is telling you that the part is only guaranteed to pass 250
microamps when the gate voltage 4V above the source voltage AND the drain voltage 10V above the source voltage.
The spec to be concerned with for the LTC1163 is the MINIMUM Vgate-Vs. That value is 5V. You can't count on the LTC1163 getting the gate more than 10V above ground. Even if you count on getting 'typical' performance, and get 14V out of the the LTC1163, that is nowhere near enough voltage to guarantee that a useful amount of current will flow through the MOSFET.
Quote:
Originally posted by bigben2k
So what else am I missing?
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A sufficient level of understanding of the issues involved in designing this.